SECTION 4 DISTRIBUTION SYSTEM ANALYSIS

Transcription

1 SECTION 4 DIRIBUTION SYEM ANALYSIS 4.1 PURPOSE/SCOPE OF SYEM ANALYSIS An analysis of the water distribution system was completed to access infrastructure improvements required to construct a desalination facility in Hull. A hydraulic model of the Hull distribution system was developed to simulate hydraulic conditions in the distribution system and to evaluate infrastructure improvements for various plant capacity and site location scenarios. Earlier studies did not consider distribution system improvements in the development of cost models for a desalination facility. Distribution system improvements discussed in this section include the following: System Transmission Main Upgrades - Water main upgrades to existing distribution and transmission main piping to maintain adequate pressure and pipeline velocities within the Hull distribution system. New Raw Water Transmission Mains - Water mains required to connect the new treatment facility to the distribution system. Water Storage Tank Upgrade - Upgrades to the existing Strawberry Hill Storage Tank will be needed to provide water storage in the Hull distribution system. Booster Pump Station Requirements - Under certain flow scenarios, booster pumping stations will be required to send surplus flows outside the geographic boundary of the Town of Hull. Required distribution system improvements were evaluated for three alternate plant capacities of 2.5 MGD, 4.0 MGD, and 5.0 MGD located at each proposed plant site included in the study. The proposed locations for the desalination facility are shown in Figure 4-1 and include the following sites: 10651A 4-1 Wright-Pierce

2 MAIN HELEN CHANNEL MAIN +C HIGHLAND AVE SOUTH MAIN Dust Bowl Site OCEAN AVE HULL RD NEWTON WEERN AVE ANDREW AVE LAFAYETTE RD VAUTRINOT AVE Hull Bay CRE RD CUSHING NANTASKET AVE CROSS MT. PLEASANT BATTERY RD CHRIINE RD FARINA RD HARBOR VIEW RD SPRING Duck Lane Site DUCK LN +C MARINA DR Wanzer Trucking Site CADISH AVE H CADISH AVE M J G F CENTRAL AVE K L Q P O N GLOVER AVE S R [Ú FITZPATRIC WAY PT ALLERTON AVE WINTHROP AVE TIERNEY AVE K J G U +C T HOLBROOK AVE ANDISH AVE BRADFORD AVE Q O N M Y W V U L L K J H BEACH AVE (NOT PAVED) BEACON RD Hull Booster Pump Station Strawberry Hill Elevated Tank Overflow EL. 186 FT. (0.5 Million Gallons) SUNSET AVE MILFORD HALVORSEN AVE LYNN AVE TOURAINE AVE PACKARD AVE BROCKTON CIR VERNON AVE CENTRAL AVE E D C B A BAY AVE EA PROSPECT VETERANS AVE BROOKLINE AVE KINGSLEY RD DRAPER AVE kj Ë COBURN WEON ADAMS SAMOSET AVE WARREN WEBER F E D HADASSAH WAY MANOMET AVE BEACH AVE (PAVED) PAVED BEACH AVE C B B A A LEWIS WARREN MASSACHUSETTS BAY WBZ Tower Site NEWPORT RD WARFIELD AVE KENBERMA KENBERMA CLIFTON AVE BATES GUILD +C TENTH NINETH EIGHTH NANTASKET RD RUSSELL REVERE BELMONT NANTASKET RD WHITEHEAD AVE EDGEWATER RD SUMNER +C!"W MALTA Proposed Well Supply Nantasket Road Intersection Hull Municipal Light Site MARGINAL RD BAY MERRILL RD ROOSEVELT AVE HILLSIDE RD WATER PORRAZZO RD EAERN AVE NANTASKET AVE HULL SHORE DR Existing Parallel 20" and 12" Mains From Nantasket Rd to Town Line HAMPTON CIR MAYFLOWER RD ANDREW AVE SAKONNET DIGHTON South Shore Charter School Site ORLEANS NORTH TRURO SOUTH TRURO HARWICH FALMOUTH SALISBURY ROCKAWAY AVE GEORGE WASHINGTON BLVD WYOLA RD PARK AVE BERKELEY RD +C GOSNOLD LOGAN AVE OCEANSIDE DR ROCKAWAY AVE ATE PARK RD ATLANTIC AVE SPRING VALLEY RD SCHOOL POND MEADE AVE ELM AVE SEA VIEW AVE ONY BEACH RD GUN ROCK AVE AVALON WAY EATE DR BATH AVE DRIFT WAY ROCKLAND WORRICK RD EAMAN RD PILGRIM WAY SUMMIT AVE HINGHAM COHASSET Legend Water Structures Existing Water Mains kj +C [Ú!"W Water Tank Proposed Water Treatment Facility Site Pump Station Proposed Well Supply Location 4" and < 6" 8" 10" 12" 14" 16" 20" Source: - Base data layers were obtained from Mass GIS. - Water main data was obtained from Aquarian Water Co., MA - Water System mapping and modeling developed by Wright-Pierce. 0 2,000 4,000 Feet Turkey Hill Standpipe Hydraulic Grade Line EL. 240 FT. (2 Million Gallons) kj Existing Water Infrastructure and Proposed Water Treatment Facility Sites Hull, Massachusettes Mar AS NOTED

3 Hull Municipal Light Site WBZ Tower Site South Shore Charter School Site Wanzer Trucking Site Duck Lane Site Dust Bowl Site As mentioned earlier in the report, the 2.5 MGD plant capacity would likely only provide the water supply needs for the Town of Hull, although a portion of the plant capacity could be supplied to neighboring communities during the winter months when the estimated water demands in Hull lower than the peak demands during the summer. The 4.0 MGD and 5.0 MGD facilities would provide additional capacity for potential sale of water to surrounding communities year round as discussed in Section 1 of this report. The 4.0 MGD and 5.0 MGD facility sizes were selected due to constraints on available offshore groundwater supply and the treatment efficiency or "recovery rate" of the desalination treatment process as well as hydraulic limitations in the distribution system. The recovery rate is defined as the ratio of treated water production rate (MGD) to the raw water supply flow rate (MGD) entering the treatment process, and this concept is discussed extensively in Section 5. As discussed previously in Section 2, the hydrogeological analysis revealed that the estimated sustained water yield from angled wells constructed within the offshore sand and gravel aquifer deposits ranges up to approximately 8 MGD. Since the desalination process recovery rate is only 50%, an 8 MGD raw water supply source would be required to produce 4 MGD of treated water. For the 5.0 MGD capacity treatment facility, a 10 MGD source would be required. An ocean intake is likely if a 5.0 MGD plant is constructed. The primary 20-inch transmission main into Hull on Nantasket Avenue would require upgrading if a flow greater than 5.0 MGD is selected for the plant capacity. This system improvement was viewed as a high cost inflection point which would limit plant development A 4-3 Wright-Pierce

4 The hydraulic evaluation and analysis included the following components: Field Hydrant Flow Testing - Hydrant tests were performed at various locations in the distribution system to provide data to develop and calibrate the hydraulic model. Development of a Hydraulic Model of the Distribution System - A model of the distribution system was developed to test hydraulic behavior of the distribution system under simulated flow conditions with a new treatment facility. Evaluation of Existing Water System Pressures and Demands - The analysis included predicted available flows and pressures at critical areas of the distribution system under simulated conditions with the new treatment facility operations. Evaluation of Existing Water Main Infrastructure and Storage Tanks - The existing water mains and storage tanks were evaluated and operating performance "calibrated" to replicate actual test conditions observed during hydrant testing. Evaluation of Water Storage Requirements - The ability of the Strawberry Hill elevated tank to track and fluctuate properly within the system was also evaluated. Sizing of Raw Water Transmission Mains by Plant Capacity and Site Location - The proper sizing of a water main from the source of supply to the treatment location was evaluated. Transmission Main Improvement Recommendations by Plant Capacity and Site Location The proper sizing of mains to interconnect the new treatment facility to the distribution system was evaluated for each site under consideration. Evaluation of Booster Pump Station Requirements - The larger flow rates will require a booster pumping station at the Hull town line. Sizing of booster was evaluated as part of the study. The following discussion provides an overview of the existing infrastructure, hydraulic model development, hydraulic analysis, and specific improvement recommendations for the three plant capacities (3.0, 4.0 and 5.0 MGD) and site location scenarios (6 candidate sites). Cost estimates developed for distribution system improvements are included in the financial models discussed in Section 7 of this report for each of the site scenarios A 4-4 Wright-Pierce

5 4.2 EXIING FACILITIES Overview An overview of the existing water distribution infrastructure within the Town of Hull is illustrated in Figure 4-1. The figure presents the network of water mains color coded by pipe diameter, water storage tank locations, the Hull booster pump station, the Turkey Hill Standpipe and transmission mains that supply water to Hull from Hingham, the proposed groundwater supply well field location, and proposed sites for construction of the desalination facility. A description of each of these key facilities follows. A complete piping database of the Hull distribution system is also included in Appendix L of this report. This database was used to develop the hydraulic model and to analyze the distribution system. Water supplied to Hull is pumped from water supply sources and treatment facilities located in Hingham as part of the Hingham-Hull distribution system. The Hingham-Hull distribution system is separated into two pressure zones or service areas each operating on a separate hydraulic grade line established by a water storage tank. The Turkey Hill Standpipe establishes the hydraulic grade line (water pressure) for the Hull service area and is the primary storage facility that supplies water to the Town of Hull. The Turkey Hill Standpipe is located in the Town of Hingham. The distribution system in Hull is hydraulically connected to the Turkey Hill Standpipe and the Hingham system at Nantasket Ave. and Atlantic Ave. The Hull distribution system contains an additional 0.5 MG storage tank (Strawberry Hill Tank) and a booster pump station located on Y Street that functions to maintain minimum operating water pressure at the highest elevations on the northern end of the peninsula. The operations of these facilities are described in more detail within sections and of this report Water System Pressures and Operating Hydraulic Gradeline The Hull distribution system operates on a hydraulic grade line that ranges from El. 230 feet to El. 240 feet depending upon the operational water level in the Turkey Hill Standpipe. The 10651A 4-5 Wright-Pierce

6 Turkey Hill Standpipe is important because it balances pressure in the large distribution system and controls pressures delivered to the Strawberry Hill Tank in Hull. A conceptual hydraulic profile of the existing Hull distribution system is presented in Figure 4-2 to illustrate the concept of hydraulic grade line and water pressure, and to draw attention to the high point elevations (points of lowest pressure) in the water system. A simplified profile of the ground surface elevation extending northerly from the Turkey Hill Standpipe across the Hull peninsula shows that that ground elevation ranges from approximately sea level (El. 0 feet) to El feet on the hills and knolls. The general location of the hill areas are identified by the road name shown below each high point in the illustrated ground profile. The Turkey Hill Standpipe has a nominal volume of 2.0 million gallons (MG) with tank overflow and base elevations of El. 240 feet and El. 170 feet, respectively. The hydraulic profile shown in Figure 4-2 was calculated with the Turkey Hill Standpipe full at El. 240 feet to illustrate maximum static pressure conditions. The approximate hydraulic grade line (maximum static pressure) was calculated as the difference between the tank water elevation (El. 240 feet) and the ground surface elevation (El-feet). This elevation is shown in Figure 4-2 as pressure, in pounds per square inch (psi) at the low and high ground elevations across the peninsula. The range in calculated pressures shown in Figure 4-2 reflects variations in operating water depths in the Turkey Hill Standpipe, changes in water system demands, and friction pressure losses as water flows through water mains. In general, when customer demands increase, pressures will decrease as the hydraulic grade line is suppressed under higher demand conditions. In addition, service areas at higher elevations typically have lower pressures because in a closed water system, pressure increases with distance below the system hydraulic grade line elevation. Under static conditions, water pressure increases approximately 1 psi for every 2.31 feet of depth below the system hydraulic grade line elevation under normal water temperature ranges in distribution systems. A water system should be designed to accommodate a range of pressures within minimum and maximum guidelines. Low pressures lead to customer complaints and restrict available flows for fire fighting. Higher pressures can also lead to increased water loss by leakage from aging water 10651A 4-6 Wright-Pierce

7 mains. Standard water works practice is to maintain minimum pressures in the distribution system above psi under normal operating conditions. Pressures during fire flow conditions should be maintained above 20 psi at all locations in the system. Normal high pressures should not exceed 80 psi without pressure reduction at service connections, as required by the State of Massachusetts Plumbing Code. As shown in Figure 4-2, the maximum static operating pressure range in the system is 90 to 105 psi and the minimum static pressure operating range is 40 to 50 psi. Additional hydraulic analysis revealed that existing pressures can range as low as psi under peak hour demands at the high elevation areas near Bluff Road and Farina Road without pressure boosting equipment. As previously mentioned, the Hull booster pump station located on Y Street maintains minimum operating pressures above 35 psi in the Bluff Road and Farina Road areas under all system operating conditions. Operation of this booster pump station is discussed briefly in section The overflow and base elevations of the Strawberry Hill Tank are also shown in Figure 4-2. The overflow elevation (El. 186 feet) of the Strawberry Hill tank is approximately 54 feet lower than the Turkey Hill Standpipe (El. 240 feet). The inlet/outlet pipe connecting the Strawberry Hill Tank to the distribution system contains an altitude valve that is hydraulically closed when the tank is full to prevent the tank from continuously overflowing under system pressures. The operation of this facility is discussed in more detail below in section This type of tank configuration is poorly conceived and does not operate properly. Multiple tank systems should be designed with the same overflow elevation and should water levels should track together. The altitude valve on this tank remains closed most of the time degrading water quality in the Hull distribution system. Our analysis and improvement recommendations focus on maintaining the existing hydraulic grade line and system operating pressures in order to prevent excessive pressures at the sea level elevations, which can lead to leakage in older pipe networks, and low pressures on the hills, which can lead to reductions in fire flow, customer complaints, and problems associated with existing booster pump station operation. Our hydraulic analysis and proposed system improvements are discussed in Section 4.4 of this report A 4-7 Wright-Pierce

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9 Strawberry Hill Tank The Strawberry Hill Tank is centrally located in the Hull distribution system and connected to the 12" water main on Kingsbury Road (Figure 4-1). The elevated tank has a diameter of approximately 60 feet and a nominal capacity of 0.5 MG. The elevated tank base is located at El. 160 feet and the overflow is at El. 186 feet. As discussed previously, the tank is normally isolated from the system by an altitude valve that is hydraulically controlled to close when tank is full to prevent continuous tank overflow induced by the higher system pressures established by the higher water level elevation in the Turkey Hill Standpipe. Because the tank overflow is much lower than the hydraulic gradeline, the altitude valve remains closed most of the time. To improve water quality, the tank is periodically pumped out by operators. The Hingham-Hull Water District operates a single speed pump located in the storage building on site to pump stored water from the Strawberry Hill tank into the distribution system. The pump has a capacity of approximately 170 gpm and is controlled remotely from the Hingham Water Treatment Facility or manually at the pump. The tank is currently pumped down to the base elevation every 3 rd or 4 th day to cycle the water from tank to the system, and is refilled by water inflow under normal system operating pressures. The Strawberry Hill Tank is the primary storage which would provide fire storage within Hull if the distribution system was segregated for the remaining of the Hull-Hingham Water District distribution system Hull Booster Pump Station The Hull booster pump station is located on Y street near the intersection with Nantasket Ave. (Figure 4-1). The facility is designed to maintain minimum operating pressures at service locations on the hills at the end on the peninsula near Bluff Road and Farina Road. The booster pump station is controlled remotely from the Hingham Water Treatment Facility and operates based on measured pressure on the discharge and suction side of the pump station. Our analysis assumes that this facility will be retained and will function similarly with the proposed desalination facility A 4-9 Wright-Pierce

10 Distribution and Transmission System Piping A significant portion of the Hull distribution piping network pre-dates 1935 and several pipes have recorded years of installation as early as the 1880's when the original system was constructed. The distribution system has had a history of maintenance problems including main leaks primarily due to the system age and a deficient schedule of capital pipe improvements. A review of the distribution piping database obtained from Aquarion Water Company (former owner and operator of the HHWD system) indicates that the majority of the pipe diameters range from 2" to 8" for distribution mains and 12" - 20" for transmission mains. The pipe material is predominately unlined cast iron, but the system also includes cement-lined cast iron and ductile iron, asbestos cement, and many of the small diameter mains are galvanized. A complete database of piping materials is included in Appendix L of this report. Our hydraulic analysis and recommendations focus on upgrades to the system transmission mains to deliver flows from the proposed desalination facility. The Hull transmission system is composed of the following main segments described below and shown in Figure 4-1: Parallel 12" and 20" Water Mains on Nantasket Ave. Extending from the Hull-Hingham Town Line to the Nantasket Road Intersection A 12" main on Nantasket Ave. and Kingsbury Road from the intersection at Nantasket Road to the intersection at Veterans Ave A 12" Main on Nantasket Ave., Spring St. and Main St. from Veterans Ave. to the End of the Hull Peninsula The transmission mains were evaluated for their capacity to transmit the required flow from each proposed plant location under all three plant capacity options. A computer model of the distribution system was developed for the analysis. An overview of the model development and analysis scenarios are summarized below in Section A 4-10 Wright-Pierce

11 4.3 HYDRAULIC MODEL DEVELOPMENT Overview A computer hydraulic simulation model of the Hull water distribution system was developed for this project to analyze system hydraulics and to determine the distribution system improvements required to construct a desalination facility in Hull. The WaterCAD pipe network program was selected for use as the software modeling tool. The characteristics of the water system such as pipe sizes (diameter, length, C-value, and ground elevation at pipe intersections), hydraulic grade line elevations, pump operation characteristics, and total system demand are the primary inputs to the model. The model generates calculated pressures, hydraulic grade line elevations, and available fire flows at pipe junctions, and average velocity, flow rate, and friction head (pressure) losses within each pipe. The existing pipe network was analyzed under stressed demand conditions for each proposed plant capacity and site location scenario. This was completed by simulating the following system operating conditions with the model: Each scenario was simulated at a hydraulic grade line of El. 235 feet to simulate existing static pressure conditions in the distribution system. Scenario #1-2.5 MGD plant production rate under a maximum day demand of 2.5 MGD. The system was modeled assuming the entire 2.5 MGD supply would be delivered to customers in Hull. Scenario #2-4.0 MGD merchant plant supplying 2.5 MGD to Hull's customers and 1.5 MGD to wholesale at the Hingham town line. Scenario #3-5.0 MGD merchant plant supplying 2.5 MGD to Hull customers and 2.5 MGD to for wholesale at the Hingham town line. The above scenarios were simulated using a standard AWWA diurnal (24-hour daily cycle) water-use pattern (extended period simulation) to simulate maximum and minimum pressure 10651A 4-11 Wright-Pierce

12 conditions during peak hour demands. In addition, the model was used to analysis tank cycling and refill operations under hydraulically stressed condition for various plant operating scenarios. An 8-hour extended period simulation was used to analyze hydraulically stressed nighttime tank filling under maximum day demand conditions. The computer model was calibrated to approximate flow test results measured in the field. Once calibrated, the model was used to simulate operating pressures throughout the distribution system for the scenarios described above. Fire flow testing and model calibration is discussed in sections 4.3.4, 4.3.5, and Development of Computer Model Schematic Developing a schematic drawing of the Hull distribution system was the first step in preparing input data for the computer model. The electronic model schematic was created within the WaterCAD TM Software Program. The electronic model base data was created using electronic distribution system maps provided by Aquarion Water Company and through use of geographic information system (GIS) technology. The existing distribution pipes and tank data were extracted and prepared for model development using AutoCAD TM drafting software and ArcMap TM mapping software. The base data was then imported into WaterCAD TM to generate the model schematic. The model schematic is a representation of the piping system in which pipes are represented as lines or "links" and pipe intersections and changes in pipe diameter and material or pipe intersections are represented as "nodes". Points of water supply (i.e. pumps, storage facilities, etc.) are represented as pipes connected to only one system node. All water mains with fire flow capabilities, generally 6-inches in diameter and larger, were included in the model schematic. For a specified demand condition (average day, maximum day, peak hour, maximum day plus fire, etc.), the computer model will solve a series of mathematical algorithms to calculate the flow in each pipe and the pressure at each node A 4-12 Wright-Pierce

13 Information on pipe size, length between nodes, and C-values (roughness coefficient) were assigned to each link. Pipe sizes and lengths were obtained from existing distribution system maps. Piping materials, age of pipe, and type of pipe lining were obtained from a pipe database provided by Aquarion Water Company, which is included in Appendix. C-values initially assigned to each pipe were assumed values based on known material types and pipe ages. For example, assigned C-values for cement-lined pipes were based on typical values for new pipes, adjusted slightly lower (as required) to reflect the accumulation of deposits in the piping after years of service. The pipe C-values were adjusted up or down during the calibration process to replicate the field data obtained from fire flow testing Water Demand Apportionment Once the distribution system schematic was developed, the next step in constructing the model was to develop a method of distributing water demands to the entire service area. A demand analysis described in Section 3 of the report was used in the model to represent water-use demands. This work was completed as part of an earlier feasibility study by Woodard & Curran (2002) estimated an average day demand of 1.0 MGD and a maximum day demand of 2.5 MGD for the Town of Hull. These demands were used for our model development and hydraulic analysis. Water demands were assigned to each node throughout the system, except at pump and tank nodes which represent points of water supply and storage, based on the apportionment methodology described herein. Zoning maps were used to identify residential, commercial and industrial zoned areas within the service area and distribution system. A comparison between zoning maps and the distribution system schematic were made and demands, based on customer class (i.e. residential, commercial etc.), were allocated to nodes within each respective land use zone. To further illustrate this methodology, the commercial demand was allocated evenly across the available number of nodes present in all commercial zones in the service area. A similar procedure was followed for industrial and residential land-use zones A 4-13 Wright-Pierce

14 These larger commercial and industrial demands were not peaked for maximum-day and peak hour simulations. We choose this method for demand apportionment for the following several reasons: An even split will reflect the highest amount of demand where the distribution system is most dense. This is true of mostly residential demands. The service area is predominately residential and demand variations follow predictable water use patterns. An even split of the average day demand is the easiest to update in the future as the average day demand varies. Background demand conditions do not stress the distribution system under a fire situation, therefore to expend a lot of effort to create a weighted split of demands does not significantly add to the accuracy of the model. The even-spit demand apportionment methodology was used as a basis for calibrating the computer model. By multiplying demands at most nodes by one appropriate factor, the performance of the system was analyzed under average day, maximum day, peak hour demand, and the nighttime demand conditions Model Calibration Upon completion of the distribution model, actual system operating data obtained from the fire flow testing program was used for calibration. Calibration generally involves simulating each fire flow test on the model and making adjustments or corrections to the input data, as required so the computer system response closely approximates the pressure and flow data measured in the field. Since most physical parameters such as pipe size, pipe age, material type etc. are fixed, the roughness coefficient is the primary variable requiring adjustment during calibration. The average-day demand of 1.0 MGD (based on water use records) was used for model calibration. The accuracy of the total system demand estimate and the demand apportionment to the nodes is not critical during calibration, because demands are so widely distributed throughout 10651A 4-14 Wright-Pierce

15 the system. The demand distribution results in minimal pipe flow velocities and virtually static conditions. For this reason, the simulated fire flow, which stresses the system at a single location, tends to govern hydraulic effects. During the field testing, system boundary conditions such as the hydraulic grade line (or water level in the storage facilities) and pumping rates are monitored and recorded during the time each flow test is completed and used to calibrate the model. In general, the model calibration can be simplified if the water system pumps are turned off and the storage facilities are the only hydraulic variable to consider in the calibration process. Initially, the average day demand was run on the model to verify static pressures against those measured during the fire flow test program. This step is completed to calibrate the ground surface elevations at the test locations. Next, iterations of each fire flow measured in the field were simulated with the model and the pipe C-factors were adjusted until the model results replicated the field results Fire Flow Testing Methodology The fire flow testing program was performed for the following reasons: Provide Actual System Data to Calibrate the Computer Model Estimate Hydraulic Capacity of Existing Transmission System Provide Indication of the Relative Strengths and Weaknesses of the System Flow test locations were selected throughout the system mainly to characterize the hydraulic properties of the existing transmission system, which are the focus of required improvements for the proposed desalination facility. The remaining fire flow test locations were selected to provide data that adequately represents the entire service area in order to calibrate the hydraulic model, and to test older segments or areas of the distribution system A 4-15 Wright-Pierce

16 Once the fire flow test location was selected, a field test was performed. In general, the fire flow test procedure is conducted as follows: At each test location, two or more hydrants are used; one to monitor system pressure and the other to measure flow. The intent of the test is to stress the system to measure the drop in system pressure at a specific hydrant flow rate. The static pressure represents the system pressure at the test location prior to imposing the hydrant flow. The residual pressure is recorded while the hydrant is flowing; and represents the resulting system pressure at that measured hydrant discharge rate. If necessary, more than one hydrant is used for flow measurement to achieve a target of a 10 psi drop or more in system pressure during the test (the greater the pressure drop, the higher the level of the accuracy). The results of the test were then used to calculate the flow rate that would be available from the system at the test location while maintaining a residual system pressure of 20 psi. This is the minimum system pressure used by the ISO to calculate available fire flow at specific locations within a distribution system. The intent of sustaining this residual pressure in the system during a fire is to maintain supply to area water users, to provide adequate suction pressure for fire fighting pumping apparatus, and to insure against drawing a vacuum which could contaminate the system Field Testing Program Fire flow tests were performed by Wright-Pierce and Aquarion Water Company personnel on November 1, Several hydrants were flow tested across the Hull distribution system to obtain system data for model development and analysis. Pressure chart recorders were installed on hydrants at the Hingham-Hull town line at Atlantic Ave. and Nantasket Ave to monitor system pressure at the town boundary during the testing period. The boundary conditions that were monitored during each fire flow test included the Turkey Hill Standpipe water level, and water pressure at the Hingham-Hull town line. The Hull Booster Pump Station and Strawberry Hill Tank pump remained off line during the flow tests. The individual field test data record sheets are included in Appendix K. The results of these tests are summarized in Table A 4-16 Wright-Pierce

17 TABLE 4-1 Fire Flow Testing Data Summary Desalination Feasibility Study Hull, Massachusetts Gauge Hydrant Flow Hydrant Boundary Conditions Test No. Time Location Static (psi) Residual (psi) Location Static (psi) Adjusted Residual (psi) Pitot Reading (psi) Field Flow (gpm) Flow (gpm) at 20 psi Strawberry Hill Tank Turkey Hill Tank Hull Booster Pump Station Nantasket Chart Recorder Atlantic Chart Recorder Tank Level (ft) HGL (ft) Tank Level (ft) HGL (ft) (gpm) Static (psi) Residual (psi) Static (psi) Residual (psi) 1 8:40 PM Park Ave Avalon ,838 3,044 Offline Offline Off :05 PM Bay St. between Fairmount and Merrill Bay St. between Fairmount and Eastern ,788 Offline Offline Off :20 PM Atlantic Gun Rock Ave Atlantic Beach Rd Offline Offline Off :10 PM Atlantic Midlegde Ave Atlantic School St ,198 2,345 Offline Offline Off :00 PM Rockland House Cir :30 PM Nantasket Road near Clifton Ave Rockland House Rd. Nantasket Road near Clifton Ave ,163 2,085 Offline Offline Off Offline Offline Off :14 PM Nantasket Rd Belmont ,278 2,681 Offline Offline Off :50 PM Brockton Cir Newport ,034 1,208 Offline Offline Off :40 PM Warren Samoset Warren Manomet ,012 1,727 Offline Offline Off :15 PM E St F St ,747 Offline Offline Off :30 PM H St K St ,300 2,164 Offline Offline Off :50 PM U St Beacon St ,061 1,611 Offline Offline Off Model Development Notes: Water Demand used for Calibration MGD Turkey Hill Standpipe overflow El. 240 Feet Strawberry Hill Tank overflow El. 186 Feet

18 4.4 HYDRAULIC ANALYSIS General The purpose of the hydraulic analysis was to evaluate the distribution infrastructure improvements necessary for the Town to construct and operate a desalination facility in Hull. The magnitude of system improvements depends on the location of the desalination facility and the proposed plant capacity. The capital cost associated with the recommended distribution improvements were used to analyze the economic feasibility of constructing the desalination facility in Hull as discussed in Section Summary of Findings A summary of the results of the hydraulic analysis are briefly discussed below. The important findings of the Hull distribution system analysis include: The storage volume of the Strawberry Hill Tank is not large enough to meet the storage needs for the Town of Hull if the town chooses to operate independently from the Hingham system. The Strawberry Hill Tank is not tall enough to maintain adequate system operating pressures at the highest elevations in the system without upgrading the existing booster pump station and construction of additional booster pump stations. A new water storage tank is required to replace the Strawberry Hill Tank if the Town chooses to operate their own water system. The 12" transmission mains on Nantasket Ave., Spring St, and Main St. from the intersection of Veterans Ave. to the end of the peninsula will not provide the hydraulic capacity to transmit the proposed flow rates from a desalination facility located at the Wanzer Day Trucking Site, Duck Lane Site, or Dust Bowl Site without significant transmission main upgrades. Upgrades to existing transmission mains will not be required for a desalination facility located at the Hull Municipal Light and Power Site, WBZ Tower Site, or South Shore Charter School Site A 4-18 Wright-Pierce

19 A new transmission main extension would be required to interconnect a desalination facility located at the WBZ Tower site or Municipal Light and Power Site to the existing 20" transmission main on Nantasket Ave. at the intersection with Nantasket Road. A booster pump station located near the town line on Nantasket Ave. will be required to pump water beyond the town limits under proposed merchant plant scenarios (4.0 and 5.0 MGD). The remainder of this section includes a discussion of water storage requirements, booster pump station requirements, transmission main upgrades and new transmission mains required for each proposed plant capacity and site location Storage Analysis Storage Requirements The primary source of water storage for the Town is currently the Turkey Hill Standpipe located in Hingham. The Turkey Hill Standpipe would no longer provide system storage for Hull if the Town decides to segregate its portion of the distribution system and separate from the Hingham system. Under this scenario, the Town would either have to operate their distribution system at a lower hydraulic grade line with the Strawberry Hill Tank (El. 186 feet) or construct a new tank to replace the Strawberry Hill Tank at a higher elevation. Figure 4-3 illustrates the approximate hydraulic profile in Hull if the Strawberry Hill Tank was retained with a lowered hydraulic grade line of El. 186 feet and the system was isolated from Hingham. A comparison with Figure 4-2 shows a dramatic decrease is static pressures across the system if the hydraulic grade line were lowered from El. 240 feet to El. 186 feet. Under this operating scenario, the static pressures in the hill areas would range from approximately at the highest elevations at the end of the peninsula to psi in the State Park Road, Roosevelt Ave, and Strawberry Hill areas. Under maximum day demands, when the gradeline is suppressed, the pressures are even lower and do not meet minimum system pressure conditions. Operating at a hydraulic grade line of El. 186 feet would require constructing new booster pump 10651A 4-19 Wright-Pierce

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21 stations to serve the higher elevation areas in addition to upgrading the Hull pump station to operate under lower pressure conditions. Also, a booster pump station located at the town line would be required to pump water from the Hull to the Hingham system, which operates at a higher hydraulic grade line elevation. Also, in addition to the height limitations of the Strawberry Hill Tank, the storage volume is inadequate for the size of the Hull water system. Both of these hydraulic deficiencies combined with the poor condition of the facility indicate that a new storage tank is required if the town chooses to separate from the Hingham system and operate their own treatment plant and distribution system. In general, system storage is necessary for the following reasons: Storage should be designed to provide all demands which exceed the maximum-day average flow rate. The volume of storage which is depleted during the daytime, peak flow periods during a maximum-day demand condition is refilled during the lower demand, early morning hours. Storage is provided for fire protection. If a fire occurred during the maximum day demand, all the water used to fight the fire would be drawn from storage volume. Storage provides water during emergency situations such as power failures, transmission main breaks, etc. To provide additional volume for pumping during off-peak electrical periods. Operating storage is used for cycling pumps during normal daily operation. All storage components described above should be available while still providing at least 20 psi of pressure at the highest service area elevations under all operating conditions. This pressure is equivalent to the volume of water stored 46 feet above the highest service. This storage volume is referred to as the available or active storage A 4-21 Wright-Pierce

22 The various storage component needs for Hull to meet these various demand components is as follows: 1. Fire Protection Storage Volume - The volume which should be stored for fire protection should be capable of providing 3,500 gpm for 3 hours or 630,000 gallons. This is the Insurance Services Office (ISO) recommended maximum amount of fire protection necessary for a public water purveyor to supply. Flow requirements in excess of 3500 gpm are the responsibility of the building owner. A volume of 630,000 gallons is appropriate in the Hull service area where some commercial and industrial land-use zoning exists. 2. Equalization Storage for Peak-Hour Storage Fluctuation - The storage volume necessary to provide the system hourly fluctuation demands was estimated to be 20 percent of the maximum day total demand. Twenty percent of the maximum-day demand of 2.5 MG is 500,000 gallons. 3. Emergency Storage - Storage should be available to meet emergencies. The desalination facility, water supply wells, and booster pump station would have back-up generator power equipment; therefore, we do not recommend additional emergency storage volume. Because of the large electrical load requirements at the proposed desalination facility, a auxiliary emergency generator would be costly and impractical. We recommend that an active emergency interconnection remain with the Hull-Hingham Water District to provide emergency flows in the event of a loss of storage or supply in Hull. Three scenarios to determine the required active storage requirements for Hull are summarized in Table 4-2. A worst case scenario would dictate that for a fire on the maximum-day, the fire flow and hourly fluctuation volume of the available storage should be available simultaneously during a 3-hour sustained 3,500 gpm fire flow demand (Condition 1). A similar approach would be to provide volume for a sustained 3-hour fire flow of 3,500 gpm occurring simultaneously under a sustained maximum day demand (Condition 3). An alternate method is to provide storage volume to meet a 1-day loss of supply during an average summer day (Condition 2). For this 10651A 4-22 Wright-Pierce

23 analysis, we assumed that the average summer-day demand in Hull was approximately 1.5 MGD, which is the midpoint of the projected maximum day demand of 2.5 MGD and the annual average day demand of 1.0 MGD. The required active storage analysis indicates that the Strawberry Hill Tank does not have the storage volume required to the meet the storage design standards under all three conditions. We suggest using Condition 2 for storage tank design basis which is most conservative. We recommended constructing a new 1.5 MG elevated storage tank at the existing Strawberry Tank site. The existing tank site is recommended for two reasons: 1) the tank is centrally located in a well looped area of the distribution system which allows fire flows to be maximized across the system and 2) additional property acquisition not would be required adding additional cost to the project. The new tank would have an elevated base set at El. 170 feet and the overflow would be set at El. 240 feet, similar to the Hull-Hingham gradeline. The new tank would allow the distribution to operate on the existing hydraulic grade line, while maintaining existing minimum operating pressures on the area hills. The hydraulic profile with the proposed new tank on Strawberry Hill operating at a hydraulic grade line of 240 feet is shown in Figure 4-4. The profile shows that the static pressures across the system will remain approximately the same as currant conditions. Under this scenario, the Hull Booster Pump Station will continue to operate intermittently to maintain minimum water pressures on the hills at the northern end of the peninsula during periods of high water demand. TABLE 4-2 REQUIRED ACTIVE ORAGE VOLUMES HULL, MASSACHUSETTS Required Active Storage Requirements Storage Capacity (gal.) Condition 1 - Storage for 3-hour 3,500 gpm plus 20% Maximum-Day Demand for Peak-hour Demand Fluctuations 1,130,000 Condition 2 - Storage for Average-Summer Day Demand 1,500,000 Condition 3 - Storage for 3-hour 3,500 gpm plus Maximum-Day Demand for 3-hours 942, A 4-23 Wright-Pierce

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25 In addition, a booster pump station would be required at the town line to supply water to Hingham because as discussed in section , under proposed merchant plant demands, the pressures available at the Hull town line are not adequate to over come friction pressure loses and fill the Turkey Hill Tank without additional pumping to increase pressure. The new storage tank will require a permit from the Federal Aviation Administration (FAA). It is likely that FAA approved lighting and painting will be required given the tanks proximity to Logan International Airport. Lastly, it should be noted that the proposed storage tank at Strawberry Hill could be located at a slightly lower elevation and still meet minimum pressure requirements on the hills in Hull. We suggest retaining the El. 240 feet gradeline for several reasons: Customers are accustomed to current water pressure, which would be retained. The same gradeline allows gravity exchange of water from Hingham in an emergency situation. Higher gradeline provides better fire protection. The capital cost to construct the new tank is included in the financial analysis discussed in Section 7. The total cost includes the new tank structure, tank foundation and site work, existing tank demolition, and tank level instrumentation equipment to communicate with the desalination facility and booster pump stations New Tank Hydraulic Analysis The hydraulic model was used to simulate tank cycling and refill operations under hydraulically stressed conditions for each proposed desalination facility site and plant capacity scenario. An 8-hour extended period simulation was used to analyze hydraulically stressed nighttime tank filling (10:00 P.M. - 6:00 A.M.) under maximum day demand conditions. The analysis revealed that the tank can refill overnight under all operational scenarios. In addition, the model was used to compare existing to projected fire flows at the hydrants flow tested with the new tank at a 10651A 4-25 Wright-Pierce

26 higher elevation on Strawberry Hill. The fire flow comparisons are shown in Table 4-3. The modeled operational conditions used as a baseline for comparison include: All Booster Pumps are not Operational Tank Hydraulic Grade Line Set as El. 235 Feet Minimum System Pressure of 20 psi During Fire Flow Simulation Minimum Residual Pressure of 20 psi at Flow Hydrant During Fire Flow Simulation Maximum-day Demand Conditions in Hull (2.5 MGD) With a new storage tank at Strawberry Hill, the fire flow simulations indicate that fire flows are expected to improve throughout the system. The higher flows can be attributed to: The Higher Gradeline More Capacity for Friction Pressure Loss During a Fire Flow Merchant Plant Booster Pump Station Requirements A booster pump station would be required to pump water from Hull to Hingham or to other surrounding communities if a plant larger than 2.5 MGD was constructed. For the analysis, we assumed that water would be supplied to Hingham, which currently operates at a hydraulic line elevation ranging from El. 230 feet to El. 240 feet. The following demand scenarios were also tested with the model: Scenario #1 - Wholesale 1.5 MGD of after Outside Hull o Desalination Plant Capacity MGD o Capacity Available for Hull Customers MGD o Capacity Available for Wholesale MGD Scenario #2 - Wholesale 2.5 MGD Outside of Hull o Desalination Plant Capacity MGD o Capacity Available or Hull Customers MGD o Capacity Available for Wholesale MGD 10651A 4-26 Wright-Pierce

27 TABLE 4-3 EIMATED AVAILABLE FIRE FLOW WITH EXIING WATER MAIN INFRARUCTURE HULL, MASSACHUSETTS Flow Test Location Existing Available Fire Flow 1 (gpm) Available Fire Flow with New Elevated Tank 1 (gpm) Avalon Bay St. between Fairmount and Eastern Atlantic Beach Rd Atlantic School St Rockland House Rd Nantasket Road near Clifton Ave Belmont Newport Warren Manomet F St K St Beacon St Notes: 1 Fire flow calculation base on maintaining minimum distribution system pressure of 20 psi and reported results are rounded to the nearest 50 gpm 10651A 4-27 Wright-Pierce

28 The wholesale demand scenarios of 1.5 and 2.5 MGD were simulated with the model under a maximum-day demand of 2.5 MGD in Hull to simulate the most hydraulically stressed condition. The simulations revealed that available water pressure at the town line on Nantasket Ave. ranged from psi for a desalination facility located at the far northern end of the peninsula (Dust Bowl or Duck Lane) and psi for a desalination facility located on the southern end of the system (Hull Municipal, WBZ Tower, South Shore Charter School). In order to supply water to Hingham, the available pressure at the town line must be high enough to fill the Turkey Hill Standpipe in Hingham, which in turn would be "wheeled" to customers in Hingham or outside the Hull-Hingham Water District service territory. Approximately 110 psi of pressure is required at the Hull town line to fill the Turkey Hill Standpipe to El. 240 feet. The estimate includes 100 psi of static pressure and an additional 10 psi of friction loses within the Hingham water mains. Since this study did not include a detailed evaluation of the Hingham distribution system, booster pumping requirements and design requirements must refined if the merchant plant options are selected for further study. Therefore, with our assumptions, the booster pump station must generate approximately psi of discharge head to supply water to Hingham depending upon the location of the desalination facility in Hull. The capital cost to construct the booster pump station is included in the financial analysis discussed in Section 7. The total cost includes the booster pump station includes: Building Enclosure and Foundation Site Work Pumps and Instrumentation Generator Heating/Electrical Systems Fire Alarm/Security Systems 10651A 4-28 Wright-Pierce