Sioux Falls, South Dakota

Transcription

1 Sioux Falls, South Dakota Final Report Update to the Water Treatment Plant Master Plan July 2001 HDR Engineering, Inc.

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6 EXECUTIVE SUMMARY BACKGROUND /PURPOSE The Sioux Falls Water Department provides water treatment and distribution to the City of Sioux Falls and some surrounding areas. Strong population growth, increasing water demands, and evolving regulations require evaluations and upgrades to the water system. The City completed a Water Purification Plan Master Plan in Since that time, several new Safe Drinking water Act (SDWA) regulations have been promulgated or proposed, water supply and plant capacity have been stressed, and plant maintenance and reliability issues are a concern. The purpose of this report is to update the Water Purification Plant Master Plan. The City identified twelve specific issues to be addressed as part of the Master Plan Update. The various components of the Plan are generally categorized as follows: Water Demands, Water Quality, and Regulations Capacity/Near-Term Regulatory Improvements Facility Capacity Upgrade Facility Maintenance and Reliability Improvements Future Regulatory/Facility Requirements A Technical Memorandum (TM) was drafted for each of these categories. The TM s summarized the background conditions and evaluations of alternatives. The Master Plan process included two intense full-day workshops with City personnel, senior water specialists and HDR staff involved in the plan. The workshop dates and objectives were as follows: Workshop No. 1 (January 11, 2001): Background information, water demands, key regulations and screening of alternatives were completed. Brainstorming of treatment concepts, new alternatives and expansion strategies were developed. Workshop No. 2 (March 14, 2001): The various alternatives were discussed and planned improvements were identified. The preliminary priority and staging of the projects was developed for incorporation into the capital improvements program. The workshop approach assembled the expertise of the City and HDR to focus on the short and long-range issues facing the City Water Department. WATER DEMANDS,QUALITY, AND REGULATIONS (TM NO.1) Demands The City of Sioux Falls and surrounding area has experienced strong population growth. The water demands have continued to increase as well and the average annual water demand has grown from 16.6 MGD in 1990 to over 21 MGD in the year The following is a summary of demand projections for the water treatment plant. Executive Summary EX-1 July 2001

7 Water Demand Projections (MGD) Year Average Day Maximum Day Maximum Hour Winter Average Dry Year Average Dry Year Winter Average Dry Year WITHOUT REDUCTIONS WITH REDUCTIONS (1) Probable reductions include Lewis & Clark (10 MGD), Lincoln County (1.0 to 1.5 MGD), Wall Lake/Southern Skunk Creek (0 to 4 MGD). Water Quality The raw water treated at the Water Purification Plant includes both surface water (Big Sioux River) and well water (ground water under the influence of surface water). The following are the general characteristics of the water supply: Substantial turbidity variations occur primarily from the surface water supply and runoff events cause turbidity levels of 200 NTU and higher. Both groundwater and surface water have high calcium and magnesium hardness. Surface water temperature can approach 0 C. Iron and manganese levels are aesthetic issues. Significant organic matter (particularly in surface water) provides high DBP precursor levels. The treatment process includes potassium permanganate addition at the surface water pumping station, softening (lime, ferric chloride, PAC, and polymer addition), recarbonation, high rate filtration (with GAC cap), primary and secondary disinfection with chlorine. Secondary disinfectant will be converted to chloramines later this year. The finished water is in full compliance with the SDWA regulations. The water has relatively high hardness and total dissolved solids, low alkalinity, and moderate disinfection byproduct levels. Regulations The SDWA regulations are very dynamic and several regulations have been recently promulgated. The following rules have been released recently or are projected to have a potential impact on the Water Purification Plant: Interim Enhanced Surface Water Treatment Rule (IESWTR) Affects surface water plants serving greater than 10,000 people, lower finished water turbidity levels and 2 log Cryptosporidium removal. Executive Summary EX-2 July 2001

8 Stage 1 Disinfection/Disinfection Byproducts Rule (D/DBP) Regulate disinfection levels and DBP s (80 µg/l TTHM, 60 µg/l HAAS) and establishes minimum organic removal percentages. Proposed Filter Backwash Rule Outlines criteria for recovery and return of filter backwash water to the treatment process. Future Long-Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) Source monitoring and further protection from Cryptosporidium by establishing log removal requirements based on source water concentrations. Future Stage 2 D/DBP Rule Modifies sampling points and methods of calculating annual running average. EPA Risk Management Outlines criteria and requirements for chemical storage and handling. Chlorine release and potential impact to the plant staff and public are evaluated. CAPACITY /NEAR-TERM REGULATORY IMPROVEMENTS (TM NO.2) This TM evaluated existing regulations and focused on near-term improvements to comply with regulations and potentially improve capacity or finished water product ratio. Clearwell Storage Capacity The clearwell is required for disinfectant contact time (CT) and for storage for variations in high service pumping due to changing demands. The following is a summary of results: Clearwells include a 4 MG belowground structure (Reservoir No. 2) used continuously for CT and a 5 MG aboveground reservoir (North Reservoir) used primarily for storage. The belowground reservoir has recently had baffles added to increase the effective storage (T 10 /T) from 0.17 to New piping and fittings to separate the inlet/outlet location are being added to the North Reservoir, which will improve the CT. The improved baffling substantially increases the disinfection capacity of the reservoir and allows greater fluctuation in the water level, which enhances plant operations. If UV disinfection (TM 5) is added, the CT for virus inactivation is easily met and a clearwell expansion can be avoided. UV is recommended in TM No. 5. If chlorine is maintained as the primary disinfectant, a 3 million gallon (MG) clearwell addition is recommended at an estimated project cost of $2,628,000. Additional costs would be required for parking space relocation. Filter Backwash Recycle Filter backwash requires a substantial volume of treated water, however, it may contain pathogenic microorganism and, as a result, is pumped to the City s wastewater facilities. The requirements to recycle this water resource were evaluated: Executive Summary EX-3 July 2001

9 Backwash volumes are 3 to 7% of total flow and amount to 600,000 to 1,400,000 gallons per day (gpd). This could increase from 950,000 to 2,200,000 gpd by the year The backwash water has significant turbidity (solids), different chemical characteristics than raw water, and may contain concentrated levels of microorganism. Backwash return upsets the softening basin (solids and different chemical requirements), which decreases filter run time. The amount of backwash water potential recovered is approximately the amount required by 3 typical vertical wells. Alternatives evaluated included: Continue to pump to wastewater plant. Membrane Treatment. Ballasted Floc/Gravity Filtration. Dissolved Air Flotation. Equalized flow to presedimentation basin. The recommended improvements include an expansion of the backwash equalization basin by 800,000 gallons and returning the backwash water to a presedimentation basin (recommended in TM No. 3). The estimated project cost is $1,030,000. Chlorine Treatment/Containment The WPP utilizes gaseous chlorine for disinfection and will continue to do so in the future. The storage and use does pose a possible risk and City has decided to address the issue and will include scrubbing or containment. The alternatives evaluated include dry scrubbers, wet scrubbers or total containment. The recommended system is a dry scrubber system with an estimated capital cost of $244,000. FACILITY CAPACITY UPGRADE (TM NO.3) Rapid Sand Filter Expansion The high rate sand filters are critical components of any water purification plant. Due to hydraulic loading, solid contact effluent fluctuations and water characteristics, the filters have been a limiting factor at the WPP. The filters include a 20-inch GAC layer over 10 inches of sand. The following is a summary of the evaluation: Fluctuations in surface water quality or backwash return can decrease filter run time to unacceptable levels. At hydraulic loading above 4 gpm/ft 2, the inlet velocity causes the GAC media to scour near the back of the filter. Baffle modifications to dissipate the inlet velocity (energy) are recommended at an estimated cost of $100,000. The City is modifying one test filter and will evaluate the allowable increase in loading. Executive Summary EX-4 July 2001

10 Many high rate filters operate at a hydraulic loading of 6 gpm/ft 2. At this rate, 3 additional filters would be required for future maximum day demands. If 5 gpm/ft 2 is the allowable rate, 5 additional filters are required. A key to hydraulic loading to the filters is consistent water quality to the filters. Presedimentation basins would eliminate the large variations and reduced quality of the surface water supply, which would provide a more consistent solid contact basin effluent and higher hydraulic loading to the filters. Alternatives evaluated include: Five (5) additional filters to the north or west. Fifty percent (50%) expansion of existing filters. Conventional Sedimentation with 3 filters. Solids Contact Clarifiers with 3 filters. Ballasted Floc Clarifiers with 3 filters. The recommended system includes ballasted floc (presedimentation) units capable of 30 MGD capacity and three high rate filters. The presedimentation units have several benefits, including consistent water quality, algae removal, backwash return treatment, and ability to operate in series with softening basin for highest softening capacity or in parallel mode for greatest hydraulic capacity. The presedimentation basins have an estimated project capital cost of $4,452,000. An additional cost of approximately $260,000 would be required to provide covers for the basins. The addition of three (3) high rate filters has an estimated project capital cost of $4,057,000. Chlorine Dioxide Chlorine dioxide is a strong oxidant used for taste and odor control, algae and organics in surface water supplies. The oxidant is produced on site from sodium chlorite and chlorine. The following is a summary of chlorine dioxide system requirements: The feed system would be sized for flows of 30 MGD and dosage of 1.5 mg/l. A new structure, including sodium chlorite storage/feed room, chlorine dioxide generating room and chlorine storage/scrubbing (if needed) is required for the system. The chlorine dioxide feed system should be tested on raw water (i.e., at surface water pumping station) and on presedimentation basin effluent (at the plant) to evaluate the benefits of physical treatment prior to oxidant addition. The estimated project capital cost for chlorine dioxide system is $782,000 at the surface water pump station. A lower capital cost is required if the facility is located at the WPP site. Big Sioux Water Supply Analysis The vast majority of the City s water supply to the WPP includes 52 wells in the Big Sioux Aquifer, 13 wells in the Middle Skunk Creek Aquifer, and three large surface water pumps at the Big Sioux Pump Station. The total capacity of the well pumps with two surface water pumps operating should be 80 MGD plus. However, at high flows, the system pressure increases, which causes a decreased pumpage from numerous wells. A hydraulic model of the system was Executive Summary EX-5 July 2001

11 developed to evaluate the water supply network, and improvement alternatives were evaluated. The following is a summary of the conclusions and recommendations: Airport Wells 20 wells with design production of 14.9 MGD. South Big Sioux Wells 14 wells with design production of 16.7 MGD. North Big Sioux Wells 18 wells with design production of 10.3 MGD. Middle Skunk Wells 13 wells with design production of 9 MGD. Big Sioux Surface Water Pump Station 3 pumps with a total capacity of 45 MGD and firm capacity of 30 MGD. The model was developed and calibrated to a total system flow (flow and known wells/pumps operating during June 2000) of 51 MGD. The model is very dynamic with a large number of variables, including friction factors, static and pumping water levels, pump curves, valve positions. The model was developed using EPA Net and has been provided to the City. The City should continue to evaluate and fine-tune the model for the varying conditions and use the model to optimize existing production by testing the various well operating scenarios. Various alternatives were developed which evaluated improvements to the system. First, the system was evaluated with all flows into the WTP. Since the presedimentation basin is a high priority, the alternatives were then tested with surface water (SW) in separate transmission lines routed to presedimentation basins. The following are the alternatives evaluated: East Main Relief Parallel line for 36/42-inch transmission main. West Main Relief Parallel line (30-inch) for the 24-inch line from the Surface Water Pumping Station connection to the WPP. Airport Booster Pumping Station Booster station on 30-inch line from airport wells to increase production due to low TDH pumps. Highway 38A Booster Pumping Station Booster station to assist all northern wells (north of diversion structure). The system flows from the various areas with combinations of improvements are summarized in the table below: Executive Summary EX-6 July 2001

12 Condition Airport South Big Sioux North Big Sioux Middle Skunk Creek SWPS Total Comments Estimated Production Existing System w/presed. Basin (1) SW through West 24-inch (1 SW Pump) shutoff SW thru West 24-inch (2 Pumps) (2) shutoff SW thru East 36-inch Main (2 Pumps) shutoff SW thru Both 24/36-inch Mains (2 Pumps) shutoff Improved System w/presed. Basin (2) Airport BPS, SW in West 24-inch (3) (1 Pump) shutoff Hwy 38A BPS; SW in West 24-inch (1 Pump) shutoff Airport BPS, SW in East 36-inch (3) (2 Pumps) shutoff Hwy 38A BPS; SW in East 36-inch (2 Pumps) shutoff Airport BPS/WMR (2 Pumps) shutoff WMR (1 Pump) shutoff WMR (2 Pumps) shutoff Hwy 38A/Airport BPS; SW in East 36-inch shutoff All: WMR/38A/Airport (2 Pumps) shutoff 1. Presedimentation basin located north of WPP approximately 5 feet higher than solids contact basin; Model Runs provide for separation of surface water. 2. An increase of 2.6 MGD from the second SW pump (300 HP) is not economical. A reasonable flow through the 24-inch line is MGD maximum. 3. Under this scenario, the Airport Booster Station has a very moderate pressure increase (10 to 20 feet). Additional pressure increase could boost production but that could cause overpumping of numerous wells. The priority of improvements for the wellfield are as follows: - The West Main relief is required when surface water and well water flows approach 45 MGD occur in the combined 24-inch and 36-inch main lines into the WPP. Separation of surface water and groundwater will be beneficial following construction of the presedimentation basins. This project has a challenging route and an estimated project cost of $1,816, The Highway 38A Booster Pump Station (BPS) has the most significant benefit (10 MGD) and the estimated project cost of $1,325, The Airport Booster station would increase airport well production by a minimum of 4 to 5 MGD at an estimated project cost of $1,090,000. Both BPS s have the advantage of operating only when required, thus do not aggravate the problem of well pumps running out on their system curves under low demand/pressures. This would occur if substantial additional transmission line capacity is added. FACILITY MAINTENANCE AND RELIABILITY IMPROVEMENTS (TM NO.4) Maintenance Building The existing maintenance facilities at the Sioux Falls WPP are inadequate to meet the growing demands of the plant. A new maintenance facility will provide the space required for proper Executive Summary EX-7 July 2001

13 maintenance of equipment to provide optimum operation of the plant. The following describes the propose maintenance building. The maintenance facilities would be a two story building located on the southeast corner of the existing plant building. Space would be allocated in the building for lime feed equipment, a dedicated paint spray booth, abrasive blasting area, washdown area, general service bay, open shop area, parts storage, toilet and locker space, and cubicle office space. The estimated capital cost for the maintenance building is $1,858, Volt Switchgear The electrical switchgear is currently operating satisfactorily from an electrical standpoint, however several mechanical limitations and reliability concerns prompt its replacement. Options for a new switchgear were evaluated. New switchgear options included reusing the existing switchgear space and providing a new building addition for the swithgear. The option of reusing the existing switchgear space requires the rental of a temporary switchgear to keep the plant functional while the new one is installed and has a number of additional disadvantages. A new building addition is recommended for the installation of a new switchgear. The estimated capital cost for the building addition and new switchgear is $699,000. Sludge Handling Improvements A number of improvements to the existing sludge withdrawal and conveyance system were evaluated to increase the reliability of the system and reduced maintenance requirements. The following is a summary of recommended improvements. Currently, a number of the sludge withdrawal lines from the solids contact basins are undersized, often resulting in plugging problems. Increased line sizes will reduce the maintenance required for these lines. The estimated capital cost for this work is $50,800. A number of improvements are recommended for the sludge conveyance system, including the removal of unused piping and valves, replacement of corroded piping and inoperable valves, and replacement of undersized lines. The estimated capital cost for these improvements is $105,500 A sludge thickening and storage basin will provide flexibility in operation and maintenance of the sludge system. The ability to thicken sludge will also decrease the volume of sludge sent to the sludge lagoons. The capital cost of a sludge thickener is estimated at $966,000. Executive Summary EX-8 July 2001

14 FUTURE REGULATORY /FACILITY IMPROVEMENTS (TM NO. 5) Several technologies were evaluated as facility improvements to aid in compliance with the anticipated requirements of the LT2ESWTR and the Stage 2 D/DBP Rule. Membrane Evaluation High-pressure membranes are capable of removing organics from water, which would aid in the reduction of disinfection byproducts. In addition, high-pressure membranes serve as a barrier to pathogenic microorganisms, including viruses. The following summarizes the evaluation of these types of membranes for use at the Sioux Falls WPP. An Information Collection Rule treatment study was previously performed by the South Dakota State University, evaluating high-pressure membranes for Sioux Falls WPP water. The following summarizes the information from the study: Membranes were tested on filtered water from the existing plant. Four membranes were tested. Softening membrane performance showed over 95% TOC removal, 78% to 100% TTHM reduction, and 88% to 100% HAA reduction. Non-softening membrane performance showed 67% to 83% TOC removal, 46% to 84% TTM reduction, and 54% to 79% HAA reduction. Three options for nanofiltration (NF) systems were evaluated for use at the Sioux Falls WPP as follows. Alternative No. 1 consists of treating both groundwater and surface water with a NF system after the water has been pretreated in the existing treatment system. Under Alternative No. 2, NF would serve as a plant expansion to meet future flow demands, treating groundwater only. Surface water and additional groundwater would be treated separately by the existing treatment system. Alternative No. 3 consists of blending surface water treated by the existing plant with raw groundwater prior to NF treatment. Both Alternative No. 1 and Alternative No. 3 require NF system capacity for the entire treatment flow, resulting in extremely high costs that are not warranted. Therefore, only Alternative No. 2 was considered. The estimated capital cost of implementing a NF system under the scheme of Alternative No. 2 is $19,665,000. Due to the raw water quality (iron and manganese) in groundwater available to Sioux Falls, pretreatment would be required upstream of the NF system to prevent fouling. Estimated costs for a greensand pretreatment system are $3,326,000. The potential benefit provided by NF does not justify the high costs associated with this type of treatment for Sioux Falls. The implementation of NF is not recommended. UV Primary Disinfection Evaluation Implementation of UV disinfection at the Sioux Falls WPP would aid in compliance with the LT2ESWTR by providing Cryptosporidium inactivation and the Stage 2 D/DBP Rule by reducing the use of chlorine and reducing disinfection byproduct formation. The following summarizes the results of the evaluation of UV disinfection for Sioux Falls. Executive Summary EX-9 July 2001

15 EPA s current stance on UV disinfection and the current regulatory outlook for the technology is as follows: UV disinfection has been proven effective against bacteria, viruses, and protozoan pathogens, including Giardia and Cryptosporidium. Inactivation credit will be recognized for UV disinfection for viruses, Giardia, and Cryptosporidium. UV dose tables will be provided for target pathogens, although EPA still needs to define the doses, safety factors, and dose-determining virus. The LT2ESWTR is expected to require equipment verification, continuous monitoring of UV intensity and flow rate, low dose alarm with redundant components or automatic shutdown, and regular calibration of UV intensity sensors. The application of a UV disinfection system at Sioux Falls would utilize either lowpressure, high-intensity or medium-pressure, high-intensity lamps. The use of UV radiation for inactivation of Giardia and Cryptosporidium in conjunction with chlorine disinfection for viral inactivation will provide the synergistic benefit of dual disinfectants. Piloting of a UV system at the Sioux Falls WPP will allow further evaluation of the feasibility of using UV disinfection at the plant. Piloting is recommended to be delayed until EPA sets the requirements for UV disinfection. The delay will also allow Sioux Falls to take advantage of any improvements on lamp, reactor, and ballast design that occurs. The implementation of UV disinfection is recommended for the Sioux Falls WPP. The design of the system should be delayed until requirements are set by EPA under the LT2ESWTR. Capital costs for implementation of UV disinfection at Sioux Falls were estimated at $1,780,000. Granular Activated Carbon Evaluation Granular activated carbon (GAC) provides organic removal, reducing the potential for disinfection byproduct formation. A summary of the evaluation of this technology for Sioux Falls follows: The GAC system would be sized to provide 15 minutes of contact time at flows of 30 MGD. System components would include four gravity concrete contactors, feed pump station, and contactor backwash pumps. In addition, a carbon regeneration system would be provided to regenerate spent carbon from the GAC system. The estimated capital costs for a GAC system is $15,120,000. The use of GAC will provide organics removal and reduce the formation of disinfection byproducts. However, the use of a GAC system is not required to meet anticipated Executive Summary EX-10 July 2001

16 regulations. The implementation of such a system may become warranted in the future, though, if stricter requirements are placed upon the plant. FUTURE WATER TREATMENT PLANT EXPANSION (TM NO.6) Proposed Improvements The Sioux Falls WPP site is constrained by Minnesota Avenue on the western boundary, Maple Street to the north, and Burlington Northern Railroad tracks on the east. The area south of the plant includes a significant area used primarily by the Light Department. Potential expansion area is available to the north of the plant across Maple Street. The majority of the plant improvements will be located directly north and west of the existing facilities as shown in the attached figure. The following summarizes each individual improvement and proposed location. Backwash Equalization Basin To allow for coordination with the existing filter washwater basin, the proposed backwash equalization basin will be located adjacent to the existing unit. Estimated Project Cost: $1,030,000. Chlorine Scrubber This unit must be located adjacent to the chlorine storage area due to ductwork requirements. Estimated Project Cost: $244,000. Presedimentation Basins The proposed ballasted flocculation basins require a small footprint and can be located in the area directly north of the existing plant. As an alternate location, the basins could be located north of Maple Street. Estimated Project Cost: $4,452,000 (an additional cost of approximately $260,000 will be required to add covers to the basins). Filter Addition The area directly west of existing Filters No. 8, 9, and 10 is recommended for the location of three additional filters. Estimated Project Cost: $4,057,000. Chlorine Dioxide Addition The preliminary location for chloride dioxide feed equipment is at the surface water intake pump station. With the addition of presedimentation basins, chloride dioxide addition after the basins may be more effective, locating the equipment at the treatment plant. Testing should be performed at each location to determine the best alternative. Estimated Project Cost: $782,000. West Main Relief This new transmission main provides additional capacity from the Surface Water Pumping Station tie-in to the existing 24- and 36-inch transmission main to the WPP. The main allows separation of surface water and groundwater flows, which is increasingly important following construction of presedimentation basins. Estimated Project Cost: $1,816,000. Hwy 38A Booster Pumping Station This booster pumping station must be located near the connection of the surface water pump station to the 24-inch and 36-inch transmission mains. This location is near the intersection of Hwy 38A and Minnesota Avenue. Estimated Project Cost $1,325,000. Airport Booster Pumping Station This booster pumping station must be located on the 30-inch line from the airport wells. An area is available at the main plant site west of the existing filter washwater basin. Estimated Project Cost: $1,090,000. Executive Summary EX-11 July 2001

17 Maintenance Building The building will located on the southeast corner of the main plant. Estimated Project Cost: $1,858,000. Switchgear Room The building space provided for the new 2300-volt switchgear will be located at the southeast corner of the high service pumping room. Estimated Project Cost: $699,000. Sludge Thickener The proposed location for the sludge thickening basin is north of Maple Street. An 8-inch sludge line exists at the north portion of the plant and turns east across the diversion channel. Estimated Project Cost: $966,000. UV Disinfection System UV disinfection reactors will be located in a below-ground vault on the effluent line from the north filters. All water must be treated by the UV system so the south filter effluent line must be routed to this location. Ballast equipment for the system will be located in building above the vault. UV pilot testing is recommended just prior to the design of the project. Estimated Project Cost: $1,788,000. Pilot Testing: $100,000. Filter Gullet/Reservoir No. 1 Modification A baffle in the filter gullet is recommended to dissipate the flow currents and separation of the inlet/outlet piping is recommended. Estimated Project Cost: $100,000 and $30,000, respectively. Sludge Piping Modifications The size of existing 4-inch sludge lines and miscellaneous sludge piping modifications are recommended. Estimated Cost: $156,300. Priority of Improvements The timing of the improvements identified in the Master Plan Update is impacted by operation and maintenance considerations, increasing water demands, and regulatory requirements. The potential improvements were evaluated and a workshop was completed to assist in defining the relative need for each improvement and the overall prioritization of improvements. The following table summarizes the priority of improvements to develop the Capital Improvements Program for the Water Department for the next five years. Executive Summary EX-12 July 2001

18 Capital Improvement Estimated Capital Cost Year 1 (2002) Presedimentation Basins $4,452,000 (1) Chlorine Scrubber $244,000 Electrical Switchgear $699,000 Filter Gullet Modifications $100,000 Reservoir No. 1 Piping Modifications $30,000 Total: $5,525, An additional cost of approximately $260,000 would be required to cover the basins. Year 2 (2003) Backwash Equalization Basin $1,030,000 Maintenance Building $1,858,000 West Main Relief $1,816,000 UV Pilot Testing $100,000 Total: $4,804,000 Year 3 (2004) UV Disinfection $1,780,000 Chlorine Dioxide $782,000 Solids Contact Basin Rehab. (2 basins) $1,100,000 Total: $3,662,000 Year 4 (2005) Sludge Piping $156,300 Sludge Thickening Basin $966,000 Hwy 38A Booster Pump Station $1,325,000 Parking and Access Site Improvements $186,000 Landscaping Site Improvements $250,000 Total: $2,883,300 Year 5 (2006) Filter Addition (3 Filters) $4,057,000 Airport Booster Pump Station $1,090,000 Total: $5,147,000 Note: All costs are April Executive Summary EX-13 July 2001

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22 TECHNICAL MEMORANDUM NO. 1 WATER DEMANDS, WATER QUALITY, AND REGULATIONS Table of Contents Section Page 1.0 INTRODUCTION WATER DEMANDS Historical Water Use Water Use Groups Seasonal Fluctuations Future Water Demands WATER QUALITY Raw Water Solids Contact Clarifier Effluent Filter Effluent Finished Water REGULATIONS Current Regulations Information Collection Rule Effect on the Sioux Falls WPP Interim Enhanced Surface Water Treatment Rule Effect on the Sioux Falls WPP Stage 1 Disinfectant/Disinfection Byproduct Rule Effect on the Sioux Falls WPP Proposed Regulations Filter Backwash Rule Effect on the Sioux Falls WPP Arsenic Rule Effect on the Sioux Falls WPP Radon Rule Effect on the Sioux Falls WPP Future Microbial and Disinfection Byproducts Rules Long Term 2 Enhanced Surface Water Treatment Rule Effect on the Sioux Falls WPP Stage 2 Disinfectants/Disinfection Byproducts Rule Effect on the Sioux Falls WPP...19 Technical Memorandum No. 1 -i- July 2001

23 List of Tables Table Page Table 1-1. Sioux Falls Water Consumption...2 Table 1-2. Residential and Commercial Water Use...3 Table 1-3. Monthly Water Demands for Table 1-4. Water Demand Factors...5 Table Projected System Water Demand...6 Table Projected System Water Demand...6 Table Projected System Water Demand...6 Table 1-8. Future Reduction in Treatment Plant Water Demand...7 Table 1-9. Projected Net Treatment Plant Capacity Required...8 Table Raw Water Quality...9 Table Finished Water Quality...11 Table Potential Regulatory Impact...12 Table TOC Removal Requirements...14 Table Bin Classifications...17 Table Microbial Toolbox...18 List of Figures Figure Following Page Figure 1-1. Existing WPP Process Schematic...20 Technical Memorandum No. 1 -ii- July 2001

24 TECHNICAL MEMORANDUM NO. 1 WATER DEMANDS, WATER QUALITY, AND REGULATIONS 1.0 INTRODUCTION This Technical Memorandum (TM) serves as the first section of the Sioux Falls Water Purification Plant (WPP) Master Plan Update. Three areas are discussed in detail as a part of this TM as follows: Water Demand Water Quality Regulations Historical water demands for Sioux Falls were reviewed and trends of water consumption were developed. The previous Master Plan water consumption projections were also reviewed and updated based upon new population projections and the trends that were developed. The updated water demand projections will be used in subsequent TMs to evaluate future capacity requirements for the WPP. A review of historical water quality of raw and finished water, as well as at various locations throughout the plant was performed. Subsequent TMs will use the water quality information to evaluate the need to implement different treatment processes to produce safe drinking water that protects the public health. Current, proposed, and future regulations that pertain to the Sioux Falls WPP were also reviewed as a part of this TM. In addition, potential impacts of the regulations on the plant were identified and discussed. 1.1 WATER DEMANDS HISTORICAL WATER USE Water system demands vary on an hourly, daily, and seasonal basis. In addition, the rate varies across geographic sections of the country. Variations of water consumption can be best explained by such factors as weather patterns, social factors, economic factors, and technological advances. A community s water system requirements are driven by the physical and climatic characteristics of the community, the type and pattern of community water use, expected trends in future commercial and industrial development, and the percentage of metered customers. Because of the unique water use characteristics of a community, past system records typically serve as the primary basis for predicting future water requirements. The operating records of the Sioux Falls WPP have been used in the preparation of this report. In addition, trends developed in previous water management and water distribution system plans for Sioux Falls have been used in the development of this study. The consumption of treated water for Sioux Falls from 1975 to 2000 is presented in Table 1-1. The average water use for the period was 158 gallons per capita per day. The average per capita consumption of treated water inversely corresponds with annual precipitation. The minimum water use of 136 gallons per capita per day occurred during 1993, which was the wettest year of Technical Memorandum No July 2001

25 the period. The maximum water consumption of 176 gallons per capita per day occurred during 1988, corresponding with low precipitation. Year Annual (MG) Table 1-1. Sioux Falls Water Consumption Water Consumption (1) Daily Average (MGD) Daily Maximum (MGD) Population Average Per Capita Consumption (gpcd) Annual Precipitation (inches) , , , , , , , , , , , , , , , , , , , , , , , , , (2) , Water consumption based on plant influent flow data. 2. Year 2000 water consumption and population results are estimated Water Use Groups The disposition of treated water for Sioux Falls generally falls into two categories, metered sales and non-metered usage. Metered sales can be further categorized as residential, commercial, and industrial use. The residential class includes domestic water users such as houses, condominiums, apartments, and trailer homes. Commercial users include schools, churches, hospitals, business offices, restaurants, and other similar institutions. Historical water Technical Memorandum No July 2001

26 consumption records were reviewed to determine the average daily per capita water usage for residential and commercial users. The data indicates that average per capita consumption has increased somewhat over the years somewhat independent of annual precipitation. This is most likely due to the increased use of automatic sprinkler systems. As a result of this trend, the use of water consumption rates from recent years is appropriate for projecting future water demand. Average daily water use and per capita consumption for residential and commercial users for the period from 1995 to 2000 is shown in Table 1-2. Table 1-2. Residential and Commercial Water Use Year Population Average Use (1) (MGD) Per Capita Consumption (gpcd) Residential Commercial Residential Commercial , , , , , (2) 129, Water use based on metered flow data. 2. Year 2000 water use and population results are estimated. Based upon the period presented above, the average residential water consumption was approximately 77 gallons per capita per day, and the average commercial water consumption was approximately 50 gallons per capita per day. A review of total average per capita consumption from Table 1-1 indicates an average of 163 gallons per capita per day for this period. The highest historical per capita consumption, which occurred in 1988 corresponding with a dry year, is 176 gallons per capita. For projections of future water demand that would occur during a dry year, a factor of 1.08 (176/163) will be applied to average day demand projections. This is a conservative assumption that neglects the fact that the industrial component is independent of population. The John Morrell Company is the only industrial water user for the Sioux Falls WPP. Historical water use records for the facility indicate that water consumption has remained fairly constant from year to year, averaging approximately 3 million gallons per day. It is anticipated that the future water use will remain essentially unchanged. Therefore, a value of 3 million gallons per day will be assumed for future industrial water use. Non-metered usage includes both unmetered and unaccounted for water and is basically the difference between the amount of total treated water and metered sales. Unmetered usage includes water for fire fighting, street sweeping, sanitary and storm sewer cleaning, hydrant flushing, tank draining, main breaks, main cleaning, and other similar sources of water consumption. The amount of non-metered usage fluctuates from year to year with no apparent trend. Previous water management and water distribution studies have used a value of 10% of total average water production to estimate non-metered water. This value is based upon historical data from Sioux Falls as well as experience with other similar Midwestern water Technical Memorandum No July 2001

27 utilities. For the purpose of this study, a non-metered usage of 10% of total water production will be used for estimating future water demands Seasonal Fluctuations Water consumption for a community will fluctuate throughout the year with higher water usage occurring during summer months and lower water usage occurring during the winter. Lawn watering during the summer accounts for a considerable portion of the increase in demand. Sioux Falls has placed lawn watering restrictions in various forms on users since 1987 in an effort to curtail high water usage. Even with these restrictions, seasonal fluctuations in water consumption have occurred and are anticipated to continue. Table 1-3 shows monthly water demands for Table 1-3. Monthly Water Demands for 1999 Month Average Day Demand (MGD) January 16.4 February 16.2 March 16.6 April 17.2 May 19.2 June 23.2 July 27.7 August 32.4 September 25.3 October 19.7 November 18.4 December 16.2 For the purpose of this study, future winter month demands will be developed to determine clearwell storage requirements when water temperature is a minimum, requiring greater disinfection contact times. Based upon the average winter monthly water consumption presented in Table 1-3 (December through March 16.35) and the average daily water consumption for 1999 (20.74), the average day demand for a winter month can be estimated to be approximately 79% of the average day consumption FUTURE WATER DEMANDS The average residential and commercial per capita demands of 77 and 50 gallons per capita per day, respectively, were used in conjunction with population projections to calculate future water consumption for a year with average precipitation. As discussed previously, industrial water usage was assumed to remain constant at 3 million gallons per day, and the non-metered water usage was calculated at 10% of total future water demand. Dry year demands were developed by applying a factor of 1.08 to the total average projections. Technical Memorandum No July 2001

28 As discussed previously, water demand will vary throughout the year with lower flow requirements occurring during the winter. Taking into account the lower water demands during the winter is important because lower water temperatures result in increased detention time required for disinfection. For the purpose of evaluating clearwell storage requirements to be discussed in detail in a subsequent TM, average day water demands for a winter month were developed based upon the estimated 79% of the average day consumption developed previously. Future maximum day and maximum hour water consumption for Sioux Falls was calculated by applying factors to the average day water use. Daily and hourly water consumption patterns will differ greatly between the residential, commercial, industrial and non-metered water use groups. Therefore, different factors must be applied to the average water demand for each user. The ratios that have been developed by previous studies appear to be consistent with the historical operating data for Sioux Falls and will be used in this study. Table 1-4 summarizes the maximum day and maximum hour water demand factors. Table 1-4. Water Demand Factors Water Use Group Maximum Day/ Maximum Hour/ Average Day Average Day (1) Residential Commercial Industrial Non-metered The maximum hour to average day ratio is based upon total system water demand. Actual WPP pumpage may be reduced due to some demand being met by pumping from distribution system reservoirs. Also as the system and service population increases the historical ratios may begin to decrease slightly. Current population projections for Sioux Falls indicate a more aggressive growth than was anticipated by previous projections. The population projected for the year 2015 is 156,000 and for the year 2025 is 185,000. Interpolating between these projections and the current population, a population of 147,000 was estimated for Based upon these population projections and the water use characteristics discussed previously, Tables 1-5, 1-6, and 1-7 summarize the future water demands. Technical Memorandum No July 2001

29 Table Projected System Water Demand Water Demand (MGD) Water Use Group Average Day Maximum Day Maximum Hour (1) Winter Average Dry Year Average Dry Year Average Dry Year Residential Commercial Industrial Non-metered Total Maximum hour demands are based upon total system water demand. Actual WPP pumpage will be reduced due to some demand being met by pumping from distribution system reservoirs. Based upon historical operating records, maximum hour pumpage from the WPP is approximately 120% of maximum day demand. Table Projected System Water Demand Water Demand (MGD) Water Use Group Average Day Maximum Day Maximum Hour (1) Winter Average Dry Year Average Dry Year Average Dry Year Residential Commercial Industrial Non-metered Total Maximum hour demands are based upon total system water demand. Actual WPP pumpage will be reduced due to some demand being met by pumping from distribution system reservoirs. Based upon historical operating records, maximum hour pumpage from the WPP is approximately 120% of maximum day demand. Table Projected System Water Demand Water Demand (MGD) Water Use Group Average Day Maximum Day Maximum Hour (1) Winter Average Dry Year Average Dry Year Average Dry Year Residential Commercial Industrial Non-metered Total Maximum hour demands are based upon total system water demand. Actual WPP pumpage will be reduced due to some demand being met by pumping from distribution system reservoirs. Based upon historical operating records, maximum hour pumpage from the WPP is approximately 120% of maximum day demand. Water demand projections in Table 1-5, 1-6, and 1-7 represent the total system water demand. The water treatment plant pumpage is anticipated to match system demand for average day and maximum day conditions. The maximum hour WPP pumpage will be lower than the total Technical Memorandum No July 2001

30 system demand as some of the demand is met by pumping from reservoirs located in the distribution system. Review of historical operating data indicates that the maximum hourly rate at the plant can be estimated at approximately 120% of maximum day demand. Sources of additional treated water available to Sioux Falls will reduce the total treatment plant requirement. Current and anticipated additional treated water sources for Sioux Falls include water from the Southern Skunk Creek aquifer, Wall Lake aquifer, and Lewis and Clark rural water project. A well currently exists in the Southern Skunk Creek aquifer with a capacity of approximately one million gallons per day, which is typically used for peaking purposes only. Use of water from the Wall Lake aquifer is currently being investigated. The water is of relatively poor quality, and the capacity of the aquifer is lower than originally anticipated. Water from this aquifer would be used for peaking purposes only, and a maximum capacity of 3 million gallons per day will be assumed for the purpose of this study. Sioux Falls anticipates that the Lewis and Clark rural water supply project will provide 10 million gallons per day of treated water. This source will not be for peaking purposes, but will be continuous throughout the year. The Lewis and Clark project will also serve as a supply to Lincoln County Rural Water, which is currently a customer of Sioux Falls. This will remove approximately one million gallons per day from the average Sioux Falls demand and approximately 1.5 million gallons per day from the maximum day and maximum hour demands. Table 1-8 summarizes the additional treated water sources and the reductions in treated water requirements under the various water demand conditions. Table 1-8. Future Reduction in Treatment Plant Water Demand Reduction (MGD) Additional Water Average Day Maximum Day Maximum Hour Source/Reduction Winter Average Dry Year Average Dry Year Winter Average Dry Year Wall Lake Southern Skunk Creek Lewis & Clark Lincoln County Rural Reduction & 2025 Reduction The Wall Lake Aquifer is assumed to be operational in 3 to 5 years. 2. The Lewis and Clark project will not be operational until about Lincoln County Rural Water will be supplied by Lewis and Clark. Table 1-9 summarizes the total treatment plant capacity anticipated after taking into account the reduction in water demand seen at the plant under maximum hour conditions, with and without the reductions shown in Table 1-8. Technical Memorandum No July 2001

31 Table 1-9. Projected Net Treatment Plant Capacity Required Treatment Plant Capacity (MGD) Year Average Day Maximum Day Maximum Hour Winter Average Dry Year Average Dry Year Winter Average Dry Year WITHOUT REDUCTIONS WITH REDUCTIONS WATER QUALITY RAW WATER The Sioux Falls WPP is a conventional filtration system with lime softening, treating both groundwater and surface water. A process schematic of the existing plant is shown in Figure 1-1 illustrating treatment units and chemical feed locations. Water from several groundwater sources are treated at the WPP including the Big Sioux Aquifer, Middle Skunk Creek Aquifer, Southern Skunk Creek Aquifer, and the Split Rock Creek Aquifer. The surface water source for the plant is the Big Sioux River. Surface water and groundwater are blended in two headers prior to entering the Sioux Falls WPP. The amount of surface water and groundwater in each header depends on a number of factors including the proportion of each type of water being used, which groundwater wells are being used, and valve positions in influent piping. Table 1-10 summarizes the raw water quality of composite water from the two influent headers to the Sioux Falls WPP as well as the surface water quality based on data from January 1, 1998 to October 20, Technical Memorandum No July 2001

32 Table Raw Water Quality Parameter (1) South Header North Header Big Sioux River Avg. Min. Max. Avg. Min. Max. Avg. Min. Max. ph, standard units Turbidity, NTU Temperature, o C Total Hardness Ca Hardness Mg Hardness Total Alkalinity Iron Manganese Fluoride Chloride Bromide Nitrate Ortho Phosphate Total Phosphate Sulfate TDS NPOC UV-254, cm All results in milligrams per liter unless otherwise noted. The composite groundwater and surface water treated at the Sioux Falls WPP is characterized as a very hard water with high concentrations of both calcium and magnesium. Very hard water can be considered to have a total hardness of over 300 mg/l. Water treated by the plant averages a total hardness of over 500 mg/l. Approximately half of the hardness is noncarbonate. The water is also high in iron and manganese with concentrations that well exceed the secondary maximum contaminant levels set for the contaminants. The high levels are primarily from the groundwater sources. Turbidity is also high, primarily from surface water, although the starting and stopping of well pumps results in high spikes of turbidity from groundwater. High levels of organics also result primarily from surface water. The water quality of the Big Sioux River is variable throughout the year depending on the source of water contributing to the river. During the winter and summer when the river is characterized by low flow, recharge of the river from groundwater occurs. This recharge typically results in increased mineral content of the water and increased hardness. Overall, the hardness of the Big Sioux River water is a bit lower than water from the groundwater sources, but the water is still considered to be very hard with total hardness averaging over 450 mg/l. During the spring, runoff significantly impacts the river water quality. Surface runoff results in a decrease in mineral content while causing significant increases in turbidity and organic carbon. In addition, taste and odor problems typically occur as a result. Technical Memorandum No July 2001

33 1.2.2 SOLIDS CONTACT CLARIFIER EFFLUENT Six solids contact clarifiers perform pretreatment or raw water at the Sioux Falls WPP. The basins were initially designed for iron and manganese removal and softening of groundwater. With the addition of surface water in 1990, the basins also perform a number of additional treatment functions including the removal of the following: Turbidity Organics Taste and odor Dissolved solids Future disinfection byproduct reduction will be discussed in detail in a subsequent technical memorandum of this Master Plan Update. Since natural organic matter (NOM) is a precursor for disinfection byproducts, the ability of the Sioux Falls WPP to remove organics is an important aspect to evaluate for the purpose of this study. The solids contact clarifiers perform the vast majority of the organic removal achieved by the plant. Evaluating operational data from 1999 indicates that basin effluent total organic carbon (TOC) ranged from a minimum of 1.8 mg/l to a maximum of 5.3 mg/l and averaged approximately 3.6 mg/l. These values of TOC are relatively high and indicate a high potential for disinfection byproduct formation. Specific ultraviolet absorbance (SUVA) is an indicator used to evaluate the molecular weight distribution of NOM in water and the ability of NOM to be removed by coagulation. A higher SUVA, typically greater than 3 L/mgm -1, indicates a greater fraction of higher molecular weight organics and that relatively high removals of dissolved organic carbon (DOC) can be achieved by coagulation. Lower values of SUVA indicate that low DOC removal is expected. Evaluation of water quality data for the Sioux Falls WPP reveals that the raw water has an average SUVA of just above 2 L/mgm -1 and the solids contact clarifier effluent averages an SUVA of just under 2 L/mgm -1. Based upon these SUVA values, increased NOM removal by the solids contact clarifiers cannot be expected FILTER EFFLUENT The Sioux Falls WPP currently operates with ten high-rate granular media filters for particulate matter and pathogenic microorganism reduction. Review of operating data indicates the filters achieve good suspended solids removal. Filter effluent turbidity typically averages approximately 0.06 NTU. An 18-inch granular activated carbon cap is maintained in the filters for organics removal. Operating data for the Sioux Falls WPP from 1999 indicates that the concentration of TOC in filter effluent averages approximately 3.2 mg/l, which is a bit lower than the solids contact clarifier effluent. The reduction in TOC is relatively small, though, resulting in a considerable amount of organics in the filter effluent that ultimately reacts with chlorine to form disinfection byproducts. Technical Memorandum No July 2001

34 1.2.4 FINISHED WATER Finished water quality for the Sioux Falls WPP from January 1, 1998 to December 31, 1999 is summarized in Table Table Finished Water Quality Parameter (1) Average Minimum Maximum ph, standard units Turbidity, NTU Temperature, o C Free Chlorine Total Chlorine Total Hardness Calcium Hardness Magnesium Hardness Total Alkalinity Iron Manganese Fluoride Chloride Bromide Nitrate Ortho Phosphate Total Phosphate Sulfate Total Dissolved Solids NPOC UV-254, cm TTHM, g/l All results in milligrams per liter unless otherwise noted. Water quality parameters of interest for this study include those that affect disinfection including, water temperature, ph, and chlorine residual. These parameters will be used in the evaluation of contact time required for disinfection and the future need for additional clearwell storage capacity. An additional finished water quality parameter of interest for this study is the TTHM concentration. As shown in Table 1-11, concentrations as high as 60 mg/l of TTHM have been present in finished water leaving the WPP. These high levels indicate that a reduction in organic matter or a switch to a disinfectant that reduces or does not form byproducts such as chloramines or UV disinfection may be required to meet future regulatory requirements. Technical Memorandum No July 2001

35 1.3 REGULATIONS Finished water quality from the Sioux Falls WPP is currently in full compliance with the requirements of Safe Drinking Water Act (SDWA) regulations. However, a number of recently promulgated regulations will require some process modifications to be implemented prior to the compliance date of the rules. In addition, a number of proposed and future regulations could potentially impact the water treatment plant. A discussion of important current, proposed, and future regulations with the potential effects on the Sioux Falls WPP follows. Table 1-12 summarizes the regulations that will potentially impact tasks to be addressed in detail as a part of this Master Plan Update. Task Table Potential Regulatory Impact Regulation ICR IESWTR Stage 1 D/DBP FBR LT2ESWTR Stage 2 D/DBP Clearwell Storage Capacity Filter Backwash Recycle Chlorine Scrubber Requirements Rapid Sand Filter Expansion Future DBP Reduction UV Primary Disinfection EPA Risk Man CURRENT REGULATIONS Information Collection Rule The Information Collection Rule (ICR) was published in the Federal Register on May 14, The ICR is intended to provide a substantial amount of background data from systems across the country on the microbial contaminants and disinfection byproducts in the various systems. This data will be used to develop future regulations for these contaminants Effect on the Sioux Falls WPP Data collected from the ICR study performed on the Sioux Falls WPP system will aid in evaluating compliance with future requirements. In particular, the ICR pilot study using membrane filtration will be discussed further in an evaluation of membrane filtration for disinfection byproduct precursor removal Interim Enhanced Surface Water Treatment Rule The Interim Enhanced Surface Water Treatment Rule (IESWTR) was promulgated on December 16, 1998 and became effective on February 16, This rule affects systems treating surface water or ground water under direct influence of surface water serving 10,000 or more people. Technical Memorandum No July 2001

36 The IESWTR builds upon the treatment technique approach of the SWTR. Some key components of this rule are as follows: Combined filter water turbidity level limit of 0.3 NTU in at least 95% of measurements. Turbidity levels shall not exceed 1.0 NTU at all times (maximum instantaneous). Individual filters shall have continuous monitoring. Turbidities greater than 1.0 NTU based on two measurements fifteen minutes apart or levels greater than 0.5 NTU after four hours of operation shall be reported to the State. Self-assessments and performance evaluations can be required if turbidity levels are exceeded. An MCLG of zero for Cryptosporidium was set to protect health. A minimum of 2-log removal of Cryptosporidium will be required Effect on the Sioux Falls WPP Filter effluent turbidimeters were installed on individual filters over a decade ago allowing for continuous turbidity monitoring. In addition, particle counters have recently been installed. A review of operating data shows that the filters have been in compliance with the turbidity requirements of the IESWTR. In addition, the Sioux Falls WPP falls under the category of a well operated conventional filtration plant and receives a 2-log credit for Cryptosporidium removal. Therefore, the IESWTR is not expected to have an effect on the facility Stage 1 Disinfectant/Disinfection Byproduct Rule The Stage 1 Disinfectants/Disinfection Byproducts (D/DBP) Rule applies to all community water systems and non-transient non-community systems that use a disinfectant at any point of the treatment process. The rule was promulgated on December 16, The compliance date for systems serving 10,000 or more people is January The following are some of the key components of this rule. Maximum residual disinfectant levels (MRDLs) for three chemical disinfectants were set as follows: - Chlorine: 4.0 mg/l as Cl 2 - Chloramine: 4.0 mg/l as Cl 2 - Chlorine Dioxide: 0.8 mg/l as ClO 2 DBPs in distribution systems must be reduced to the following MCLs: - Total Trihalomethanes (TTHMs): mg/l (running annual average) - Five Haloacetic Acids (HAA5): mg/l (running annual average) - Bromate Ion: mg/l (running annual average) - Chlorite Ion: 1.0 mg/l (three-sample average) Systems must meet the required TOC removal by enhanced coagulation and enhanced softening as set forth in the following table or meet one of the alternative compliance criteria. Technical Memorandum No July 2001

37 Table TOC Removal Requirements Source Water Alkalinity (mg/l as CaCO 3 ) Source Water < 60 mg/l TOC 60 mg/l mg/l mg/l mg/l 35% 25% 15% mg/l 45% 35% 25% > 8.0 mg/l 50% 40% 30% Effect on the Sioux Falls WPP Sioux Falls has performed distribution system testing for TTHM since 1994 and for HAA5 since While results from the testing has shown that the four-quarter running annual average for HAA5 has been well within the MCL set by the Stage 1 D/DBP Rule, the 0.08 mg/l limit for TTHM has periodically been exceeded. To provide a reduction in TTHM formation and meet the requirements of the Stage 1 D/DBP Rule, the Sioux Falls WPP will convert their disinfection system to chloramines in the following year. Ammonia will be fed to treated water exiting the clearwell to quench the free chlorine residual and form chloramines for the distribution system. It is anticipated that the conversion will allow the system to be in compliance with the disinfection byproduct MCL requirements of the rule. Review of operating data indicates that the Sioux Falls WPP complies with the TOC removal requirements of the Stage 1 D/DBP Rule. In addition, the plant meets one of the alternative compliance criteria for softening plants by removing over 10mg/L of magnesium hardness. Therefore, the TOC removal requirement of the rule is not anticipated to prompt any action for the Sioux Falls WPP PROPOSED REGULATIONS Filter Backwash Rule The proposed Filter Backwash Rule (FBR) is expected to be promulgated in the beginning of 2001 and become effective in late This rule will require all water systems using rapid sand filters with surface water supplies to return filter backwash, thickener supernatants, and liquids from dewatering processes prior to the point of primary coagulant chemical addition. Alternative recycle locations may be approved by the State, however, it must be demonstrated that the alternative location is required to provide optimal finished water quality, the plant needs the recycle flow as an intrinsic component of the process, or that the plant has unique treatment requirements or processes. Softening plants may recycle solids at the point of lime addition preceding the softening process, however, all liquid recycle must be returned prior to the point of chemical addition. Under the proposed rule, backwash water equalization or treatment is not required before it is recycled. For systems that employ conventional filtration, employ 20 or fewer filters to meet production requirements during the highest production month, and recycle directly to the treatment process without any equalization or treatment, a recycle self-assessment must be performed and the results reported to the State. The main purpose of this self-assessment is to Technical Memorandum No July 2001

38 determine whether recycle overloads the treatment system. Based upon the self-assessment, the State will determine if any modifications must be made Effect on the Sioux Falls WPP Filter backwash water is not currently recycled at the Sioux Falls WPP. Due to concerns with the accumulation of pathogenic microorganisms in backwash water and process upsets in the solids contact clarifiers associated with its recycle, filter backwash water is sent to the Water Reclamation Facility. If the current practice of wasting filter backwash is continued, the FBR will not be applicable to the Sioux Falls WPP. Wasting of filter backwash results in a loss of approximately three to five percent of treated water. If Sioux Falls decides to recycle the water to promote the conservation of water resources available to the city, the WPP will need to comply with the FBR. The recycle must be returned at or prior to the point of lime addition preceding the softening process. In addition, a recycle self-assessment will be required to determine if returning backwash water overloads the treatment system. If the backwash basin volume is greater than or equal to the volume of spent filter backwash water from one backwash event or if treatment is implemented, a recycle selfassessment will not be required. The overriding issue for Sioux Falls is to insure that the ability to provide safe drinking water to its customers is not compromised. In order to protect public health, a conservative approach of exceeding the minimum FBR requirements will be required by providing treatment of filter backwash water. Some form of treatment will be necessary to prevent the disruption of the softening process and remove accumulated pathogenic microorganisms Arsenic Rule The Arsenic Rule published in the Federal Register on June 22, 2000 proposes to lower the existing MCL for Arsenic from 50 g/l to 5 g/l and seeks comment on alternate MCLs of 3 g/l, 10 g/l, and 20 g/l. As of this date (April 5, 2001), the promulgation of the Arsenic Rule is on hold as the rule is being reviewed. The lowered standard aims at further protecting public health by reducing the risk of chronic effects of long-term exposure to arsenic in drinking water. The long-term consumption of water with low concentrations of arsenic can lead to various forms of cancer including bladder, skin, and lung. Other non-cancer adverse health effects include cardiovascular disease, diabetes, developmental, and neurological effects Effect on the Sioux Falls WPP Water quality testing results of finished water from the Sioux Falls WPP have demonstrated arsenic levels less than the proposed 5 g/l standard. Therefore, it is not anticipated that the Arsenic Rule will have an effect on the Sioux Falls WPP Radon Rule Radon is a naturally occurring radioactive gas that has been shown to be a major contributor to lung cancer. According to a 1999 report by the National Academy of Science, the inhalation of radon from indoor air contributes to approximately 20,000 lung cancer deaths in the United States each year. The release of radon from drinking water contributes an estimated one to two Technical Memorandum No July 2001

39 percent of the total radon of indoor air, increasing the risk of lung cancer. In addition, the consumption of drinking water with radon poses a small risk of stomach cancer. Based upon the cancer risks associated with radon in drinking water, the Radon Rule was proposed in the Federal Register on November 2, 1999 and is expected to be finalized in the first half of The rule will require the following: An MCL of 300 picocuries per liter for radon in drinking water. An alternate MCL of 4,000 picocuries per liter for radon in drinking water if the state implements a Multimedia Mitigation (MMM) program. The MMM program is aimed at a cost-effective method of radon reduction by addressing the soil source of radon in indoor air, while also addressing high levels of radon in drinking water. The goal of an MMM program is to reduce the public health risk from radon by an amount comparable to that achieved by treating drinking water to the 300 picocuries per liter MCL Effect on the Sioux Falls WPP Review of past testing results indicates that the concentration of radon in finished water from the Sioux Falls WPP has consistently been below the 300 picocuries per liter MCL proposed by the Radon Rule. Therefore, it is anticipated that the Sioux Falls WPP will meet the requirements of the rule without implementing any type of radon treatment, regardless of whether or not the State of South Dakota implements an MMM program FUTURE MICROBIAL AND DISINFECTION BYPRODUCTS RULES A negotiative rulemaking process for the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) and the Stage 2 D/DBP Rule came to a conclusion in the form of a Federal Advisory Committee Act (FACA) committee agreement approved September 29, The agreement in principle resulting from this negotiative process will serve as the basis for the Environmental Protection Agency to formally propose the Stage 2 D/DBP rule and LT2ESWTR in Spring 2001 and issue a final rule May The Stage 2 D/DBP rule and LT2ESWTR will contain the principle of simultaneous compliance. This means that systems will address the Stage 2 D/DBP rule and LT2ESWTR requirements concurrently in order to protect public health by ensuring a proper balance between microbial and DBP risks while optimizing technology choice decisions Long Term 2 Enhanced Surface Water Treatment Rule The LT2ESWTR will be proposed to provide further protection from Cryptosporidium contamination of drinking water. Based upon the recommendations of the FACA committee agreement, the following are the anticipated requirements of the LT2ESWTR The total Cryptosporidium removal requirement for a system will be based upon the source water quality. Conventional treatment plants in compliance with the IESWTR will be given a 3- log removal credit for Cryptosporidium. Technical Memorandum No July 2001

40 Source water monitoring for Cryptosporidium will be required to determine the bin classification of the system. Bins are categories of additional treatment (beyond conventional treatment) required based upon source water Cryptosporidium concentrations as follows: Bin Number Average Cryptosporidium Concentration Table Bin Classifications 1 Cryptosporidium < 0.075/L No action /L Cryptosporidium < 1.0/L 3 1.0/L Cryptosporidium < 3.0/L Additional treatment requirements for systems with conventional treatment that are in full compliance with IESWTR 1-log treatment (systems may use any technology or combination of technologies from toolbox as long as total credit is at least 1-log). 2.0-log treatment (systems must achieve at least 1- log of the required 2-log treatment using ozone, chlorine dioxide, UV, membranes, bag/cartridge filters, or in-bank filtration). 4 Cryptosporidium 3.0/L 2.5-log treatment (systems must achieve at least 1- log of the required 2.5-log treatment using ozone, chlorine dioxide, UV, membranes, bag/cartridge filters, or in-bank filtration). The total Cryptosporidium removal requirement depending upon bin classification will be 3, 4, 5, or 5.5-log removal. Treatment options allowed to meet the additional removal requirements are listed in Table Technical Memorandum No July 2001

41 Table Microbial Toolbox APPROACH Potential Log Credit >2.5 Watershed Control Watershed Control Program (1) Reduction in oocyst concentration (3) As measured Reduction in viable oocyst concentration (3) As measured Alternative Source Intake Relocation (3) As measured Change to Alternative Source of Supply (3) As measured Management of Intake to Reduce Capture of Oocysts As measured in Source Water (3) Managing Timing of Withdrawal (3) As measured Managing Level of Withdrawal in Water Column (3) As measured Pretreatment Off-Stream Raw Water Storage w/detention ~ X days (1) Off-Stream Raw Water Storage w/detention ~ Y weeks (1) Pre-Settling Basin w/coagulant Lime Softening (1) In-Bank Filtration (1) Improved Treatment Lower Finished Water Turbidity (0.15 NTU 95% tile CFE) Slow Sand Filters (1) X Roughing Filter (1) Membranes (MF, UF, NF, RO) (1) X Bag Filters (1) Cartridge Filters (1) Improved Disinfection Chlorine Dioxide (2) Ozone (2) UV (2) Peer Review/Other Demonstration/Validation or System Performance Peer Review Program (ex. Partnership Phase IV) Performance studies demonstrating reliabile specific log removals for technologies not listed above. This prpovision does not supercede other inactivation As demonstrated requirements. 1. Criteria to be specified in guidance to determine allowed credit. 2. Inactivation dependent on dose and source water characteristics. 3. Additional monitoring for Cryptosporidium after this action would determine new bin classification and whether additional treatment is required. Technical Memorandum No July 2001

42 Effect on the Sioux Falls WPP Sioux Falls will be required to monitor their source water for Cryptosporidium. If the presence of Cryptosporidium in the source water is low, it is possible that no action will be required. If higher concentrations are discovered, additional treatment will be required to provide from 1 to 2.5-log removal of Cryptosporidium. Monitoring that has been performed to date has found cysts in the raw water. None of the cysts found have been viable, as all detections have been empty cysts or cysts with very few internal parts. A number of treatment alternatives are listed in Table 1-15 that can be implemented by Sioux Falls to meet additional treatment requirements that may be placed upon the treatment system. Membrane filtration or UV disinfection may be the most feasible options if the source water is found to be highly susceptible to Cryptosporidium contamination. These technologies provide excellent pathogen removal or inactivation and are anticipated to receive the highest log removal credit Stage 2 Disinfectants/Disinfection Byproducts Rule To further protect the public from the adverse health effects of disinfection byproducts, the Stage 2 D/DBP Rule will build upon the requirements of the Stage 1 D/DBP Rule. The following summarizes the anticipated requirements of the rule based upon the September 29, 2000 FACA committee agreement. MCLs for TTHMs, HAA5, bromate, and chlorite will not be reduced from the Stage 1 levels. The bromate level will be reviewed as part of the 6 year review process to determine whether a reduction to mg/l or lower concentration is required. TTHM and HAA5 monitoring will be a location running annual average as opposed to averaging across the distribution system that is required under the Stage 1 D/DBP Rule. Sampling points to determine compliance with the rule will be identified by an initial distribution system evaluation (IDSE). Monitoring will be required every other month (approximately 60 days) for one year at eight distribution sites that are different from sites monitored under the Stage 1 requirements. Based upon the IDSE, compliance monitoring will be required at four locations: - One for the representative average from the Stage 1 locations. - One at the high HAA5 site location as identified by the IDSE. - Two at the highest TTHM site locations as identified by the IDSE. Compliance sample frequency will remain quarterly Effect on the Sioux Falls WPP Review of monitoring data indicates that the concentration of HAA5 at individual distribution system locations has remained within the expected MCL for the Stage 2 D/DBP rule. Concentrations of TTHM, though, have exceeded the expected MCL at various monitoring Technical Memorandum No July 2001

43 locations. As discussed under the Stage 1 D/DBP Rule, the Sioux Falls WPP will convert to chloramines in the following year. It is expected that the conversion will reduce the formation of disinfection byproducts. Whether the use of chloramines will result in compliance with the Stage 2 D/DBP Rule requirements for TTHM cannot be determined at this time. If it is discovered after the conversion that the anticipated requirements would not be met, several alternatives exist for implementation in the following years to aid the Sioux Falls WPP in further reducing disinfection byproduct formation. The alternatives that show the most promise for implementation at the Sioux Falls WPP include: Membrane filtration for the removal of natural organic matter. UV disinfection to reduce the requirement for chlorine/chloramines. Technical Memorandum No July 2001

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46 TECHNICAL MEMORANDUM NO. 2 CAPACITY/NEAR TERM REGULATORY IMPROVEMENTS Table of Contents Section Page 2.0 INTRODUCTION CLEARWELL STORAGE CAPACITY Existing Conditions Disinfection Requirements Current Disinfection Practice Existing Clearwells Water Quality Disinfection Capacity Future Conditions Future Disinfection Practice Projected Water Demands Future Disinfection Capacity Clearwell Operation to Maximize Disinfection Capacity Clearwell Operation to Provide Operating Volume Future Clearwell Requirements FILTER BACKWASH RECYCLE Backwash Procedures Current Backwash Generation Future Backwash Generation Backwash Storage Existing Storage Basin Backwash Storage Pumping Facilities Backwash Water Quality Effects of Backwash Recycle Past Plant Experience with Backwash Recycle Other Potential Effects Alternatives for Filter Backwash Handling Pump Backwash to City WWTP Membrane Treatment Ballasted Floc and Gravity Filtration Treatment Alternative Treatment and Recycle Equalized Flow to Presedimentation Basin Irrigation of Backwash Water Estimated Total Cost Summary Recommendations CHLORINE TREATMENT/CONTAINMENT Chlorine Use, Storage, and Handling Current use and layout Needs Evaluation...28 Technical Memorandum No. 2 -i- July 2001

47 Risk management plan Uniform Fire Code Chlorine Scrubbing/Containment Alternatives Scrubbers Wet Scrubbers Dry Scrubbers Scrubbing Comparison Total Containment Systems Scrubbing Cost Comparison Wet Scrubber Dry Scrubber Estimated Total Cost Summary Unloading Protection Recommendations...35 Technical Memorandum No. 2 -ii- July 2001

48 List of Tables Table Page Table 2-1. Existing Clearwells...2 Table 2-2. Finished Water Quality...3 Table 2-3. Existing Clearwell Disinfection Capacity...4 Table 2-4. Projected Water Demand...6 Table 2-5. Disinfection CT with Clearwell Volume Maximized...7 Table 2-6. Operational Flow Data and Calculated Operating Volumes...8 Table 2-7. Disinfection CT with Clearwell Operating Volume...9 Table 2-8. Opinion of Probable Capital Cost for 3 MG Clearwell...11 Table 2-9. Design and Actual Filter and Filter Backwash Facilities...12 Table Current Backwash Volumes...13 Table Water Demand Projections...13 Table Projected Backwash Volumes...13 Table Characteristics of Filter Backwash Water ( )...15 Table Opinion of Probable Capital Cost for Vertical Wells...17 Table Opinion of Probable Cost to Dispose of Filter Backwash Water...18 Table Opinion of Probable Capital Cost for Membrane System...20 Table Opinion of Probable Operation and Maintenance Costs for Membrane System...20 Table Opinion of Probable Capital Cost for Ballasted Floc/Filtration System...21 Table Opinion of Probable Operation and Maintenance Costs for Ballasted Floc/Filtration System...22 Table Opinion of Probable Cost for Dissolved Air Flotation System...23 Table Opinion of Probable Operation and Maintenance Costs for Dissolved Air Flotation System...23 Table Opinion of Probable Capital Cost for Ballasted Floc System...24 Table Opinion of Probable Operation and Maintenance Costs for Ballasted Floc System24 Table Opinion of Probable Capital Cost for Recycle to Presedimentation Basin...25 Table Opinion of Probable Operation and Maintenance Costs for Recycle to Presedimentation Basin...26 Table Backwash Treatment Estimated Cost Summary...26 Table Opinion of Probable Capital Cost for Wet Scrubber System...33 Table Opinion of Probable Operation and Maintenance Costs for Wet Scrubber System.33 Table Opinion of Probable Capital Cost for Dry Scrubber System...34 Table Opinion of Probable Operation and Maintenance Costs for Dry Scrubber System.34 Table Chlorine Scrubber Estimated Cost Summary...34 Technical Memorandum No. 2 -iii- July 2001

49 List of Figures Figure Following Page Figure 2-1. Summer Day Plant Flow...7 Figure 2-2. Winter Day Plant Flow...7 Figure MG Clearwell Expansion...35 Figure 2-4. Backwash Treatment System...35 Figure 2-5. Typical Wet Scrubbing System...28 Figure 2-6. Typical Dry Scrubbing System...28 Figure 2-7. One-Ton Chlorine Containment Vessel...30 Technical Memorandum No. 2 -iv- July 2001

50 TECHNICAL MEMORANDUM NO. 2 CAPACITY/NEAR TERM REGULATORY IMPROVEMENTS 2.0 INTRODUCTION This Technical Memorandum (TM) serves as the second section of the Sioux Falls Water Purification Plant (WPP) Master Plan Update. Included in this TM are evaluations of near-term improvements required to meet capacity and regulatory requirements as follows: Clearwell Storage Capacity Filter Backwash Recycle Chlorine Treatment/Containment 2.1 CLEARWELL STORAGE CAPACITY EXISTING CONDITIONS Disinfection Requirements The Surface Water Treatment Rule (SWTR) requires that systems treating surface water or groundwater under direct influence of surface water provide 3-log (99.9 percent) removal/inactivation of Giardia cysts and 4-log (99.99 percent) removal/inactivation of viruses. Treatment methods to achieve the requirements include filtration, which removes microorganisms, and disinfection, which inactivates microorganisms. The Sioux Falls WPP is considered a well operated conventional filtration plant and receives a 2.5-log removal credit for Giardia and 2-log removal for viruses by filtration. Therefore, disinfection at the WPP must provide 0.5-log inactivation for Giardia and 2-log inactivation for viruses. Determination of log inactivation for Giardia and viruses by various disinfectants under the SWTR is made through the calculation of CT for the system. CT is defined as the multiplication of the concentration of residual disinfectant (C, mg/l) by the contact time (T, minutes) between the point of application of the disinfectant and the point at which the disinfectant residual is measured. The calculated CT for the system must exceed the required CT that is dependent upon various water quality parameters. Giardia cysts are considerably more resistant to inactivation by chlorine than are viruses. Review of CT requirements for chlorine disinfection indicates that the requirements for 0.5-log inactivation of Giardia cysts are greater than the requirements for 2.0-log inactivation of viruses under similar conditions. Therefore, only CT calculations for Giardia inactivation need to be evaluated. If the CT requirements for Giardia are met, than the CT requirements for viruses are simultaneously met Current Disinfection Practice The Sioux Falls WPP uses chlorine as the primary disinfectant. Several feed points in the treatment process are available for chlorination including: Upstream of the filters after recarbonation Between the filters and clearwells Technical Memorandum No July 2001

51 The current disinfection practice is to prechlorinate water upstream of the filters primarily to control biological growth and to chlorinate prior to the clearwells for disinfection. Although some disinfection contact occurs in the filters and piping prior to the clearwells, Sioux Falls includes disinfection detention time in the clearwells only in CT calculations Existing Clearwells Finished water storage at the Sioux Falls WPP currently includes two clearwells. The primary reservoir used to meet CT requirements is a 3.6 million gallon clearwell. This is a below ground tank located on the southwest side of the plant. Currently, the clearwell has limited baffling to prevent short-circuiting through the tank. A ratio of T 10 to T is used to describe the baffling of a clearwell. T 10 is defined as the time required for 10% of the flow to pass through the basin, and T is the theoretical detention time of the tank. Based upon tracer tests that have been performed in the clearwell, the WPP currently uses a baffling factor of 0.17 for calculating CT values. To reduce the amount of short-circuiting in the reservoir, the City is improving the flow pattern through the basin. The modifications are expected to significantly increase the effective detention time in the clearwell. The second finished water reservoir at the Sioux Falls WPP is the North Reservoir, which is a 5.0 million gallon basin located directly south of the 3.6 million gallon clearwell. This reservoir is an above ground tank that requires pumps to lift water into the basin and results in a loss of head when water drains from the reservoir to the high service pump wetwell. In addition, the reservoir is poorly baffled for the purpose of CT with short detention times resulting from shortcircuiting. As a result of the energy inefficient characteristic of the tank and poor baffling, the reservoir is not typically used to provide CT contact time. The reservoir is used to meet some of the short-term demand fluctuations in the distribution system and to refill storage reservoirs. Some turnover in the reservoir is also desirable for water quality purposes. The assumption that the above ground storage will not be used for disinfection contact time will be made for the evaluation of future clearwell requirements. A summary of the characteristics of the two existing reservoirs is included in Table 2-1. Table 2-1. Existing Clearwells Parameter 3.6 MG Clearwell North Reservoir Volume 3.6 MG 5.0 MG Depth/Height 11.2 feet 39 feet Type Below Ground Above Ground Baffling Average (1) Poor Use Continual Infrequent 1. After modifications to clearwell. The total storage volume available for disinfection contact time is limited because the North Reservoir is not used for CT purposes, leaving the 3.6 million gallon clearwell to provide all the disinfection contact time. As a result, a minimum side water depth of 10 feet currently must be maintained in the clearwell to provide sufficient disinfection contact time. Maintaining this Technical Memorandum No July 2001

52 clearwell water level results in a relatively small operating range of approximately one foot. With this minimal operating range in the clearwell, the North Reservoir typically must be operated to mitigate the effect of varying system water demands on the water treatment plant Water Quality Several water quality parameters affect the rate of reaction for chlorine disinfection and will impact the evaluation of clearwell storage capacity. These parameters include ph, temperature, and chlorine residual. Finished water quality will be used in this analysis because it is the best available data to represent the condition of water in the clearwells, where disinfection contact time is considered for CT calculations. Table 2-2 summarizes the finished water quality based upon operating data from January 1, 1998 to December 31, Disinfection Capacity Table 2-2. Finished Water Quality Parameter Average Minimum Maximum ph, standard units Temperature, o C Free Chlorine, mg/l As discussed previously, because of the inefficiencies of the North Reservoir, the 3.6 million gallon clearwell is the primary reservoir for providing disinfection contact time. Although the North Reservoir can be used to provide additional storage time, it will not be considered in the evaluation of the disinfection capacity of the Sioux Falls WPP. Based upon current operation of the clearwell, a side water depth of 10 feet was assumed as the minimum water level. In addition, the baffling factor (T 10 /T) of 0.17 that is currently used by the Sioux Falls WPP to determine CT was used to evaluate current disinfection capacity. Table 2-3 summarizes the maximum hydraulic capacity of the clearwell based upon disinfection requirements for several water quality conditions. Technical Memorandum No July 2001

53 Table 2-3. Existing Clearwell Disinfection Capacity Water Temp. Chlorine Res. CT Flow Capacity (1) ( o ph C) (mg/l) Required (MGD) Based on side water depth of 10 feet and baffling factor of FUTURE CONDITIONS Future Disinfection Practice To reduce the potential for disinfection byproduct (DBP) formation, the Sioux Falls WPP will convert their disinfection system to chloramines in the following year. Ammonia will be fed to finished water exiting the clearwell to quench the free chlorine residual and form chloramines for the distribution system. Since ammonia will not be fed until after the clearwells, this conversion will not affect the disinfection method used for CT compliance. Free chlorine will remain the primary disinfectant, and contact time will be provided in the clearwells. System demand fluctuates throughout the day according to the diurnal variation. Typically, the desired water system operation is to maintain a constant flow through the treatment plant and allow the varying water consumption to be handled by storage. The concept is to allow reservoirs to fill during periods of low water demand and empty to meet increased water consumption during periods of high water demand. Reservoirs in the Sioux Falls water distribution system provide only a portion of the water storage operating capacity. Therefore, some of the demand fluctuations are encountered at the Sioux Falls WPP. Ideally, the plant s clearwells would provide the required operating volume to meet the changes in demand. Since the side water depth of the 3.6 million gallon clearwell must be maintained at 10 feet to provide sufficient disinfection contact time, the operating range of the clearwell is minimal for meeting system demand variations. As a result, the North Reservoir must be operated to reduce the effect of varying system demand on the water treatment plant. The reservoir does not provide a complete buffer, though, requiring the WPP treatment flow to be varied somewhat throughout the day. This current mode of operation is inefficient. Use of the North Reservoir is energy intensive as water must be pumped into the reservoir, and a loss of head occurs as water drains to the high service pump wetwell. In addition, operation of the plant at varying flows is inefficient Technical Memorandum No July 2001

54 as hydraulic loading on the solids contact basins and filters fluctuates or the number of solids contact basins and filters operated must be varied throughout the day. Baffling improvements planned for the existing 3.6 million gallon clearwell will reduce shortcircuiting and increase the effective retention time of the basin. A goal for the baffling improvements is to provide a T 10 /T of 0.5. For the purpose of this study, a low value of 0.3 will be assumed for reduced baffling improvements, and a high value of 0.5 will be assumed according to the improvement objectives. Under near-term system water demands, the improvements will allow the clearwell to operate at lower levels and increase the operating range. As system water demand increases in the future, the operating range will decrease. Two options of clearwell operation will be evaluated for future clearwell sizing as follows: Maximize the disinfection capacity of the existing clearwell by operating the reservoir with a high minimum side water depth and small operating range similar to the current operation. As discussed, this will require the use of the North Reservoir to meet some of the flow variations and operation of the WPP at the remaining varying flow conditions throughout the day. Provide an operating range in the clearwell to meet the system demand fluctuations to maintain a constant WPP treatment flow without the use of the North Reservoir. This will require that a larger total clearwell volume be available resulting in increased capital costs associated with future clearwell construction, but will reduce the inefficiencies of the plant operation Projected Water Demands Water demand for Sioux Falls varies according to seasonal fluctuations. High water demands result primarily from lawn watering during the summer when water temperature is higher. Conversely, low demand is encountered during the winter when water temperature is lower. For disinfection purposes, this seasonal water demand variation is offset by the fact that chlorine reaction rates directly correspond with water temperature. Reduced contact time is required during the summer when water temperature is higher, and increased contact time is required during the winter when water temperature is lower. Due to the flow and reaction rate characteristics, maximum hour conditions for both summer and winter were used as the basis to evaluate the requirements for future clearwell storage capacity. Based upon the maximum hour water demand projections developed in TM No. 1 and the requirements discussed above, Table 2-4 presents the future water demand conditions: Technical Memorandum No July 2001

55 Table 2-4. Projected Water Demand Water Demand (MGD) Summer Condition Winter Condition Year Normal (1) Reduced (2) Normal (1) Reduced (3) Main Break (4) Normal water demand condition does not include additional water sources and demand reductions as discussed in TM No Reduced water demand condition includes additional treated water sources including Southern Skunk Creek Aquifer and Wall Lake Aquifer for all years. Additional treated water from the Lewis and Clark project included for years 2015 and Reduced water demand condition includes additional treated water from the Lewis and Clark project for years 2015 and Condition of main break requiring additional high service pump (10 MGD) to maintain system pressure. Demand is shown for main break at reduced condition. The condition of a main break when Lewis and Clark is not operational is a very unlikely event. For disinfection capacity evaluations, only the highest water demand for each condition will be used to calculate future clearwell storage requirements. Therefore, the 2025 demand will be used to evaluate the normal and reduced summer conditions and the normal winter condition. The 2010 demand will be used to evaluate the reduced and main break winter conditions Future Disinfection Capacity The disinfection capacity of the existing 3.6 million gallon clearwell was evaluated at the projected future water demand conditions for both options of future clearwell operation, and additional clearwell capacity requirements were determined. The following assumptions were made for the calculations: Conservative water temperatures were assumed for the evaluation. A summer water temperature of 15 o C was used in the calculations, and a cold water temperature of 0.5 o C was used for winter conditions. Conservative values for water quality parameters were assumed to evaluate worstcase conditions. A high ph value of 9 and low chlorine concentration of 1.5 milligrams per liter were used in the calculations. Two baffling factor (T 10 /T) values were used based upon the Sioux Falls WPP plans to improve baffling. A value of 0.5 is anticipated to result from the improvements. A lower baffling factor may result, though, and a value of 0.3 was assumed for this evaluation Clearwell Operation to Maximize Disinfection Capacity This evaluation is based upon the assumption that Sioux Falls will operate the existing clearwell to maintain a minimum operating level to maximize clearwell volume for disinfection contact Technical Memorandum No July 2001

56 time. A side water depth of 10 feet was assumed. The ratios of disinfection CT available to disinfection CT required were calculated for the various conditions. Values greater than or equal to 1.0 indicate that sufficient CT is available at that condition. Values less than 1.0 indicate that insufficient CT is available and increased clearwell storage is required. Results of disinfection CT for the future water demands under this option are summarized in Table 2-5. Year Condition (1) Rate Flow (MGD) Table 2-5. Disinfection CT with Clearwell Volume Maximized T 10 /T CT Req. (2) CT Avail. (3) CT Avail./ CT Req. Add. Volume Req. (4) (MG) Summer Condition 2025 Normal Reduced Normal Reduced Winter Condition 2025 Normal Reduced Main Break Normal Reduced Main Break Conditions as defined in Table CT Required based upon 0.5-log Giardia inactivation, ph of 9, 1.5 mg/l chlorine residual, and water temperature of 15 o C for summer conditions and 0.5 o C for winter conditions. 3. CT Available based upon a 10-foot side water depth, 1.5 mg/l chlorine residual, and baffling factor as shown. 4. Additional clearwell volume calculated assuming a 0.5 baffling factor in new clearwell. As shown in Table 2-5, baffling improvements will greatly increase the disinfection capacity of the existing clearwell. Improvements to a baffling factor of 0.5 will provide sufficient effective detention time for disinfection for all conditions. Several conditions will require additional clearwell volume if the baffling improvements are increased to a factor of 0.3. The additional volume required would be less than one million gallons Clearwell Operation to Provide Operating Volume To reduce the need to use the inefficient North Reservoir and reduce plant flow fluctuations, the existing clearwell could be operated to allow for a varying water level to meet system demand fluctuations seen at the WPP. Historical hourly high service pumpage was evaluated to determine the diurnal variation experienced at the plant to project operating volume requirements. Average effluent, hourly effluent, and hourly influent flows for a summer and winter day are shown in Figures 2-1 and 2-2, respectively, demonstrating the diurnal variation of water demand seen at the WPP. Table 2-6 summarizes flow information for selected days during Also included in the table is the theoretical clearwell operating volume that would allow Technical Memorandum No July 2001

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59 the WPP to continuously operate at the daily average flow. For the purpose of evaluating future clearwell operating volumes required, ratios of volume to flow were also calculated. Date Min. Hourly Flow (MGD) Table 2-6. Operational Flow Data and Calculated Operating Volumes Avg. Hourly Flow (MGD) Max. Hourly Flow (MGD) Operating Volume (MG) Volume/ Min. Flow Volume/ Avg. Flow Volume/ Max. Flow 11/15/ % 3.9% 2.8% 11/16/ % 11.8% 9.4% 11/17/ % 12.7% 6.8% 11/18/ % 9.6% 5.9% 11/19/ % 11.0% 8.8% 11/20/ % 13.2% 9.2% 11/21/ % 6.0% 4.6% 9/23/ % 4.9% 3.6% 9/24/ % 4.5% 3.8% 9/25/ % 8.2% 5.5% 9/26/ % 3.5% 3.0% 9/27/ % 3.6% 2.8% 9/28/ % 6.7% 4.8% 9/29/ % 6.0% 4.3% 7/19/ % 5.1% 4.0% 7/20/ % 4.5% 3.6% 7/21/ % 8.1% 5.4% 7/22/ % 6.5% 5.1% 7/23/ % 4.6% 3.4% 7/24/ % 9.8% 6.4% 7/25/ % 5.3% 4.0% 6/14/ % 6.5% 4.6% 6/15/ % 7.9% 5.7% 6/16/ % 7.4% 5.0% 6/17/ % 7.4% 5.4% 6/18/ % 7.9% 5.7% 6/19/ % 5.5% 4.6% 6/20/ % 5.8% 4.6% 5/10/ % 6.6% 5.2% 5/11/ % 6.7% 5.1% 5/12/ % 3.9% 3.2% 5/13/ % 9.7% 6.9% 5/14/ % 9.4% 7.2% 5/15/ % 9.9% 7.1% 5/16/ % 8.8% 6.6% 2/22/ % 6.1% 4.6% 2/23/ % 7.2% 5.1% 2/24/ % 5.7% 4.1% 2/25/ % 5.6% 4.1% 2/26/ % 7.9% 5.6% 2/27/ % 9.0% 6.1% 2/28/ % 5.0% 4.0% Min % 3.5% 2.8% Avg % 7.1% 5.2% Max % 13.2% 9.4% Technical Memorandum No July 2001

60 Based upon the information presented in Table 2-6, an average value of 7% of flow was used to calculate the operating volume required in the clearwells to meet future water demand fluctuations. Table 2-7 presents the volume required for disinfection contact time and operating volume required in the old and new clearwell and the total new clearwell volume required at the future water demand conditions. Year Condition (1) Rate Flow (MGD) Table 2-7. Disinfection CT with Clearwell Operating Volume T 10 /T CT Req. (2) Old Clearwell Volume for CT (3) (MG) Operating Volume (MG) New Clearwell Volume for CT (4) (MG) Operating Volume (MG) New Clearwell Volume (MG) Summer Condition 2025 Normal Reduced Normal Reduced Winter Condition 2025 Normal Reduced Main Break Normal Reduced Main Break Conditions as defined in Table CT Required based upon 0.5-log Giardia inactivation, ph of 9, 1.5 mg/l chlorine residual, and water temperature of 15 o C for summer conditions and 0.5 o C for winter conditions. 3. Volume required for CT in Old Clearwell based upon CT Required, 1.5 mg/l chlorine residual, and baffling factor as shown. 4. Volume required for CT in New Clearwell based upon CT Required, 1.5 mg/l chlorine residual, and assuming a 0.5 baffling factor in new clearwell. As expected, the operating volumes for summer conditions are significantly greater than the volumes required for winter conditions due to greater flow fluctuations related to higher flows during the summer. The larger operating volumes offset the lower volumes required for CT for summer conditions as compared to the winter conditions. Therefore, clearwell volume sizing to provide an operating volume should be based on the summer conditions Future Clearwell Requirements Clearwell expansion requirements under the option of clearwell operation to maximize the volume for CT disinfection contact time are relatively small as shown in Table 2-5. Although the capital costs associated with clearwell expansion would be reduced, this option is not recommended. The operation of the clearwell in this manner requires the plant to be operated at varying flows to match changing flow demands experienced at the plant effluent. This results in Technical Memorandum No July 2001

61 inefficient operation of the water treatment plant. In addition, the reduced clearwell volume results in little flexibility. Additional clearwell capacity to provide an operating volume to meet varying flow demands experienced at the plant is recommended. This option allows the treatment plant to be operated at a more consistent flow. In addition, an additional clearwell sized with increased capacity provides flexibility of operation and maintenance. Use of the North Reservoir would also be reduced, and the reservoir would mainly serve as a backup. Turnover of water in the North Reservoir would be required, though, to prevent long detention times resulting in high DBPs. Ammonia would be fed prior to the reservoir to aid in reducing DBP formation. Modifications to the influent piping in the North Reservoir could be made to provide a flow pattern in the tank to reduce short-circuiting and dead zones. The modifications would consist of installing piping that would extend the influent line across the floor of the tank to the opposite wall and install a 90-degree fitting to direct the discharge upwards. Although the modification is not intended to allow the reservoir to be used for disinfection CT, the changes could create a baffling factor in the tank and the potential exists. The cost of this installation would be minimal using PVC piping, and the piping modifications are recommended to be installed when the North Reservoir is down for scheduled maintenance to occur later this year. Based upon the new clearwell volume requirements at the future water demand conditions summarized in Table 2-7, a new 3.0 million gallon clearwell is recommended. This clearwell volume in conjunction with the existing 3.6 million gallon clearwell will provide a total volume sufficient to meet CT requirements and allow for an operating volume at the projected 2025 future water demand. The larger clearwell volumes greater than 4 million gallons shown in Table 2-7 represent the condition that water from Lewis and Clark is not available. This condition, if encountered, would be temporary. The clearwells could be temporarily operated with a reduced operating volume under this condition to meet CT requirements. The recommended clearwell design follows: 3.0 million gallon volume. Below ground clearwell located north of existing 3.6 million gallon clearwell (see Figure 2-3). Side water depth to match existing clearwell elevation. Piping arrangement to allow clearwells to be operated either in series or in parallel. This piping arrangement will allow for one clearwell to be shut down for maintenance. Baffling factor of 0.7. Consideration should be given in baffling design to prevent excessive headloss. The estimated cost of construction for the new clearwell is summarized below: Technical Memorandum No July 2001

62 Table 2-8. Opinion of Probable Capital Cost for 3 MG Clearwell Item Estimated Cost Sitework $104,000 Concrete $625,000 Steel $365,000 Labor $637,000 Piping and Valves $173,000 Subtotal $1,904,000 Contingency (20%) $381,000 Total Estimated Construction Cost $2,285,000 Engineering/Legal/Administrative (15%) $343,000 Total Estimated Capital Cost $2,628,000 Note: Cost for parking lot relocation is not included. Several factors should be taken into consideration for the timing and implementation of the new clearwell as follows: The existing clearwell baffling improvements will increase the effective detention time of the basin for CT disinfection purposes. Tracer testing should be performed after the completion of the improvements to determine the actual resulting T 10 /T, and the future clearwell capacity requirements should be reevaluated based upon the actual resulting baffling. (Since the writing of this TM, a test to evaluate the T 10 /T of the reservoir with the baffle modifications was completed. A preliminary result indicates a T 10 /T of approximately 0.41 is applicable for average flow conditions of approximately 20 MGD.) The implementation of UV disinfection will be discussed in a subsequent TM. The use of UV disinfection will reduce or eliminate the requirements of chlorine as a primary disinfectant, reducing or eliminating the additional clearwell requirements. 2.2 FILTER BACKWASH RECYCLE BACKWASH PROCEDURES Current Backwash Generation The Sioux Falls WPP has a total of ten (10) granular media filters treating water from the upflow basins. As the headloss through a filter bed increases, the filter must be periodically backwashed using a combination of air scour, surface wash, and filtered water backflow. The spent backwash flow contains particulate matter, both inorganic and organic, and other contaminants removed by the filter, including pathogenic microorganisms such as Cryptosporidium. The current practice at the WPP is to send the spent backwash flow to a Filter Waste Washwater Basin and then pump this flow to the City s Wastewater Treatment Plant (WWTP) for final treatment. The capability exists to pump spent backwash flow back to the head of the WPP and retreat it along with the raw flow. Recycling in this manner was practiced in the past, but was found by plant staff to cause problems with the treatment process. That in conjunction with concerns about the Technical Memorandum No July 2001

63 possibility of returning concentrated microbial contaminants to the head of the plant, resulted in the decision to waste the backwash flow to the City s WWTP. The following table provides a summary of the filter backwash facilities, design backwash rates and volumes, and actual backwash rates and volumes. Table 2-9. Design and Actual Filter and Filter Backwash Facilities Parameter Design Actual No. of Filters No. of Cells/Filter 2 2 Cell Area 350 ft 2 /cell 350 ft 2 /cell Backwash Rate 18 gpm/ft gpm/ft 2 Backwash Duration 8 minutes 14 minutes Surface Wash Rate 3 gpm/ft 2 3 gpm/ft 2 Surface Wash Duration 3 min. duration 3 min. duration Total Backwash Volume/Filter 112,400 gallons 170, ,000 gallons No. of Backwash Feed Pumps 7,000 gpm (50 HP) 7,000 gpm (50 HP) No. of Backwash Waste Pumps 600 gpm (15 HP) 600 gpm (15 HP) As shown in Table 2-9, actual backwash practices differ from design values. Discussion with plant staff indicates that during the winter, the backwash rate is approximately 16.5 gpm/ft 2 (5,800 gpm), and during the summer, the backwash rate is approximately 20 gpm/ft 2 (7,000 gpm). The duration of the backwash is approximately 14 minutes, which results in peak spent backwash volumes of about 170,000 to 200,000 gallons per backwash event. Filter runs (time between backwashes) varies between 40 and 50 hours when a combination of groundwater and surface water is being treated to 50 to 60 hours when the raw water is predominantly groundwater. Recent plant operating data for 1998 and 1999 was reviewed to determine the percentage of raw water that is used for backwashing the filters. The average percentages for 1998 and 1999 were 2.68% and 2.37%, respectively, so a conservative value for use in determining costs of backwash handling alternatives will be assumed to be 3%. The peak daily percentage of backwash to raw water was verified for both 1998 and 1999 and found to be approximately 7%. This value will be used in sizing of backwash treatment alternatives. The volume of backwash water generated on both a yearly and daily basis constitutes a substantial amount of water that can be considered a valuable resource that is essentially wasted if the flow is sent to the WWTP. The following table shows the projected volumes of backwash flow for a current water production of approximately 20 million gallons per day. Technical Memorandum No July 2001

64 Table Current Backwash Volumes Year Average Average Peak 3% Raw Flow 3% Raw Flow 7% Raw Flow Current 219,000,000 gal/yr 600,000 gpd 1,400,000 gpd Future Backwash Generation Projections of water demand were developed in TM No. 1. Average day demands for a dry year will be used in evaluating future backwash generation. Table 2-11 summarizes the demand conditions. Table Water Demand Projections Year Water Demand (MGD) Normal Reduced (1) N/A Reduced condition includes 10 MGD of treated water from Lewis and Clark project and 1 MGD reduction in demand from Lincoln County Rural Water. Future backwash volumes were generated using the raw water pumping projections presented above and further assessing that the backwash volumes will average approximately 3 percent of the raw water treated. Table 2-12 presents the projected backwash volumes. Year Raw Water Flow (MGD) Table Projected Backwash Volumes Average 3% of Raw Flow (gal/year) Projected Backwash Volumes Average 3% Raw Flow (MGD) Peak 7% Raw Flow (MGD) ,000, ,000, (1) ,000, ,000, (1) ,000, Reduced demands primarily due to Lewis and Clark system BACKWASH STORAGE Existing Storage Basin In 1994, a new reinforced concrete backwash storage basin was constructed at the WPP. This structure has dimensions of 80 feet by 40 feet with a 10-foot side water depth and contains a Technical Memorandum No July 2001

65 usable volume of 239,360 gallons. This volume was designed to hold in excess of two successive backwashes at the design backwash rate of 112,400 gallons per filter. However, since the actual backwash practices use more water than anticipated (up to 200,000 gallons), the basin actually contains in excess of only one backwash volume. Expansion of the existing filter capacity will be evaluated in a subsequent TM. One alternative to be evaluated is 50% expansion of the existing filter surface area. The increase in filter surface area will result in a 50% increase in the volume of each backwash cycle, resulting in up to approximately 300,000 gallons. This volume exceeds the capacity of the existing storage basin. The ability of this structure to hold more than one backwash volume is important since the Filter Backwash Rule (FBR) will require water treatment plants to perform a self-assessment if the water is used for direct recycle. However, if the plant has a backwash holding basin that can contain at least one backwash volume, the self-assessment will not be required Backwash Storage Pumping Facilities The contents of the backwash storage basin may be pumped to either the head of the plant or to the City s WWTP by a system of three submersible 600 gpm pumps located at the effluent end of the storage basin. As discussed previously, the current practice is to pump the basin contents to the City s WWTP to prevent process upsets in the solids contact basins. Assuming two pumps operating and one standby at a nominal pumping rate of 1,200 gallons per minute, the estimated time to pump out the contents of the backwash storage basin is estimated to be 2.4 to 2.8 hours. If it is assumed a second backwash event would not proceed until the backwash storage basin is empty from the previous backwash, then the current system could handle about 8 backwash events per day. If only one pump is used to empty the backwash storage basin, the pump down time would be 4.8 to 5.6 hours, reducing the allowable daily backwash events to approximately four. With all ten filters operating and further assuming 8 backwashes per day are practiced, the minimum allowable filter run time is 30 hours. At 4 backwashes per day, the minimum filter runs must approach 60 hours. The existing filters will not have the capacity to handle future flow requirements and additional filter capacity will be required. Two alternatives will be evaluated in a subsequent TM to effectively increase filter capacity by 50% as follows: Alternative No. 1 - Construct five additional filters. Alternative No. 2 - Increase existing filter surface are by 50%. Since Alternative No. 1 will not change the total backwash volume of each individual backwash event, the only effect is an increase in the minimum allowable run time, which will increase by 50% to 45 hours with two backwash pumps operating and 90 hours with only one backwash pump operating. Backwash volumes for each backwash event will increase under Alternative No. 2 since the filter surface area is increased. Backwash volumes will increase by approximately 50% to almost 300,000 gallons. This alternative will require additional backwash storage volume. Assuming Technical Memorandum No July 2001

66 the same pumping capacity, it will take approximately 4.2 hours to pump the volume of each backwash cycle with two pumps and 8.4 hours with one pump. This would result in similar minimum allowable filter run times as Alternative No. 1. The hydraulic load imposed by pumping the backwash flow back to the treatment plant can be determined. For example, if the average daily flow is 20 millions gallons per day, and the backwash pumping rate is 1,200 gallons per minute, the introduction of backwash flow into the plant would increase the flow by 8.6 percent. The percentage increase would be approximately 2.4 percent for the maximum hourly rate BACKWASH WATER QUALITY The quality of the backwash flow varies considerably over the entire backwash period, with most of the solids and associated constituents coming during the first phase of the backwash. Some information on the quality of the backwash flow is available from data collected in accordance with the requirements of the Information Collection Rule. The data is summarized below in Table Table Characteristics of Filter Backwash Water ( ) Parameter Date Avg. TOC, mg/l Ammonia, mg/l <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 Turbidity, NTU Total Hardness, mg/l (as CaCO 3 ) CA Hardness, mg/l (as CaCO 3 ) T alkalinity, mg/l (as CaCO 3 ) ph Temp, C UV-254, cu TOX, mg/l Comparing these values with other plants is difficult since each plant treats a different raw water flow, and hence the material retained on the filters and removed during backwash is variable. A review of the literature shows that typical backwash water will contain suspended solids both organic and inorganic, microbial contaminants, and residual chemicals that were used in the treatment processes prior to the filters. Higher concentrations of suspended solids are normally discharged from the filter during the initial phases of a backwash event. Diminished concentrations are encountered as the backwash proceeds. For example, a study performed by HDR on the filter backwash from the Metropolitan Utilities District (MUD) Platte South plant shows that 90% of the solids are discharged to backwash in the first 4 minutes of a 12-minute backwash cycle, and 70 percent in the first two Technical Memorandum No July 2001

67 minutes. The suspended solids concentrations varied from 490 mg/l at the beginning of backwash to 110 mg/l after two minutes and 20 mg/l or less after 8 minutes. The flow proportional TSS level was found to be approximately 60 mg/l, therefore, the total of solids discharged at a total backwash flow of 284,000 gallons was approximately 160 lbs. The settleability of the backwash solids at the MUD Platte South plant was tested, and the heavy materials were found to settle readily when put into a 9-foot high settling column for 45 minutes. The quality of the water above the sludge layer in the bottom was cloudy, consisting of what was apparently a substantial amount of colloidal material. Total solids removal was 10 to 15 percent even when polymers were added to the backwash flow. It is expected that the backwashing of the filters at the Sioux Falls WPP results in similar solids generation to that tested at MUD. Most of the solids will be assumed to come off the filters in the first four minutes of the backwash EFFECTS OF BACKWASH RECYCLE Past Plant Experience with Backwash Recycle In the past, the Sioux Falls WPP has attempted to recycle filter backwash flow back through the plant. Discussions with plant staff indicated that the introduction of the recycle flow had an adverse impact on the operation of the upflow solids contact basins. Originally, the recycle flow was introduced equally to all the basins, but this caused the sludge blanket levels to rise with resulting performance deterioration. All backwash water was then discharged into one upflow basin, accepting performance deterioration in that basin while preserving excellent performance in the remaining upflow basins. The problems with introducing backwash as recycle noted by the operations staff included rising sludge blanket levels with turbidity carryover to the filters, effects on chemical feed rates (lime, ferric, and polymer), and degradation of floc formation. These problems led the City to discontinue recycle and waste backwash water to the WWTP instead Other Potential Effects Several other issues can arise from recycle of backwash water other than those discussed above. One of the most important factors is a potential to concentrate pathogenic microorganisms removed by the filters. While no data exists for the Sioux Falls plant, the available literature indicates that pathogens such as Cryptosporidium can become concentrated in the filter backwash water so that the concentration may be 20 times higher than the raw water levels. Theoretically, if these microorganisms were not removed from the system over time, the levels would build up and a pass through of the filter could potentially occur. The potential concentration of pathogenic microorganisms can be resolved by backwash treatment methods that will be discussed in subsequent sections of this TM. Another potential problem with backwash water recycle is that an increased concentration of precipitates such as iron and manganese in backwash water may release ions into solution, resulting in an increase in ferric salt concentrations used in the main treatment process. Technical Memorandum No July 2001

68 2.2.5 ALTERNATIVES FOR FILTER BACKWASH HANDLING This section of the TM presents several alternatives for handling filter backwash flows. The current method of wasting the flows to the City s WWTP is compared with other alternatives that treat and return the flows to the plant. Each of the filter backwash treatment alternatives are sized for a treatment capacity of 2 MGD Pump Backwash to City WWTP Under this alternative, filter backwash flows will be pumped to the City s WWTP for final treatment and disposal as is currently practiced. This alternative eliminates possible problems with process upsets, increased concentrations of pathogens, and other undesirable contaminants, but results in approximately three percent of the total raw water pumped being wasted, reducing the product water ratio. This wasted water is a resource that could be conserved, providing more water for the Utility while conserving a valuable resource. The total amount of backwash water would amount to 1.5 to 2.0 million gallons per day at future flow conditions, which is the equivalent of two to three vertical wells in the Big Sioux Aquifer. Capital costs for the installation of vertical wells that would be required under this option is included in Table Table Opinion of Probable Capital Cost for Vertical Wells Item Estimated Cost Well Construction $50,000 Well Pump $40,000 Housing, Electrical, and Instrumentation $30,000 Piping $20,000 Cost Per Well $140,000 Cost for Three Wells $420,000 Contingency (20%) $84,000 Total Estimated Construction Cost $504,000 Engineering/Legal/Administrative (15%) $76,000 Total Estimated Capital Cost $580,000 In addition to the capital cost for well construction, the economics of continuing to pump backwash water to the WWTP include annual operation and maintenance costs in three major categories: cost of chemicals to treat the water initially; cost of power to pump to the City WWTP; and user charge costs imposed by the WWTP for accepting the wastewater. For this analysis, other miscellaneous costs for treating the raw water were assumed to be negligible. Table 2-15 summarizes the operational costs to dispose of filter backwash water. Technical Memorandum No July 2001

69 Table Opinion of Probable Cost to Dispose of Filter Backwash Water Cost Item Cost/1000 gal (1) Annual Cost (2) Present Worth (3) Chemicals $0.11 $30,100 $345,000 Power $ $100 $1,000 Disposal Cost at WWTP $1.18 $323,000 $3,705,000 Total Cost/1000 gallons $ Total Annual Cost $353,200 Net Present Worth $4,051, Based upon operating information for Annual cost based on an average filter backwash flow of 0.75 MGD. 3. Present worth based on a 6% discount rate and a period of 20 years Membrane Treatment Membrane systems for potable water treatment fall into two general categories: low-pressure systems, which include microfiltration (MF) and ultrafiltration (UF); and high-pressure systems, which include reverse osmosis and nanofiltration. The high-pressure systems are capable of the finest separations, which is not required for this application. In comparison to MF, UF has smaller pore sizes providing additional removal capabilities but requiring higher operating pressures. Nominal pore sizes of MF systems are typically 0.2 microns or smaller. Since Cryptosporidium and Giardia are larger than the MF openings, this type of membrane system will provide a barrier to these specific constituents. Therefore, the emphasis of this evaluation has been placed on MF and loose UF systems. Under this option, a new backwash water basin (800,000 gallon capacity) will be installed to provide equalization upstream of the membrane system. Piping and valving will allow for the new equalization basin to be operated in parallel with the existing filter backwash basin. Backwash water from the first few minutes of each cycle, which contains the greatest portion of solids, could be wasted to the existing basin, with the remaining backwash water going to the equalization basin. This operation will reduce the solids loading to the membrane system. Pumps will feed water at a constant rate from the backwash equalization basin to the membrane system. These pumps will be located at a raised elevation in the backwash basin to allow for solids to settle below the suction. The water quality of filtrate from the membrane system should allow for the water to be discharged directly to the clearwell, which would eliminate problems with hydraulic loadings to the upflow clarifiers resulting from recycle. In addition, direct discharge to the clearwells will prevent retreatment by the granular media filters, increasing plant capacity. Since the FBR requires that backwash water, untreated or treated, be recycled prior to initial coagulant addition or lime addition, an approval from the State would be required to allow for filtered water from the membrane system to be discharged directly to the clearwell. Several operating parameters need to be evaluated by pilot testing to determine the limitations of using low-pressure membranes for this application as follows: Technical Memorandum No July 2001

70 Flux Rate The hydraulic loading to the membranes (flux rate) can be defined as gallons per day of filtered water per square foot of membrane surface. The flux rate will determine the membrane sizing requirements for the application. The feed water turbidity will have a significant impact on the flux rate of the system. Recovery The amount of concentrated waste from the membranes will vary depending upon flux rate and feed water turbidity. Fouling Over time, particles accumulate on the surface of the membranes, reducing the flux rate of the system, requiring periodical backwashes to cleanse the system. Over longer periods, the membranes can experience more extensive fouling that requires a clean in place system to restore permeability. Ultimately, membrane fouling results in a permanent flux rate reduction that requires the membranes to be replaced. The extent of fouling needs to be evaluated to determine membrane life and replacement requirements. Chemical Compatibility Some chemicals (polymers in particular) have the potential to foul membranes quickly, effectively reducing the flux rate of the membranes. The extent of fouling may be extreme with some chemicals, creating an unacceptable level of membrane fouling and replacement. Taste and Odor Low-pressure membranes will not provide taste and odor reduction for the backwash water. Recycle of membrane filtrate upstream of the filters may be required at times when taste and odor are present. After each backwash cycle, filtered water (filter to waste) is recycled upstream of the filters for several minutes to allow for the filters to ripen. The filter to waste could potentially be combined with backwash water and treated by the membranes for direct discharge to the clearwell. This will reduce additional loading on filters from recycle, effectively increasing the plant capacity. As compared with the backwash water quality, the improved water quality of filter to waste will allow the membranes to operate at higher flux rates and increased capacity. The approximate costs associated with using membranes to treat backwash water are shown below. Technical Memorandum No July 2001

71 Table Opinion of Probable Capital Cost for Membrane System Item Estimated Cost Backwash Equalization Basin Sitework $40,000 Concrete $193,000 Steel $119,000 Labor $235,000 Piping and Valves $60,000 Membrane System Sitework $25,000 Feed Pumps $80,000 Membrane Equipment $1,600,000 Housing $265,000 Piping and Valves $270,000 Electrical and Mechanical $180,000 Pilot Testing $40,000 Subtotal $3,107,000 Contingency (20%) $621,000 Total Estimated Construction Cost $3,728,000 Engineering/Legal/Administrative (15%) $559,000 Total Estimated Capital Cost $4,287,000 The operation and maintenance costs for membrane systems vary considerably between different applications. Water quality will determine the flux rate capacity, extent of fouling, cleaning frequency, and membrane replacement. An estimate of probable operation and maintenance costs for the application of membranes for backwash water treatment at Sioux Falls is included in Table Table Opinion of Probable Operation and Maintenance Costs for Membrane System Cost Item Cost/1000 gal Annual Cost (1) Present Worth (2) Power $0.040 $11,000 $126,000 Chemicals $0.025 $6,800 $78,000 Labor $0.048 $13,100 $150,000 Membrane Replacement $0.057 $15,600 $179,000 Disposal Cost at WWTP $ $17,700 $203,000 Total Cost/1000 gallons $0.235 Total Annual Cost $64,200 Net Present Worth $736, Annual cost based on an average filter backwash flow of 0.75 MGD except for disposal cost, which is assumed to be 5% of backwash flow (0.075 MGD). 2. Present worth based on a 6% discount rate and a period of 20 years. Technical Memorandum No July 2001

72 Ballasted Floc and Gravity Filtration Treatment As an alternative to membrane filtration, a ballasted floc (BF) and dual media gravity filtration system could be implemented for backwash water treatment. Under this option, the backwash flow would be collected in a new backwash equalization basin, as discussed under the membrane treatment option, and pumped to a BF/filtration system. Since the system is essentially an enhanced coagulation/filtration treatment unit, effluent could potentially be discharged directly to the clearwell. Again, approval by the State would be required to allow for direct discharge to the clearwell. As under the membrane treatment option, filter to waste could potentially be combined with backwash water for treatment and discharge to the clearwell to prevent recycle of this water. Although the BF/filtration system has been shown to provide 2.5 to 4.0-log removal of particles in the Cryptosporidium and Giardia size range, it does not provide a barrier to these contaminants as provided by a MF system. Since this type of system does not provide the reliability and protection from pathogenic microorganisms as provided with MF, it is only recommended if pilot testing indicates that MF is not feasible for this application or the barrier is not an overriding consideration. An estimate of probable capital cost for implementation of a BF/filtration system is included in Table Estimated operation and maintenance costs are summarized in Table Table Opinion of Probable Capital Cost for Ballasted Floc/Filtration System Item Estimated Cost Backwash Equalization Basin Sitework $40,000 Concrete $193,000 Steel $119,000 Labor $235,000 Piping and Valves $60,000 Ballasted Floc/Filtration System Sitework $25,000 Feed Pumps $80,000 Ballasted Floc/Filtration Equipment $680,000 Housing $270,000 Piping and Valves $158,000 Electrical and Mechanical $106,000 Subtotal $1,966,000 Contingency (20%) $393,000 Total Estimated Construction Cost $2,359,000 Engineering/Legal/Administrative (15%) $354,000 Total Estimated Capital Cost $2,713,000 Technical Memorandum No July 2001

73 Table Opinion of Probable Operation and Maintenance Costs for Ballasted Floc/Filtration System Cost Item Cost/1000 gal Annual Cost (1) Present Worth (2) Power $0.016 $4,400 $51,000 Chemicals $0.035 $9,600 $110,000 Labor $0.049 $13,400 $154,000 Disposal Cost at WWTP $ $17,700 $203,000 Total Cost/1000 gallons $0.165 Total Annual Cost $45,100 Net Present Worth $518, Annual cost based on an average filter backwash flow of 0.75 MGD except for disposal cost, which is assumed to be 5% of backwash flow (0.075 MGD). 2. Present worth based on a 6% discount rate and a period of 20 years Alternative Treatment and Recycle Two alternative treatment technologies have been identified as treatment methods that could be used to for recycle treatment. Other treatment technologies such as plate settling have also been acknowledged, but will provide reduced solids removal capability, and are not recommended. The alternatives that have been identified are: Dissolved air flotation (DAF) with polymer addition Ballasted floc (without filtration) with polymer addition Under this alternative, the backwash flow would be collected in a new backwash equalization basin as discussed under the membrane treatment option, and pumped to one of the alternative treatment units for removal of solids. Effluent from the treatment unit will be pumped to the solids contact basins influent channel or the recarbonation basin (if allowed by the State). Sludge removed in both the equalization basin and treatment unit would be wasted to the City WWTP. Use of DAF and BF with polymer addition has been shown to be fairly effective in removing turbidity and pathogenic microorganisms. Research has indicated a 2.0-log reduction for both turbidity and Cryptosporidium. Such a system would not provide an absolute barrier for pathogenic microorganisms, though, so its use would introduce a level of risk. In addition, such a system would still result in hydraulic loads to the upflow basins, potentially causing some of the same problems encountered at the plant previously. Tables 2-20 through 2-23 summarize the capital and operation and maintenance costs associated with the implementation of the DAF and BF backwash treatment alternatives. Technical Memorandum No July 2001

74 Table Opinion of Probable Cost for Dissolved Air Flotation System Item Estimated Cost Backwash Equalization Basin Sitework $40,000 Concrete $193,000 Steel $119,000 Labor $235,000 Piping and Valves $60,000 DAF System Sitework $25,000 Feed Pumps $80,000 DAF Equipment $665,000 Housing $270,000 Piping and Valves $156,000 Electrical and Mechanical $104,000 Subtotal $1,947,000 Contingency (20%) $389,000 Total Estimated Construction Cost $2,336,000 Engineering/Legal/Administrative (15%) $350,000 Total Estimated Capital Cost $2,686,000 Table Opinion of Probable Operation and Maintenance Costs for Dissolved Air Flotation System Cost Item Cost/1000 gal Annual Cost (1) Present Worth (2) Power $0.022 $6,000 $69,000 Chemicals $0.035 $9,600 $110,000 Labor $0.044 $12,000 $138,000 Disposal Cost at WWTP $ $17,700 $203,000 Total Cost/1000 gallons $0.165 Total Annual Cost $45,300 Net Present Worth $520, Annual cost based on an average filter backwash flow of 0.75 MGD except for disposal cost, which is assumed to be 5% of backwash flow (0.075 MGD). 2. Present worth based on a 6% discount rate and a period of 20 years. Technical Memorandum No July 2001

75 Table Opinion of Probable Capital Cost for Ballasted Floc System Item Estimated Cost Backwash Equalization Basin Sitework $40,000 Concrete $193,000 Steel $119,000 Labor $235,000 Piping and Valves $60,000 BF System Sitework $25,000 Feed Pumps $80,000 BF Equipment $700,000 Housing $270,000 Piping and Valves $161,000 Electrical and Mechanical $108,000 Subtotal $1,991,000 Contingency (20%) $398,000 Total Estimated Construction Cost $2,389,000 Engineering/Legal/Administrative (15%) $358,000 Total Estimated Capital Cost $2,747,000 Table Opinion of Probable Operation and Maintenance Costs for Ballasted Floc System Cost Item Cost/1000 gal Annual Cost (1) Present Worth (2) Power $0.014 $3,800 $44,000 Chemicals $0.035 $9,600 $110,000 Labor $0.044 $12,000 $138,000 Disposal Cost at WWTP $ $17,700 $203,000 Total Cost/1000 gallons $0.157 Total Annual Cost $43,100 Net Present Worth $495, Annual cost based on an average filter backwash flow of 0.75 MGD except for disposal cost, which is assumed to be 5% of backwash flow (0.075 MGD). 2. Present worth based on a 6% discount rate and a period of 20 years Equalized Flow to Presedimentation Basin The implementation of a presedimentation basin for pretreatment of surface water upstream of the solids contact basins will be discussed in a subsequent TM. If a presedimentation basin is constructed, recycle of backwash water to the basin for treatment is an additional alternative. A backwash equalization basin with approximately 800,000 gallons of storage would be required under this option to reduce the effect of hydraulic surges on the presedimentation basin and Technical Memorandum No July 2001

76 downstream processes. Recycle pumps would be sized to feed backwash water into the process at a continuous rate, rather than in intermittent slugs. Costs associated with this alternative mainly consist of the installation of a backwash equalization basin and recycle pumps. An estimate of probable capital cost for this alternative is included in Table Estimated operation and maintenance costs are summarized in Table Table Opinion of Probable Capital Cost for Recycle to Presedimentation Basin Item Estimated Cost Backwash Equalization Basin Sitework $40,000 Concrete $193,000 Steel $119,000 Labor $235,000 Piping and Valves $60,000 Subtotal $647,000 Contingency (20%) $129,000 Subtotal Estimated Construction Cost $776,000 Engineering/Legal/Administrative (15%) $116,000 Subtotal Estimated Capital Cost $892,000 Ancillary Equipment Recycle Pumps $80,000 Electrical and Instrumentation $20,000 Subtotal $100,000 Contingency (20%) $20,000 Subtotal Estimated Construction Cost $120,000 Engineering/Legal/Administrative (15%) $18,000 Subtotal Estimated Capital Cost $138,000 Total Estimated Capital Cost $1,030,000 Technical Memorandum No July 2001

77 Table Opinion of Probable Operation and Maintenance Costs for Recycle to Presedimentation Basin Cost Item Annual Cost Present Worth (1) Power $2,000 $23,000 Chemicals $8,500 $97,000 Labor $5,000 $57,000 Total Cost/1000 gallons Total Annual Cost $15,500 Net Present Worth $177, Present worth based on a 6% discount rate and a period of 20 years Irrigation of Backwash Water Using filter backwash as irrigation water is an additional alternative for handling backwash water for the Sioux Falls WPP. This option would allow for the water to be used with little to no treatment provided for the water. However, a readily available customer in close proximity to the plant would need to be located and is unlikely. In addition, a separate non-potable water piping system to the customer would need to be installed. Therefore, this alternative was not considered further and no cost estimates were generated Estimated Total Cost Summary The estimated total capital cost and operation and maintenance costs for each of the backwash treatment alternatives are summarized in Table Table Backwash Treatment Estimated Cost Summary Alternative Estimated Estimated O&M Total Present Capital Cost Annual Cost Present Worth (1) Worth No. 1 Backwash to WWTP $580,000 $353,200 $4,051,000 $4,631,000 (2) No. 2 MF Membrane $4,287,000 $64,200 $736,000 $5,023,000 No. 3 Ballasted Floc/Filters (3) $2,713,000 $45,100 $518,000 $3,231,000 No. 4 DAF (3)(4) $2,686,000 $45,300 $520,000 $3,206,000 No. 5 Ballasted Floc (3)(4) $2,747,000 $43,100 $495,000 $3,242,000 No. 6 Recycle to Presed. (3) $1,030,000 $15,500 $177,000 $1,207, Present worth based on 6% at 20 years. 2. Cost does not include impact on WWTF capacity, which could be $2-3/gallon of capacity or $1.5 to $2.5 million for a total of $6 to $7 million total present worth. 3. Does not provide barrier against microbial recycle. 4. Could cause softening basin upset similar to current problem RECOMMENDATIONS The water resources available to Sioux Falls are limited and should be conserved to the extent possible. Due to process upsets related to recycle and the concern of concentrated pathogens, filter backwash water is currently wasted to the City s WWTP, reducing the maximum efficient use of the water resources available to the City. In addition, there is a cost associated with this Technical Memorandum No July 2001

78 wasting including well development and construction costs, the cost of treating the wasted water, and the cost charged by the WWTP to treat the water. The alternative to equalize filter backwash water flow and recycle to a presedimentation basin is the recommended option for handling backwash water at the Sioux Falls WPP if a presedimentation basin as discussed in a subsequent TM is implemented. This option will prevent the wasting of backwash water at the least cost, while preventing process upsets that previously occurred. If a presedimentation basin is not provided, low-pressure membranes present the best option for treating the Sioux Falls WPP filter backwash water. This technology provides a barrier to pathogens, such as Giardia and Cryptosporidium, which may be concentrated in the backwash. The water quality produced from membrane treatment should allow for the water to be discharged directly to the clearwells, preventing any problems associated with recycle, preventing retreatment of the water by the main process, and effectively increasing plant capacity. The application of this technology is dependent upon the compatibility with the water being treated. Piloting will be required to determine the feasibility of membranes for backwash water treatment at the Sioux Falls WPP and to determine operating parameters for design. Several additional treatment options have been identified for filter backwash water treatment including ballasted floc with and without filtration and dissolved air flotation. Although these treatment technologies will provide good turbidity and pathogenic microorganism removal, they do not provide the level of removal that would be achieved with membranes. These options are available, though, if a presedimentation basin is not provided and it is determined that the filter backwash water is incompatible with low-pressure membranes. Although not required for their application, piloting of the alternatives will allow for the determination of the best feasible option. Figure 2-4 shows the layout of a filter backwash equalization basin and treatment system on the site plan. The layout is representative of all the treatment options since the alternatives have similar footprints. The option of equalization only if a presedimentation basin is implemented will not require the treatment system building. 2.3 CHLORINE TREATMENT/CONTAINMENT CHLORINE USE,STORAGE, AND HANDLING Current use and layout The Sioux Falls WPP currently utilizes gaseous chlorine as the sole disinfectant, which poses a potential hazard to personnel, as well as the public in close proximity to the facility. Modifications to the disinfection system are planned (conversion to chloramines) and are being evaluated as part of this master plan update (ultraviolet as a primary disinfectant), however, gaseous chlorine will continue to be used in the foreseeable future. The existing chlorine feed system feeds chlorine supplied in one-ton cylinders, which are manifolded together in parallel, to provide the peak capacity without freeze-up. Recently (summer 2000), modifications were made to the system to improve safety, changing from a Technical Memorandum No July 2001

79 manifold carried gas under pressure to a common vacuum regulator, to individual vacuum regulators on each cylinder that is in the feed locations. The gas piping is now a complete vacuum system, drawn from the cylinders to the feeders via a vacuum supplied by the eductors at the chlorinators. Vacuum handling of chlorine provides a much safer system than pressure systems. While converting to a vacuum system improved safety, hazards remain from the cylinders themselves, such as in the event of a soft plug rupture, valve failure, etc NEEDS EVALUATION Risk management plan A Risk Management Plan was completed in January 2000, by CH2MHill for the Water Purification Plant. While this plan did not indicate chlorine scrubbing or containment would be required, the potential still exists that a major leak could cause concerns due to the Plant's close proximity to a businesses and residences to the south and the airport to the northwest Uniform Fire Code The Uniform Fire Code (Article 80) requires that newly constructed or modified chlorine storage and feed facilities provide a means of mitigation of released chlorine in the event of a chlorine leak. This requires that the contents of the single largest container of chlorine must be able to be mitigated in 30 minutes. In the case of an over-filled one-ton cylinder, this mass could be as high as 2,350 pounds. Since the chlorine feed system at the Sioux Falls WPP was modified in the summer of 2000, compliance with the Uniform Fire Code requires that the addition of some form of release mitigation be implemented. The code does not require stored cylinders to be included if containment is utilized as a mitigation measure. Instead, mitigation is required for the connected cylinders only. The potential exists that a variance from the Uniform Fire Code could be granted for this application, and HDR has been involved in modifications where a variation was allowed. Due to the proximity of the public and as per the direction of the City, the need for scrubbing will not be debated within the master plan update, rather that decision will be made by the City. The focus of scrubbing herein will be on the options available, operational considerations, costs and applicability to the Sioux Falls system CHLORINE SCRUBBING/CONTAINMENT ALTERNATIVES To comply with the requirements of Article 80 of the Uniform Fire Code, dealing with chlorine feed and storage facilities, there are essentially two options 1) containment and scrubbing to remove the escaped chlorine, or 2) total containment of the vessel Scrubbers Typically with a scrubbing system the room is sealed off in the event of a chlorine leak and the chlorine gas is "scrubbed" from the room air, which is then discharged to the atmosphere. Scrubber systems are typically required to be sized to scrub the contents of one entire storage vessel, or in the case of the Sioux Falls WPP, a one-ton cylinder. Additionally, a flow-rate of Technical Memorandum No July 2001

80 3000 cfm for the chlorine/air to be scrubbed, would be required to be able to handle the vaporization rate if the soft plug of a cylinder were to rupture, spilling liquid chlorine out to the floor to vaporize at room temperature. This flow-rate can be reduced if a containment sump is constructed. The sump would collect the liquid chlorine and reduce the vaporization rate due to restriction of the surface area. This is typically only cost effective in new chlorine storage installations or if trench drains or sumps exist. Scrubbers may be separated into wet and dry scrubbers Wet Scrubbers The wet scrubbers utilize a liquid to scrub the chlorine from the air. The scrubbants are typically caustic (most commonly sodium hydroxide). The scrubbers draw the air/chlorine through the system using a venturi device (similar to the PAC scrubbers at the Sioux Falls WPP) or use a separate fan. Both types have their associated advantages and disadvantages. Caustic does have a limited life and precipitates can develop while stored. For this reason, this type of system will require some maintenance, even if not called upon. Due to the use of scrubbants, these systems require that they be housed in a climate controlled area. A likely location for this structure would be immediately south of the existing chlorine building, east of the North Reservoir. Figure Typical Wet Scrubbing System Source: Environmental Systems Technology There are also deluge systems that fall into the wet scrubber category, which use large volumes of water (approximately 300 gpm) as the scrubbant, delivered via misters, laid out similarly to a fire protection system. These units remove the chlorine via the water mist, which is collected in a sump and discharged to the sanitary sewer Dry Scrubbers Dry scrubbers utilize a granular media, chemically impregnated to remove chlorine from the ventilation air. One manufacturer utilizes Figure Typical Dry Scrubbing System Source: Purafil Environmental Systems Division Technical Memorandum No July 2001

81 sodium thiosulfate to impregnate the media, and claim it will operate as designed down to -40 degrees F. That system is acceptable for installation outdoors, without a building, as shown. The equipment cost is higher for this type of system, however, elimination of building requirements quickly offset those costs. If the dry scrubber is required to operate, the media may be landfilled and replaced. This system could also be located immediately south of the existing chlorine building, east of "Big Blue", however, it is more flexible and could also be located on the west end of the chlorine building to be closer to the chlorine cylinder storage location and existing exhaust system Scrubbing Comparison This section will present the advantages and disadvantages of the various scrubbing systems, separated into dry and wet scrubbers. Wet Scrubbers Advantages Lower cost for scrubbing equipment, approximately $85,000 with one caustic recycle /venturi pump, $110,000 with two. The scrubbant that reacts with the chlorine is caustic, most typically sodium hydroxide. This is readily available and can be competitively bid. Disadvantages Dry Scrubbers Advantages Requires insulation and heat tracing or a separate, heated building for seasonally cold climates such as exist Sioux Falls. Caustic will need to be replaced every few years due to degradation of the product, at approximately $10,000 per replacement. Caustic is a very hazardous chemical. Physical contact can cause severe dermal damage. Caustic has a tendency to scale and can freeze and relatively high temperatures, depending on concentration. Does not require special insulation or heating. Rated down to -40 degrees F. Routine maintenance is much lower than with wet scrubbing Media is non-toxic both when new and when spent. Spent media can be landfilled. Reported higher degree of removal, in the low ppb range, vs. low ppm range for wet scrubbers. Only one moving part, a fan. Technical Memorandum No July 2001

82 Disadvantages Capital cost is higher, approximately $127,000. Only one source of media, therefore cannot be competitively bid. Media costs $1.35/lb; $1.50 with freight. And the scrubber utilizes 25,000 lbs of media, therefore replacement costs are approximately $37,500 per replacement. Media insurance can be provided for $3000 for ten years, and $3000 for another ten years (20 total), that guarantees complete media replacement if 50% or greater of the media is exhausted in a single chlorine release. Media will need periodic sampling and analysis to ensure adequate capacity in the event of a spill incident. The media is proprietary now. If the company would go out of business or quit making the product it could cause problems until another manufacturer would produce a replacement product. Only one fan on standard unit. There is no redundancy if this would fail. Adding a second adds a significant cost Total Containment Systems In addition to scrubbing, there are total containment systems available that totally encapsulate the chlorine cylinder with an oversized cylinder, capable of containing the gas in the event of a failure. If a failure occurs, the gas is passed through the chlorinator, using normal procedures until exhausted. Benefits include simplicity and reduction in the probability that the operator needs to come in contact with a chlorine laden atmosphere. The drawback is ease of cylinder handling and the possibility of a rupture before the cylinders are placed into the containment device. This type of system becomes very expensive when dealing with multiple cylinders, such as at the Sioux Falls Facility. With a gas feed system, the maximum realistic feed rate per cylinder is 400 pounds per day at room temperature. In order to meet the current maximum feed rate, a minimum of five cylinders need to be manifolded together in parallel. Currently there are six connected on each side with one side being on-line and the other side waiting to be brought into service, once the first bank is exhausted. Figure One-Ton Chlorine Containment Vessel Source: TGO Technologies We believe the current setup, using six manifolded cylinders per side in the correct arrangement for the Sioux Falls facility and do not recommend making changes to the number of feed Technical Memorandum No July 2001

83 cylinders. With this type of system, therefore, twelve (12) containment vessels would be required, along with an elaborate system for conveying the cylinders into the vessels. Preliminary costs for total containment systems are listed at $118,000 for the double ton cylinder model, with two bolt with chain drive door. The Sioux Falls WPP would require six of the double cylinder models, for a list price of $708,000 for the equipment only. With an installation of this size, the manufacturer indicated that a discount would be given. Even assuming a 25% discount, the capital costs are still much higher that the scrubbing alternatives, at $531,000. A preliminary estimate including installation and conveying system modifications would be in the $700,000 to $900,000 range. For this reason and the additional undesirable handling that would be required for placement of the cylinders into the vessels, this option will be dropped from consideration at the Sioux Falls WPP SCRUBBING COST COMPARISON This section will present a total present worth cost for the scrubbing alternatives, to compare wet versus dry scrubber costs. Costs will include capital cost, annual O&M and scheduled costs, all brought back to a present worth at an interest rate of 6%. The costs are based on a twenty-year life Wet Scrubber Wet scrubber capital costs will include the initial cost of the equipment, caustic, building addition and appurtenances. In lieu of a building, the manufacturer states that insulation and heat tracing can be used to avoid caustic freeze-up, however, that alternative is not as reliable as housing it in a climate-controlled building. With the insulation and heat tracing, leaks could occur and not be readily apparent, since the inner tank and piping is covered with insulation. This could also hinder locating of a leak, since the caustic travel along the insulation, taking the path of least resistance, and emerge in a different location from the leak. Heat tracing could also pose additional problems if it were to fail. Due to the nature of heat tracing, which allows elements to heat up via internal resistance to electrical current, failure is common and can be expected on a routine basis, with frequency depending upon quality of the equipment. Replacement or repair of heat tracing could be hindered by the insulation required. Insulation would also make routine maintenance of the pump and fan more difficult. Failure of heat tracing during very cold conditions would rapidly result in failure of the scrubbing system due to freeze-up and it would be very difficult to make repairs and replace caustic under such conditions. For the aforementioned reasons, we do not believe heat tracing and insulation of a caustic wet scrubber is an acceptable alternative, and it should be housed in a climate-controlled building. Technical Memorandum No July 2001

84 Table Opinion of Probable Capital Cost for Wet Scrubber System Item Estimated Cost Caustic Scrubber $85,000 Equipment Installation $34,000 Caustic (initial Fill) $10,000 Housing $80,000 Ducting & Control Modifications $25,000 Subtotal $234,000 Contingency (20%) $47,000 Total Estimated Construction Cost $281,000 Engineering/Legal/Administrative (15%) $42,000 Total Estimated Capital Cost $323,000 Table Opinion of Probable Operation and Maintenance Costs for Wet Scrubber System Cost Item Replacement Cost Annual Cost Present Worth (1) Caustic Replacement 3 yrs.) $10,000 - $8,400 Caustic Replacement (@ 6 yrs.) $10,000 - $7,100 Caustic Replacement (@ 9 yrs.) $10,000 - $5,900 Caustic Replacement (@ 12 yrs.) $10,000 - $5,000 Caustic Replacement (@ 15 yrs.) $10,000 - $4,200 Parts - $2,500 $28,700 Pump Replacement (@ 5yrs.) $3,500 - $2,600 Pump Replacement (@ 10 yrs) $3,500 - $2,000 Pump Replacement (@ 15 yrs) $3,500 - $1,500 Blower Replacement (@ 10 yrs) $3,000 - $1,700 Labor - $4,800 $55,100 Net Present Worth $122, Present worth based on a 6% discount rate and a period as shown for replacement costs and a period of 20 years for annual costs Dry Scrubber Dry scrubber capital costs will include the initial cost of the equipment, media and appurtenances. A building will not be required with a dry scrubber, since it is rated to -40 degrees Fahrenheit. Technical Memorandum No July 2001

85 Table Opinion of Probable Capital Cost for Dry Scrubber System Item Estimated Costs Dry Scrubber and media $127,000 Equipment Installation $26,000 Foundation and Pad $4,000 Ducting & Control Modifications $20,000 Subtotal $177,000 Contingency (20%) $35,000 Total Estimated Construction Cost $212,000 Engineering/Legal/Administrative (15%) $32,000 Total Estimated Capital Cost $244,000 Table Opinion of Probable Operation and Maintenance Costs for Dry Scrubber System Cost Item Replacement Cost Annual Cost Present Worth (1) Media Insurance 10 yrs.) $3,000 - $1,700 Sampling - $300 $3,400 Parts - $1,000 $11,500 Blower Replacement (@ 10 yrs.) $3,000 - $1,700 Media Replacement (@ 10 yrs.) $33,750 - $18,800 Labor - $1,200 $13,800 Net Present Worth $50, Present worth based on a 6% discount rate and a period as shown for replacement costs and a period of 20 years for annual costs Estimated Total Cost Summary The estimated total capital cost and operation and maintenance costs for each of the chlorine scrubber alternatives are summarized in Table Alternative Table Chlorine Scrubber Estimated Cost Summary Estimated Capital Cost Estimated O&M Present Worth (1) Total Present Worth Wet Scrubber System $323,000 $122,200 $445,200 Dry Scrubber System $244,000 $50,900 $294, Present worth based on 6% at 20 years UNLOADING PROTECTION Release of chlorine in the unloading process is a potential, due to dropping, however it is not common, and has not happened at the Sioux Falls WPP. Essentially, the only way to ensure that such an incident would not result in a release would be to totally contain the unloading process. Technical Memorandum No July 2001

86 This has been done at a small percentage of installations, where safety is of utmost concern due to close proximity to schools, hospitals, etc. To provide this option at the Sioux Falls WPP, a drive through building would be required, due to the unloading location. An estimated building size is 92-ft x 26-ft (2392 SF) and 18-ft high, to accommodate the delivery tractor/trailer. Utilizing a block and brick construction to be consistent with the other structures at the plant an estimate of costs would range from $150 to $175/SF; or a total cost of $358,800 to $418,600. Exhaust from this building would be routed to the scrubber to treat an accidental release RECOMMENDATIONS From the previous analysis we recommend that a dry scrubbing system be implemented at the Sioux Falls WPP, installed outside on a pad, due to the significantly lower present worth cost and the minimal operator and maintenance attention required. A likely location would be adjacent to the Chlorine Building on the south and east of the above ground reservoir. This will provide access for media replacement and maintenance and shield it from the north and west winds. We do not recommend attempting to enclose the unloading process by adding a building as described above. The risks do not appear to be significant enough to justify the additional cost. We recommend compliance with the operational procedures outlined in the Risk Management Plan to minimize potential accidents and releases. Technical Memorandum No July 2001

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90 TECHNICAL MEMORANDUM NO. 3 FACILITY CAPACITY UPGRADE Table of Contents Section Page 3.0 INTRODUCTION RAPID SAND FILTER EXPANSION Water Demands Existing Filters Media Scouring Maximum Loading Rate Additional Filters Required Future Filter Expansion Alternatives Alternative 1 - Construct 5 additional filters to the north Alternative 2 - Construct 5 additional filters to the west Alternative 3 - Expand existing filters Alternative Cost Comparison Treatment Enhancement Options Presedimentation Basin Conventional Sedimentation with Tube Settlers Solids Contact with Tube Settlers Ballasted Floc (Actiflo) Presedimentation Recommendations Chlorine Dioxide Recommendations BIG SIOUX WATER SUPPLY ANALYSIS Influent Piping System and Well Fields Airport Wells South Big Sioux Wells North Big Sioux Wells Middle Skunk Creek Wells System Modeling Model Calibration Existing System Performance Airport Wells Southern Big Sioux Wells Northern Big Sioux Wells Southern Skunk Creek Wells Future System Analysis Future System Demands Improvement Alternatives Summary of Results Preliminary Priority of Improvements Timing and Coordination with Presedimentation Basin Estimated Cost Recommendations...38 Technical Memorandum No. 3 -i- July 2001

91 Conclusion/Priority...40 List of Tables Table Page Table 3-1. Existing and Future Water Treatment Capacity Required...1 Table 3-2. Existing Filters Maximum Treatment Capacity...2 Table 3-3. Historical Filtration Rates...2 Table 3-4. Future Filters Required...4 Table 3-5. Advantages/Disadvantages of the Filter Expansion Alternatives...6 Table 3-5. (Continued) Advantages/Disadvantages of the Filter Expansion Alternatives...7 Table 3-6. Alternative Cost Comparison...7 Table 3-7. Opinion of Probable Capital Cost for Three Filters...9 Table 3-8. Conventional Sedimentation Design Criteria...10 Table 3-9. Opinion of Probable Capital Cost for Conventional Sedimentation...10 Table Solids Contact with Tube Settlers Design Criteria...11 Table Opinion of Probable Capital Cost for Solids Contact with Tube Settlers...12 Table Ballasted Floc Design Criteria...13 Table Opinion of Probable Capital Cost for Ballasted Floc Presedimentation...13 Table Opinion of Probable Capital Cost for Ballasted Floc Basin Covers...14 Table Intake Flow and Anticipated Chlorine Dioxide Dosage...14 Table Chlorine Dioxide Generation System Chemical Requirements...15 Table Opinion of Probable Capital Cost for Chlorine Dioxide System...16 Table Capacity Upgrade Alternatives...16 Table Sioux Falls Water Resources...17 Table Big Sioux Aquifer Well Installation Data Summary...19 Table Historical Output Airport Wells...20 Table Historical Output South Big Sioux Wells...21 Table Historical Output North Big Sioux Wells...22 Table Historical Output Middle Skunk Creek...23 Table Existing System Performance with Surface Water Pump Station...26 Table Existing System Performance without Surface Water Pump Station...27 Table Future System Demands...29 Table Water Supply Influent Piping Alternatives...31 Table System Flows with Presedimentation Basin...36 Table Booster Pump Station Estimated Cost...37 Table Relief Lines Estimated Costs...38 Table Alternative Summary Cost/MGD...39 Technical Memorandum No. 3 -ii- July 2001

92 List of Figures Figure Following Page Figure 3-1. Test Gullet Baffle...3 Figure 3-2. North Filter Gallery and Operating Level Proposed Addition Site Plan of Expansion Alternatives...41 Figure 3-3. North Filter Gallery and Operating Level Proposed Addition Alternative No. 1 Addition of 5 Filters to the North...41 Figure 3-4. North Filter Gallery and Operating Level Proposed Addition Alternative No. 2 Addition of 5 Filters to the West...41 Figure 3-5. North Filter Gallery and Operating Level Proposed Addition Alternative No. 3 Increase Size of Existing Filters...41 Figure 3-6. Presedimentation Basins...41 Figure 3-7. Big Sioux and MSC Well Fields Piping/Well Locations...41 Figure 3-8. Big Sioux and MSC Well Fields Model Nodes and Piping Segments...41 Figure 3-9. Big Sioux Wellfield Alternative Improvements...29 Technical Memorandum No. 3 -iii- July 2001

93 3.0 INTRODUCTION TECHNICAL MEMORANDUM NO. 3 FACILITY CAPACITY UPGRADE The purpose of this Technical Memorandum (TM) is to evaluate expansion requirements to increase the facility capacity to meet future water demands. The following areas will be discussed in detail: Rapid Sand Filter Expansion Water Purification Plant (WPP) Influent Piping 3.1 RAPID SAND FILTER EXPANSION WATER DEMANDS Based on the Water Demands/Quality technical memorandum (TM No.1), the existing and future water demands in Sioux Falls are as shown in Table 3-1 below. The flows shown for the years 2010, 2015 and 2025 are based on dry year estimates, representing the more conservative demand values. Filter systems are typically designed and sized to provide enough treatment to meet maximum day demands. As also discussed in TM No. 1, there are future additional water sources that may be used to help meet the Sioux Falls future water demands. These sources are the Skunk Creek Aquifer, the Wall Lake Aquifer and the Lewis and Clark rural water project, and are discussed in detail in TM No. 1. The impacts of these additional sources on the treatment capacity required based on dry year estimates are also shown in Table 3-1. Table 3-1. Existing and Future Water Treatment Capacity Required Year Average Day Maximum Day Maximum Hour (MGD) (MGD) (MGD) (w/ additional sources) (w/ additional sources) (w/ additional sources) EXISTING FILTERS Currently, the Sioux Falls WPP consists of 10 filters, five (5) in the South Filter Gallery serving Contact Basins 1, 2 and 3, five (5) in the North Filter Gallery serving Contact Basins 4, 5 and 6. Each filter is split into two filter cells with a center drain gullet. Each cell is 14-3 x 25-0, about 356 square feet, with the total surface area of each filter being 712 square feet. The filters are dual media with a 10-inch layer of sand overlain by a 20-inch layer of granular activated carbon. A 3-inch layer of torpedo sand overlays the air/water underdrain laterals. Technical Memorandum No July 2001

94 With the assumption that all 10 filters are running, the existing loading rate to each filter at average demand is about 2 gallons per minute per square foot (gpm/sf). This rate increases to about 4.5 gpm/sf at maximum day demand. A summary of historical filter loading rates for the years 1998 through 2000 is given in Table 3-3 below. The maximum treatment capacity of the existing filters is somewhat questionable due to media scouring that occurs at hydraulic loading rates at or above 4 gpm/sf. Maximum capacities for all filter operating and with one filter off line are shown below using loading rates of 4 and 5 gpm/sf. Table 3-2. Existing Filters Maximum Treatment Capacity Filter Loading Rate Treatment Capacity (MGD) (gpm/sf) 10 Filters Operating 9 Filters Operating It should be noted that the filters have not been able to operate with a 5 gpm/sf loading rate due to media scouring mentioned above. The media scour problem will be discussed in more detail later in this document. Table 3-3. Historical Filtration Rates Average Day Maximum Day Year Flow (MGD) Filtration Rate (1) (gpm/sf) Flow (MGD) Filtration Rate (1) (gpm/sf) Filtration rates based on all 10 filters operating. Maximum day flows are based on dry year conditions. In current operation, the existing filter run times range from 50 to 60 hours between backwashes. The typical backwash rates range from 16.5 gpm/sf during winter months up to 20 gpm/sf in summer months. According to information received from the plant, the water purification plant loses approximately 3% of their total product as backwash waste. It is possible to run the filters at higher loading rates as demands increase. However, an increase in filter loading rates will increase the frequency of backwashes, subsequently increasing the percentage of product lost as backwash waste Media Scouring Based on information given by City staff, it appears that the GAC media begins to scour at filter loading rates at or above 4 gpm/sf. The scouring seems to be localized at the back of each filter. Technical Memorandum No July 2001

95 Observations in the field show that at loading rates 4 gpm/sf and above, the flow velocity in the influent gullet is high enough to create a significant transition zone at the back of the gullet. The influent velocity is converted (or transitions) to a pressure head at the back of the gullet, creating a more turbulent zone as it flows into the filters. This additional turbulence, in combination with the low density of the GAC, appears to be the cause for the media scouring. Higher filter loading rates will exacerbate this problem. The City performed additional filtration rate tests with the water level just below the top of the gullet. This would force all of the water through the troughs which helps distribute the influent more evenly over the filter bed and would keep the velocity of the water from being transmitted to the back of the filter wall and scouring media near the back of each cell in the filter. The filtration rate was taken up to 6.0 gpm/sf. There was no pronounced scouring of GAC in the back of the filter cells, but the top of the GAC was observed to be shifting. The traditional solids covering that takes place on top of the filter during a filter run was disturbed. Areas of black GAC were noted. While the shifting media was a new phenomenon in a filter during operation, it did not appear to be a significant issue with filter performance. A significant problem noted operating at the 6.0 gpm/sf filtration rate occurred during initial operation after backwashing. The filter-to-waste cycle is limited to a maximum of approximately 4.0 gpm/sf because of piping constraints, even though the rate is set at 6.0 gpm/sf. The effluent valve is automatically fully opened in an attempt to meet the input flow of 6.0 gpm/sf. At the end of the filter-to-waste cycle, the filter-to-waste valve is closed and filtered water is sent to the clearwell. When the transition from filter-to-waste to normal filtration mode is made, the effluent valve is fully opened and the filtration rate surges to 8.5 gpm/sf causing a turbidity spike that lasts for several minutes. In addition, the filters operated for approximately 30 hours before backwashing was required. Backwashing was not based on headloss, but turbidity breakthrough. The key to reducing the media scour is the dissipation of the energy/velocity in the filter influent. Installation of a baffle in the gullet of filters configured similarly to Sioux Falls were successful in eliminating a media-scouring problem. Figure 3-1 shows a typical baffle installation. Construction of the baffle uses readily available materials. A baffle should be constructed and tested by the City. Once the baffle has been successfully tested, materials for a more permanent installation will be selected. The hydraulic surge problem when a filter is transitioning from filter-to-waste to normal filtration can be resolved by making changes to PLC ladder logic. The main focus will be to ensure that the effluent valves on a filter are closed to a point to where the flow rate will not surge initially in the filtration mode. Eliminating the scour and the hydraulic surge problems should allow an increase in filter loading to 5.5 to 6.0 gpm/sf. Technical Memorandum No July 2001

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97 Maximum Loading Rate Due to the current media scour problem, the filters in their current configuration should not be loaded at a rate greater than 4 gpm/sf. As mentioned above, the media scouring is likely to get worse as the rate increases beyond 4 gpm/sf. The City has indicated that anthracite had been used prior to GAC, and that the filters could be run at higher rates without causing media scour. As indicated above, a higher loading is likely if the velocity current in the filter gullet is reduced. Another factor impacting filtration rate is the raw water quality. Poor surface water quality (high turbidity, algae, etc.) results in increased turbidity carryover from the solids contact units. This causes higher turbidity and more rapid breakthrough in the filters if the hydraulic loading is high. Thus, a more consistent water quality into the solids contact units would facilitate operations and the ability to maintain a consistent, low turbidity influent to the filters. A presedimentation basin (turbidity reduction) and chlorine dioxide (strong oxidant for algae, taste/odors) should enhance filtration rates. The American Water Works Association Research Foundation is currently conducting research on the use of various oxidants in raw water and the benefit on filter turbidity levels. This concept is verification of the City s experience that indicates KmnO 4 fed at the surface water pump station is very important in maintaining low filter effluent turbidities. The implementation of presedimentation and chlorine dioxide will be discussed further later in this TM Additional Filters Required The number of future filters required is determined by the future maximum day flow rate selected for design, the design filtration rate for the filters and the performance of the future presedimentation basin. Table 3-4 shows the number of filters needed based on the maximum day flow rate and filtration rate design parameters. The assumption of one filter out-of-service is made and that the future filters will be the same size as the existing. Table 3-4. Future Filters Required Dry Year Max Additional Filters Required (1) Year Day Event (MGD) 4 gpm/sf 5 gpm/sf 6 gpm/sf (w/ additional sources) (2) (w/ additional sources) (w/ additional sources) With one filter out of service. 2. Prior to start of Lewis and Clark 10 MGD supply. Technical Memorandum No July 2001

98 3.1.3 FUTURE FILTER EXPANSION ALTERNATIVES The current plant has 10 filters with a total filter area of 7,120 sf. A 50% expansion would increase the total filter area to 10,680 sf. Using a maximum filter loading rate of 5 gpm/sf and all 15 filters operating gives a total treatment capacity of approximately 77 mgd (72 mgd with one filter out of service). Assuming a backwash waste percentage the same as the existing filters (3%) gives a total product of 74.7 with all filters running and 69.8 mgd with one filter out of service. Therefore, the 50% expansion would provide sufficient product water to meet the year 2025 projected maximum day (dry year) water demand of 69.5 mgd. Three alternatives were evaluated for providing the additional filter area requested. Construct five (5) additional filters identical in size to the existing filters, either to the north side (Alternative 1) or west side (Alternative 2). Expand all of the existing filters by 50% to approximately 1070 square feet per filter. Figure 3-2 is a site plan showing the approximate footprint for each alternative. Below is a brief summary of the three alternatives, followed by Table 3-5, entitled Advantages/Disadvantages of the Filter Expansion Alternatives listing the advantages and disadvantages of each alternative Alternative 1 - Construct 5 additional filters to the north The additional filters would be constructed on the north side of the existing filter building and would consist of the five additional filters as well as an extension of the existing pipe gallery and filter influent channel. Filter construction and dimensions would be identical to the existing filters (two cells, each 14-3 W x 25-0 L, with a center influent/drain gullet). A layout of the additional filters is shown in Figure 3-3. Hydraulically, the additional filters will have minimal impact on the existing system. The existing influent and effluent channels are large enough that the increased flow will not have a significant impact on the overall plant hydraulic profile. The extended influent channel will carry a small velocity, but the effluent control valves will ensure an equal flow split to the new filters. Backwash of each filter can still be accomplished using the existing backwash pumps Alternative 2 - Construct 5 additional filters to the west This alternative is similar to Alternative 1, except the filters would be constructed on the west side of the existing building. The filters would be located adjacent to the existing North filters (Filters 6 thru 10). This location would reduce the cost for relocating the existing utilities and would provide additional flexibility for future expansion further west, if necessary. A layout of the additional filters is shown in Figure Alternative 3 - Expand existing filters This alternative would add an extra 50% filter area to all of the existing filters. A filter extension would be attached to the west side of these filters, increasing the length of each filter cell by 12- feet, 6-inches. The existing influent gullets and effluent channels for each filter would be extended to the new area. A layout of the filter extensions is shown in Figure 3-5. Technical Memorandum No July 2001

99 The increased flow to the expanded filters would increase headlosses in the influent and drain lines. Headloss in the existing 30-inch influent lines would increase by about 3 inches, while headloss in the existing 24-inch drain would increase about 12 inches. Neither would have a significant impact to the hydraulic profile. However, the headloss through the existing 14-inch effluent venturi meters would see an increase of almost 3 feet, based on an assumed neck diameter of 60% of the existing pipe diameter. If the water surface in the filter could not be raised, the increased headloss in the effluent line would reduce the headloss available to the filter, thereby reducing run times. In order to minimize or eliminate the increase in head, the effluent pipe, meters and valves would need to be upsized to either 16 inches or 18 inches. Backwash water rates would also increase. Assuming a maximum backwash rate of 20 gpm/sf and an increased filter area of 534 sf gives a backwash rate of 10,680 gpm. As the existing pumps have a flow rating of about 6000 gpm, new pumps would likely be required. In addition, the existing backwash storage basin would be marginal based on current backwash practice. The existing volumes reach up to 200,000 gallons per backwash, based on the current size of filters. A 50% increase in filter area would imply a required storage volume of 300,000 gallons. In addition, the number of filters that could be backwashed per day would decrease. Existing storage in the basin is about 240,000 gallons. Therefore, to accommodate two full backwashes, the existing basin size would need to be increased or a second basin constructed to provide a total storage volume of about 600,000 gallons. In addition, the number of filters that could be backwashed per day would decrease. With the present size of the filters and a 600 gpm capacity pump from the backwash waste storage basin, the existing backwash storage basin and pump could handle 4 filter backwashes a day. With the increased filter size this would decrease to 2-3 filter backwashes a day. This is probably too restrictive, and would require the increase of the backwash storage basin and backwash waste pump. Table 3-5. Advantages/Disadvantages of the Filter Expansion Alternatives Advantages Disadvantages Alternatives 1 and 2 - Construct 5 additional filters New filters can be constructed without More additional land space required having to take existing filters offline Could still use existing backwash pumps Additional instrumentation and control required Operation identical to existing filters New piping and valves needed Easier to connect to existing structure than Highest cost alternative Alternative 2. Ideal set-up for future solids contact basins Will require rerouting a number of existing lines and service road Technical Memorandum No July 2001

100 Table 3-5. (Continued) Advantages/Disadvantages of the Filter Expansion Alternatives Advantages Disadvantages Alternative 3 - Increase size of existing filters by 50% Less land space required Will need to increase backwash pump capacity Can use existing instrumentation and control Building connection may be more difficult No additional piping, valves needed 3:1 length to width ratio may create uneven backwash from front to back (needs to be checked) Lower cost than Alternative 1 Operator will not be able to see entire filter from operating floor (doorways to new area) Impact on existing utilities will be minimal Filters will need to be taken off line for and service road can be easily rerouted. construction Headlosses through filter (piping, channels) will increase (needs confirmation) Effluent pipe venturi and meter may need to be upsized (needs confirmation) Existing backwash storage basin volume and backwash waste pump size needs to be increased ALTERNATIVE COST COMPARISON Costs for each alternative are summarized in Table 3-6 below. Table 3-6. Alternative Cost Comparison Item Alternative 1 & 2 (1) Alternative 3 Civil/Earthwork (incl. utility relocates) $650,000 $470,000 Structural $940,000 $940,000 Process $530,000 $1,060,000 Mechanical $1,120,000 $530,000 Electrical/Instrumentation $1,180,000 $710,000 Building $1,350,000 $1,120,000 Subtotal $5,770,000 $4,830,000 Contingency (20%) $1,150,000 $970,000 Total Estimated Construction Cost $6,920,000 $5,800,000 Engineering/Legal/Administrative (15%) $1,040,000 $870,000 Total Estimated Project Capital Cost $7,960,000 $6,670, Alternative 2 will be about 5% less due to the reduced number of utility relocations needed, however, the west location would need to be coordinated with clearwell expansion and backwash storage and treatment systems. Technical Memorandum No July 2001

101 3.1.5 TREATMENT ENHANCEMENT OPTIONS As discussed previously, two treatment options, presedimentation and chlorine dioxide, have been identified to potentially improve raw water quality to the filters. A discussion of these options is included in the following sections Presedimentation Basin Addition of the presedimentation basin was identified as the highest priority for increasing plant capacity by targeting the treatment of surface water and improving the quality for water entering the filters to increase the filtration rate. The number of filters required based upon the achievable filter loading rates can be evaluated after presedimentation is constructed and operated for a period of approximately one year. Providing consistent low turbidity water to the filters is important for DBP reduction and maximizing the hydraulic loading to the filters. Ferric chloride and PAC are currently dosed to the existing softening basins, but due to the high ph from the lime addition, removal may not be optimized. The proposed new basin would be designed for presedimentation prior to the lime softeners for turbidity and TOC removal when demands require the use of poor quality surface water (series mode ahead of existing solids contact basins). The main function of the basin would be to provide a less turbid, more consistent feed water to the filters to allow a higher filter loading rate. The effluent water quality from this type of basin should allow a higher filtration rate, thereby reducing the number of additional filters needed. If the media scour problem discussed previously is resolved, and assuming that a presedimentation basin is constructed and the additional water sources (such as Lewis and Clark) are acquired, the plant may be able to meet the future maximum day demands without adding more filters. If the additional water sources are not available but a presedimentation basin is provided allowing a filter loading rate as high as 6 gpm/sf, the number of additional filters required would be reduced to three (refer to Table 3-4). These higher loading rates should be confirmed with additional piloting or bench-scale studies. Table 3-7 summarizes the estimated capital costs for the design and construction of three filters. Technical Memorandum No July 2001

102 Table 3-7. Opinion of Probable Capital Cost for Three Filters Item Estimated Cost Civil/Earthwork (incl. utility relocates) $330,000 Structural $480,000 Process $270,000 Mechanical $570,000 Electrical/Instrumentation $600,000 Building $690,000 Subtotal $2,940,000 Contingency (20%) $588,000 Total Estimated Construction Cost $3,528,000 Engineering/Legal/Administrative (15%) $529,000 Total Estimated Project Capital Cost $4,057,000 Three types of presedimentation have been evaluated for implementation at the Sioux Falls WPP and are discussed in the following sections Conventional Sedimentation with Tube Settlers Conventional sedimentation consists of rapid mix, flocculation, and sedimentation. Tube settlers would be installed in the sedimentation tank to increase the surface overflow rate and decrease the required footprint. Advantages of conventional sedimentation include: Provides predictable performance under most conditions. Relatively tolerant to hydraulic and solids shock loading. Easy operation and low maintenance requirements. Conventional sedimentation has the following disadvantages: Requires separate rapid mix and flocculation process units. Requires the largest footprint. Potentially the highest capital costs. Subject to density flow in sedimentation basin, resulting in decreased effluent quality. Two conventional sedimentation units would be provided, each with a capacity of 15 MGD. Design criteria under this alternative are included in Table 3-8. Technical Memorandum No July 2001

103 Table 3-8. Conventional Sedimentation Design Criteria Description Criteria Rapid Mix Chamber Number of units 2 Detention Time 30 seconds Flocculation Basin Number of units 2 Detention time 30 minutes Minimum flow thru velocity 0.5 feet per minute Maximum flow thru velocity 1.5 feet per minute Sedimentation Basin Number of Units 2 Surface Overflow Rate 2 Detailed estimates of capital costs for the conventional sedimentation alternative are summarized in Table 3-9. Table 3-9. Opinion of Probable Capital Cost for Conventional Sedimentation Item Estimated Cost Sitework $100,000 Equipment $1,300,000 Concrete Tanks $1,800,000 Cover $900,000 Electrical/Instrumentation $195,000 Mechanical/Piping $325,000 Subtotal $4,620,000 Contingency (20%) $924,000 Total Estimated Construction Cost $5,544,000 Engineering/Legal/Administrative (15%) $832,000 Total Estimated Project Capital Cost $6,376, Solids Contact with Tube Settlers Solids contact units combine the flocculation and sedimentation processes into a single unit. In addition, a sludge blanket is utilized in the basin to increase particle contact and removal from process flow. Technical Memorandum No July 2001

104 Advantages of the use of solids contact for presedimentation include: Provides more efficient flocculation and greater particle contact than conventional filtration allowing for a smaller footprint. Sludge removal is simpler. The sludge blanket provides a buffering effect to delay degradation of effluent if coagulant dosage is interrupted. Solids contact units have the following disadvantages: Require greater operational control. Vulnerable to upsets of sludge blanket and turbidity carryover due to hydraulic or solids shock loading. Temperature fluctuations can lead to short-circuiting. More time is required at start-up for sludge blanket formation. Initially, two basins could be provided without tube settlers that would have a total treatment capacity of approximately 15 MGD. Tube settlers could then be added later as required to increase the total presedimentation treatment capacity to approximately 30 MGD. Basin design criteria used for this evaluation are summarized below in Table Table Solids Contact with Tube Settlers Design Criteria Description Criteria Number of units 2 Surface overflow rate (without tube settlers) 1 gpm/sf Surface overflow rate (with tube settlers) 2 gpm/sf Detention Time 2 hours Technical Memorandum No July 2001

105 Approximate capital costs for the presedimentation option of implementing solids contact units with tube settlers are shown in Table Table Opinion of Probable Capital Cost for Solids Contact with Tube Settlers Item Estimated Cost Solids Contact Units Sitework $70,000 Equipment $600,000 Concrete Tanks $1,400,000 Cover $624,000 Electrical/Instrumentation $90,000 Mechanical/Piping $150,000 Subtotal $2,934,000 Contingency (20%) $587,000 Subtotal Estimated Construction Cost $3,521,000 Engineering/Legal/Administrative (15%) $528,000 Subtotal Estimated Project Capital Cost $4,049,000 Tube Settlers $750,000 Subtotal $750,000 Contingency (20%) $150,000 Subtotal Estimated Construction Cost $900,000 Engineering/Legal/Administrative (15%) $135,000 Subtotal Estimated Project Capital Cost $1,035,000 Total Estimated Project Capital Cost $5,084, Ballasted Floc (Actiflo) Ballasted floc is similar to conventional sedimentation, consisting of rapid mix, flocculation and sedimentation. Microsand is used as a seed for floc formation, providing a large surface contact area and increasing settling velocity. The microsand ballasted floc allows for higher surface overflow rates and shorter retention times, greatly reducing the footprint of the sedimentation system. Ballasted floc sedimentation presents the following advantages: Very small footprint. Very good performance even with hydraulic and solids overloading. Potential savings in capital costs. Efficient algae removal. (Additional information on algae removal is included in Appendix A.) Very quick process startup. Technical Memorandum No July 2001

106 Disadvantages of ballasted floc include the following: Heavy dependence on mechanical equipment. Short processing time. Must be shutdown if loss of power occurs. Design criteria for a ballasted floc system is included in Table Table Ballasted Floc Design Criteria Description Criteria Coagulation Tank Number of units 2 Retention time 2 minutes Injection Tank Number of units 2 Retention time 2 minutes Maturation Tank Number of Units 2 Retention time 6 minutes Settling Tank Number of units 2 Surface overflow rate 25 gpm/sf Estimated capital costs for ballasted floc presedimentation are summarized below in Table Table Opinion of Probable Capital Cost for Ballasted Floc Presedimentation Item Estimated Cost Sitework $50,000 Equipment $1,530,000 Concrete Tanks $1,033,000 Electrical/Instrumentation $230,000 Mechanical/Piping $383,000 Subtotal $3,226,000 Contingency (20%) $645,000 Total Estimated Construction Cost $3,871,000 Engineering/Legal/Administrative (15%) $581,000 Total Estimated Project Capital Cost 4,452,000 Cost for basin covers were not included in the capital costs shown in Table 3-13 as the high overflow rate of the ballasted floc system will result in high flow rates through the units, Technical Memorandum No July 2001

107 preventing freezing. However, the addition of covers may aid in the operation and maintenance of the units. Table 3-14 summarizes costs for the addition of covers for the basins. Table Opinion of Probable Capital Cost for Ballasted Floc Basin Covers Item Estimated Cost Covers (2) $83,000 Bridge (Connection to existing building) $90,000 Electrical/Mechanical $15,000 Subtotal $188,000 Contingency (20%) $38,000 Total Estimated Construction Cost $226,000 Engineering/Legal/Administrative (15%) $34,000 Total Estimated Project Capital Cost $260, Presedimentation Recommendations Presedimentation has been identified as a high priority for surface water treatment to improve water quality to the filters and increasing plant capacity by increasing the filter hydraulic loading rate. Based upon the alternatives discussed above, ballasted floc appears to be the most attractive option for presedimentation at the Sioux Falls WPP. The high overflow rate of the unit results in a smaller footprint and reduced capital cost. The process will provide very good performance even at hydraulic and solids shock loading and will also provide good algae removal. The proposed location for the presedimentation basins is shown in Figure Chlorine Dioxide Chlorine dioxide is a strong oxidant that could be used for algae, taste and odor control in the surface water. In discussions in previous meetings with City staff, chlorine dioxide was mentioned as a possible treatment option at the surface water intake pump station for organics control. Table 3-15 summarizes the estimated flow to be treated and anticipated dosage. Table Intake Flow and Anticipated Chlorine Dioxide Dosage Criteria Maximum Flow (Summer peak) Average Flow Maximum Dosage Rate Average Dosage Rate Flow/Dosage 30 mgd 20 mgd 1.5 mg/l 1.0 mg/l A chlorine dioxide generation system works by combining chlorine, primarily gaseous chlorine, and sodium chlorite. There are systems available that use aqueous chlorine, but these systems require sulfuric acid to complete the reaction. For the purposes of this evaluation, it was assumed that gaseous chlorine would be utilized. Technical Memorandum No July 2001

108 The chemical reaction to produce 1 pound of chlorine dioxide requires 1.34 pounds of pure sodium chlorite and 0.5 pounds chlorine. Gaseous chlorine is pure, while sodium chlorite can be provided in either dry or liquid form. The dry form is a crystalline powder with a purity of 80%, while the liquid form has a purity of 25%. Table 3-16 summarizes the daily dosage rates and storage volumes required for each chemical. Storage volumes were computed for both maximum chlorine dioxide dosage at maximum flow and average dosage at average flow. Table Chlorine Dioxide Generation System Chemical Requirements Chemical Average Flow Maximum Flow and Dosage and Dosage Sodium Chlorite Dose (dry), lb/day Sodium Chlorite Dose (liquid), gal/day Chlorine Dose, lb/day day Storage Volume, Sodium Chlorite (dry), lb day Storage Volume, Sodium Chlorite (dry), lb day Storage Volume, Sodium Chlorite (liquid), gal day Storage Volume, Sodium Chlorite (liquid), gal day Storage Volume, Chlorine, lb day Storage Volume, Chlorine, lb Providing for chlorine dioxide feed at the surface water intake pump station would require the addition of four separate rooms: chlorine storage room, sodium chlorite storage and feed room, chlorine dioxide generation system room, and chlorine scrubber room. A brief description of each room is given below: Chlorine Storage Room: This room would consist of two (2) one-ton chlorine cylinders (one in service to provide the required volume and one backup), associated cylinder feed equipment, trunnions, gas detection system and a monorail for cylinder loading. Room size would be approximately 15-ft x 30-ft with a 10-ft x 20-ft loading dock. Sodium Chlorite Storage and Feed Room: This room would contain the dry or liquid storage tankage, feed pumps and associated piping, and control equipment. A 20-ft x 20-ft room would house this equipment. Chlorine Dioxide Generation Room: Chlorine dioxide generation systems typically are skid or panel mounted systems with the necessary feed and control equipment. The chlorine feeder panels would also be included in this room. Room size would be about 15-ft x 20-ft. Chlorine Scrubber Pad: For this evaluation, it was assumed a dry scrubber system would be utilized. As discussed in TM No. 2, this type of chlorine scrubbing system can be located outdoors on a concrete pad. Technical Memorandum No July 2001

109 The table below gives an opinion of probable construction cost for adding a chlorine dioxide generation system at the existing intake pump station. Table Opinion of Probable Capital Cost for Chlorine Dioxide System Item Estimated Cost Chemical Rooms $180,000 Loading Dock $10,000 Chlorine Feed System $80,000 Sodium Chlorite Feed System $40,000 Chlorine Dioxide System $40,000 Chlorine Scrubber $177,000 Monorail $20,000 Solution Piping and Valving $20,000 Subtotal $567,000 Contingency (20%) $113,000 Total Estimated Construction Cost $680,000 Engineering/Legal/Administrative (15%) $102,000 Total Estimated Project Capital Cost $782, RECOMMENDATIONS Several different options were evaluated for the expansion of the Sioux Falls WPP to meet future capacity requirements. Table 3-18 summarizes the alternatives and capital costs associated with each option. Table Capacity Upgrade Alternatives Alternative Estimated Cost Alternative No. 1 & No. 2 5 Additional Filters $7,960,000 Alternative No. 3 50% Filter Expansion $6,670,000 Alternative No. 4 Presedimentation Basin + 3 Additional Filters $8,509,000 (1) Chlorine Dioxide System $782, Eliminates the need for a backwash treatment cost of $1,683,000 (See Table 2-26, Alternative No. 3 - $2,713,000 minus backwash equalization tank $1,030,000). Additional cost of approximately $260,000 required to cover presedimentation basins. Although Alternative No. 4 presents a higher capital cost, it is the most attractive option for future capacity expansion. As discussed previously, treatment of surface water in the presedimentation basins will provide a more consistent and improved water quality for filter influent. This will allow for increased filter hydraulic loading while maintaining the filter effluent turbidity quality. In addition, the presedimentation basins will serve as treatment for filter backwash recycle (see TM No. 2). Technical Memorandum No July 2001

110 The chlorine dioxide system is included in Table 3-18, although it is not considered as an alternative to the other filter expansion options. Instead, the implementation of such a system should be considered as an additional treatment technique to be used in conjunction with the capacity expansion alternative selected to provide additional reliability in the treatment of surface water. Installation of the chlorine dioxide system at the main plant as opposed to the surface water intake pump station is an additional consideration. Following construction of the presedimentation basins, chlorine dioxide should be tested at the intake pump station, as well as the influent and effluent of the presedimentation basins. Testing at these locations will help determine the most effective and beneficial location for chlorine dioxide addition. Furthermore, implementation of a chlorine dioxide system at the main plant may reduce the capital costs of the system. 3.2 BIG SIOUX WATER SUPPLY ANALYSIS Currently, there are several water resources available to the City. They include the Big Sioux, Middle Skunk Creek, Southern Skunk Creek, Split Rock Creek Aquifers, and the Big Sioux Surface Water Pump Station. At this time, there are a total of 68 groundwater wells in the system. The wells are of varying age, size and type. In addition to the groundwater wells, the City also withdraws water from the Big Sioux River via the Surface Water Pump Station (SWPS). Output from the various resources varies by year and is influenced by a number of factors. A summary of the water resources is presented in Table Location Table Sioux Falls Water Resources Number of Wells/Pumps Design Pumping Capacity (MGD) 1999 Pumpage (MGD) % of Total Big Sioux Aquifer Middle Skunk Creek Aquifer Big Sioux Pump Station (surface water) 3 45 (30) (1) Subtotal (2) Split Rock Creek Aquifer Southern Skunk Creek Aquifer TOTAL % 1. SWPS has 3 pumps each rated at 11,000 gpm. Firm capacity with 2 pumps operating is approximately 30 MGD. 2. These subtotals represent the totals to the WPP from the Big Sioux/Wellfield piping system. As indicated above, the vast majority of supply (98%) enters the WPP through the well field piping system north of the WPP. Under current average demand conditions, the influent system is able to supply adequate water to the WPP. However, it has recently been shown that under high demand, the system is reaching its maximum capacity. Technical Memorandum No July 2001

111 Flows above 45 to 50 MGD result in high headloss or pump inefficiency, which limits increased production capability. As discussed previously in TM 1, future maximum day demand could be as high as 69.9 MGD. Modeling was performed to determine the ability of the current system to meet future demands. In addition, alternate piping systems were analyzed to determine the benefit of improvements INFLUENT PIPING SYSTEM AND WELL FIELDS The well/pump station locations and well field piping are shown in Figure 3-7. Table 3-20 summarizes the Big Sioux Aquifer wells and provides information on the well type, water levels and pumps. The oldest portion of the Big Sioux Aquifer well field is located in the area of the Sioux Falls Regional Airport directly northwest of the WPP. Some of the wells in this area are low usage, and the potential for contamination exists in the southern airport area. The piping that serves this part of the system is generally older, small diameter piping. Some parallel relief lines have been added to provide additional capacity. More recent additions to the well field have extended collection lines up to eight miles north of the WPP. A large percentage of the groundwater supply is provided by wells north of the diversion channel. The water produced in this portion of the Big Sioux Aquifer well fields is carried to the WPP in two large diameter (24 inch and 36/42 inch) transmission lines. The 24 and 36/42-inch lines are tied at several points to allow cross flow. The Big Sioux River Pump Station was built at the junction of the Big Sioux River and the Diversion Channel in Water is withdrawn from the river and pumped through a 48-inch line into the piping system and ties into both the 24 and 36-inch mains. The Pump Station consists of 3 pumps each rated at 11,800 gpm (16.8 MGD) at 60 ft. TDH. The firm capacity of the SWPS with two of the three pumps running is approximately 30 MGD because of the increased pressure/headloss in the piping system. Surface water now makes up a large percentage of the City s water supply, but this supply could be limited during dry years. To provide additional groundwater supply, especially during dry years, development of the Skunk Creek Aquifer was undertaken in Thirteen wells were constructed in the Skunk Creek Aquifer located approximately 12 miles northwest of the WPP. One 24-inch line connects the Skunk Creek well field to the north end of the Big Sioux Aquifer well field. In evaluating the well field and piping system, the supplies were subdivided into various areas as follows: Airport Wells: All wells south of Diversion Channel South Big Sioux Wells: Wells from Diversion Channel to 84 th St. North (one mile south of Renner Road) North Big Sioux Wells: Wells north of 84 th St. North Middle Skunk Creek Wells: Middle Skunk Creek area Surface Water Pump Station: At Big Sioux River and Diversion Channel. Technical Memorandum No July 2001

112 Table Big Sioux Aquifer Well Installation Data Summary Well Number Year Well Type Estimated Well Yield (gpm) Ground Elevation Top Screen Bottom Screen Bottom Well Center of Gauge Static Water Level 2000 (Range) Pumping Wtr Lvl Well Pump 1989 (Min) H.P. Stages Technical Memorandum No July 2001 Original Design Pt. Column Diameter Comments Wolfe Bragstad Bragstad Bragstad Bragstad Bragstad Bragstad Bragstad Bragstad Bragstad Bragstad Bragstad Bragstad Bragstad Bragstad Bragstad Bragstad Bragstad Ranney Ranney (est.) Impeller Changed in Ranney Ranney Ranney Gravel Pack Ranney New Pump Ranney Ranney Number of Stages reduced in Ranney Number of Stages reduced in Gravel Pack Number of Stages reduced Gravel Pack Gravel Pack Number of Stages reduced Ranney Ranney Gravel Pack (est.) Gravel Pack (est.) Gravel Pack (est.) Gravel Pack (est.) Gravel Pack (est.) Gravel Pack (est.) Gravel Pack (est.) Gravel Pack (est.) Gravel Pack (est.) Gravel Pack (est.) Gravel Pack (est.) Gravel Pack Gravel Pack Gravel Pack Gravel Pack Gravel Pack Gravel Pack Gravel Pack Gravel Pack

113 The historical output for each of these areas and the change in average production rate for each well is summarized in the following tables. The average GPM for 1993, 1996 and 1999 was taken from the Annual Report. The current operating point is taken from the pump curve as evaluated in the Big Sioux Aquifer Study completed by HDR. These were adjusted based on the operating data (flow and pressure) from each well report maintained by the City. The well performance is not the focus (or scope) of this evaluation; however, the trends do identify possible concerns Airport Wells Table 3-21 summarizes the data for the twenty (20) Airport Wells. Table Historical Output Airport Wells Airport Wells Design Average Use 1999 Average Use 1996 Average Use 1993 Well No. Region Flow gpm Flow gpm Percentage use Flow gpm Percentage use Flow gpm Percentage use Change 93-96' gpm Change 96'-99' gpm Change 93'-99' gpm 3 Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Totals MGD 14.8 MGD 19.5 MGD 20.3 MGD -0.8 MGD -4.8 MGD -5.5 MGD SWPS Totals 3 60 FT) MGD 10.9 MGD 6.7 MGD 4.3 MGD -0.6 MGD 3.6 MGD Technical Memorandum No July 2001

114 South Big Sioux Wells Well Region No. The following are comments regarding this area: Well No. 4 (Bragstad): Production dropped substantially (378 gpm) from 1996 to 1999; however, this well is used very little. Well No. 20 (Bragstad): Appears to have decreased in the last 3 years by 209 gpm. Well No. 21 (Bragstad): Decreased 242 gpm in last 3 years, 482 gpm in 6 years. Well No. 23 (Bragstad): Decreased 261 gpm in last 3 years. Well No. 29 (Bragstad): Decreased 1385 gpm in last 3 years. This well was rehabilitated in 1992 (1993 production averaged 2416 gpm). Possible rehab candidate may have had discharge valve throttled, which would reduce production. Overall, the average production rate declined by 4.7 MGD in last 3 years. These wells have low TDH pumps, which may result in some of the decrease as overall pumpage and pressures increase South Big Sioux Wells Table 3-22 summarizes the operating data for the fourteen (14) Southern Big Sioux Wells. Table Historical Output South Big Sioux Wells Design Average Use 1999 Average Use 1996 Average Use 1993 Flow (gpm) Flow Percentage (gpm) use Flow Percentage (gpm) use Flow (gpm) Percentage use Change 93'-96' (gpm) Change 96'-99' (gpm) Change 93'-99' (gpm) 25 S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx Totals MGD 17.4 MGD 18.3 MGD 21.7 MGD -3.5 MGD -0.9 MGD -4.3 MGD Technical Memorandum No July 2001

115 Well No. Comments regarding these wells are as follows: Well No. 6 (Bragstad): Steadily declined over last 6 years. Well No. 31 (Raney): Declined 690 gpm since Well No. 60 (Gravel Pack): Declined 214 gpm since Clean well? Well No. 61 (Gravel Pack): Declined 355 gpm since Clean well? Reasonably consistent average production over last 3 years; however, 3 MGD decline from 1993 to North Big Sioux Wells Table 3-23 summarizes the data for eighteen (18) Northern Big Sioux Wells. North Big Sioux Region Type Design Flow Gpm Table Historical Output North Big Sioux Wells Average Use 1999 Flow gpm Percentage use Flow gpm Average Use 1996 Percentage Use Flow gpm Average Use 1993 Percentage use Change 93'-96' gpm Change 96'-99' gpm Change 93'-99' gpm 42 N Big Sx Gravel Pack N Big Sx Gravel Pack N Big Sx Gravel Pack N Big Sx Raney N Big Sx Gravel Pack N Big Sx Gravel Pack N Big Sx Gravel Pack N Big Sx Gravel Pack N Big Sx Gravel Pack N Big Sx Gravel Pack N Big Sx Gravel Pack N Big Sx Gravel Pack N Big Sx Gravel Pack N Big Sx Gravel Pack N Big Sx Gravel Pack N Big Sx Gravel Pack N Big Sx Gravel Pack N Big Sx Gravel Pack Totals MGD 8.7 MGD 10.8 MGD 11.8 MGD -1.0 MGD -2.2 MGD -3.1 MGD Technical Memorandum No July 2001

116 Well No. Comments regarding these wells are as follows: Well No. s 42, 43 and 44 (Group of 3 gravel packs): Declined 127, 192 and 342 gpm respectively since Well 46 (Raney): Good producing well (4% of total production; however, declined by 395 gpm since 1996 (total is still 1350 gpm +, so it is still a good well). Well No. 47 (Gravel Pack): Declined by 500 gpm in last 6 years. Clean well? Well No. 58 (Gravel Pack): Declined by 211 gpm in last 3 years, and is no longer used very frequently. Fairly consistent average production Middle Skunk Creek Wells Table 3-24 summarizes the historical pumping for the thirteen (13) Middle Skunk Creek Wells. Middle Skunk Creek Region Type Design Flow Gpm Table Historical Output Middle Skunk Creek Average Use 1999 Flow gpm Percentage use Flow gpm Average Use 1996 Percentage use Flow gpm Average Use 1993 Percentage use Change 93'-96' gpm Change 96'-99' gpm 101 MSC Gravel Pack MSC Gravel Pack MSC Gravel Pack MSC Gravel Pack MSC Gravel Pack MSC Gravel Pack MSC Gravel Pack MSC Gravel Pack MSC Gravel Pack MSC Gravel Pack MSC Gravel Pack MSC Gravel Pack MSC Gravel Pack Totals Change 93'-99' gpm MGD 6.6 MGD 7.1 MGD 0.0 MGD 0.0 MGD -0.5 MGD 0.0 MGD Comments regarding these wells are as follows: Well No. 101 (Gravel Pack): Declined by 100 gpm in last 3 years. Well No. 110 (Gravel Pack): Declined by 187 gpm in last 3 years. Minor decrease in production in last 3 years. Wells have consistently produced about 2-3 MGD less than intended. Technical Memorandum No July 2001

117 3.2.2 SYSTEM MODELING The analysis of the well fields and influent piping was performed using the EPA s EPANET2 modeling software. During operation, the output of each pump is affected by system conditions. Various parameters such as ground water level, well condition, characteristic pump curve, and system pressure influence the output of each well. Currently, 65 wells make up the Big Sioux and Middle Skunk Creek well fields. Various well field scenarios were input in to the model to simulate system conditions. Analyses of alternate piping and pumping stations were undertaken to maximize the output of the existing well fields Model Calibration Figure 3-8 shows the model nodes and line segments. Input data included size, lengths, C factors, pump curves, groundwater elevations and fixed grade elevations. A baseline run was performed to model current conditions. Actual pumpage of about 50 to 51 MGD during June 2000 was experienced. The City indicated forty-nine of the 65 wells were operating under this condition, and approximately 16.7 MGD was pumped from the SWPS. This run was used to calibrate the model. Calibration was accomplished by varying C values for the transmission lines. Input files for the calibration run have been provided to the City. Generally the piping systems have C factors assigned as follows: Smaller diameter laterals for 8 to 12-inch have C values of 80 to 100. Larger diameter collector mains have C values of 100 to 120. The East Transmission Main (42 /36 ) lines were generally assigned values of 120 except where a significant number of fittings exist in a localized area. The West Transmission Main (24 ) was assigned values of 95 to 120 depending on the age and fittings for each area. The City has indicated approximately 15 to 16 MGD is the maximum pumpage rate possible through the 24-inch portion with the surface water pumps. With one pump running, the maximum is 11 to 12 MGD. The increased horsepower (300 HP motor) required to operate the second pump for an increase of 3 to 4 MGD has limited benefit. The model developed is a very useful tool in analyzing the results of well operations and evaluating improvement alternatives. However, the operation of a well field (particularly a shallow aquifer such as the Big Sioux Aquifer) is a very complex interaction of variables. Several items are dynamic and this cannot be accurately accounted for in all operating scenarios. Following are a summary of model limitation: Static water levels in the aquifer change seasonally and as a result of individual well operation. Thus, water level at each well is based on a set value which includes an amount for draw down and pump column and discharge head losses, however the model input value does not change as the overall aquifer is lowered. Well losses through the gravel pack and screen increase as well efficiency decreases, which can also ultimately result in an additional increase in static pumping pressure. Technical Memorandum No July 2001

118 The Big Sioux Aquifer is very shallow and with low system demand, the pumps run out on their curves and the pumping rate may need to be throttled (discharge valve partially closed) to avoid the draw down extending into the well screen. Pump curves are input based on pump curve information and well operating data for each well. As pumps age and wear, the pump performance may operate below the characteristic curves. This was noticed on several wells and the curves were adjusted accordingly. Thus, the pump output could be below model projection if substantial wear has occurred. Pump wear can be a significant factor, and many utilities check pump performance as compared to the original curves on a regular (yearly if possible) basis. Also, occasionally pump modifications are made for one reason or another, which may dramatically alter its performance. Examples include removal of a stage on a vertical turbine pump or adjustment of impellors, which increase slip and decrease TDH EXISTING SYSTEM PERFORMANCE Table 3-25 summarizes the results of the calibration or baseline evaluation as well as other operating scenarios discussed below. Under the current maximum demand excessive head loss is experienced in the transmission lines from the Big Sioux Aquifer to the WPP. As flow increases under high demand, the head loss increases. This head loss increases system pressure, causing all pumps to back-up on their curves, which decreases the pumping rate. This effectively reduces the effect of turning on additional pumps. Several model runs were performed to determine the capacity of the current system. The initial run was used to calibrate the model for system output with specific wells operating. The other model runs were tested to determine if different well combinations would have theoretically increased flow. These included: Ninety (90) percent of the wells plus one SWPS unit 16.7 MGD. All (100%) wells plus one SWPS unit operating at 16.7 MGD. Ninety percent (90%) of wells plus 30 MGD (two units) from SWPS. Three additional scenarios were tested without any pumpage from the SWPS as shown in Table These included: Calibration/Baseline Same wells operating as 51 MGD calibration scenario Ninety percent (90%) of wells which allows for a reasonable reliability for the wellfield overall. One hundred percent (100%) of the wells. The results are summarized into the same regional areas (i.e. Airport, South Big Sioux, etc.) Table 3-25 summarizes the output by region and for each well. A summary of the evaluation of the existing system is as follows: Technical Memorandum No July 2001

119 Table Existing System Performance with Surface Water Pump Station Est. Operating Pt. Calibration/Baseline 90% Wells + 1 pump SWPS All Wells + 1 pump SWPS 90% Wells + 2 pumps SWPS Well No. Region Flow Head Flow Head Flow Head Flow Head Flow Head (gpm) ft (gpm) ft (gpm) ft (gpm) ft (gpm) ft 3 Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Subtotal MGD MGD MGD MGD MGD 25 S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx Subtotal MGD MGD MGD MGD MGD 42 N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx Subtotal MGD MGD MGD MGD MGD 101 MSC MSC MSC MSC MSC MSC MSC MSC MSC MSC MSC MSC MSC Subtotal MGD MGD MGD MGD MGD SWPS MGD MGD MGD MGD Totals gpm (MGD) MGD MGD MGD MGD Pump off Pump at shut off head Technical Memorandum No July 2001

120 Table Existing System Performance without Surface Water Pump Station Est. Operating Pt. Calibration/Baseline 90% Wells All Wells Well No. Region Flow Head Flow Head Flow Head Flow Head (gpm) ft (gpm) ft (gpm) ft (gpm) ft 3 Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Airport Subtotal MGD MGD MGD MGD 25 S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx S Big Sx Subtotal MGD MGD MGD MGD 42 N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx N Big Sx Subtotal MGD MGD MGD MGD 101 MSC MSC MSC MSC MSC MSC MSC MSC MSC MSC MSC MSC MSC Subtotal MGD MGD MGD MGD SWPS 0 0 MGD 0 0 MGD 0 0 MGD Totals gpm (MGD) MGD MGD MGD Pump off Pump at shut off head Technical Memorandum No July 2001

121 Airport Wells Of the wells operating on the day the facility flows were 50 MGD +, eighteen (18) are located in the airport area. These wells and pumps are the oldest in the well field and generally have a lower head (TDH) capability. The model estimates that 4 of the airport wells were producing no flow (backed up on curve to shutoff head). Also, Wells No. 10 and 21 are near shutoff. This area was producing about 11 MGD compared to the potential production of 16 MGD or greater. As additional wells are operated, no appreciable increase in flow occurs (only increases from 11.4 to 11.7 MGD). If SWPS is increased to about 30 MGD, this area decreases in production. With no surface water, pumpage increases slightly, but several wells are still at shutoff. The overall increase in system pressure and high losses as the flow combines to enter the WPP restrict the output of these wells. Possible alternatives to restore the production in this area include changing rebuilding the well pumps at No. 3, 10, 11, 14, 17, 18, 21, 23, and 65. A booster pump station on the main(s) servicing the airport wells is another alternative, which would prevent runout at low demands and operate as required when demands increase Southern Big Sioux Wells Total output is MGD of a desired production of about 16 MGD. Well Nos. 25, 33, 37, 38, 39 and 63 are operating significantly lower than desired or actually reached shutoff head. High surface water pumpage (30 MGD) reduces production by about 4 MGD. A moderate increase to 13 MGD is predicted without surface water pumps. A common booster pump station or increased line capacity could minimize this impact Northern Big Sioux Wells Overall production is impacted by increased flows. Projected pumpage is only 7-9 MGD rather than 10.9 MGD. Wells Nos. 42, 44, 48 and 54 were substantially reduced or hit shutoff head if SWPS is increased to 30 MGD. Northern wells increased by 1-2 MGD if surface water is eliminated Southern Skunk Creek Wells These wells must all pump over a high ridge and then flow by gravity to the WPP. They are relatively unaffected by all modeled conditions. Technical Memorandum No July 2001

122 3.2.4 FUTURE SYSTEM ANALYSIS Future System Demands Future demands on the collection system will be impacted by additional water supplied by other resources. Additional water sources could include the Southern Skunk Creek Aquifer, Wall Lake Aquifer, and the Lewis and Clark Rural Water Project. The additional water sources could supply an additional 15.5 MGD under peak demand. If none of the additional sources were available the existing (or improved) wellfield system would be required to supply as much as possible. Table 3-27 summarizes future ground and surface water demands with and without supply from additional resources. Table Future System Demands Surface Water Available Year Maximum Day w/additional Sources Maximum Day w/o Additional Sources Total Groundwater Surface Water Total Groundwater Surface Water No Surface Water Available Year Maximum Day w/o Additional Sources Maximum Day w/o Additional Sources Total Groundwater Surface Water Total Groundwater Surface Water As indicated in Tables 3-25 and 3-26, the existing system cannot meet several of the future maximum day requirements. Prior to the completion of Lewis and Clark in 2010, up to 56.5 MGD may be required. This TM does not address the drought year yield of the aquifer, which is approximately 23 MGD when fully developed. The optimum use of the existing water resources is the focus of this evaluation. Thus future droughts may require the construction of additional wells. This will not be defined in the evaluation; however, the improvements required to allow reasonable use of the existing resources will be evaluated Improvement Alternatives The decreasing well production resulting from increasing system pressure can be addressed by various alternatives. Booster pump stations, parallel piping for key sections, or piping to increase transmission networking are typical examples. These alternatives are identified in Figure 3-9. The following are descriptions of each alternative. Technical Memorandum No July 2001

123

124 Alternate 1 Airport Booster Pump Station This alternative incorporates a booster pump station on the 30-inch line from the airport to the Water Treatment Facilities as shown on Figure 3-9. The intent is to facilitate production from the airport wells, which are negatively impacted by high flows. The booster station is preferred over modifying individual well pumps because the higher head well pumps would run out excessively during low demands which tend to exceed the production capability of the well. Model results with one and two surface water pumps operating are shown in Table B-1 in Appendix B. Alternate 2 Hwy 38A Booster Pump Station This alternate analyzed the use of a booster pump station located just south of Hwy 38 as shown in Figure 3-9. The pump was sized to increase the system head by approximately feet. The use of a booster pump in this location increases the capacity of the wells located north of the station. Most future well field capacity will be added in the northern Big Sioux and Skunk Creek Aquifers. These future wells would also benefit from the booster station. Well output downstream is decreased under this model. Model results are summarized in Table B-1 in Appendix B. Alternate 3 East Main Relief Line (EMR) This alternate is the addition of a parallel pipe to the main transmission line northeast of the airport terminal from approximately node 162 to 127 as shown on Figure 3-9. The use of an additional 36-inch line in this area increases the flow capacity in that area. Head loss will decrease and the bottleneck effect in that area will be reduced. Again the system shows an increase in output at wells in the northern portion of the system and a decrease in the downstream wells. This alternative does not allow separation of the well supply and surface water supply to be optimized, and as a result, was dropped from further development. Results are summarized in Table B-2 in Appendix B. Alternate 4 SWPS Relief Line The fourth alternate is the construction of a 24 line from the SWPS to the piping system in the airport area (see Figure 3-9). This line would allow diversion of some of the surface water away from the two main transmission lines, thereby reducing the overall flow in those two lines. This alternate causes several of the pumps in the airport region to exceed their shut-off heads and therefore was not developed further. Results are summarized in Table B-2 in Appendix B. Alternate 5 West Main Relief Line (WMR) This alternative would allow separate transmission of surface water to the WPP for treatment in the north basins or in separate pretreatment basins. The SWPS flows would all be directed to either the 24-inch (west) main or the 36-inch and 42-inch (east) main to the WPP. The northern wells would be routed to the alternate east or west main. This would require additional line capacity for the 24-inch west main. A 30-inch line would be constructed for just north of the SWPS line to the WPP. The SWPS flows could be directed to separate pretreatment basins, which would be 4 to 5 feet higher in elevation to allow a series treatment mode to be used. The model runs were based on 30 to 35 MGD of surface water. If a higher amount (3 pumps totaling 45 MGD) is desired, a larger line should be considered during pre-design of that project. This is shown in Figure 3-9 and the results are summarized in Table B-3 in Appendix B. Technical Memorandum No July 2001

125 Alternate 6 Modify Individual Well Pumps Increasing the TDH capability of numerous individual pumps is an option; however, the system already has several wells throttled at low flow conditions to prevent runout of individual wells. This alternative would only aggravate this problem and would burn additional head and energy the vast majority of the year. Also, the modification of a large number of wells would be costly. This alternative will not be further developed. Various combinations of alternative were also evaluated. These include: Airport Booster with West Main Relief Line. Airport Booster with Hwy 38A Booster Station. Airport Booster, Hwy 38 Booster Stations and the West Main Relief Summary of Results Table 3-28 summarizes the results of the various improvements and combination of improvements. The well operation and Surface Water Pump operation used run in varying combinations. Table Water Supply Influent Piping Alternatives Condition Production (MGD) Existing System (1) Airport South Big Sioux North Big Sioux Middle Skunk Creek SWPS Total Comments Estimated Production Capacity Calibration/Baseline shutoff 100% Wells shutoff 90% Wells/1 SW Pump shutoff 100% Wells/1 SW Pump shutoff 90% Wells/2 SW Pumps shutoff Alternatives Airport BPS (2) 90% Wells/1 SW Pump shutoff 90% Wells/2 SW Pumps shutoff WMR (3) 90% Wells/1 SW Pump shutoff 90% of Wells/2 SW Pumps shutoff Highway 38A BPS (2) 90% Wells/1 SW Pump shutoff 90% Wells/2 SW Pumps shutoff Combination (2, 3) Airport/WMR 90% Wells/1 SW Pump shutoff 90% Wells/2 SW Pumps shutoff Technical Memorandum No July 2001

126 Table (Continued) Water Supply Influent Piping Alternatives Condition Production (MGD) Existing System (1) South North Middle Airport Big Sioux Big Sioux Skunk Creek SWPS Total Comments Airport/38A (2) 90% Wells/1 SW Pump shutoff 90 Wells/2 SW Pumps shutoff (2, 3) Airport/38A/WMR 90% Wells/1 SW Pump shutoff 90% Wells/2 SW Pumps shutoff 1. Assumes all system valves are open and discharge valves at well are not throttled. 2. Valves at booster pump station configured to prevent recirculation. 3. Valves position to route SWPS through separate line to the WPP. The following is a summary of the impacts of the various improvements considered individual projects. Airport Booster Pump Station The Airport Booster Pump Station would provide a pressure increase of 25 to 50 feet TDH. This station would provide the following benefits: Production increases to 15.8 MGD, with one surface water pump operating. A minor decrease to 15.0 MGD occurs when a second surface water pump is operating. The number of wells at shutoff in the airport area is reduced from 6 to 2 wells. Well No. s 17 and 18 are still negatively impacted and rehabilitation or replacement is required to make these wells function properly during high pumpage periods. Overall production increases to 57 MGD and 63 MGD, respectively, with one and two SW pumps operating. East Main Relief The East Main Relief (Results are in Table B-2 in Appendix) increases the hydraulic capacity of the main north/south transmission mains and northern well production increases a moderate amount. However, separation of the supplies is not improved, thus this alternative is not further developed. Highway 38A Booster Pump Station This booster pump station also provided a pressure increase of feet TDH. The results summarized in Table B-1 did isolate valves to allow proper suction/discharge control, however, the valves and the 24-inch, 36-inch and 42-inch mains were open to allow networking of the flow in those mains. The following is a summary of the results: Technical Memorandum No July 2001

127 Southern Big Sioux wells production increases from 9.1 to 11.6 MGD (1 SW Pump) and 6.5 to 10.2 MGD with 2 SW Pumps are operating. Well No. 36 and 63 is at shutoff, however, by positioning the pump station further to the south, this problem could probably be avoided. Some wells are actually running out a little beyond the desired operating point. This must be balanced to avoid overpumping the well (operating significantly into the screen area or causing turbulence due to high entrance velocities). Northern Big Sioux production increases from 8.1 to 10.9 MGD with 1 SW Pump and from 7.0 to 10.1 MGD with 2 SW Pumps operating. Since the Southern Big Sioux and Northern Big Sioux wells increase production is attributed to the pressure increase from the booster pumps, a decrease in the boost will decrease production of all wells in the area. Total production increases to 57.2 and 63.7 MGD, respectively, with one and two SW Pumps. West Main Relief The West Main relief (Table B-3 in Appendix) is intended to accommodate increased flows from the north and allow separation of surface water and well suppliers; thus the valving is set to eliminate networking south of the SWPS tie in location. The following is a summary of the results: Southern Big Sioux Wells increase from 9.1 to 11.5 MGD with one SW Pump operating and two wells (No. 38 and 39) are experienced decreased production. With 2 SW Pumps operating, several wells are at shutoff and have very low production and production drops to 9.2 MGD. Northern Big Sioux Wells increase from 8 to 9 MGD with one SW Pump operating and one pump (No. 54) is at shutoff. The second SW Pump decreases the production to 8.2 MGD and four wells (42, 48, 49 and 54) are at shutoff or experience decreased production. The West Main Relief is effective in transporting 30 MGD + surface water flows to the WPP in dedicated lines, however, at total system flows greater than 60 MGD, the wells north of the diversion structure are negatively impacted. Technical Memorandum No July 2001

128 Combination Alternatives Airport/Highway 38A Booster Pump Stations The combination of Booster Pumps (Table B-4 in Appendix) effectively minimizes shutoff problems for most wells. The key results are as follows: Total system flow increases to 61.3 and 67.7 MGD for 1 and 2 SW pumps, respectively. This is with piping system networked to maximize flows. Isolation of surface water into one main will be evaluated later to fine tune the improvements. Wells 17 and 18 (Airport Area) are at shutoff. These have been identified as wells requiring improvements. Wells 36 and 63 (Southern Big Sioux Area), just north of the diversion channel, are at shutoff. Relocation of the booster pump station should eliminate this problem. An area just north of the SWPS tie-in location may be best for the Highway 38A booster station. Well No. 44 (Northern Big Sioux) is near shutoff and may require upgrade. Airport Booster Pump Station/West Main Relief This combination is intended to allow the airport wells maximum production and provide capacity for the SWPS and northern wells. The following are the results (Table B-3 in Appendix B): Overall production is 62.5 and 72.0 MGD, with 1 and 2 SW Pumps, respectively. This is very similar to the two booster pump stations alternative. With two SW Pumps, several northern wells are at shutoff or have substantially reduced production (No. 25, 33, 37, 38, 39, 42, 44, 48, 54 and 63). Airport/Highway 38A Booster Pump Station and West Main Relief This allows an increase in flow over the Airport/Highway 38A Booster Pump Stations above. A total flow of 74.4 MGD is estimated. A few wells (similar to the booster alternatives) are still at shutoff. These are the wells most likely to require upgrades regardless of the improvements implemented. This does allow complete separation of surface water and well water flows. As surface flow (30 MGD) and northern wells flows (15 MGD) (including Middle Skunk Creek) approach a combined total of MGD and/or separation of the supplies is desired, the West Main Relief will be required. The results are summarized in Table B-4 in Appendix B. Technical Memorandum No July 2001

129 Preliminary Priority of Improvements The above summary of alternatives indicates the Booster Pump Stations are slightly less effective in providing increased production during high demand periods. However, well runout would be a larger problem during low demands if additional transmission line capacity were constructed. The following are the improvements which warrant further consideration: Highway 38A Booster Station: This is a larger station (approximately 36 MGD plus future northern wells at 0 to 75 feet TDH) located just north of the SWPS tiein location to the 24- and 36-inch transmission mains. The station should allow suction from either the 24- or 36-inch mains and discharge into either main. Flexibility to route 1 SW Pump to the 24-inch main and 2 SW Pumps to the 36- inch main would be desirable. Airport Booster Station: Slightly smaller, less costly station which can be constructed on the WPP site. This also reduces problems with a significant number of airport wells which have shutoff problems. Approximate size would be 15 to 20 MGD, with 0 to 40 feet TDH of pressure increase. West Main Relief: As total surface water and northern well pumpage continues to increase, the West Main Relief will be required. Separation of flow and pumpage of surface water above 30 to 35 MGD will require this transmission main from the SW tie-in location to the WPP TIMING AND COORDINATION WITH PRESEDIMENTATION BASIN A high priority improvement to the WPP includes the presedimentation units to improve the quality and consistency of the water quality to the softening units. These basins would have a water surface elevation approximately 3 to 5 feet above the softening basins to allow series (normal mode of operation to provide desired finished water quality) or parallel operation. Several model runs were completed to evaluate the impact of the presedimentation basin on the existing system. Also, the staging was sequenced to determine the impact of the various alternatives. Generally, these runs were completed with the surface water separated into either the 24-inch or 36/42-inch main lines to the WPP; however, one run with networking to maximize the flow rate was completed. The results of these evaluations are summarized in Table Additional detail regarding the performance of each well is included Tables B-5 through B-10 in Appendix B. Technical Memorandum No July 2001

130 Condition Table System Flows with Presedimentation Basin Airport South Big Sioux North Big Sioux Middle Skunk Creek SWPS Total Comments Estimated Production Existing System w/presed. Basin (1) SW through West 24-inch (1 SW Pump) shutoff SW thru West 24-inch (2 Pumps) (2) shutoff SW thru East 36-inch Main (2 Pumps) shutoff SW thru Both 24/36-inch Mains (2 Pumps) shutoff Improved System w/presed. Basin (2) Airport BPS, SW in West 24-inch (3) (1 Pump) shutoff Hwy 38A BPS; SW in West 24-inch (1 Pump) shutoff Airport BPS, SW in East 36-inch (3) (2 Pumps) shutoff Hwy 38A BPS; SW in East 36-inch (2 Pumps) shutoff Airport BPS/WMR (2 Pumps) shutoff WMR (1 Pump) shutoff WMR (2 Pumps) shutoff Hwy 38A/Airport BPS; SW in East 36-inch shutoff All: WMR/38A/Airport (2 Pumps) shutoff 1. Presedimentation basin located north of WPP approximately 5 feet higher than solids contact basin; Model Runs provide for separation of surface water. 2. An increase of 2.6 MGD from the second SW pump (300 HP) is not economical. A reasonable flow through the 24-inch line is MGD maximum. 3. Under this scenario, the Airport Booster Station has a very moderate pressure increase (10 to 20 feet). Additional pressure increase could boost production but that could cause overpumping of numerous wells. The following are comments regarding the water production and impact of the separate routing of surface water to a presedimentation basin: The 24-inch, west transmission line has a reasonable capacity of 11 to 13 MGD, regardless of whether it is groundwater or surface water. The 36/42-inch east main has a capacity of 30 to 40 MGD. Thus, with the separation of flows, the 24- inch line will be a restriction. Airport Booster Station. This BPS can increase airport well production by 4 to 5 MGD, depending on the pressure increase. The limiting factor will be the reasonable production capacity of the wells. With separate routing of flows, this station provides about a 5 MGD benefit. Technical Memorandum No July 2001

131 Hwy 38A Booster Station. This BPS helps all northern wells and provides about a 9 to 11 MGD increase when wells are routed to the 36-inch main. This decreases to 6 to 8 MGD if groundwater is routed to the 24-inch line. It was noted that a large number of airport wells are negatively impacted if the groundwater flow is networked through the 20-inch crosstie line from the 24-inch main to the airport wells. Closing the crosstie line would improve the airport wells. The Hwy 38A booster appears to provide more benefit (increased capacity) than the Airport Booster. The West Main Relief provides 7 MGD increase if only one SW pump is operated. If a second SW pump is required, a MGD increase can be obtained and reasonable balance exists in various areas of the wellfield. The timing for the West Main is driven by system demands greater than 55 MGD. The major advantage of the WMR is that any surface water flows up to 35 MGD could be directed to the WPP without constantly balancing the amount of surface water flow and groundwater flow between the existing 24- and 36-inch mains ESTIMATED COST The cost for booster pump stations (Airport and Hwy 38A) are summarized in Table The estimated cost for the various relief lines is summarized in Table Table Booster Pump Station Estimated Cost Estimated Cost Item Airport BPS (20 MGD) Hwy 38 BPS (40 MGD) Structure/Foundation/Building $240,000 $260,000 Mechanical/Piping $210,000 $240,000 Electrical/Instrumentation $80,000 $120,000 Pumps/Drives/Mechanical $150,000 $180,000 Site Work/Site Piping/Vaults $110,000 $160,000 Subtotal $790,000 $960,000 Contingency (20%) $158,000 $192,000 Estimated Construction Cost $948,000 $1,152,000 Engineering and Legal (15%) $142,000 $173,000 Total Project Cost $1,090,000 $1,325,000 Technical Memorandum No July 2001

132 Table Relief Lines Estimated Costs Item EMR (36 ) WMR (30 ) (1) SWPS Relief (24 ) Quantity Cost Quantity Cost Quantity Cost Piping 4000 $600,000 9,800 $1,056,000 3,500 $333,000 Connections 2 $20,000 4 $40,000 2 $15,000 Crossing 2 $60,000 4 $100,000 1 $30,000 Misc. Valve/Hydrants LS (10%) $68,000 LS (10%) $120,000 LS (10%) $38,000 Subtotal $748,000 $1,316,000 $416,000 Contingency (20%) $150,000 $213,000 $83,000 Estimated Construction Cost $898,000 $1,579,000 $499,000 Engineering/Legal/Admin (15%) $135,000 $237,000 $75,000 Estimated Total Cost $1,033,000 $1,816,000 $574, Sized for approximately 30 to 35 MGD of surface water between the 24 and 30 lines. This line size should be increased if 45 MGD of surface water is desired at the time this line is being constructed. These costs will be evaluated in conjunction with the benefit (increased capacity) to determine the priority of improvements RECOMMENDATIONS The vast majority of water supplied to the Sioux Falls WPP is through the wellfield piping system north of the Plant. At flows above 50 MGD, the well production is impacted by increasing system pressures and numerous well pumps reach shutoff head (at or near zero flow). Alternatives to increase the capacity of the 65 production wells and surface water pumps include: Construction of Booster Pumping Stations at key locations to increase flow through the critical transmission pipeline. Increase transmission line capacity at specific location(s) to reduce overall system pressure losses. Increase the pressure capability of many wellfield pumps to increase flow at high demand periods. This alternative was not developed because it would aggravate individual well runout problems and involve a large number of individual wells. The presedimentation basin (a high priority improvement), ahead of the existing softening basins, will modify the influent hydraulics to the plant and raise the elevation of the surface water pump discharge by 3 to 5 feet. Also, the discharge from these basins will be separated from the existing 36-inch east and west headers. As a result, some of the bottleneck entering the plant will be reduced. The elimination of this constraint does improve the performance of the airport area wells (particularly when the 20-inch crosstie line near the airport terminal is closed). Table 3-32 summarizes the net improvement in total flow, and the cost/mgd for the various improvements (with surface water separate, routed to a presedimentation basin). Technical Memorandum No July 2001

133 Table Alternative Summary Cost/MGD Alternative Existing Flow Flow with Improvement Flow Increase Estimated Cost Cost Per MGD Surface Water in 24 West Main (1) 50.8 Airport BPS $1,090,000 $218,000 Hwy 38A BPS $1,325,000 $128,600 West Main Relief (2) $1,816,000 $111,400 Airport BPS/WMR (2) $2,906,000 $137,100 Both BPS and WMR (2) $4,231,000 $141,500 Surface Water in 36 East Main 53.6 Airport BPS $1,090,000 $242,000 Hwy 38A BPS $1,325,000 $217,000 Both BPS $2,415,000 $236, The practical limit through the existing 24-inch is limited to one 11.2 MGD. A second pump consistently increases the maximum flow by 2.8 MGD to 55.6 MGD, however, it wastes significant energy for the minor flow increase. 2. The West Main Relief allows major increase in surface water flow from 11 to about 27 MGD. The Highway 38A BPS has a higher capital cost than the Airport Booster Station, however, the estimated production increase is significantly higher. The Airport BPS has a significant benefit for all airport area wells, however, the construction of a presedimentation basin will relieve some of the high headloss problems near the entrance to the WPP, which would allow some delay in the construction. The West Main Relief substantially increases the hydraulic capacity of the two main transmission lines from the north (24 inch west line and 36/42-inch east line). In general terms, the capacity of the 24-inch line is MGD and the 36-inch line is 30 to 35 MGD. Assuming separation of supplies, surface water flows of about MGD can be routed to the presedimentation basin through the 24-inch line and adequate capacity exists for the wells in the 36/42-inch main. Surface flows from more than one pump would have to be routed to the east transmission main. This would cause a severe bottleneck for northern wells shutoff) without a booster station or relief line. The timing for the western main relief appears to be when combined surface and groundwater flows through the east and west mains approach 45 to 50 MGD. This amount, in conjunction with MGD from the airport wells, would amount to about 55 to 60 MGD of total system flows. A major disadvantage of the Booster Pumps Station is that surface water flow between MGD would require re-routing the surface water to the 36-inch main. This would be very cumbersome if the demands vary routinely. It s easy to model the change in mains but operation of several inch valves is very difficult. A negative factor regarding the construction of additional transmission main capacity is the fact that more pipeline capacity will not only reduce system headloss during the higher flow periods, but low flow periods as well. These low to moderate flows occur 95+% of the time in a year, and the pump runout problem for many wells will only be aggravated. The ability to start/stop a booster pump station and operate a selected number of valves at higher flow conditions would appear to be more desirable from an operations and maintenance perspective. Technical Memorandum No July 2001

134 Conclusion/Priority The following is a summary of conclusions and recommendations for the water supply improvements (assumes presedimentation basin is constructed): The model and data files to analyze the water supply have been provided to the City. The City has reviewed and tested some scenarios. This model is a valuable tool for evaluation of the system, however, the input files contain a large number of variables, some of which are dynamic in nature. The system is complex, and the model has conditions, which can change over time (ground water elevations, throttled valves, open/closed valves, pump conditions, etc.). The City should work with this model on an ongoing basis to better understand its capabilities and, over time, improve the calibration for various conditions and its accuracy for predicting the flows. Examples of the benefits of the model include: Tool to decide which wells should be operated at high flows. Track valve position (open, closed, throttled). Evaluate the possibility of closing selected system valves to throttle wells rather than throttling individual wells at the pump (for example, routing northern wells during the winter months through the 24-inch west main may reduce well throttling). Develop system to track pump curve changes. The system curve for the actual performance of each pump should be tested regularly. This is the key to understanding the performance of individual wells. Prior to any construction, the modeling indicates that closing the cross-tie line (line connecting the 24- and 36-inch mains with airport wells just north of airport terminal) would reduce the impact on the airport wells by preventing the higher TDH northern wells from increasing the pressure in that portion of the system (i.e. the reduced production of the northern wells should be more than offset by increase production of airport wells). West Main Relief is recommended as a high priority improvement. The estimated project cost is $1,816,000. Combined surface water and groundwater flow of 45 MGD and higher through the 24-inch and 36-inch main will require this improvement. The construction of presedimentation basins will allow increased opportunity to use surface water and will increase the need for separate transmission of flows to the WPP. As indicated, a negative factor is the increased runout of wells at low system flows. The Hwy 38A Booster Station has similar priority. This station, located just north of the Diversion Channel, increases system capacity by approximately 10 MGD and has an estimated project cost of $1,325,000. The Airport BPS would be located on the 30-inch main at the Treatment Plant Site. This station would substantially improve the production of the airport area wells (by 4 to 5 MGD). The estimated project cost is $1,090,000. The location of Technical Memorandum No July 2001

135 this station would be in close proximity to the WPP and thus would be readily accessible for operation and maintenance purposes. Some of the system wells have low head pumps and are negatively impacted by high system flows, even after construction of the Booster Pumping Stations. Following construction of the Highway 38A BPS, but prior to the Airport BPS, the following wells are inspected: Airport Wells: No. s 3, 14, 17, 18, 23. South Big Sioux Wells: No. 30 (only connected to 24-inch main and south of the Hwy 38A BPS). This is a good well, which should be upgraded. Other wells are impacted when all well water is pushed through 24-inch main, but the West Main Relief would address that problem. North Big Sioux Wells: No. s 44 and 54 are substantially reduced. Following construction of both the Airport and Hwy 38A BPS, the following wells are still impacted: Airport Wells: No. s 17, 18 and 23. The pumps have a TDH ranging from 48 to 53 feet. Modification of pumps/impellors to increase the TDH to approximately 65 feet is required. North and South Big Sioux Wells: Impacted wells are the same as above. Technical Memorandum No July 2001

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144 TECHNICAL MEMORANDUM NO. 4 FACILITY MAINTENANCE AND RELIABILITY IMPROVMENTS Table of Contents Section Page 4.0 INTRODUCTION MAINTENANCE BUILDING Design Standards Design Considerations Site Existing Building Structure Proposed Maintenance Shop Addition Space Requirements and Program Aesthetics Materials of Construction Building Components Specialty Equipment and Furnishings Equipment Provided by Owner Estimated Costs VOLT SWITCHGEAR Existing Switchgear New Switchgear Option 1 - Reuse the existing space Option 2 - New building addition Summary and Recommendation SLUDGE WITHDRAWAL LINES Existing Sludge Piping Proposed Piping Improvements Description of Work and Associated Costs SLUDGE PUMPING/PIPING Existing Sludge Pumping/Piping Pump capacity Piping and Valving Information Sludge Production Sludge Pumping/Piping Capacity Proposed Piping Modifications Unused or Redundant Materials/Piping Replacement of Corroded Piping and Inoperable Valves Capacity Driven Replacement Recommendations and Opinion of Probable Construction Costs Sludge Thickening and Storage...16 Technical Memorandum No. 4 -i- July 2001

145 List of Tables Table Page Table 4-1. Opinion of Probable Capital Cost for Maintenance Building...4 Table 4-2. Opinion of Probable Capital Cost for Option 1 for New Switchgear...7 Table 4-3. Opinion of Probable Capital Cost for Option 2 for New Switchgear...7 Table 4-4. Opinion of Probable Capital Cost for Sludge Withdrawal Piping Improvements...10 Table 4-5. Projections of Estimated Sludge Production...12 Table 4-6. Opinion of Probable Capital Cost for Sludge Pumping/Piping Improvements...16 Table 4-7. Opinion of Probable Capital Cost for Sludge Thickening and Pumping Improvements...18 List of Figures Figure Following Page Figure 4-1. Proposed Maintenance Building Site Plan...18 Figure 4-2. Proposed Maintenance Building Ground Floor Plan Final Scheme...18 Figure 4-3. Proposed Maintenance Building Mezanine/Second Floor Plan Final Scheme...18 Figure 4-4. Proposed Maintenance Building Ground Floor Plan Final Scheme...18 Figure 4-5. Proposed 2300V Switchgear Floor Plan...18 Figure V Switchgear One-line Diagram and Proposed Elevations...18 Figure 4-7. Gallery Sludge Drawoff Line Basin 1 Sludge Pit Penetration and Manual and Actuated Valves...8 Figure 4-8. Gallery Sludge Drawoff Line Basin 1 Floor Penetration and Direct Draw Connection...8 Figure 4-9. Sludge Direct Draw and Gravity Lines showing Severe External Corrosion...10 Figure Unused Interconnection...13 Figure Unused Diaphragm and Plug Valves...14 Figure Sludge Thickener...18 Technical Memorandum No. 4 -ii- July 2001

146 TECHNICAL MEMORANDUM NO. 4 FACILITY MAINTENANCE AND RELIABILITY IMPROVMENTS 4.0 INTRODUCTION This Technical Memorandum (TM) includes discussions of upgrades to the existing plant facilities including: Maintenance Building 2300 Volt Switchgear Sludge Withdrawal Lines Sludge Pumping/Piping 4.1 MAINTENANCE BUILDING The maintenance facilities at the existing plant are inadequate to meet the growing demands of the facility. Proper maintenance of the equipment is required to provide optimum operation and the existing garage has neither the require equipment or space to properly perform these functions. Thus a new maintenance building is an important component of the future facilities improvements DESIGN STANDARDS The design of the new maintenance building will be in compliance with the requirements of the following standards. Uniform Building Code 1997 and all associated codes (UBC) Americans with Disabilities Act 1991 Updated 1998 (ADA) American National Standards (ANS) Underwriters Laboratories (UL) DESIGN CONSIDERATIONS Site A number of existing site constraints need to be taken into consideration for the design of the new maintenance building including: Existing active railroad spur track immediately east of proposed building addition area. Existing electrical transformer on the southwest corner area of proposed building addition area. Existing building exit along the north side of the proposed building addition area. Existing natural gas service along the north side of the proposed building addition area. A site plan of the water treatment plant showing the location of the proposed maintenance building is illustrated in Figure 4-1. Technical Memorandum No July 2001

147 Existing Building Structure The existing building structure will be used to enclose the proposed building addition on the north and west side. It is not known if these existing structures are capable of supporting new structural loads from the proposed building addition. Therefore, the proposed building addition will be designed with column offset from the existing structure sufficient distance to allow for foundations required by the proposed building addition. The structure will cantilever off of these columns and only soft connection will be made to the existing building structure Proposed Maintenance Shop Addition Space Requirements and Program The proposed shop addition will serve as a repair facility for equipment used in the process of providing drinking water for the City of Sioux Falls. Equipment to be repaired in the proposed maintenance shop may include: Pumps and pump assemblies Motors Well casings Miscellaneous repair. No repairing of motor vehicles will be done. Space allocation in the ground level of the facility will include: Lime Sludge Loadout Dedicated paint spray booth Abrasive blasting bay Washdown bay, grit removal General service bay Open shop area Parts storage Toilet and locker space for 20 males Cubicle office space for: - Well and main maintenance supervisor - Plant systems maintenance supervisor - Electrical repair supervisor Space Allocation in the ground level mezzanine level will include: Enlarge the existing lime slaker room Mezzanine storage for parts The space allocations, basic building layout and functions have been reviewed with the Water Department personnel. The preliminary building layout is shown in Figures 4-2, 4-3, and 4-4. Technical Memorandum No July 2001

148 No space has been allocated for lunchroom, chemical storage (other than in cabinets), shower facilities, lawn storage, fueling of vehicles or vehicle servicing Aesthetics The new maintenance shop addition aesthetics will be similar to the existing water plant MATERIALS OF CONSTRUCTION Building Components Exterior walls will be designed using reinforced load bearing concrete masonry cavity wall construction with brick veneer. Brick veneer will match or compliment the existing buff colored brick veneer. Building frame will be steel columns and steel beams with steel bar joists and metal deck. Roofing will be single ply membrane, ballasted or adhered over insulation and tapered insulation to provide roof slopes to interior roof drains. Average R values of roof insulation will be approximately R25. Parapet walls will be capped using clad metal coping. Skylights may be included to provide natural lighting to exterior spaces. Pedestrian doors in non-corrosive areas will be insulated with steel doorframes. Doors and frame will be painted. Doors in corrosive areas will be insulated with aluminum doors and aluminum frames. Aluminum doors and frames will have factory applied finishes. Neckhead doors will be 14-ft x 14-ft insulated steel sectional doors with motor operators and vision panels. Overhead door finish will be manufacturer s standard factory applied primer paint capable of receiving field applied paint finish coats. All non-operable windows (where used) will be aluminum frames, thermally broken with insulating tinted glass. Door hardware will match existing finish and new door locusts will be keyed to the existing master and/or grandmaster keying system. Interior wall finishes will be high performance industrial grade epoxy paint systems on concrete masonry walls and the existing brick walls that will become part of the shop interior. Interior concrete slab floors will be provided with an industrial grade sealer, dust proofer hardener Specialty Equipment and Furnishings A number of specialty equipment and furnishings will be provided in the new maintenance building including the following: Technical Memorandum No July 2001

149 The Maintenance Shop Addition will be provided with a 5-ton capacity bridge crane capable of running from the south exterior wall to the south wall of the second floor lime slaker room expansion. A prefabricated self-contained spray paint booth will be provided capable of accommodating small service vehicles. Exact specifications for this item will be developed during the design phase based on anticipated vehicle size and cost. Existing shop equipment will be relocated to the new shop addition Equipment Provided by Owner. The following equipment will be provided by owner for installation in the new maintenance building: Cubicle office partitions Paint and solvent storage cabinets Parts storage furniture ESTIMATED COSTS The capital costs associated with the design and construction of a maintenance building as discussed is included in Table 4-1. Table 4-1. Opinion of Probable Capital Cost for Maintenance Building Item Estimated Cost Ground Level $1,091,000 Mezzanine Level/Second Floor $168,000 Specialties Bridge Crane $44,000 Spray Paint Booth $44,000 Subtotal $1,347,000 Contingency (20%) $269,000 Total Estimated Construction Cost $1,616,000 Engineering/Legal/Administrative (15%) $242,000 Total Estimated Capital Cost $1,858, VOLT SWITCHGEAR EXISTING SWITCHGEAR The existing Main Switchgear is a General Electric Magna Blast Series (1972 vintage) lineup utilizing Magna Blast air break type circuit breakers. The switchgear line up has 10 sections with each section having a footprint of 26-inches wide by 65-inches deep (see Figures 4-5 and 4-6). The power utility company s service consists of two 1500kVA transformers connected in parallel and fed with one circuit from a substation. An 1825kW diesel generator is also Technical Memorandum No July 2001

150 connected to the switchgear for backup power and through the use of the Schweitzer relay the generator can be paralleled with the utility. Since 1985 and on a five-year cycle, the circuit breakers and associated relays have been maintained and adjusted by a qualified service company. Electrically, the switchgear is working in a satisfactorily manor, but mechanically there are several problems. Some concerns are as follows: NEW SWITCHGEAR The circuit breakers cannot be interchanged between the switchgear sections because of settling and racking of the switchgear framing. Switchgear sectional doors are hard to open and close because of settling and racking of the switchgear framing. The switchgear sits on a housekeeping pad making it difficult to roll the circuit breakers out for maintenance or replacement. The air break circuit breakers and electro-mechanical relays are an older technology and have been in service past their useful life of 25 years. Spare parts will be increasingly harder to get. The new switchgear will utilize vacuum break type circuit breakers (e.g. GE Power/VAC) with electronic relays (e.g. GE UR). The switchgear will be configured to allow double stacking of the breakers; the City prefers to have all the breakers located in the bottom location. The microprocessor-based relay will provide the required circuit/load protection, circuit breaker control, customer metering and communications. The existing Plant SCADA system will be connected to the relays to provide metering data and breaker status/alarms via a compatible communication system with the SCADA system. The existing switchgear is mounted on a housekeeping pad with roll-out type breakers (breakers have wheels). The housekeeping pad and roll-out type breakers are not compatible when maintenance is required. The new breakers will also be mounted on a housekeeping pad and the breakers are a rack-out type (similar to a desk drawer). Maintenance can be done while the breaker is supported by the rack. If the breaker needs to be moved a portable lifter is used to lift the breaker off the rack and a transport dolly is used to move the breaker long distances. The new vacuum breakers, as an option, can be purchased as a roll-out type (bottom position only) but it is not the standard configuration and the housekeeping pad creates a problem when rolling out the breaker. The new switchgear s footprint is significantly larger than the existing switchgears. General Electric s standard footprint size is 36-inches wide by 94-inches deep with an optional 36-inches wide by 82-inches deep size. The limitation of the 82-inch deep version is in the feeder conductor space. In a double stack arrangement, the bottom breaker is required to be fed from below, and the top breaker is required to be fed from the top. The 94-inch deep version allows both breakers to be fed from below. Technical Memorandum No July 2001

151 Working clearances around the switchgear include the National Electrical Code (NEC) required 48-inches in front of the gear, 30-inches on the sides and 30-inches in the rear for de-energized gear or 48-inches for energized gear. NEC clearances are the minimum required for safety. General Electric recommends 66-inches in front of the gear, 26-inches in the rear and 36-inches from the left side to a wall to allow the front door to open 180 degrees. See Figure 4-4 for identification of these areas. The utility company is upgrading their substation so that the Plant can be fed from two different distribution feeders. The utility company will also replace the paralleled transformers with a single 3000kVA unit. There are two options on how to install the new switchgear. The first option is to reuse the existing location, and the second option is to build an addition to the building to house the new switchgear Option 1 - Reuse the existing space There are several technical issues or limitation of the switchgear that need to be addressed if the existing space is to be reused. New switchgear is significantly larger than the existing switchgear so fitting the switchgear into the existing space will require some compromises. The maximum number of sections that will fit into the space is seven requiring double stacking the breakers to accommodate the required number of breakers. See Figure 4-5. Switchgear depth of 82-inches can be used but conductor routing to the top mounted breaker will be more difficult since it has to enter the gear from the top and the recommended front working clearance is not meet. NEC clearances can be met. See Figure 4-4. Temporary switchgear will need to be rented to keep the plant functional while the new switchgear is installed. Technical Memorandum No July 2001

152 Table 4-2. Opinion of Probable Capital Cost for Option 1 for New Switchgear Item Estimated Cost Temporary switchgear rental $125,000 Temp. switchgear wire and conduit $35,000 Installation, breaker relay adjustments, testing, and demolition of temporary switchgear $125,000 New 5kV class switchgear (7 section) $260,000 New wire (reuse conduit) $25,000 Subtotal $570,000 Contingency (20%) $114,000 Total Estimated Construction Cost $684,000 Engineering/Legal/Administrative (15%) $103,000 Total Estimated Capital Cost $787, Option 2 - New building addition The new building addition will be in the southeast corner of the building. A new room is required because the standard sized switchgear with all the required breakers located in the bottom location will not fit into the same space as the existing switchgear. A vault will be built under the switchgear room to allow easy installation of the cable into the bottom of the switchgear. Since bottom entry of the cables is the most efficient, a 94-inch deep switchgear is the only choice. The new Switchgear Room addition will also allow the new switchgear to be constructed and the transfer of the load to the new switchgear while still energizing the Plant from the existing switchgear. Figure 4-4 indicates two options on the layout of the new room. Option 2A is the preferred layout because both the manufacturers and NEC working clearances are met. While Option 2B meets the NEC working clearances, the additional required space recommended by GE to do effective maintenance is not met. Table 4-3. Opinion of Probable Capital Cost for Option 2 for New Switchgear Item Estimated Cost Building addition (including mechanical) $110,000 5kV class switchgear (10 section) $340,000 Conduit and wire $57,000 Subtotal $507,000 Contingency (20%) $101,000 Total Estimated Construction Cost $608,000 Engineering/Legal/Administrative (15%) $91,000 Total Estimated Capital Cost $699,000 Note: Approximately $50,000 in switchgear material costs could be saved if the breakers were allowed to be double stacked. Technical Memorandum No July 2001

153 Summary and Recommendation Considerations regarding the differences in the two options include the following: Option 1 is custom equipment and the actual breaker will be purchased by that supplier. As a result, their estimated cost is not necessarily based on General Electric while Option 1 is a quote from General Electric. Option 2 has 10 sections of single stack breakers while Option 1 has 7 sections. This allows all breakers to be installed in the lower section (preferred by the City) and allows more space for a future breaker in the upper section if required. Option 1 will require several plant shutdowns to switch over then back from the temporary equipment. Option 2 will significantly reduce disruptions to plant operations. Some concern exists regarding safety and reliability when using temporary switchgear and open conductors. The condition of the rental equipment is difficult to control. No generator backup will be available for the temporary switchgear. The replacement of the switchgear in the same space as the existing switchgear has the significant advantage of not requiring a building addition. There are, however, several disadvantages as defined above which should be considered in the alternative selection. 4.3 SLUDGE WITHDRAWAL LINES EXISTING SLUDGE PIPING The sludge draw-off lines in basins 2 and 3 are currently 4-inch diameter lines, which limit the withdrawal rate and are more prone to plugging, than the other four basins. Basin 1 also had a 4- inch draw-off line, which was upsized to an 8" line during the recent installation of a new solids contact clarifier in that basin. Basins 4, 5 and 6 have 6-inch draw-off lines. Basins 2 and 3 are limited in their draw down rate due to the existing size of their under-slab sludge withdrawal lines. While operations continue to work around this bottleneck successfully, it remains a limitation on the operability of those basins. This has become more apparent following the upsizing of the Basin 1 draw-off line to eight inch, which allows for more rapid adjustment of blanket depths. The negative impacts of limited sludge withdrawal on these two basins will continue to escalate as flow demands increase PROPOSED PIPING IMPROVEMENTS In conversation with plant operations, maintenance and management staff, the consensus was that the lines on basins 2 and 3 need to be upsized. These lines run under the basin floors and the majority of the cost associated with replacement is due to the installation costs, not pipe material costs. For this reason, and to maintain consistency on the south basins, the replacement line is recommended to be an 8-inch line, to match Basin 1. The 8-inch line will provide additional capacity and more flexibility than a six-inch line would, for a minimal increase in cost. Since the basins need to be off-line for this project, the work would need to be done during the off-peak Technical Memorandum No July 2001

154 season (October through April). Additional scheduled maintenance could coincide with these repairs, such as the sludge pumping and piping improvements proposed in Section DESCRIPTION OF WORK AND ASSOCIATED COSTS The four-inch sludge draw-off lines for basins 2 and 3 would be replaced in their entirety, from the sludge collection sump in the center of the lime softening basins, to the east, under the basin wall, elbowing up and branching off for a direct draw, or continuing up to the individual basin sludge pit. Piping will be reinstalled as existing, only upsized from 4-inch to 8-inch. The photos below (Figures 4-7 and 4-8) are of the existing basin 1 piping, which basins two and three will match following these improvements. Figure 4-7. Gallery Sludge Draw-Off Line - Basin 1 Sludge Pit Penetration & Manual & Actuated Valves Figure 4-8. Gallery Sludge Draw-Off Line - Basin 1 Floor Penetration & Direct Draw Connection The piping under the floor would be replaced by cutting a band of the floor out over the existing four-inch draw-off line and hand excavating the line for removal. An opening would be cut into the floor in the pipe gallery where the existing draw-off line enters. The area under the basin wall to this opening would also need to be hand excavated. The new line would be re-laid in the trench and up through the opening cut in the pipe gallery. The pipe would be bedded back in place, and concrete and reinforcing tie bars would be placed to repair the band cut from the existing floor, and the seams would be sealed using a chemical grout. The remaining piping to the sludge pit would also be replaced with eight-inch, including installing a gear-operated plug valve for isolation and a pneumatically operated plug valve for sludge draw-off operations. A summary of the costs associated with these improvements is presented in the following table. Technical Memorandum No July 2001

155 Table 4-4. Opinion of Probable Capital Cost for Sludge Withdrawal Piping Improvements Item Estimated Cost Cutout and remove concrete slab Basin 2 $3,800 Cutout and remove concrete slab Basin 3 $4,800 Remove old 4 line Basin 2 $300 Remove old 4 line Basin 3 $400 Hand excavated under wall installation Basin 2 $300 Hand excavated under wall installation Basin 3 $400 Install new 8 line Basin 2 $500 Install new 8 line Basin 3 $700 8 Elbows $1,000 8 x 6 Tee (direct draw connection) $1,100 8 x 4 Wye (flush water connection) $1,100 8 DIP $800 8 Pneumatically operation plug valve $6,000 8 Gear operated plug valve $2,700 Coring for 8 line w/ link seal $3,000 Replace concrete in trench and grout Basin 2 $2,800 Replace concrete in trench and grout Basin 3 $3,600 Cut and patch gallery floor for new penetration $3,000 Painting $500 Subtotal $36,800 Contingency (20%) $7,400 Total Estimated Construction Cost $44,200 Engineering/Legal/Administrative (15%) $6,600 Total Estimated Capital Cost $50,800 Note: The connection to the direct draw is currently a four-inch line. It is recommended to go to a six-inch line in a subsequent section, therefore the tee above for this connection is an 8 x 6 rather than an 8 x SLUDGE PUMPING/PIPING EXISTING SLUDGE PUMPING/PIPING Pump capacity The existing lime sludge pumping includes three (3) progressing cavity pumps as manufactured by Moyno. These pumps were initially installed in the 1972 expansion. The pumping capacity of the system was approximately 650 gpm prior to improvements made to the lime sludge discharge line in In those improvements, a new discharge line was constructed to convey the sludge to the holding/dewatering lagoons, which dramatically reduced headloss and resultant operating pressure in the system. After these improvements the capacity has been estimated to be 1200 gpm with all three pumps running. This is an estimate, since the flowmeter only reads to 650 gpm. Prior to the 1997 improvements, maintenance on the pumps and discharge system, particularly rupture discs, was a significant concern. The reduction in operating pressures has Technical Memorandum No July 2001

156 significantly reduced these maintenance problems, to a level that the plant personnel considers negligible Piping and Valving Information The existing in-plant sludge piping was installed with the initial basin project in 1953, the major expansion in 1972, and with various other projects such as the chemical feed building addition in 1994 and the lime handling improvements in Modifications that occurred with these projects, operational changes, problems with operability of valves and changes made to the piping by staff, has left the existing sludge piping system with components not used, pipe runs that are not used or are not well laid out for the current operational conditions. The existing piping is a combination of four, six and eight-inch piping, essentially serving three purposes; 1) direct draw (from the basin), 2) gravity drain (suction form the sludge pits) and 3) pump discharge. As mentioned previously, the piping has been modified at various times and has resulted in a system that is not optimal and has several components that are not used. Some of the lines run low to the floor (approximately two feet above) and are out toward the front (east) for the equipment and piping, limiting access to the area behind. This requires stepping over these lines and lifting components over the lines also. The physical condition of many of these lines is poor, primarily from exterior corrosion. This is severe in some cases, particularly where sample sinks have been installed and spilling onto the pipes is occurring, as shown in Figure 4-9. Plant personnel indicated that the interior condition of the sludge lines do not appear to be a problem, as observed during maintenance and disassembly procedures. Figure 4-9. Sludge Direct Draw and Gravity Lines Showing Severe External Corrosion Valving on the lime sludge lines is comprised largely of 1/4-turn plug valves for isolation and pneumatically operated diaphragm or plug valves for remote modulation. Most of the plug valves are not gear operated and operation has been a problem. These have a tendency to bind and sometimes require using long extensions ( cheaters ) on the operating lever or wrench to change the position. This creates a safety concern due to the forces that are being used to operate that valves and should be corrected. One probable contributing factor to the valve failure is that almost all of these valves are installed with the shaft of the valve in the vertical position. In a sludge application the sludge tends to settle and pack into the lower journal and binds the bearings, accelerating failure. The new plug valves added in the 1997 sludge improvements are gear operated and have not experienced the same problems. Technical Memorandum No July 2001

157 4.4.2 SLUDGE PRODUCTION Sludge production in recent years has been trending downward, with respect to water treated. The reasons for this trend are potentially attributed to the following: There has been a tendency to keep a thicker sludge blanket in the clarifiers, thus a higher solids concentration and less sludge. This has been facilitated due to the discharge piping improvements made in 1997, which allows for pumping a thicker sludge. The ph levels have been reduced as possible, decreasing lime costs. The ratio of surface water to ground water has been increasing in this period, which theoretically increases lime consumption, however this is apparently off-set by the sludge reduction factors stated above. The addition of a solids contact clarifier in basin 1 in 1997 did not achieve the desired results, and actually requires more lime than each of the other five basins to operate properly. This increase, although noted, did not significantly impact total sludge production. In the 1993 Master Plan, maximum day sludge production values were estimated through These estimates have been updated using the same sludge volume produced per million gallons produced (4888 gallons of sludge/mg) and newly projected flow data developed in this master plan update and extended to the year 2025, as presented in the table below. Due to the decreasing trend in sludge pumping volume per volume produced, these numbers may tend to be slightly conservative, if recent trends in operation continue. Table 4-5. Projections of Estimated Sludge Production Year Maximum Daily Demand Maximum Daily Lime (MGD) Sludge Volume (gallons) , , ,000 Note: These are slightly higher than predicted in the 1993 master plan due to higher predicted demands SLUDGE PUMPING/PIPING CAPACITY The existing sludge pumps are commonly considered to be the most applicable pump design, progressing cavity, to be used for pumping lime sludge. The existing pumps are quite old, however, with the maintenance that has been done on these units, many of the components have been replaced and their current condition is good. Maintenance included replacement of all three of the drives, one in 1989, the second in 1992 and the third in With the lime sludge modifications made in 1997, the pressures and demands on these pumps has been significantly reduced, which reduced maintenance dramatically. With recent upgrades, it is anticipated that there remains a significant useful life of these pumps. Due to this and conversations with plant personnel, it is not recommended to make changes to the pumps at this time, based on condition and remaining useful life. Technical Memorandum No July 2001

158 With regards to the capacity of the pumps, the approximate capacity of all three pumps is 1200 gpm. The actual capacity of two pumps (one out of service) has not been determined, but should be in the range of 800 gpm. It has been verified that the capacity of two does exceed the maximum meter reading of 650 gpm. At the maximum day sludge pumping of 316,000 in 2025, that would equate to a constant rate of 219 gpm. While a constant rate is not probable, the required pumping time if two were on line would only be approximately 6.5 hours per day for the maximum day in Due to the existing age of the pumps, expecting them to remain in service to 2025 would be optimistic, however, that sludge flow was used to show available capacity for the foreseeable future. For this reason replacement of the lime sludge pumps due to capacity is not warranted. In summary, the existing condition of the pumps indicate that they currently have a significant useful life remaining, with a system capacity in excess of foreseeable production and replacement of these pumps is not recommended. With the reported pumping capacities following the 1997 improvements, it appears that the desired capacities of lines are approaching their limits. Typical desired velocities in lime sludge applications are in the 3 to 4 feet per second range. Using this typical velocity range, the resulting flow ranges are: 8-inch: 470 to 625 gpm 6-inch: 265 to 350 gpm 4-inch: 115 to 155 gpm With all pumps running (approximately 1200 gpm), the velocity in the 8-inch discharge line is much higher than recommended, at approximately 7.5 fps. This is not an unusually high velocity for piping applications, however, it is recommended that use of all three pumps when going to direct discharge should be limited to two pumps whenever possible. This will reduce stress to the system associated with pumping the high solids slurry at relatively high velocities. Limiting to two pumps reduces direct discharge velocities to approximately 5 fps, which is acceptable. Given past experience and the two pumps are normally more than adequate to meet pumping demands, upsizing of the discharge line due to size alone is not recommended. A 6-inch supplying one pump (approximate capacity of 400 gpm) would result in a velocity of approximately 4.5 fps, not much higher than typical desired numbers and acceptable. As shown above, the typical desired flow range is quite limited for the 4-inch line, and if direct draw or fill occurs through the 4-inch line, the resulting velocities would be over 10 fps. In our opinion, this is excessive and should be reduced by increasing line size. On the north, and existing line that is no longer in service can be reused for a direct draw/fill line. We recommend making that modification on the north, see Section , and replacing the 4" direct draw/fill on the south as well, to improve flow conditions and provide similar conditions between the north and south sides of the basins. This will also eliminate several corroded areas as described previously PROPOSED PIPING MODIFICATIONS The requirements of the sludge piping system were summarized by operations to include: 1) direct draw capabilities from each basin, 2) to be able to discharge sludge back to any of the Technical Memorandum No July 2001

159 basins (done through the direct draw line) and 3) be able to operate the valves without a "cheater bar". In addition, it is desirable to "clean-up" the piping, removing unused or unnecessary piping and valves, and improve access where possible. It was also discussed that it is difficult to access the pumps and other piping and equipment along the west side of the gallery, due to the direct draw and gravity drain lines being low, along the floor and located in front of these items. This requires stepping over these lines to access and lifting materials over. With reduced maintenance requirements on the pumps (since 1997 improvements) this will be less of an issue than in the past. Relocation of the pumps and rerouting of the lines solely to improve access would be costly and will not be considered at this time. When replacement of piping is recommended, access improvement should be considered in the design. Elimination of unused or unnecessary materials will provide additional space that could facilitate improvements to the access. When making changes to the lime sludge pumping system, it is critical to maintain the ability to flush the lines with water, however, new flush valves should be ball valves. The majority of the existing valves are gate or globe valves, which plug, stick or do not shutoff tightly after in use for a while Unused or Redundant Materials/Piping As mentioned previously, there are a number of items and piping that are not functional, not used and occupy space in the gallery that is undesirable. It is recommended that these components be removed to provide a simplified installation and provide additional space. One such line is the four-inch direct draw line on the north half of the facility. This line is severely corroded, particularly adjacent to the sinks. This line can be eliminated with minor modifications to the piping, using the existing 6-inch discharge line that is available for use due to previous rerouting of the discharge line, to discharge out through the north end of the building, rather than the center as the prior arrangement had. To accomplish this, an interconnection will need to be made to the aforementioned 6-inch line and the direct draw lines from basins 4, 5 and 6. This modification is recommended, to eliminate a redundant section of piping, portions of which are severely corroded. Another specific condition is the interconnection made with the influent line as shown in Figure This was an attempt to provide sludge recycle that has not functioned satisfactorily and is not used. It is recommended that this line be removed to improve access and to eliminate potential operational problems that could occur due to this interconnection. Figure Unused Interconnection There are several valves that do not operate or are no longer needed and are recommended to be removed. An example of such a condition Technical Memorandum No July 2001

160 is shown in Figure 4-11, where a discharge to the sludge sump has been disconnected, with the valves remaining in place, merely being blind-flanged off. It is recommended that all of these unused valve also be removed to provide additional operational space, eliminate the need to paint these items and to reduce confusion in the piping Replacement of Corroded Piping and Inoperable Valves Figure Unused Diaphragm and Plug Valves There are several areas that have corroded piping, as described previously. Several of these areas on the north side will be eliminated in association with the elimination of the 4-inch direct draw on that half of the gallery, as described in the previous section. A number of segments remain that require repair or replacement. Due to the severity of the corrosion, it is likely to cost more to attempt to correct the problem, rather than replace the piping. It is for this reason that replacement of the corroded piping is proposed. In addition, we recommend additional surface protection be provided at the wet areas, particularly at the sink locations. This could include modifying the sinks to avoid splashing directly onto the remaining line(s), moving the sinks, relocating the piping as feasible, providing a more durable surface on the piping or running the line through a casing of a non-corroding material, such as PVC or polyethylene. In this analysis we recommend using a PVC casing line. As mentioned previously, there are several quarter-turn plug valves that are very difficult to operate, and some that may not be able to be operated. It was also noted previously, that a contributing factor to the valve failure is that many of these valves are installed with the shaft of the valve in the vertical position. In a sludge application the sludge tends to settle and pack into the lower journal and binds the bearings, accelerating failure. It is recommended that these be replaced in conjunction with the piping modifications proposed. This will restore operability and improve safety since operation will be simplified and will not require excessive force. The replacement valves can be accomplished with plug valves with a geared operator (to reduce required operating force) or diaphragm valves. Diaphragm valves are less prone to plugging and binding, however the cost is significantly higher. In the improvements made to Basin 1 in 1997, isolation and modulated valves were chosen to be plug type valves, and have been operating satisfactorily since their installation. To maintain consistency, we are recommending use of gear-operated plug valves in these replacement situations, with the shafts installed in the horizontal position to reduce premature failure Capacity Driven Replacement Recommended replacement of lines due to capacity is limited to the 4-inch direct draw/fill lines as described previously, upsizing to a 6-inch. This requires new line on the south and reuse of an existing line on the north. Technical Memorandum No July 2001

161 4.4.5 RECOMMENDATIONS AND OPINION OF PROBABLE CONSTRUCTION COSTS The following bullets summarize the recommendations to the lime sludge piping and pumping system as described in this section: Eliminate existing 4-inch direct draw/fill on north and use existing 6-inch line, providing three interconnections to basins 4, 5 and 6, to allow for direct draw/fill. Remove unused valves. Replace corroded piping. Replace valves that are inoperable or very difficult to operate (note: new plug valves are to be installed with shaft horizontal to reduce potential for failure). Place non-corroding sleeves over piping near sinks and wet areas to keep direct contact from splashing water from occurring. The budget estimate for these recommended improvements are presented in the following table: Table 4-6. Opinion of Probable Capital Cost for Sludge Pumping/Piping Improvements Item Estimated Cost Remove 4 DIP and valves $3,500 Remove 6 DIP and valves $900 Influent piping repair $800 Furnish and install 6 DIP $12,900 6 Gear Operation Plug Valves $11,600 8 Gear Operation Plug Valves $6,800 Remove unused valves and piping $5,400 6 x 6 Wyes $3,500 PVC casing pipe $2,000 Piping Supports $3,500 Blind flanges and misc. piping $4,500 Miscellaneous fittings $6,000 Painting $15,000 Subtotal $76,400 Contingency (20%) $15,300 Total Estimated Construction Cost $91,700 Engineering/Legal/Administrative (15%) $13,800 Total Estimated Capital Cost $105, SLUDGE THICKENING AND STORAGE The existing lime sludge system has very limited storage capabilities, essentially requiring pumping whenever blanket levels are adjusted and sludge is drawn off. It is common for softening plants to provide capabilities to allow for the sludge to be removed, typically by gravity flow, from the softening basins to a large collection tank. The sludge from the collection Technical Memorandum No July 2001

162 tank can be thickened, decanted, etc., depending upon the desired functions and sludge disposal techniques of the facility. Availability of adequate storage provides flexibility in operations, reduces upsets and provides a source for establishing a starting sludge blanket when putting a basin back on-line. It is recommended that some means of sludge storage be provided at the Sioux Falls Water Purification Plant, to enhance operability and reliability. In addition, it is recommended that the ability to thicken the sludge be provided, to reduce the sludge volume delivered to the dewatering lagoons. This will enhance operation of the dewatering process at the lagoons, by reducing the incoming sludge volume, as well as the decant water volume. The decant or overflow water would be able to be returned to the head of the proposed presedimentation basin or discharged to the sanitary sewer. Typical design surface loading rates for lime sludge thickeners are between 60 and 200 pounds of solids per square foot per day. The estimated maximum day lime sludge production for 2025 is approximately 147 dry tons/day (316,000 gpd - see Table 4-5). This was calculated using values and procedures utilized in the 1993 Master Plan and presented therein in Table 8-3. For the purposes of this evaluation, a circular, stand-alone thickener is proposed with a geodesic aluminum dome cover (with dormer and drive access ring) to reduce freezing potential. Using a surface loading rate of 100 pounds of solids per square foot per day results in a thickener diameter of approximately 61 feet. Rounding this to 60 feet to be more conventional, the resulting surface loading rate is 104 pounds of solids per square foot per day, for the maximum day sludge production. Using a sidewater depth of 14 feet and a bottom slope of 1:4 (to facilitate sludge removal) the resulting total volume is 46,630 cubic feet or 348,785 gallons. This results in a retention time of approximately 1.1 days at the maximum daily sludge production for The location of the thickener could be to the north of the facility (See Figure 4-12). When constructing this facility, it is recommended to complete the sludge piping modifications described previously, and to provide new sludge pumping from the thickener in a new vault constructed adjacent to the thickener. Costs associated with the proposed improvements, thickener and sludge pumping, are summarized in Table 4-7. Technical Memorandum No July 2001

163 Table 4-7. Opinion of Probable Capital Cost for Sludge Thickening and Pumping Improvements Item Estimated Cost Thickener Excavation and Sitework $10,000 Sitework Piping $55,000 Equipment $198,000 Concrete $28,000 Steel $76,000 Piping and Valves $28,000 Electrical and Instrumentation $31,000 Cover $126,000 Pumping Equipment $102,000 Piping and Valves $22,000 Electrical and Instrumentation $15,000 Housing/Structures $9,000 Subtotal $700,000 Contingency (20%) $140,000 Total Estimated Construction Cost $840,000 Engineering/Legal/Administrative (15%) $126,000 Total Estimated Capital Cost $966,000 Technical Memorandum No July 2001

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172 TECHNICAL MEMORANDUM NO. 5 FUTURE REGULATORY/FACILITY REQUIREMENTS Table of Contents Section Page 5.0 INTRODUCTION FUTURE REGULATORY REQUIREMENTS Long Term 2 Enhanced Surface Water Treatment Rule Stage 2 Disinfectant/Disinfection Byproduct Rule WATER QUALITY MEMBRANE EVALUATION Background Data Water Quality Information Information Collection Rule Information Overview Data Summary Membrane Technology Screening Information Nanofiltration Suppliers Hydranautics Koch (formerly Fluid Systems) Osmonics Nanofiltration Limitations Membrane Treatment Options Option 1 - Polishing Treatment: Treat current blend-water filter effluent Process Description Advantages Disadvantages Option 2 - Split treatment: NF for Groundwater only Process Description Advantages Disadvantages Option 3 - Joint Treatment Process Description Advantages Disadvantages Estimated Costs Nanofiltration System Pretreatment Issues Recommendations UV PRIMARY DISINFECTION EVALUATION Current Regulatory Status Background Data Background/Definitions...13 Technical Memorandum No. 5 -i- July 2001

173 Effectiveness Advantages/Disadvantages Design Considerations Equipment Specific Factors Site-Specific Factors Applicability to Sioux Falls WPP Disinfectant Alternatives Option 1 Chlorine/Chloramines Option 2 UV/Chloramines Option 3 UV/Chlorine/Chloramines Option 4 UV/Chloramines/Chloramines Organic Oxidation UV Disinfection Piloting Estimated Costs Recommendations GRANULAR ACTIVATED CARBON EVALUATION Purpose Carbon Contactors Carbon Regeneration System Estimated Costs Recommendations...24 Technical Memorandum No. 5 -ii- July 2001

174 List of Tables Table Page Table 5-1. Opinion of Probable Capital Cost for Nanofiltration System...9 Table 5-2. Opinion of Probable Operation and Maintenance Costs for Nanofiltration System...9 Table 5-3. Opinion of Probable Capital Cost for NF Pretreatment Systems...10 Table 5-4. Opinion of Probable Operation and Maintenance Costs for NF Pretreatment System...11 Table 5-5. UV Dose Required to Inactivate Pathogens...14 Table 5-6. Mercury UV Lamp Characteristics...16 Table 5-7. Opinion of Probable Capital Cost for UV Disinfection System...20 Table 5-8. Opinion of Probable Operation and Maintenance Costs for UV Disinfection System...21 Table 5-9. Opinion of Probable Capital Cost for GAC System...23 Table Opinion of Probable Operation and Maintenance Costs for GAC System...23 List of Figures Figure Following Page Figure 5-1. Option 1 Polishing Treatment Schematic...5 Figure 5-2. Option 2 Split Treatment Schematic...6 Figure 5-3. Option 3 Joint Treatment Schematic...7 Figure 5-4. Cell Inactivation Effectiveness...12 Figure 5-5. UV Disinfection System...24 Technical Memorandum No. 5 -iii- July 2001

175 5.0 INTRODUCTION TECHNICAL MEMORANDUM NO. 5 FUTURE REGULATORY/FACILITY REQUIREMENTS This Technical Memorandum (TM) includes evaluations of improvement alternatives to meet future regulatory requirements as follows: Membranes UV Disinfection Granular Activated Carbon 5.1 FUTURE REGULATORY REQUIREMENTS The regulatory focus of this TM will be on anticipated future microbial and disinfection byproduct rules, including the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) and the Stage 2 Disinfectants/Disinfection Byproducts (D/DBP) Rule. Systems will be required to concurrently meet the requirements of the LT2ESWTR and Stage 2 D/DBP Rule in order to protect public health by ensuring a proper balance between microbial and DBP risks while optimizing technology choice decisions LONG TERM 2ENHANCED SURFACE WATER TREATMENT RULE A detailed description of the anticipated requirements of the LT2ESWTR is included in TM No. 1, Section The main objective of this rule is to provide further protection from Cryptosporidium oocysts that have shown a resistance to traditional disinfectants such as chlorine. Monitoring will be required to determine the source water Cryptosporidium concentration, and additional treatment methods may be required depending upon the source water concentration. Note that the Big Sioux River, as with any surface water, would be susceptible to elevated microbial contamination. Consequently, it is likely that the Sioux Falls supply would fall into Bin Classification 2, or greater. Any membrane application (MF, UF, NF, RO) potentially utilized by Sioux Falls would achieve Cryptosporidium removal to the highest Bin Classification STAGE 2DISINFECTANT/DISINFECTION BYPRODUCT RULE Refer to Technical Memorandum No. 1, Section for a detailed description of the Stage 2 D/DBP Rule. The purpose of this rule is to build upon the requirements of the Stage 1 D/DBP Rule to further protect the public from the adverse health effects of disinfection byproducts. Anticipated requirement of the rule include: MCLs for TTHMs, HAA5, bromate, and chlorite will not be reduced from the Stage 1 levels. TTHM and HAA5 monitoring will be a location running annual average as opposed to averaging across the distribution system that is required under the Stage 1 D/DBP rule. Technical Memorandum No July 2001

176 5.2 WATER QUALITY A detailed summary of the raw and treated water quality for the Sioux Falls WPP is included in TM No. 1. For the evaluation of treatment requirements to meet future anticipated regulations, raw water quality parameters of interest include TOC and Cryptosporidium concentrations. The surface water source for Sioux Falls has high TOC levels, particularly with surface runoff during the spring. The high TOC levels contribute to a potential for high DBP formation. Sioux Falls has performed Cryptosporidium monitoring since The monitoring has resulted in a few detections of Cryptosporidium in the raw water, although all detections have not been viable oocysts. Although the detected oocysts have not been viable, their presence indicates the possibility of Cryptosporidium contamination of the raw water. Finished water quality of concern for this evaluation is the current DBP concentrations in the Sioux Falls distribution system. Concentrations of HAA5 that have been recorded indicate that the system will be in compliance with the Stage 1 D/DBP Rule requirements and the anticipated Stage 2 requirements. Detected concentrations of TTHM are periodically in excess of the Stage 1 and anticipated Stage 2 requirements. In order to reduce TTHM concentrations, Sioux Falls will switch the distribution disinfectant residual from chlorine to chloramines. Although the conversion is expected to reduce the formation of DBPs, future regulations may require additional or alternative treatment methods to provide further DBP reduction. 5.3 MEMBRANE EVALUATION Membrane systems for potable water treatment fall into two general categories: low-pressure systems, which include microfiltration (MF) and ultrafiltration (UF); and high-pressure systems, which include nanofiltration (NF) and reverse osmosis (RO). The emphasis of this TM has been placed on the application of nanofiltration. This type of membrane system will provide reduction in TOC levels, thereby reducing DBP formation. In addition, when used for the entire process flow, the membranes will serve as a barrier to pathogens such as Cryptosporidium. A discussion of the use of membranes to meet future regulatory requirements is included in the following sections BACKGROUND DATA Water Quality Information Water quality is an important consideration in the application of membranes. TM No. 1 presents a detailed summary of historical and current water quality parameters for both surface water and groundwater sources for the Sioux Falls WPP. Water quality concerns of particular interest for the membrane evaluation include the following: Water Quality Concerns for Surface Water (Big Sioux River) High TOC (high DBPs): 7.33 mg/l (maximum mg/l) High Turbidity: 33 NTU (maximum 148 NTU) High Hardness: 466 mg/l (maximum 653 mg/l) Technical Memorandum No July 2001

177 High Fe: 0.66 mg/l (maximum 2.18 mg/l) High Mn: 0.25 mg/l (maximum 3.36 mg/l) High SO 4 : 261 mg/l (maximum 365 mg/l) Taste and Odor during spring runoff and algae bloom Water Quality Concerns for Groundwater High Hardness High Fe High Mn High SO Information Collection Rule Information Overview An ICR Treatment Study evaluating high-pressure membranes for the Sioux Falls WPP was completed in July of The information from that report is summarized below as it relates to the further evaluation of membrane treatment as a viable option for the Sioux Falls WPP. The study collected quarterly data from April 1998 to February 10, Data Summary The current softening process removes about 34% (in average) of TOC from the blended influent. According to the ICR Treatment Study Report prepared by NGPWRRC at South Dakota State University in 1999, this level of TOC reduction allows the SDS-DBPs in the finished water to remain in compliance with the MCL specified in Stage 1 D/DBP Rule. Although the proposed Stage 2 D/DBP Rule did not further lower the MCL for both TTHM and HAA5, concentrations of TTHM at various sampling points in the distribution system exceed the 80 g/l MCL. In order to reduce DBP formation for future compliance, the Sioux Falls WPP has decided to convert to chloramines for secondary disinfection. However, with more than 3 mg/l of TOC remains in the filtered effluent, it is not clear whether using chloramines will always maintain the DBPs below regulated levels. One of the alternatives to resolve this potential problem is to use high-pressure membranes (NF and RO) to remove more TOC. The ICR report has concluded that nanofiltration membranes can effectively remove TOC and thereby reduce the formation of DBPs. Among four tested membranes, three membranes (Film- Tec NF-70, Fluid System TFC-S, and Film-Tec NF-200B) were able to consistently remove more than 95% of TOC and reduce % of TTHM and % of HAA5, depending on the membrane type and recovery ratio. Although the fourth membrane (Hydranautics NTR- 7450), which is a non-softening membrane, demonstrated slightly lower TOC removal (67-83%), its performance is still considered satisfactory since the reduction of TTHM and HAA5 was significant enough (46-68% and 54-79%, respectively) to guarantee the compliance with Stage 2 D/DBP Rule. There are several possible configurations for the NF implementation at Sioux Falls WPP. In order to optimize the process design so that the unique features of NF membranes can be fully Technical Memorandum No July 2001

178 utilized, it is necessary to understand the limitation of NF membranes and the specific water quality concerns associated with different water sources MEMBRANE TECHNOLOGY SCREENING INFORMATION Nanofiltration Suppliers Three manufacturers were screened to provide a baseline of technology screening information. These suppliers have been screened as they have demonstrated experience with organics removal and softening applications Hydranautics Membrane Configuration: spiral wound Membrane Chemistry: polyamide TOC removal: typically 97 to 99 % Acceptable ph range: 3 to 10 Acceptable feed turbidity: < 1.0 NTU PAC compatible: yes Polymer compatible: yes, anionic Oxidant compatible: yes SDI requirement: < 5 Similar applications: Additional information: Koch (formerly Fluid Systems) Membrane Configuration: spiral wound Membrane Chemistry: poly amide TOC removal: 96 to 98 %. Low molecular weight organics can be problematic. Acceptable ph range: 2 to 11 Acceptable feed turbidity: PAC compatible: yes Polymer compatible: anionic ok, cationic should be avoided Oxidant compatible: no SDI requirement: <5, most plants run at 2-3 Similar Applications: multiple, particularly in Florida Additional Information: % rejection of monovalent ions, 99% rejection of sulfate, Osmonics Membrane Configuration: Spiral Wound Membrane Chemistry: proprietary thin film membrane. TOC removal: Acceptable ph range: 2.5 to 9.5 Acceptable feed turbidity: PAC compatible: yes Polymer compatible: anionic ok, cationic is problematic Oxidant compatible: very minimal and for short duration. Chlorine exposure needs to be limited to 1000 hours at 1 ppm Technical Memorandum No July 2001

179 SDI requirement: < 5 Similar Applications: yes Additional Information: nickel has been shown to be problematic. Peroxide is also problematic Nanofiltration Limitations The limitations of nanofiltration systems can be summarized as follows: Sensitive to high ph. Potential scaling (for softening membranes) and material hydrolysis (for cellulose acetate membranes) problems may emerge at ph above 9.0 for most NF membranes. Sensitive to oxidant. Most NF membranes are very sensitive to oxidant. In general, the residual chlorine in the NF feed stream may not exceed 0.1 ppm. Fouling by NOM. All membranes are subject to fouling by natural organic matter (NOM). Tighter membranes (NF and RO) may experience more fouling than large-pore membranes (MF and UF). Incompatibility with synthetic polymers. Synthetic polymers that are commonly used in water treatment as coagulant and filter aids tend to foul all membranes. Cationic polymers may have a higher fouling tendency than nonionic and anionic polymers since most membrane surfaces are negatively charged. Any pretreatment process (for either raw water or backwash water treatment) that utilizes polymers may not be suitable for downstream membrane processes MEMBRANE TREATMENT OPTIONS The ICR study concluded that NF membranes are capable of rejecting more than 90% of alkalinity, TDS, total harness, and sulfate. Although the removal efficiencies of Fe and Mn were not illustrated in the ICR study due to low concentrations of Fe and Mn in the filter effluent, those NF membranes are expected to achieve more than 90% rejection of Fe and Mn based on the specification provided by the vendors (95% mineral rejection). Polyphosphate that is currently used for scaling prevention can also be used with NF processes to prevent the fouling caused by Fe and Mn. Although the advanced NF treatment can provide pristine finished water quality, it comes with high capital and O&M costs. Therefore, putting NF s strength at the most challenging situation (for other treatment processes) and avoiding high fouling scenario would be the key to the process design. Three different NF implementation options are presented in the following section and their comparisons will also be provided. Technical Memorandum No July 2001

180 Option 1 - Polishing Treatment: Treat current blend-water filter effluent Process Description Under this option, NF membranes would be used as the downstream polishing step for existing treatment processes (Figure 5-1). This is the base scenario among the three options that are presented here. Groundwater Big Sioux Chloramines Existing Treatment Facility NF Figure 5-1. Option 1 Polishing Treatment Schematic Advantages The treatability of this option has been fully explored in the ICR study. The concentrations of targeted constituents are lower and therefore the overall recovery ratio (productivity) can be maximized. Current piping and treatment systems can be retained. The disturbance to the daily production during NF implementation will be minimum. TOC level in the finished water will be minimum. NF protects the entire finished water from all waterborne pathogens outbreaks. Therefore, NF can serve as the primary disinfection process and chloramines can be used as the secondary disinfection. Additional disinfection for Cryptosporidium and Giardia (such as UV) may not be needed Disadvantages The required NF capacity will be maximum. This option does not provide additional overall treatment capacity. In fact, the finished water quality will be reduced due to the low recovery ratio of NF process (30-90%). Unfortunately, at summer time when the water demand is high, the water quality is the worst and therefore the recovery ratio must be reduced to as low as 30-70%. In order to compensate the lost of productivity, multiple-stage NF must be used. Also, additional CIP must be done for future expansion since this treatment option does not address this issue. The ph of the softening effluent is around 9.0, which is a potential threat to NF membranes. High ph value also possess higher scaling tendency and therefore adjusting ph down to around 7.3 will be required. Residual oxidants from taste and odor (T&O) control and Fe & Mn oxidation must be reduced prior to NF process. Technical Memorandum No July 2001

181 Option 2 - Split treatment: NF for Groundwater only Process Description In this treatment configuration, NF membranes will be used for treatment of a portion of the groundwater only (Figure 5-2). It is expected the hardness, sulfate, iron, manganese, and arsenic in the groundwater supplies can be effectively removed. The existing softening and filtration facility will be used for separate ground water and surface water treatment. Groundwater treatment will continue as under the existing softening process. The surface water treatment will be similar to the existing treatment, except the softening process can be replaced with enhanced coagulation for optimal TOC removal and T&O control. The treated surface water and treated groundwater will be merged, chlorine will be added for primary disinfection, and ammonia will be added to form chloramines for the distribution system residual. If enhanced coagulation option is used for surface water treatment, the hardness in the surface water will not be reduced. However, after blending with groundwater, the final hardness is estimated to be around the level of the existing finished water. Big Sioux Groundwater Existing Treatment Facility (Enhanced Coagulation & Filtration) Existing Treatment Facility (Lime Softening) NF Chlorine/ Chloramines Figure 5-2. Option 2 Split Treatment Schematic Advantages The required NF capacity will be minimum. NF membranes will not be threatened by high TOC scenario. The ph of the ground water is low enough so that ph adjustment for NF protection is not required. This option utilizes conventional processes for TOC removal. With appropriate coagulant and PAC dosages, TOC removal and T&O control can be maximized at higher TOC concentration (without dilution) and lower ph. No need for further filter expansion (NF system serves as plant expansion). Residual oxidants from the surface water treatment process need not be reduced Disadvantages Additional pipelines need to be constructed for separate treatment trains. Conventional treatment processes for surface water treatment do not provide additional Cryptosporidium removal credit that may be needed if the watershed is Technical Memorandum No July 2001

182 vulnerable to Cryptosporidium intrusion. UV disinfection may be needed for this reason. TOC in the finished water may not be as low as that can be achieved in Option 1. Pretreatment required prior to NF system Option 3 - Joint Treatment Process Description Under this option, the existing treatment facility will treat surface water only using enhanced coagulation for optimal TOC removal and T&M control. Treated surface water will merge with the raw groundwater supply and then be treated by NF (Figure 5-3). Big Sioux Groundwater Existing Treatment Facility (Enhanced Coagulation & Filtration) NF Figure 5-3. Option 3 Joint Treatment Schematic Chloramines Advantages NF membranes will not be threatened by high TOC scenario. This option utilizes conventional processes for TOC removal. With appropriate coagulant and PAC dosages, TOC removal and T&O control can be maximized at higher TOC concentration (without dilution) and lower ph. No need for further filter expansion. NF will protect all finished water from pathogen breakout. NF will soften all of the waters. TOC level in the finished water will be minimum Disadvantages Additional pipelines need to be constructed for separate treatment trains. Required NF capacity will be maximum. Residual oxidants from T&O control and Fe & Mn oxidation must be reduced prior to NF process. Pretreatment of groundwater required prior to NF system ESTIMATED COSTS Both Option 1 and Option 3 require the NF system to be sized with a capacity to treat the entire plant flow. Although this would provide the highest quality water, this level of treatment is not Technical Memorandum No July 2001

183 required, and the capital cost (as well as annual operation and maintenance costs) associated with a NF system of this size is not warranted. Therefore, estimated costs were generated for Option 2 only Nanofiltration System Quotations for NF equipment were solicited from three manufacturers: Hydranautics, Osmonics, and Koch. Based upon budgetary quotations received, capital costs and annual operation and maintenance costs are summarized in Table 5-1 and 5-2, respectively. The NF systems are based on a treated water capacity of 10 MGD. A water recovery of 75 % was assumed for the membrane equipment sizing such that the total influent water to the system is 13.3 MGD (3.3 MGD waste stream). Table 5-1. Opinion of Probable Capital Cost for Nanofiltration System Pretreatment Option Estimated Cost Membrane Equipment $4,250,000 Construction/Installation $10,000,000 Subtotal $14,250,000 Contingency (20%) $2,850,000 Total Estimated Construction Cost $17,100,000 Engineering/Legal/Administrative (15%) $2,565,000 Total Estimated Capital Cost $19,665,000 Table 5-2. Opinion of Probable Operation and Maintenance Costs for Nanofiltration System Cost Item Annual Cost Present Worth (1) Membrane Replacement $180,000 $2,065,000 Power $684,000 $7,845,000 Pre/Post-treatment Chemicals $485,000 $5,563,000 Membrane Cleaning $72,000 $826,000 Labor $480,000 $5,506,000 Maintenance $214,000 $2,455,000 Waste Disposal Cost at WWTP $700,000 $8,029,000 Total Annual Cost $2,815,000 Net Present Worth $32,289, Present worth based on a 6% discount rate and a period of 20 years Pretreatment Issues The NF process requires turbidities of typically less than one NTU and silt density index (SDI) of less than three. Groundwater sources typically meet these requirements with little or no pretreatment upstream of the NF system. The Sioux Falls raw groundwater quality is relatively poor and characterized by turbidity levels that are unusually high for a groundwater. These Technical Memorandum No July 2001

184 turbidity levels are possibly caused by oxidation of dissolved iron and manganese. The removal of these particles using a pretreatment system will be required to prevent fouling of the membranes and ensure reliable operation. Potential pretreatment options for iron and manganese removal are as follows: Oxidation followed by filtration (media filtration or MF/UF) Greensand filtration Chemical co-precipitation followed by filtration Manganese is more difficult to oxidize compared to iron because of slower oxidation kinetics. Powerful oxidants such as ozone, chlorine dioxide, or permanganate can be used for this purpose. For example, permanganate oxidizes dissolved iron and manganese through the following chemical reactions: 3Fe 2+ + KMnO 4 + 7H 2 O 3Fe(OH) 3 (s) + MnO 2 (s) + K + + 5H + 3Mn KMnO 4 + 2H 2 O 5MnO 2 (s) + 2K + + 4H + The stoichiometry of these equations are such that 0.94 mg of KMnO 4 is required to oxidize 1 mg of Fe 2+ and 1.92 mg of KMnO 4 is required to oxidize 1 mg of Mn 2+. The resulting precipitate is subsequently removed by either settling or filtration. Similarly, ozone and chlorine dioxide oxidize soluble iron and manganese to insoluble trivalent ferric hydroxide and manganic dioxide, respectively. Estimated capital costs and operation and maintenance costs for the various pretreatment options are shown in Table 5-3 and 5-4, respectively. Table 5-3. Opinion of Probable Capital Cost for NF Pretreatment Systems Pretreatment Option Total Estimated Total Estimated Construction Cost Capital Cost Ozone + Gravity Filtration $4,050,000 $4,658,000 Permanganate + Gravity Filtration $923,000 $1,062,000 Lime Soft. + Clarif. + Gravity Filtration $2,106,000 $2,422,000 Greensand Filtration $2,430,000 $2,795,000 MF/UF Filtration $7,452,000 $8,570, Total capital cost includes 15% for engineering, legal, and administrative costs. Technical Memorandum No July 2001

185 Table 5-4. Opinion of Probable Operation and Maintenance Costs for NF Pretreatment System Pretreatment Option Total Annual Cost Net Present Worth (1) Ozone + Gravity Filtration $315,000 $3,613,000 Permanganate + Gravity Filtration $360,000 $4,129,000 Lime Soft. + Clarif. + Gravity Filtration $480,000 $5,506,000 Greensand Filtration $290,000 $3,326,000 MF/UF Filtration $1,450,000 $16,631, Present worth based on a 6% discount rate and a period of 20 years RECOMMENDATIONS The use of NF at the Sioux Falls WPP has the potential to provide improved finished water quality and aid in compliance with the anticipated requirements of the LT2ESWTR and Stage 2 D/DBP Rule. The capital costs as well as operation and maintenance costs associated with NF are high when compared to the costs associated with conventional treatment processes. As discussed, the implementation of a NF system sized for the entire treatment process flow was not considered because of the high costs associated with such a system. Instead, a NF sized as a plant expansion to meet increased water demands was considered. The process flow under this option would allow for separate surface water treatment by a portion of the existing treatment plant to maximize TOC removal. By providing additional organics reduction, this alternative could potentially reduce DBP formation. Since the NF system is not used on the entire process flow, no additional Cryptosporidium removal benefit would be realized. The implementation of a NF system as discussed under Option 2 is not recommended. The potential benefit of reduced DBP formation does not justify the high costs associated with this system. In addition to the high costs, other disadvantages of a NF system for this application include: NF system would require operators to become familiar with a different system operation from existing treatment process. Large amounts of waste are produced that would have to be wasted to the City s WWTP, reducing the efficient use of the water resources available to Sioux Falls. No additional Cryptosporidium protection would be provided. 5.4 UV PRIMARY DISINFECTION EVALUATION The use of UV disinfection at the Sioux Falls WPP would aid in compliance with the LT2ESWTR by providing protection against Cryptosporidium and the Stage 2 D/DBP Rule by indirectly reducing DBP formation if the use of chlorine for disinfection is reduced or eliminated. A discussion of UV disinfection and its application at the Sioux Falls WPP to meet future regulatory requirements is included in the following sections. Technical Memorandum No July 2001

186 5.4.1 CURRENT REGULATORY STATUS Ultraviolet disinfection was not addressed in the Surface Water Treatment Rule, Interim Enhanced Surface Water Treatment Rule, or the Stage 1 Disinfection/Disinfectant Byproduct Rule, although some discussion was included in the guidance documents. The proposed Ground Water Rule recognizes that 4-log inactivation of viruses can be achieved using UV disinfection, but States will have to determine the UV dose necessary. The LT2ESWTR is expected to provide further protection from Cryptosporidium by requiring source water monitoring for the pathogen and placing additional treatment requirements on systems that detect set concentrations. If a set concentration of Cryptosporidium is detected in a system s source water, the system will be required to implement one of several treatment alternatives that may include chlorine dioxide, ozone, membranes, bag/cartridge filters, or inbank filtration. For the LT2ESWTR and Stage 2 D/DBP Rule, EPA has formed a UV technical workgroup to evaluate UV disinfection as a possible treatment alternative to meet the rules objectives. The significant issues being evaluated by the workgroup and current stance are as follows: Efficacy of inactivation UV is effective against bacteria, viruses, Giardia, and Cryptosporidium. Current use in potable water treatment Currently, there is substantial use in drinking water treatment, although there is low usage in large plants. Applicability to different types of water treatment systems UV is applicable to most water treatment systems but is questionable for unfiltered systems and very large plants. Performance and reliability of critical components of UV equipment A German certification program for UV indicates that well performing UV systems are available. Feasibility for a major technology shift to UV in the water industry There are logistical limitations for a rapid technology shift to UV for the water industry. Risk of mercury contamination from lamps The risk of mercury contamination from lamps is low and manageable with standard operating procedures. Based upon the evaluation of the workgroup, the projected outcome for UV disinfection in the LT2ESWTR and Stage 2 D/DBP Rule is as follows: UV disinfection will be recognized for inactivation of viruses, Giardia, and Cryptosporidium UV dose tables will be provided for regulated pathogens. EPA still needs to define dose, safety factors, dose-determining virus, and application to unfiltered systems. The rule would require the following: - Equipment verification using State approved protocol (inactivation of test organism under worst case condition) Technical Memorandum No July 2001

187 - Continuous monitoring of UV intensity and flow rate - Low dose alarm with redundant components or automatic shutdown - Regular calibration of sensors Guidance will be provided on - Verification protocol - Application, operation, and maintenance BACKGROUND DATA Background/Definitions Ultraviolet light can be defined as electromagnetic waves between 100 and 400 nanometers in wavelength. The optimal germicidal effects occur approximately in the UV-C range, which is from approximately 200 to 280 nanometers. The maximum disinfection efficiency is at a wavelength of approximately 262 nanometers. Figure 5-4 illustrates the relative efficiency of cell inactivation at varying wavelengths. Figure 5-4. Cell Inactivation Effectiveness 262 nm (Maximum Disinfection Efficiency) E f f i c i e n c y Spectral Curve of Cell Inactivation DNA Absorption Curve Protein Absorption Curve Wavelength (nm) Technical Memorandum No July 2001

188 For the purpose of this study, the following definitions will apply: Irradiance or Intensity total radiant power of all germicidal wavelengths passing from all incident directions onto an infinitesimally small area. (expressed as milliwatts per square centimeter - mw/cm 2 ) Dose = Intensity x Time (expressed as milliwatts seconds per square centimeter - mws/cm 2 or millijoules per square centimeter mj/cm 2 ) Effectiveness Early research with UV disinfection measured the viability ( dead or alive ) of microorganisms after exposure to UV light. The results indicated that very high dosages are necessary to kill Cryptosporidium and Giardia (greater than 8000 mj/cm 2 required for Cryptosporidium inactivation). More recent research has focused on the infectivity of pathogens (in mice and gerbils) after exposure to UV light. The results indicate that low dosages are effective in inactivating microorganisms. The mode of operation for inactivation at the lower dosages is absorbance of UV light by microorganisms DNA or RNA, which causes deleterious changes to the DNA or RNA. These changes prevent microorganisms from replicating. Since the pathogens cannot replicate, they cannot infect and ultimately die. Each individual pathogen has a certain level of resistance to UV disinfection. Viruses demonstrate the greatest resistance, bacteria show a lower resistance, and protozoa demonstrate the least resistance. Table 5-5 summarizes the average UV dose required to inactivate different pathogens based upon the available research. Table 5-5. UV Dose Required to Inactivate Pathogens Average UV Dose (mj/cm 2 ) Required to Pathogen Inactivate 1 log 2 log 3 log 4 log Cryptosporidium parvum Giardia lamblia cysts NA <5 <10 <10 Giardia muris cysts NA NA Vibrio cholerae Shigella dysenteriae Escherichia coli Salmonella typhi Shigella sonnei Salmonella enteritidis Hepatitis A virus Poliovirus Type Coxsackie B5 virus Rotavirus SA NA data not available Based on information provided by Trojan Technologies, Inc. Technical Memorandum No July 2001

189 Advantages/Disadvantages The advantages and disadvantages of implementing UV light disinfection as the primary disinfectant are summarized as follows: Advantages: Effective against bacteria, viruses, and protozoan pathogens (2 to 5-log inactivation of virus, protozoa, and bacteria at relatively low doses) No known disinfection byproducts formed Does not increase DBP formation Ease of operation and maintenance Small footprint Cost effective alternative to membranes and ozone Disadvantages: No disinfectant residual for distribution system Difficult to monitor on-line Risk of mercury contamination from lamps Design Considerations Design considerations for the implementation of UV disinfection can be generally grouped into two categories: equipment specific factors and site-specific factors Equipment Specific Factors Mercury lamps are currently the only commercially available type of UV lamp for drinking water disinfection. These lamps produce UV radiation from electron flow through ionized mercury vapor. In addition to mercury lamps, several emerging technologies including pulsed Xenon flash tubes and narrow-band Excimer are in development. These technologies are still in the research stage and are not currently commercially available. Mercury UV lamps can be classified by pressure and intensity as follows: Low Pressure, Low Intensity Low Pressure, High Intensity Medium Pressure, High Intensity Low-pressure, low-intensity and low-pressure, high intensity lamps emit an essentially monochromatic UV light with the majority of the light at nm and are more efficient than medium pressure lamps, which emit a polychromatic UV light with peak wavelengths at 265, 254, and 248 nm. The intensity of low-pressure lamps is lower than the intensity of mediumpressure lamps, requiring an increased number of lamps to produce the same total output intensity. Table 5-6 summarizes some the characteristics of each type of mercury UV lamp. Technical Memorandum No July 2001

190 Table 5-6. Mercury UV Lamp Characteristics Parameter Low-Pressure Low-Pressure Medium-Pressure Low-Intensity High-Intensity High-Intensity Mercury Vapor Pressure (torr) 10-3 to to to 10 3 Operating Temperature ( o C) 40 to to to 900 UV Light Spectrum Monochromatic Monochromatic Polychromatic Power Consumption (W) to 1,600 2,000 to 5,000 UV Output Efficiency 35% to 40% 35% to 40% 15% to 25% Lamp Output Constant Adjustable Adjustable Cleaning Manual Automatic Automatic A number of additional UV lamp factors must be considered for the design and implementation of a UV system: Lamp aging: The output intensity of UV lamps decreases as the lamps age. A number of factors will impact the rate and extent of reduction in intensity due to aging including amount of operation, on and off cycling, and lamp output adjustment. Proper UV system design must take into account this lamp age reduction in intensity. Lamp life: UV lamps have a life and must be replaced periodically. Lamp life for low-pressure systems (8,000 to 14,000 hours) is typically greater than the lamp life for medium-pressure systems (5,000 to 9,000 hours). Fouling: In addition to lamp aging, accumulation of solids on the sleeves of UV lamps will reduce the output intensity of the UV system. Water quality components such as hardness and iron can lead to fouling of the sleeves and reduce the disinfection effectiveness of the system. Cleaning: Manual or automatic wiping with or without food-grade chemical assistance is required to remove solids that have accumulated on the surface of UV sleeves. Redundancy: UV systems must be designed with a redundant number of lamps to ensure that the required disinfection capability is present at times of maintenance or lamp replacement. UV disinfection systems are available in either open-channel or closed conduit configurations with lamps either horizontal or vertical and either parallel or perpendicular to the direction of flow. More important is the reactor hydraulics. The ideal hydraulics for a UV disinfection system is plug flow with some turbulence between the lamps to provide radial mixing of flow. This will prevent any dead spaces and ensure that flow is uniformly distributed through the varying regions of UV intensity throughout the UV reactor. Verification of UV intensity is provided by sensors for online monitoring of a UV system. Typically, online radiometers with sensitivity for a wavelength of 254 nm are used. The sensors are subject to fouling, requiring automatic cleaning systems in applications with high fouling Technical Memorandum No July 2001

191 water. In addition, the currently available sensors are relatively inconsistent and require frequent calibration Site-Specific Factors Water quality is an important aspect to be considered for the design and implementation of UV disinfection. The ability of UV light to disinfect is dependent upon the ability of the light to be absorbed by microorganisms. Any water quality parameters that may scatter or absorb light may shield microorganisms from UV radiation and will impact the disinfection effectiveness of UV light. These parameters include particles, turbidity, natural organic matter, phenols, iron, sulfites, and nitrites. By either absorbing or scattering UV light, each of these parameters affects the UV transmittance of a water. Conversely, chemical water quality parameters such as ph, alkalinity, and temperature do not appear to have a direct impact on the effectiveness of UV disinfection. Hardness, though, can lead to UV lamp sleeve fouling, reducing the effective UV output. The hydraulics of an application are an additional site-specific design consideration. The flow rate will determine the number of lamps and reactors required. In addition, headloss through the UV system must also be accounted for in the design APPLICABILITY TO SIOUX FALLS WPP The design of a UV disinfection system for the Sioux Falls WPP will be based on a low-pressure, high-intensity or medium-pressure, high-intensity type UV system. A low-pressure, lowintensity UV system will not be considered as the lamp requirements for this type of system sized for the Sioux Falls water demand would be extremely high, resulting in high capital costs. The design will be based on closed-conduit type reactors located in a valve vault adjacent to the existing below ground clearwell (Figure 5-5). A number of factors for the design and implementation of UV disinfection at the Sioux Falls WPP may be defined by EPA in the future including: UV Dose and Safety Factor: The dose required to provide a certain log inactivation of each target pathogen will be defined in guidance documents to the LT2ESWTR. A safety factor is expected to be applied to the average dosage found to inactivate each microorganism based upon existing research. The dose required will determine the sizing of the UV system. Redundancy: Redundant lamps or reactors may be required by EPA to ensure that uninterrupted disinfection is provided. Requirements may range from a maximum of 100% redundancy to a minimum of the plant capacity plus one unit out of service. If this parameter is not defined by EPA, redundancy should be provided to the extent that the City of Sioux Falls is comfortable that a reliable disinfection system is provided to protect the public health. Lamp Age Reduction: The reduction in UV output intensity due to lamp age must be factored into the design of a UV system. This reduction may vary among equipment suppliers and may not be defined by EPA. Technical Memorandum No July 2001

192 Fouling Reduction: The reduction in UV output intensity due to fouling of the lamp sleeves must also be a consideration for the design of a UV system. This reduction is specific to the water quality of each application. In addition, the use of automatic cleaning systems will lessen or prevent the effect. The finished water quality of the Sioux Falls WPP has high hardness that could potentially result in fouling problems. The design of the UV system should include an automatic wiping system with a food grade chemical cleaner DISINFECTANT ALTERNATIVES Several disinfectant alternatives identified for implementation at the Sioux Falls WPP are presented in the following sections Option 1 Chlorine/Chloramines This option represents the condition of continuing the current disinfection practice and not implementing UV disinfection. Chlorine would continue to be used as the primary disinfectant with chloramines used for the distribution system residual. This option will require that additional clearwell capacity be provided at the WPP to provide sufficient contact time at future flow demands as discussed in TM No. 2. Continuing the use of chlorine as a primary disinfectant may pose problems with complying with the Stage 2 D/DBP Rule or future D/DBP rules if no additional form of DBP precursor removal reduction is implemented (i.e. highpressure membranes). Another regulatory aspect to be considered is the LT2ESWTR. This rule is expected to require raw water Cryptosporidium monitoring, and, depending upon results, additional treatment may be required in the form of one of the following: ozone, chlorine dioxide, UV, membranes, bag/cartridge filters, or in-bank filtration. UV disinfection may be the most attractive option Option 2 UV/Chloramines Under this option, UV disinfection would be implemented as the primary disinfectant for inactivation of all pathogens. Chloramines would be used to provide a distribution system residual. As a result of the elimination of chlorine as the primary disinfectant under this option, the additional clearwell capacity needed for disinfection contact time under Option 1 will not be required. In addition, the elimination of chlorine as a primary disinfectant will provide the best protection against DBP formation (although some DBP formation will result from chloramination) Option 3 UV/Chlorine/Chloramines Under this option, UV disinfection would be implemented for inactivation of Giardia and Cryptosporidium, chlorine would be used for viral inactivation, and chloramines would be used to maintain the distribution system residual. The UV dose required for each pathogen needs to be set by the EPA after the LT2ESWTR is promulgated. The dose required for protozoan inactivation will possibly be less than the dose required for viral inactivation. Using a reduced dose for protozoan inactivation only may be a cost effective alternative to Option 2. The CT requirements for viral inactivation using chlorine are much lower than those required for Giardia. The additional clearwell capacity of Option 1 will not be required as a result of the reduced CT requirements. In addition, the potential for DBP formation will be reduced as Technical Memorandum No July 2001

193 compared to Option 1, although greater than the potential in Option 2. The use of UV and chlorine will provide a beneficial synergistic effect for disinfection that is not available under the two previous options Option 4 UV/Chloramines/Chloramines The option of implementing UV for Cryptosporidium and Giardia inactivation and chloramines for viral inactivation was also considered. This option is not feasible as the CT requirements for viral inactivation using chloramines are substantially higher than the CT requirements of chlorine ORGANIC OXIDATION Hydrogen peroxide used in conjunction with UV light has been shown to provide TOC reduction. Hydroxyl radicals, which are formed by the activation of hydrogen peroxide by UV light, are highly reactive and quickly oxidize organics. Reduction in TOC by this method would help reduce DBP formation by subsequent chlorination or chloramination. Typically, this method of organic oxidation is used for hazardous waste remediation where the water being treated is typically of higher organic concentration and lower quantity. The UV dose required for the activation of hydrogen peroxide to form hydroxyl radicals is considerably higher than the dosages required to inactivate microorganisms (greater than 1000 mj/cm 2 ). The additional equipment and power requirements for organic oxidation greatly exceed the organic removal benefits. Therefore, this type of treatment is not recommended UV DISINFECTION PILOTING Piloting of UV disinfection equipment will help to investigate and determine the feasibility of using UV light for disinfection at the Sioux Falls WPP. Two areas can be investigated through piloting, including the ability to meet regulatory requirements and operation and maintenance requirements and considerations. From a regulatory standpoint, piloting may be required under the LT2ESWTR to obtain credit for pathogen inactivation. The requirements for equipment verification are not clear at this point, though. Therefore, it may be premature to perform UV piloting to determine disinfection efficacy at the Sioux Falls WPP. Finished water quality from the plant is high in hardness, and scaling of the UV quartz sleeves will most likely occur. Piloting will allow for the determination of the effectiveness of a cleaning system to minimize scaling; however, piloting units with mechanical cleaning capability may not be readily available for testing at this time. Piloting will also provide Sioux Falls personnel the opportunity to operate and maintain a UV system and become familiar with the system and equipment. Operation and maintenance requirements for full-scale installation of UV disinfection can be generated during the piloting period. Technical Memorandum No July 2001

194 Based upon input from UV disinfection system manufacturers, a piloting period of approximately three months is recommended to obtain sufficient data on the operation of the system at the Sioux Falls WPP. Costs associated with the piloting study would consist of costs charged by the equipment manufacturer, testing costs, and costs incurred by Sioux Falls during the piloting period such as personnel labor. A total cost of anywhere from $25,000 to $100,000 is anticipated, depending on the complexity of the study. Piloting of UV disinfection equipment at the Sioux Falls WPP may be premature at this time. If UV disinfection will not be implemented at the plant for several years, piloting is not recommended at this time. The timing of UV piloting is recommended to be delayed until the requirements of equipment verification for UV disinfection allowance are developed. In addition, the delay will allow for Sioux Falls to take advantage of any improvements that are made on UV lamp and reactor design ESTIMATED COSTS Detailed estimates of capital and operating costs for a UV disinfection system for the Sioux Falls WPP are included in Table 5-7 and 5-8, respectively. The cost estimates are based on a UV dose of 40 mj/cm 2. Table 5-7. Opinion of Probable Capital Cost for UV Disinfection System Pretreatment Option Estimated Cost UV Equipment $800,000 Sitework $30,000 UV Reactor Vault $ Housing $27,000 Piping and Valves $149,000 Electrical and Mechanical $149,000 Subtotal $1,290,000 Contingency (20%) $258,000 Total Estimated Construction Cost $1,548,000 Engineering/Legal/Administrative (15%) $232,000 Total Estimated Capital Cost $1,780,000 Technical Memorandum No July 2001

195 Table 5-8. Opinion of Probable Operation and Maintenance Costs for UV Disinfection System Cost Item Annual Cost (1) Present Worth (2) Power $13,900 $160,000 Lamp Replacement $10,100 $116,000 Ballast Replacement $1,700 $20,000 Cleaning Chemicals $600 $7,000 Labor $1,700 $20,000 Licensing Fee (3) $109,500 $806,000 Total Annual Cost $137,500 Net Present Worth $1,129, Annual cost based on an average flow of 20 MGD. 2. Present worth based on a 6% discount rate and a period of 20 years, except for licensing fee, which is assumed for a period of 10 years. 3. Calgon Carbon Corporation has obtained a process patent for the use of UV light for the disinfection of Cryptosporidium and has stated their intention to charge utilities a licensing fee of $0.015 per 1000 gallons of water treated. It is possible that this patent will be challenged by other UV system manufacturers, eliminating this cost RECOMMENDATIONS UV disinfection has been shown to be effective against bacteria, viruses, and protozoan pathogens at relatively low doses without producing any known disinfectant byproducts. In addition, it is a cost effective alternative to other treatment technologies for DBP reduction and pathogen disinfection such as ozone and high-pressure membranes. As a result, it is a very attractive application for the Sioux Falls WPP to help comply with the LT2ESWTR and Stage 2 D/DBP Rule as well as any subsequent microbial and DBP regulations. As discussed previously, a number of items need to be defined by EPA including the dose required for inactivation of individual pathogens. If selected, the design and implementation of a UV disinfection system for the Sioux Falls WPP should occur after these items have been addressed. The baffling improvements being made to the existing below ground clearwell is anticipated to provide sufficient clearwell volume for disinfection contact time for projected flows beyond year 2010 (see TM No. 2). Therefore, the additional clearwell requirements discussed in TM No. 2 will not be necessary if UV disinfection is implemented. The disinfectant alternative recommended for implementation is Option 3 using UV disinfection for Giardia and Cryptosporidium inactivation, chlorine for viral inactivation, and chloramines for distribution system residual. The advantages of this option include: Reduction in chlorine use resulting in reduction in DBP formation. No increased clearwell capacity required. Beneficial synergistic effect of UV disinfection and chlorine. Potentially lower UV dose required (when compared with UV dose for viral inactivation). Technical Memorandum No July 2001

196 5.5 GRANULAR ACTIVATED CARBON EVALUATION Granular activated carbon (GAC) provides removal of organics, reducing the potential for DBP formation. Its application would aid in compliance with the requirements of the Stage 2 D/DBP Rule. The use of GAC at the Sioux Falls WPP is discussed in the following sections PURPOSE The purpose of the GAC system is to adsorb and remove organic contaminants that contribute to the formation of disinfection byproducts as well as taste and odor in the finished water. The purpose of the carbon regeneration system is to recover and reuse the GAC to reduce the amount of fresh carbon that must be purchased. The carbon contactors, carbon storage tanks, carbon regeneration system, influent pumping station and carbon backwash pumps would be located in a common, concrete structure occupying about 23,600 square feet of space CARBON CONTACTORS Filtered water will be treated by GAC contained in four parallel, gravity concrete contactors, each 30 feet by 35 feet with an effective carbon depth of 10 feet. The contactors will provide 15 minutes of contact time at flows of 30 mgd. The contactors will each contain about 283,500 pounds of 12 x 40 mesh coal-based activated carbon. The filtered water will be pumped from a carbon contactor influent wet well to an inlet channel that will distribute the water to the contactors. The carbon contactor influent pumping station will have a capacity of 45 mgd so that, if necessary for short periods of time, the contactors could be operated at a higher rate than 30 mgd. During these periods, the carbon usage will be higher. Carbon-treated water is collected through a series of 8-inch diameter stainless steel vee-wire wrapped underdrain laterals, very similar to well screens in appearance. The 8-inch laterals feed into an internal header. The carbon effluent is discharged from this internal header to an external pipe header in the contactor pipe gallery and conveyed to the clearwell. The effluent flow rate will be controlled by a rate control meter and valve. Contactor operating valves will be electric actuated butterfly valves. Headloss and flow rate will be monitored for each contactor. Two contactor backwash pumps will be provided. The pumps will draw their suction from the carbon contactor influent pumping station wet well CARBON REGENERATION SYSTEM Spent carbon will be transported as a slurry to three concrete carbon storage bins, each with a capacity of 425,000 pounds of carbon. A multiple hearth furnace with a capacity of 9,000 pounds per day of carbon will be provided. This will enable a carbon usage of 300 lbs/million gallons to be regenerated at a flow of 30 mgd. It is expected that the average carbon usage rate will be somewhat less than 300 lbs/million gallons but pilot tests should be conducted to determine the usage rate if the granular carbon option is pursued. The cost estimates are based on an average usage of 300 lbs/million gallons and the treatment of 20 mgd of water for 365 days per year. The furnace will operate at temperatures of degrees F in the reactivation zones and be loaded at a rate of 40 lbs of carbon per sq. ft. per day. Steam will be added to the furnace to Technical Memorandum No July 2001

197 improve regeneration. Constant speed dewatering screws feed the carbon to the furnaces. Regenerated carbon is cooled in a quench tank and then is transported to either carbon storage or directly to a carbon contactor. It is anticipated that the furnace will be in constant operation for normal carbon exhaustion rates and a flow of 30 mgd to the carbon with the excess spent carbon being stored in the carbon storage tanks when greater than normal regeneration frequency may be required. The stored carbon will be regenerated on-site when flows drop below 30 mgd or the usage rate decreases. A carbon loss rate of 10% per regeneration cycle is assumed. The exhaust gases from the furnace will pass through an afterburner and Venturi-type wet scrubber with a second-stage tray scrubber ESTIMATED COSTS The estimated capital and operating costs are detailed in Table 5-9 and Annual operation and maintenance costs are based on the GAC system treating 20 mgd every day of the year. Table 5-9. Opinion of Probable Capital Cost for GAC System Item Estimated Cost Concrete (All structures) $3,329,000 Piping and Valves $2,736,000 GAC $1,643,000 Backwash Pumping $444,000 Influent Pump Station $222,000 Mechanical $220,000 Carbon Regeneration $2,363,000 Subtotal $10,957,000 Contingency (20%) $2,191,000 Total Estimated Construction Cost $13,148,000 Engineering/Legal/Administrative (15%) $1,972,000 Total Estimated Project Capital Cost $15,120,000 Table Opinion of Probable Operation and Maintenance Costs for GAC System Cost Item Annual Cost (1) Present Worth (2) Labor $155,800 $1,787,000 Power $43,500 $499,000 Fuel $13,100 $150,000 Makeup Carbon $229,600 $2,633,000 Maintenance Materials $27,300 $313,000 Total Annual Cost $469,300 Net Present Worth $5,382, Annual cost based on an average flow of 20 MGD. 2. Present worth based on a 6% discount rate and a period of 20 years. Technical Memorandum No July 2001

198 5.5.5 RECOMMENDATIONS The use of a GAC system at the Sioux Falls WPP is not required to meet the anticipated requirements of the Stage 2 D/DBP Rule. However, the potential exists for future DBP regulations that will impose lower levels requiring further DBP reduction. In addition, the application of a GAC system will provide additional taste and odor reduction, providing better quality finished water from an aesthetic standpoint. Again, the use of GAC for this purpose is not required from a regulatory standpoint. Although a GAC system is not currently required, the above discussion will provide information for the potential future application of GAC at the Sioux Falls WPP. Technical Memorandum No July 2001

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201 TECHNICAL MEMORANDUM NO. 6 FUTURE WATER TREATMENT PLANT EXPANSION Table of Contents Section Page 6.0 INTRODUCTION Technical Memorandum Summary Master Plan Workshops IMPROVMENTS AND FUTURE EXPANSION Clearwell Storage Capacity Below Ground Clearwell Expansion North Reservoir Piping Modifications Purpose Size and Location Other Considerations Estimated Capital Cost Filter Backwash Recycle Purpose Size and Location Other Considerations Estimated Capital Cost Chlorine Scrubber Purpose Size and Location Estimated Capital Cost Presedimentation Purpose Size and Location Estimated Capital Cost Filter Gullet Modifications Purpose Other Considerations Estimated Capital Cost Rapid Filter Expansion Purpose Size and Location Other Considerations Estimated Capital Cost Chlorine Dioxide Purpose Other Considerations Size and Location Estimated Capital Cost Influent Piping Improvements Purpose Size and Location Estimated Capital Cost...7 Technical Memorandum No. 6 -i- July 2001

202 Maintenance Building Purpose Size and Location Other Considerations Estimated Capital Cost Volt Switchgear Purpose Size and Location Estimated Capital Cost Sludge Piping Improvements Purpose Size and Location Estimated Capital Cost Sludge Thickening and Storage Purpose Size and Location Other Considerations Estimated Capital Cost UV Disinfection Purpose Size and Location Other Considerations Estimated Capital Cost Existing Upflow Basin Rehabilitation SITE CONSIDERATIONS Site Constraints Master Plan Improvements Site Improvements PRIORITY OF IMPROVEMENTS...14 Technical Memorandum No. 6 -ii- July 2001

203 List of Tables Table Page Table 6-1. Prioritization of Improvements...15 List of Figures Figure Following Page Figure 6-1. Proposed Improvements...15 Figure 6-2. Aerial of Proposed Improvements...13 Figure 6-3. Aerial of Proposed Improvements South View...13 Figure 6-4. Aerial of Proposed Improvements North View...13 Figure 6-5. Water Demand, Treatment Capacity, and Improvement Timing...14 Technical Memorandum No. 6 -iii- July 2001

204 6.0 INTRODUCTION TECHNICAL MEMORANDUM NO. 6 FUTURE WATER TREATMENT PLANT EXPANSION The various components of the Master Plan, including demands, regulatory issues, and alternative improvements have been developed in the previous Technical Memorandum. The Master Plan for the Water Purification Plant site or Campus must outline the priority, location and estimated project cost for each of these improvements. The objectives of this Technical Memorandum are as follows: Summarize Future Water Purification Plant Improvements Define Site Consideration and Constraints Outline Locations and Site Considerations for the Proposed Improvements Develop Implementation Plan to Prioritize the Improvements and Develop a Capital Improvements Plan TECHNICAL MEMORANDUM SUMMARY TM s No. 1 through 5 each address specific components of the Master Plan. The following is a summary of the content and relationship of each TM: TM No. 1: Water Demand, Water Quality and Regulations. This provides the basis for the timing of improvements as impacted by capacity or regulatory issues. TM No. 2: Possible Near-Term Improvements, including clearwell expansion, filter backwash treatment and chlorine scrubbing. These improvements were preliminarily identified as regulatory or capacity issues, which had an immediate need or benefit. TM No. 3: Facility Capacity Improvements included rapid sand filter expansion and surface water pumping station/wellfield water supply transmission main capacity. This TM lead to evaluation of additional alternatives, including presedimentation basins to enhance hydraulic loading to the filters, booster pumping stations, in lieu of pipelines, to increase water supply production, and chlorine dioxide addition to facilitate surface water treatment. TM No. 4: General Facility Upgrades to enhance reliability and operation/maintenance issues. A maintenance building, main electrical switchgear, sludge piping/pumping and sludge thickening were evaluated. These improvements do not directly impact the capacity or ability to comply with regulations, however, are integral to reliability and performance of the facilities. TM No. 5: Future Regulatory Requirements, including alternatives such as membranes. UV disinfection and granular activated carbon (GAC). Future regulations will continue to impact the water industry and advanced treatment technology are possible requirements. Technical Memorandum No July 2001

205 6.0.2 MASTER PLAN WORKSHOPS The development of these TMs was completed to summarize background conditions and preliminary evaluation of alternatives. The Master Plan process included two full-day workshops with HDR staff involved in the plan, senior water treatment specialists and numerous City personnel. The workshop objectives and dates were as follows: January 11, 2001: Review background information, water demands, key regulations and screening of alternatives. Also brainstorming of treatment concepts, additional alternatives and expansion strategies were developed. March 14, 2001: Discuss the various alternatives and outlined improvements to be incorporated into the facilities. Developed preliminary priority and staging of projects for incorporation into capital improvements program. 6.1 IMPROVMENTS AND FUTURE EXPANSION The following sections include a discussion of each of the proposed improvements for the Sioux Falls WPP. Each section will include a discussion of the improvement, its purpose, size and location, other considerations, and capital costs. Figure 6-1 illustrates the water plant site plan with proposed locations for each improvement CLEARWELL STORAGE CAPACITY BELOW GROUND CLEARWELL EXPANSION Based upon projections of future flow demand, disinfection requirements, and operational considerations, a new clearwell with a capacity of 3.0 million gallons was recommended if chlorine disinfection is continued as the primary disinfectant. However, UV disinfection has been identified as a viable alternative to chlorine disinfection and no clearwell addition will be required if UV disinfection is implemented. If a clearwell is required, the location would be immediately north of the existing Reservoir No. 2 and the estimated project cost is $2,628,000. Note that this does not include the cost to relocate the existing parking space in this area NORTH RESERVOIR PIPING MODIFICATIONS Purpose The City can achieve current regulatory requirements by modifying the existing clearwells. Modifications to the below ground clearwell to increase the baffling of the tank are currently underway. The North Reservoir should also be modified by adding a pipe from the reservoir influent across the floor to maximize the distance from the outlet. Short-circuiting and dead zones can be minimized, however, the modification is not intended to allow the North Reservoir to be used for CT purposes. Testing following the modifications could allow for some credit, but the primary purpose of the reservoir is for storage and an emergency reserve Size and Location The influent pipe installed will be 30 inches in diameter across the floor of the 5 MG reservoir with a 90 fitting to direct the flow upward. Technical Memorandum No July 2001

206 Other Considerations Installation of the pipe can be accomplished concurrently with tank structural repairs that are to be made when the North Reservoir is taken out of service. The structural tank repairs have already been scheduled Estimated Capital Cost The engineer s opinion of cost for the addition of influent pipe to Reservoir No. 1 is $30, FILTER BACKWASH RECYCLE Purpose Several alternatives were evaluated for the treatment and recycle of filter backwash water. The option selected for implementation is equalization of the backwash flow and recycle to presedimentation basins that will be installed for pretreatment of surface water. Currently, filter backwash water is not recycled due to process upsets resulting from its recycle, difficulty in treating the backwash water, and concern about returning concentrated pathogens such as Giardia and Cryptosporidium to the treatment process. As a result, the City is sending filter backwash water to the sanitary sewer. Equalization of the flow will reduce or eliminate the problems associated with hydraulic surges, and the presedimentation basins will provide removal of turbidity and pathogens. By allowing for the recycle, treatment, and use of filter backwash water, several objectives are realized including: Costs associated with the treatment of backwash water at the wastewater treatment plant are significantly reduced. Process upsets due to hydraulic and turbidity surges will be significantly reduced from backwash water equalization and treatment in the presedimentation basins. Conservation of the water resources available to Sioux Falls can be achieved by reuse of backwash water. A 3 to 5 percent reduction in raw water is projected Size and Location The backwash equalization basin will have a volume capacity of approximately 800,000 gallons and can be located directly south of the existing filter washwater basin Other Considerations Additional alternatives for treatment of backwash water are available if the presedimentation basins do not provide the level of treatment required. The treatment alternatives include membrane filtration, ballasted floc, and dissolved air floatation Estimated Capital Cost The engineer s opinion of probable capital cost for the equalization basin is $1,030,000. Technical Memorandum No July 2001

207 6.1.4 CHLORINE SCRUBBER Purpose Liquid chlorine in one-ton cylinders has been used by water utilities for decades for disinfection and oxidation of water. Chlorine in the liquid or gas form is very dangerous and must be handled with extreme care. The risk management plan for the City identifies chlorine storage as an issue for the plant and surrounding area. A dry scrubbing system is recommended for treating and neutralizing the chlorine. The dry scrubber system presents the least capital cost, requires a minimum of operation and maintenance, and does not require a building. The purpose of the chlorine scrubber is to improve safety conditions working around the chlorine system by containing and neutralizing chlorine leakage. A chlorine scrubber would ensure that the hazardous conditions created by the leak could be eliminated, and chlorine exposure risk in the entire area would be reduced Size and Location The scrubber system will be sized to neutralize 2,000 pounds of chlorine. The system could be located just south of the existing chlorine building, east of the North Reservoir, or it can be located at the west end of the chlorine building which is nearer to the chlorine tank storage area Estimated Capital Cost The Engineer s estimate of probable capital costs for the chlorine scrubbing system is $244, PRESEDIMENTATION Purpose Presedimentation basins are proposed to provide coagulation, flocculation, and sedimentation treatment to surface water upstream of the softening basins. The purpose of the basins is to provide additional turbidity removal to allow for improved and more consistent water quality to the softening basins and the filters. Presedimentation will also improve water quality by providing algae removal when growth occurs in the surface water during the summer Size and Location Two presedimentation basins are proposed to provide pretreatment of surface water. Two units would provide needed flexibility of operation and maintenance. Each basin will be sized to treat 15 million gallons per day. A ballasted floc system is recommended as this type of system has the lowest cost and the smallest footprint for presedimentation. The units will be located directly north of the existing treatment plant building Estimated Capital Cost The Engineer s estimate of probable capital cost for the presedimentation basins is $4,452,000. An additional cost estimated at $260,000 would be required to provide covers for the basins. Technical Memorandum No July 2001

208 6.1.6 FILTER GULLET MODIFICATIONS Purpose Currently, filter loading rates exceeding approximately 4 gpm/sf cause scouring of the filter media, which may result in turbidity breakthrough. Modifications to the filter gullet are proposed to dissipate energy of flow entering the gullet and prevent or reduce the media scour problem. Eliminating or reducing media scour will allow for high filter loading rates and increase the plant treatment capacity Other Considerations Reduction of media scouring is vital for increased filter loading and impacts the numbers of additional filters required to meet anticipated future flows Estimated Capital Cost The Engineer s estimate of probably capital cost for the gullet modifications is $100, RAPID FILTER EXPANSION Purpose Additional filters will be required to increase the plant treatment capacity. Three filters are proposed for the expansion to meet the projected treatment capacity requirements through Size and Location The new filters will be sized similar to the existing filters. Each filter will consist of two cells with a center influent gullet. The filter addition will be located directly west of existing filters Nos. 8, 9, and Other Considerations The number of filters required to meet projected future flows is dependent upon the achievable filter loading rate. Therefore, the maximum loading rate should be established and additional filters should be constructed as appropriate. The location of the new filters will block the current entrance to the plant parking area. The prior entrance from Minnesota Avenue will be restored with the construction of the new filters. This new access location must be coordinated with the City street requirements Estimated Capital Cost The Engineer s estimate of probable capital cost for three additional filters is $4,057,000. Technical Memorandum No July 2001

209 6.1.8 CHLORINE DIOXIDE Purpose Chlorine dioxide is proposed to be fed at the surface water intake station to provide oxidation of organics, algae removal, and taste and odor control. Treatment of the raw water with chlorine dioxide will provide improved water quality to the filters and should allow for improved filter effluent Other Considerations Following construction of the presedimentation basins, chlorine dioxide addition should be tested on the basin effluent versus a feed location at the surface water pump station. The ballasted flocculation process is reportedly very effective on algae removal, thus the addition of chlorine dioxide may be more beneficial following the physical removal of the algae Size and Location Chlorine dioxide equipment and chemicals will be installed in a new building located adjacent to the existing surface water intake pump station Estimated Capital Cost The Engineer s estimate of probable capital cost for the chlorine dioxide system is $782, INFLUENT PIPING IMPROVEMENTS Purpose Limitations in the existing influent piping system to the Sioux Falls WPP reduce the capacity of the well system. Two booster pump stations and a relief line (West Main Line) for the existing 24-inch west transmission main were evaluated to reduce the effect of the piping limitation of the system. The Hwy 38A booster pump station will increase the output of the northern wells, while the Airport booster pump station will increase the airport well production. The West Main Relief (minimum size of 30 inches) would be constructed from the surface water pumping station tie-in location to the WPP. The line provides a substantial increase in transmission main capacity and allows for convenient separation of surface water and well water flows over a wide range of pumping conditions Size and Location Each booster pump station will require a footprint of approximately 30 feet by 40 feet. The Airport booster pump station (about 20 MGD at up to 40 feet TDH) is proposed to be located at the water treatment plant site adjacent to the filter washwater basin. The Hwy 38A booster pump station (about 40 MGD at up to 70 feet TDH) will be located near the diversion structure and Minnesota Avenue, adjacent to the existing 24-inch and 36-inch well lines. The West Main Relief provides separation of surface water and groundwater flows. The modeling used the parallel 24-inch line to transport the flows. The route for the pipeline could be just on the west side of Minnesota Avenue, however, congestion in the airport area make portions of the route difficult and expensive. An alternate route is along the east side of the diversion channel. That route requires two crossings of the diversion channel. This line could be constructed in segments Technical Memorandum No July 2001

210 from the WPP to a 30-inch cross tie line between the existing 24- and 36-inch mains located north of the airport terminal (approximately 6,000 feet). An additional segment would be from that location to the location that the surface water pumping station ties into the existing 24- and 36-inch transmission mains (approximately 3,800 feet) Estimated Capital Cost The Engineer s estimate for the probable capital cost for the Hwy 38A and Airport booster pump stations are $1,325,000 and $1,090,000, respectively. The West Main Relief (30-inch) has an estimated cost of $1,816, MAINTENANCE BUILDING Purpose The existing maintenance facilities at the Sioux Falls WPP are inadequate to meet the growing demands of the plant. A new maintenance facility will provide the area required for proper maintenance of equipment Size and Location The new maintenance facilities will be a two-story structure located on the southeast corner of the existing water treatment facility Other Considerations The location of the maintenance building will require the relocation of parking space. A possible location for additional parking is directly east of the proposed maintenance building location Estimated Capital Cost The Engineer s estimate of probable capital cost for the maintenance building is $1,858, VOLT SWITCHGEAR Purpose Although the existing switchgear is working satisfactorily from an electrical standpoint, it has several mechanical limitations. The new switchgear will replace the existing switchgear to provide operational reliability of electrical service to the plant Size and Location The new 2300-volt switchgear is proposed to be located in building approximately 18 feet by 41 feet at the southeast corner of the existing water treatment building Estimated Capital Cost The Engineer s estimate of probable capital cost for the new 2300-volt switchgear is $699,000. Technical Memorandum No July 2001

211 SLUDGE PIPING IMPROVEMENTS Purpose Improvements to the sludge piping lines are proposed to increase the sludge withdrawal and transfer capacity of the system and reduce maintenance requirements associated with plugging of lines Size and Location Piping and valves will be replaced in a number of locations to increase the capacity of the sludge withdrawal and transfer system and reduce maintenance requirements Estimated Capital Cost The Engineer s estimate of probably capital cost for the sludge piping improvements is $156, SLUDGE THICKENING AND STORAGE Purpose Sludge thickening and storage will provide flexibility in operation and maintenance of the sludge system. The ability to thicken sludge will also allow for a reduction in sludge volume to the lagoons Size and Location The sludge thickener will be approximately 60 feet in diameter with a 14-foot side water depth. The proposed location of the thickener is north of Maple Street and west of the existing railroad Other Considerations Land north of Maple Street and east of Minnesota Avenue may need to be acquired by the City to allow for the proposed location of the thickener Estimated Capital Cost The Engineer s estimate of probably capital cost for the sludge thickener is $966, UV DISINFECTION Purpose UV disinfection is proposed as an improved method of disinfection over chlorine. The use of UV radiation for disinfection will aid in compliance with the anticipated requirements of the LT2ESWTR and the Stage 2 D/DBP Rule as UV has been proven to be effective against pathogens, including Cryptosporidium, while producing no known disinfection byproducts. In addition, no additional clearwell capacity will be required with the use of UV. Technical Memorandum No July 2001

212 Size and Location The UV disinfection reactors will be installed in-line on the piping entering the below ground reservoir and will be located in a vault directly north of the reservoir. Ballast equipment for the system will be located in building above the UV reactor vault Other Considerations Piloting of UV equipment at the plant will allow for further evaluation of the feasibility of using UV disinfection from both a regulatory and operation and maintenance standpoint. The requirements for equipment verification of UV disinfection systems have not yet been developed for water treatment. Piloting is recommended to occur after these requirements have been developed (which should be within the next two years). The delay in piloting will also allow Sioux Falls to take advantage of any improvements that are made on UV lamp and reactor design. If UV disinfection is not implemented at the Sioux Falls WPP and the use of chlorine is continued as the primary disinfectant, a new 3.0 million gallon clearwell will be required. The clearwell will allow for sufficient disinfection contact time at future flows projected Estimated Capital Cost The Engineer s estimate of probably capital cost for the UV disinfection system is $1,780,000 and pilot testing is $100, EXISTING UPFLOW BASIN REHABILITATION The City has planned for the rehabilitation of two existing upflow basins. This improvement is a previously identified need and was discussed at the workshop. Although not evaluated in this Master Plan Update, the work will be included here as a future improvement for consideration in the prioritization of improvements. The estimated cost for this improvement is $1,100, SITE CONSIDERATIONS The site plan with proposed improvements is shown in Figure 6-1. The Water Purification Facilities are located at North Minnesota Avenue on approximately 10 to 15 acres of property. The property is located just east of the southern portion of the Sioux Falls Regional Airport. Most of the main treatment facilities are located in a common building which connects the solids contact basin, filters, chemical feed area, laboratory, administration area and high service pumping. Other units on the Water Plant campus include backwash reclaim basin, Reservoir No. 2, North Reservoir, Transfer Pumping Station, chlorine storage and feed area, carbon dioxide storage and standby generator SITE CONSTRAINTS The Water Facilities site is accessed from Minnesota Avenue along Maple Street. A second access from the south at Algonquin Street also exists. The site also has several rail lines, including a spur for chemical delivery. The site does have areas for expansion, however, the following constraints must be considered: Technical Memorandum No July 2001

213 Minnesota Avenue is the western boundary for the site. Primary access to the plant is from Minnesota Avenue on Maple Street. Some improvements to the facilities (filter addition) could impact access to the parking lot. The northern property line is near Maple Street. The land just north of the site is owned by the Airport. This 2 to 3-acre triangular portion of property north of the plant should be pursued for future improvements. The east portion of the site is limited by Burlington Northern Railroad Tracks. Additional track are being added parallel to existing lines for switching and rail car storage. A materials storage building shared by the Light Department and Water Department is located east of the tracks. The Light Department building offices and maintenance buildings are at the Southeast portion of the site. The area south of the Plant includes a significant area used primarily by the Light Department for material storage (power poles, etc.). Also, railroad spur lines dissect the area and extend along the west portion of the site near the aboveground North Reservoir and the underground clearwell (Reservoir No. 2). Rail cars are often parked on the spur very near the Reservoir. This is a concern due to the unknown nature of materials in rail cars and the proximity to the finished water storage MASTER PLAN IMPROVEMENTS The majority of process related improvements are located north and west of the main treatment units as shown in Figure 6-1. These locations facilitate the overall flow pattern through the facility and proximity of the proposed and existing treatment units. The following are the comments on individual unit locations: Presedimentation Basins: The proposed ballasted flocculation basin has a small area requirement and appears to fit in the area immediately north of the existing main building. The water surface elevation in these units must be higher (3 to 5 feet) than the solids contact basin to allow for series or parallel operation. Raw water connection to the 36 and 42-inch east transmission main and the 24-inch west transmission main are required. Effluent for series operation through the solids contact basin could connect into a 36-inch existing influent line, however, the bottleneck of routing all flow through the two 36-inch influent lines could be reduced by a separate connection into the 5-foot x 9- foot influent conduit. An effluent connection for parallel operation would connect into 5- foot x 5-foot effluent conduit. A 60-inch line was installed as part of the Chemical Feed Building project, which could be considered as an optimal route into the effluent conduit (installed at that time for future ozone process). A penetration between the effluent box and channel would have to be completed. An alternate location to be evaluated in Predesign for the presedimentation basin is north across Maple Street on the land currently owned by the Airport. This area does have Technical Memorandum No July 2001

214 more available space, and influent connections are in a less congested area (piping, utilities, etc.). The disadvantage is the units would be a little further from the main treatment building and the effluent piping would be further from the connections to the main building. Filter Addition: The three additional filters must be coordinated with the proposed hydraulic loading to the filters (5.5 to 6 gpm/ft 2 ). The existing loading should be improved with the inlet baffling modifications and more consistent water quality to the softening basins (eliminate spikes in surface water quality). The proposed location is just west of the existing north filters. The distance from the existing structure must be evaluated with respect to the foundation requirements to the existing and proposed structures. This location will impact the main plant access from Maple Street. The location of the filters could be impacted by the presedimentation basin. If the presedimentation basins are located on the Airport property, the new filters could be located directly north of the existing filter as extension of the existing filter complex. Backwash Equalization Basin: This basin is located near the existing reclaim basin to allow coordination with backwash drain line and existing basin. This basin could be located further west if the access road (alternate route) to the west parking is from Maple Street. UV Disinfection System: This unit is located near the north filter effluent line (between filter No. s 5 and 6). All filter effluent must be routed through the unit so the south filter effluent line must also be routed from the clearwell to the UV unit. At last one of the UV discharge lines should be routed to the far northeast corner of the clearwell to provide turnover in that baffled portion of the reservoir. A bypass line around Reservoir No. 2 to the transfer lift station and into the North Reservoir is desirable to allow the belowground reservoir to be removed from service for maintenance/cleaning. Reservoir No. 2 also has limited access hatches for maintenance purposes. The proposed location does allow for a future clearwell addition between the UV system and Reservoir No. 2. West Main Relief: The transmission line from the surface water pumping station connection to the WPP significantly increases the hydraulic capacity to the plant and allows for a major improvement in the capacity and ease of separating the surface water and groundwater. The construction of presedimentation basins will increase the need for separation of flows and allow for the increased use of surface water. The required size (in conjunction with the existing 24-inch main) is a 30-inch transmission main. The City should consider the condition of the existing 24-inch main prior to the final sizing of this main. When the line is being installed, it may be beneficial to consider a 36-inch main that would allow the 24-inch line to ultimately be abandoned. This would increase the estimated cost of this main from approximately $1,816,00 to $2,360,000. Airport Booster Pumping Station: This booster pumping station must be located on the 30-inch line from the airport wells. The location on the plant site (northwest corner) is desirable because of the proximity to the plant for purpose of operation/maintenance. Just west of Minnesota Avenue (about 80 to 100 feet), the 30-inch main divides into 3 Technical Memorandum No July 2001

215 branches (two 16-inch and one 24-inch lines), which continue west across the airport property. Hwy 38A Booster Pumping Station: This booster station must be in the vicinity of the Diversion Channel and Silver Creek just south of Highway 38A near the connection of the Surface Water Pumping Station to the 24-inch and 36-inch transmission mains. Connections (suction and discharge) to both the 24- and 36-inch lines are required for flexibility in optimizing of the use of surface water or well water. This pump station will require the addition of electric valve operators (manual controlled or automatic) which properly configure the system to direct surface water to either the 24- or 36-inch lines, as well as valves to control the routing of well water to the appropriate line. This station could be moved further south, however, during the modeling run, a boost of 50 feet ± was included at the station. The pressure at the pumping station suction must be considered in the station location, such that adequate pressure must exist at the pump suction to assure proper operation. Other considerations for the pumping station include pump type (horizontal split case), drives (VFD), or throttling valve required due to varying pressure, ground elevation, flood elevations, and airport runway approach (FAA requirements). Maintenance Building: This building is located on the southeast corner of the main plant. The proximity to plant equipment, existing line slaking area, truck access for materials delivery and pickup, and existing shop area are considerations for this location. This building location requires relocation of an electrical transformer and displaces about 15 parking spaces. Chlorine Scrubber: This unit must be placed close to the chlorine storage area due to the ductwork requirements. A location just south of the chlorine room is most appropriate. Switchgear Room: This building is located at the southeast corner of the high service pumping room. These pumps are the major electrical load on the site, and the new switchgear should be close to the existing switchgear location. Chlorine Dioxide Addition: The preliminary location for this unit is at the surface water intake pumping station. The purpose of this unit is to oxidize the organics and algae in the surface water supply. The time of this construction will follow the presedimentation basin. Therefore, the chlorine dioxide addition should be tested at both locations (intake pumping and presedimentation effluent) prior to finalization of the application location. The physical removal of substantial organics and algae prior to the C1O 2 addition could improve the effectiveness or significantly lower the dosage. Also, the availability of gaseous chlorine at the WPP site could simplify the chlorine storage/scrubbing requirements and reduce the associated capital cost. Sludge Thickener: This unit is located north across Maple Street. An 8-inch sludge line exists at the north portion of the plant and turns east across the diversion channel. Increased sludge production will allow reduction in the amount of water pumped to the sludge drying ponds along Cliff Avenue. Some recovery of water for return to the Technical Memorandum No July 2001

216 presedimentation unit does exist. This must be balanced with pressure and the ability to pump a thick lime sludge (could thicken to 30% ±) a significant distance to the lagoons SITE IMPROVEMENTS The proposed process and reliability improvements will require modification to the site. In addition, other improvements to the site are being completed or should be implemented for the long-range benefit of the Water Department. These process and site improvements are shown in Figures 6-2, 6-3, and 6-4. The following is a summary of these improvements: The Water Purification Plant is currently revising the parking and paving on the entire east of the site from the Light Department Building to the northeast corner of the treatment facilities at Benson Road. This is being completed in conjunction with rail line additions (two parallel lines) which cross the east side of the site. The area is being reworked to provide a substantial amount of angle parking along the entire east side (adjacent to tracks). Access and parking for the plant staff will be from the south, and the exit will be to Maple Street. This parking addition is intended to accommodate the spaces lost for construction of the Maintenance Building. An improved access across the existing and new railroad lines is being constructed for access on the east side of the tracks. A rail spur line currently exists from an area south of the plant to a point very near Reservoir No. 2. As previously indicated, the storage of rail cars in the area of the finished water storage is a concern and removal of about 400 feet of the track is recommended. The probable location of the filter addition will require modification to the west parking area. One alternative is relocation of the primary access off Minnesota Avenue (requires State approval). Revision to the existing route from Maple Street may be possible. The final location of the Filter Building could preclude or make this route less desirable. Parking on the west side of the plant must be able to accommodate some staff and visitors attending meetings in the conference room. The minimum number of spaces required is 45 to 50, plus the ability to accommodate larger vehicles such as buses. The parking configuration includes approximately 50 spaces as shown. The area in front (west) of the Plant includes a fountain (no longer used) and large grass/treed area. Although some new structures will be required in that area to accommodate future treatment requirements, the city would like to improve the aesthetics of the area. The Water Department is working with the South Dakota State University (SDSU) to develop long-range landscaping plans to enhance the aesthetics of the site. Boards showing some of the landscaping designs put together by the SDSU are shown in Appendix C. Diversion Channel Pumping Station No. 1 and No. 2 are located northeast of the treatment plant at the Diversion Channel. These stations have not been used since the Technical Memorandum No July 2001

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220 construction of the surface water pumping station. Ultimately, these pumping stations and associated 12-inch and 16-inch piping to the connection with the 36-inch east raw water main could be removed or abandoned. The estimated cost for parking and access improvements is $186,000. The improvements would include the removal of approximately 400 feet of rail spur, addition of a parking access road from Minnesota Avenue, and improvements to the parking lot area. The City has discussed a preliminary budget of approximately $250,000 for the long-range landscaping plan to improve the site aesthetics. 6.3 PRIORITY OF IMPROVEMENTS The timing of the improvements outlined in the Master Plan Update are impacted by regulatory issues, increasing water demands, and reliability of the existing facilities. The potential improvements were evaluated and a workshop completed to assist in defining the overall priority and need. This information was used to develop the Capital Improvements Program (CIP) from the Water Department for the next 5 years. The CIP considers the immediacy of the improvement, timing of the proposed regulations, and available funding for capital expenditures. Table 6-1 summarizes the priority and the proposed year the various improvements are incorporated into the CIP. Figure 6-5 illustrates the flow demand projected, treatment plant capacity, and timing of improvements. Technical Memorandum No July 2001

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222 Table 6-1. Prioritization of Improvements Capital Improvement Estimated Capital Cost Year 1 (2002) Presedimentation Basins $4,452,000 (1) Chlorine Scrubber $244,000 Electrical Switchgear $699,000 Filter Gullet Modifications $100,000 Reservoir No. 1 Piping Modifications $30,000 Total: $5,525, An additional cost of approximately $260,000 would be required to cover the basins. Year 2 (2003) Backwash Equalization Basin $1,030,000 Maintenance Building $1,858,000 West Main Relief $1,816,000 UV Pilot Testing $100,000 Total: $4,804,000 Year 3 (2004) UV Disinfection $1,780,000 Chlorine Dioxide $782,000 Solids Contact Basin Rehab. (2 basins) $1,100,000 Total: $3,662,000 Year 4 (2005) Sludge Piping $156,300 Sludge Thickening Basin $966,000 Hwy 38A Booster Pump Station $1,325,000 Parking and Access Site Improvements $186,000 Landscaping Site Improvements $250,000 Total: $2,883,300 Year 5 (2006) Filter Addition (3 Filters) $4,057,000 Airport Booster Pump Station $1,090,000 Total: $5,147,000 Note: All costs are April Technical Memorandum No July 2001

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