WASTEWATER TREATMENT PLANT AND DALE AVENUE PUMP STATION WET WEATHER CAPACITY ANALYSIS AND ALTERNATIVES EVALUATION

Transcription

1 WASTEWATER TREATMENT PLANT AND DALE AVENUE PUMP STATION WET WEATHER CAPACITY ANALYSIS AND ALTERNATIVES EVALUATION Prepared for City of San M ateo, California July 7, 2009

2 WASTEWATER TREATMENT PLANT AND DALE AVENUE PUMP STATION WET WEATHER CAPACITY ANALYSIS AND ALTERNATIVES EVALUATION Prepared for City of San Mateo, California July 7, 2009 Project No: This is a draft and is not intended to be a final representation of the work done or recommendations made by Brown and Caldwell. It should not be relied upon; consult the final report. Peter Bellows, Engineer in Responsible Charge, P.E. C N. Civic Drive, Suite 5 Walnut Creek, CA, 94596

3 Table of Contents TABLE OF CONTENTS LIST OF FIGURES...II LIST OF TABLES...II EXECUTIVE SUMMARY...ES- Background...ES- Assessment...ES-2 Existing Facilities Evaluation...ES-2 Wet Weather Flow Projections...ES-2 Treatment Facilities, Effluent PS, and Outfall Deficiencies...ES-3 Dale Avenue Pumping Station and Force Main Deficiencies...ES-3 Recommended Wet Weather Management Program...ES-3 Wet Weather Flow Monitoring for Hillsborough and Crystal Springs...ES-3 WWTP Master Plan Update...ES-3 Hydraulic Model Update...ES-4 Collection System Rehabilitation...ES-4 Flint Pump Station Force Main...ES-4 Dale Avenue Pump Station Expansion...ES-4 South Trunk Relief Sewer...ES-5 North Trunk Relief Sewer...ES-5 WWTP Upgrades...ES-5 Wet Weather Storage Facility...ES-5 Capital Improvement Projects...ES-6 Other Recommendations...ES-8 Private Lateral Rehabilitation Program...ES-8 Collection System Rehabilitation...ES-8 Satellite Collection Systems Rehabilitation...ES-8 Satellite Collection Systems Agreements...ES-8 Screening and Grit Removal...ES-8 No Blending Conditions...ES-8 i

4 Table of Contents LIST OF FIGURES Figure - Capital Improvement Projects...ES-0 LIST OF TABLES Table - Peak Wet Weather Flow Projections...ES-2 Table 2 - Capital Improvement Project Summary...ES-6 ii

5 W A S T E W A T E R T R E A T M E N T P L A N T A N D D A L E A V E N U E P U M P S T A T I O N W E T W E A T H E R C A P A C I T Y A N A L Y S I S A N D A L T E R N A T I V E S E V A L U A T I O N E X E C U T I V E S U M M A R Y This summarizes the findings and recommendations of the Wastewater Treatment Plant and Dale Avenue Pump Station (Evaluation) for the City of San Mateo, California (City). The Evaluation is based on assessments of the hydraulic, physical condition and maintenance of the wastewater collection system, wastewater treatment plant (WWTP), and outfall and recommends improvements to provide adequate wet weather capacity and improve the reliability of the collection system and treatment plant. Supporting information for this can be found in the following draft Technical Memoranda which were prepared for this Evaluation: Task 2. Satellite Collection Systems Task 2.2 Collection System Dry Weather Performance Task 2.3 Dale Avenue Pumping Station and Force Main Condition Assessment Task 2.4 Effluent Pumping Station and Outfall Task 2.5 WWTP Process and Hydraulic Capacity Analysis Tasks 3.0 and 4.0 Options and Screening Task 5.0 Alternatives Development Task 6.0 Alternatives Analysis Task 7.0 Preferred Alternative Development Background The City s collection system, Dale Avenue Pumping Station (PS), and WWTP experience large increases in flow during wet weather. By the year 2020, the average daily flow of 4.6 mgd is projected to increase to 88 mgd under five-year design storm conditions. This increase in flow is attributable to rainfall dependant inflow/infiltration (RDI/I) of storm water into the wastewater collection system s tributary to the San Mateo WWTP. The City s collection system, Dale Avenue PS, and WWTP were not designed to handle these peak wet weather flows (PWWFs). This Evaluation recommends a wet weather flow management program, which includes RDI/I reduction through collection system rehabilitation, equalization storage, pump station and force main improvements, and wet weather flow blending. Some WWTP improvements may also be needed to handle future PWWFs. ES-

6 Assessment The wet weather assessments performed in this Evaluation are summarized in the following sections. Existing Facilities Evaluation The Existing Facilities Evaluation forms the basis for addressing wet weather flows, and consists of the following series of five TMs. Task 2.: Satellite Collection Systems Documents the review of available information and the development of wet weather flows in satellite collection systems served by the City s wastewater collection system and WWTP. Summarizes wastewater flow projections for the City of San Mateo (including Los Prados and Mariner s Island), the City of Foster City/Estero Municipal Improvement District, the Town of Hillsborough, and the Crystal Springs County Sanitation District. Task 2.2: Collection System Dry Weather Performance Correlates dry weather performance data and the occurrence of high RDI/I rates and identifies portions of the City s collection system as potential candidates for sewer rehabilitation/replacement to reduce dry weather blockages and sanitary sewer overflows (Os). Task 2.3: Dale Avenue Pumping Station and Force Main Condition Assessment Evaluates the hydraulic capacity and general condition of the Dale Avenue PS and force mains based on a site visit and the review of existing drawings and reports. Task 2.4: Effluent Pumping Station and Outfall Capacity Evaluates the hydraulic capacity and general condition of the WWTP Effluent Pumping Station and Outfall based on a site visit and the review of existing drawings and reports. Task 2.5: WWTP Process and Hydraulic Capacity Analysis Identifies the hydraulic and process capacities of the existing primary and secondary treatment facilities and identifies hydraulic bottlenecks that limit treatment and wet weather blending capacities at the WWTP. Wet Weather Flow Projections The City s hydraulic model was developed for the City-Wide Sewer System Study and is based on the six-hour duration, five-year frequency design storm. Modeling results were combined with flow projections for Mariner s Island and the City of Foster City (from TM addressing Task 2.: Satellite Collection Systems) to project flows at the Dale Avenue PS and the WWTP. The flows are summarized in Table. Collection System Table - Peak Wet Weather Flow Projections Average Day Flow Peak Wet Weather Flows (mgd) (mgd) Dale Ave. PS WWTP City of San Mateo Los Prados Mariner's Island Foster City Hillsborough, CSCSD, County Ultimate Flows Peak wet weather flows are typically based on a 5-year, 6-hour design storm. See TM 2. for further information. 2 Ultimate flows are not the sum of the collection system flows because of time lags associated with flow routing through the collection systems. ES-2

7 Treatment Facilities, Effluent PS, and Outfall Deficiencies The hydraulic capacity of the outfall is 60 mgd. This capacity cannot be readily increased because of limitations of the outfall pipeline. The best means to increase outfall capacity would be to construct another outfall. However, this is considered impractical because of cost, environmental issues, and regulatory requirements. Consequently, increasing the capacity of the effluent PS and outfall was not considered. As discussed in the TMs for Task 2.4: Effluent Pumping Station and Outfall and Task 2.5: WWTP Process and Hydraulic Capacity Analysis, the WWTP primary and secondary treatment facilities can hydraulically handle peak wet weather flows of 60 mgd, which is the design capacity of the outfall system. However, the secondary treatment facilities have a process capacity of approximately 40 mgd, which necessitates bypassing approximately 20 mgd of PWWF around the secondary treatment system and then blending this bypassed flow with the secondary effluent for disinfection before discharge via the outfall. Flow in excess of 60 mgd (the capacity of the outfall) would need to be temporarily stored until capacity was available at the WWTP and in the outfall to process and dispose of the excess wet weather flow. Dale Avenue Pumping Station and Force Main Deficiencies The existing Dale Avenue PS consists of two separate wet wells, operated at two different hydraulic grade lines (HGL). The wet wells are operated at two different water surface elevations to prevent surcharging of the collection system. The PWWF to Wet Well No. 2 is approximately 8.4 mgd, which is less than its firm pumping capacity. The firm pumping capacity of Wet Well No. is 30 mgd, which is less than PWWFs. The effective combined pumping capacity is approximately 38 mgd. Dale Avenue PS has two reinforced concrete pipe (RCP) force mains: 30 inches and 33 inches in diameter, installed in the 930s and 950s, respectively. The RCP force mains have not been recently inspected and their conditions are not known. The combined capacity of the force mains is approximately 56 mgd, based on limiting the force main velocity to 8 feet per second. Recommended Wet Weather Management Program The recommended program for managing wet weather flows is outlined below. The recommended program includes capital projects and other recommendations. Draft project information sheets for capital improvement projects are included with the TM addressing Task Preferred Alternative Development. Wet Weather Flow Monitoring for Hillsborough and Crystal Springs The Town of Hillsborough and the Crystal Springs Sanitation District contribute significant peak wet weather flow to the City s collection system and WWTP, and accurate flow projections are needed to ensure adequate sizing of facilities. Wet weather flow data are needed to confirm the flow projections for Hillsborough and Crystal Springs Sanitation District in the City s hydraulic model. The current projections were provided by Hillsborough and may not match the methodology used in the City-Wide Sewer System Study. WWTP Master Plan Update The TM addressing Task 5.0 Alternative Development evaluated the performance of the WWTP using available data and identified potential modifications at the WWTP to improve plant performance under wet weather conditions. The modifications are similar to the basic Phase 3 improvements identified in the 99 WWTP master plan. The City recently (2008) began operating the WWTP under bypass conditions during wet weather as allowed in its NPDES permit. The City should monitor the treatment performance of the WWTP and determine if modifications are needed. The next step in modifying the WWTP is to update the ES-3

8 99 master plan by conducting detailed evaluation of the WWTP operation. In addition, the update to the WWTP master plan should consider influent screening and grit removal. Hydraulic Model Update The existing hydraulic model should be updated periodically to reflect changes in the collection system, including sewer rehabilitation and relief sewer construction. Wet weather flow monitoring including monitoring flows from Hillsborough and Crystal Springs should be performed to recalibrate the model. Future flow monitoring should include long-term (2 month) flow monitoring at selected locations to update the calibration of the continuous simulation modeling for storage at the WWTP. Collection System Rehabilitation In order to reduce RDI/I (and thus reduce PWWFs), intensive collection system rehabilitation is recommended in subbasins S-03 and S-032. Intensive rehabilitation includes the sewer mains, manholes, upper (private) laterals, and lower (public) laterals. More intensive flow monitoring and detailed field investigations in these two subbasins are necessary to characterize how RDI/I is distributed within the subbasins and to identify portions of the system that may not need rehabilitation. Flint Pump Station Force Main Wastewater flows from the proposed Bay Meadows development will be pumped to the southeast corner of the intersection of Highway 92 and Highway 0 where it will join with flow from Flint Pump Station in a new force main (LPS-) which will bypass the Dale Avenue Pump Station and discharge directly to the WWTP. The City performed a separate analysis of the hydraulic requirements to convey the combined wastewater and determined the horizontal alignment of the new force main (LPS-). Dale Avenue Pump Station Expansion The existing Dale Avenue PS is not large enough for the larger pumps, motors, valves, and piping that are needed to handle the projected peak wet weather flows, so a new wet weather pump station is recommended. The new wet weather pump station can be constructed at a lower elevation than the existing lower wet well at the Dale Avenue PS. This would allow upstream relief sewers to be constructed at lower elevations which could provide several benefits including:. Reduce interferences with other existing buried utilities. 2. Eliminate inverted siphons at existing storm drainage channels. 3. Relief sewers could be dedicated to wet weather flows and would not convey dry weather sanitary flows. The primary disadvantage of lowering the elevation of the Wet Weather PS is increased construction costs due to additional excavation. Since the Wet Weather PS would operate for limited times each year, the cost for extra energy for the higher static head would be minimal. The distribution of flows between the two existing wet wells and the proposed wet weather wet well depends on the design of the proposed wet weather relief sewers. The capacity and elevation of the Wet Weather PS should be coordinated with the North and South Relief Sewer projects. In order to maximize the existing station s capacity, overflow provisions should be made within the influent sewers or the wet wells to allow wet weather overflows from Wet Well no. to Wet Well no. 2 or the Wet Weather PS. ES-4

9 South Trunk Relief Sewer The South Trunk Sewer (projects SAT-, T-, and T-2) will be operated as a wet weather relief sewer and will be constructed deeper than the existing collection system to avoid conveying dry weather flows. The South Trunk Sewer will intercept the North Trunk Sewer and discharge to the proposed wet weather pumping facility at Dale Avenue PS. North Trunk Relief Sewer The North Trunk Sewer (projects SNT - and SNT-4) will convey Town of Hillsborough wet weather flows from the El Cerrito Avenue connection. The North Trunk Sewer will be constructed deeper than the existing collection system to avoid conveying dry weather flows, and will discharge to the South Trunk Sewer at the intersection of Birch Avenue and Sunnybrae Boulevard. The alignments for these projects are conceptual and need to be evaluated with the hydraulic model. WWTP Upgrades The following potential modifications and upgrades to the WWTP were identified for wet weather flow management: Demolish primary clarifiers No. and No. 2. Construct four new primary clarifiers (7 ft x 7 ft, each) where primary clarifiers No. and No. 2 are currently located to increase primary capacity to 60 mgd. Install anaerobic selectors in existing aeration basins to improve sludge settleability. Install new flocculator centerwells in existing secondary clarifiers to provide about 40 mgd capacity. Divert influent flows greater than 60 mgd to wet weather equalization storage, and return flows to the head of the plant when influent flows subside. In addition, screening and grit removal facilities should be considered either at the WWTP or at remote locations such as Dale Avenue PS. Wet Weather Storage Facility Wet weather flow equalization storage will be provided at the City s corporation yard across street to the north of the WWTP. This site is also being considered for proposed City offices and corporation yard. The site can have joint use with careful planning to determine the amount of space available for storage facilities. Storage facilities can be placed underground and parking or landscape features can be placed on top. Buildings are not typically placed over storage facilities because of the added costs, potential corrosion of the storage facilities, and code requirements associated with protecting inhabited spaces from potentially dangerous sewer gases. If the City Corp Yard does not have adequate space, the storage facility may need to be constructed at Joinville Park, which is located south of the WWTP. Storage facility preliminary design should consider the following: Flows from Dale Avenue Wet Weather PS could be conveyed directly to the WWTP storage facility. This would require coordination with the design of Dale Avenue Wet Weather PS and new force main so that the peak flow to the WWTP is limited to 60 mgd. The evaluation of the size of the WWTP storage facility should consider the impact of multiple consecutive storms which would not allow the storage facility to be emptied before the next storm occurs. This scenario requires a larger storage facility than a facility sized for a single storm event. ES-5

10 If flows are received from the WWTP headworks, construct a diversion structure to send flows in excess of 60 mgd to storage. Multiple modular storage basins to minimize cleanup during less intense storms. First basin module should be designed to collect solids and floatables. Wash down facilities for solids and grease removal. Odor control facilities. Flows are pumped out of the storage facility to the WWTP headworks. Supervisory Control and Data Acquisition (SCADA) system: Monitor influent flow rate at the WWTP to trigger return pumps to start emptying basins. Pump operation. Depth of wastewater in storage. Capital Improvement Projects The capital improvement projects needed to implement the preferred alternative (including the additional analysis presented above) are summarized in Table 2 and shown on Figure. Capital costs include a 35 percent contingency and a 35 percent allowance for engineering, legal services, construction management, and administration. Potential projects at the WWTP are not included. Project Name Collection System Rehabilitation Subbasin S-03 Collection System Rehabilitation Subbasin S-032 Collection System Rehabilitation Relief Sewers Table 2 - Capital Improvement Project Summary Element Existing Conditions Project Quantity/Size Total Capital Cost 4 to 6 inch Rehabilitation 0,370 LF $3,478,000 8 inch Rehabilitation 40 LF $38,000 0 inch Rehabilitation 800 LF $292,000 2 inch Rehabilitation,035 LF $453,000 Lower Lateral Replacement 330 $723,000 Upper Lateral Replacement 330 $2,286,000 Manhole Rehabilitation 70 $639,000 4 to 6 inch Rehabilitation 6,790 LF $2,278,000 8 inch Rehabilitation 200 LF $68,000 0 inch Rehabilitation 330 LF $22,000 2 inch Rehabilitation,55 LF $665,000 Lower Lateral Replacement 20 $46,000 Upper Lateral Replacement 20 $,456,000 Manhole Rehabilitation 50 $457,000 SAT- Dale Avenue PS Easement Parallel Sewer 60-inch 39-inch 400 LF $,224,000 SAT-2 Patricia Avenue Relief Sewer 5-inch 0-inch 800 LF $809,000 SNT- North Trunk Relief Sewer Phase 8-inch 8,000 LF $9,648,000 SNT-2 North Trunk Relief Sewer Phase 2 8-inch 5,300 LF $5,738,000 ES-6

11 Project Name Table 2 - Capital Improvement Project Summary Element Existing Conditions Project Quantity/Size Total Capital Cost SNT-3 El Camino/Poplar Relief Sewer 5-inch 2,650 LF $2,595,000 SNT-4 El Cerrito Trunk Parallel Sewer 8-inch,300 LF $,407,000 SNT-5 Barroilhet/El Camino Relief Sewer 5-inch,900 LF $,88,000 SNT-6 West 5th Avenue Relief Sewer 5-inch,600 LF $,53,000 SNT-7 Cypress Avenue Relief Sewer 5-inch 830 LF $832,000 T- Lower Dale/Delaware Trunk Relief 48-inch 4,600 LF $0,764,000 T-2 Lower Dale/Delaware Trunk Relief 33-inch, 39-inch 3,200 LF $6,005,000 T-3 South Delaware/Bay Meadows Parallel Trunk 5-inch 3,250 LF $3,222,000 T-4 25th Avenue Relief Sewer 2-inch, 24-inch, 30-inch, 33-inch,300 LF $,920,000 T-5 Hacienda/Flores Relief Sewer 2-inch, 8-inch, 2-inch 4,800 LF $5,442,000 T-6 7th Avenue Relief Trunk Sewer 5-inch, 8-inch 3,450 LF $3,869,000 T-7 Maple Street Replacement Sewer 8-inch 2-inch,00 LF $,9,000 T-8 24th Avenue Sewer Phase 0-inch 8-inch 2,700 LF $2,07,000 T-9 24th Avenue Sewer Phase 2 2-inch 0-inch,250 LF $,040,000 T-0 Casanova Drive Relief Sewer 0-inch, 5-inch, 8-inch 2,740 LF $2,4,000 T- Santa Clara Way Sewer 5-inch 0-inch 750 LF $78,000 T-2 El Camino Sewer 2-inch, 5-inch 8-inch, 0-inch,370 LF $,292,000 T-3 4st/Pacific Pump Station Force Main 2-inch 3,950 LF $2,985,000 T-4 Glendora/Shasta Relief Sewers 8-inch, 0-inch 8-inch,00 LF $790,000 LPS- Flint-Norfolk Force Main 6-inch 7,700 LF $6,64,000 LPS-3 Upper Norfolk Relief Sewer 2-inch, 24-inch,650 LF $,396,000 LPS-4 Dale Avenue Relief Sewer 0-inch 600 LF $470,000 LPS-5 Kehoe-Van Buren Relief Sewer 2-inch 3,300 LF $2,743,000 LPS-6 Los Prados Relief Sewer 0-inch 8-inch,20 LF $905,000 Pump Station Upgrades LPS-7 Flint-Norfolk Pump Station Upgrades.9 mgd 2.9 mgd $878,000 LPS-8 Los Prados Pump Station No. 2 Upgrades 0.4 mgd 0.7 mgd $594,000 T-5 Santa Clara Pump Station Upgrades 2.9 mgd 3.4 mgd $35,000 T-6 38 th /El Camino Pump Station Upgrades.2 mgd.4 mgd $527,000 T-7 4 st /Pacific Pump Station Upgrades.3 mgd.8 mgd $89,000 Dale Avenue Pump Station Dale Avenue Wet Weather Pump Station Wet Weather Pump Station mgd $3,200,000 Dale Avenue Force Main Replacement Force Main Replacement 30-inch 36 inch $2,700,000 Wastewater Treatment Plant Storage WWTP On-site Storage Facility Wet Weather Storage 6.0 mgal $20,00,000 Grand Total Cost $34,80,000 ES-7

12 Other Recommendations Other recommendations were developed during the course of this Evaluation, and are listed below. Private Lateral Rehabilitation Program The City should expand its efforts to control and reduce RDI/I by implementing a rigorous private lateral inspection and rehabilitation program. RDI/I from private laterals has been found to account for approximately 50 percent of the total RDI/I in several Bay Area cities. A program to inspect and rehabilitate private service laterals can provide on-going RDI/I control at low cost to the City. Collection System Rehabilitation The City should continue its sewer rehabilitation program. This program is focused on structural and maintenance problems in the collection system. Addressing these problems reduces the risk of sanitary sewer overflows and can reduce RDI/I. Satellite Collection Systems Rehabilitation The satellite collection systems should perform sewer rehabilitation evaluations using a similar approach to this project. This project did not consider sewer rehabilitation to reduce RDI/I in satellite collection systems because of limited information on satellite PWWFs. Some satellites may need to undertake collection system rehabilitation programs to reduce current levels of PWWFs and prevent future increases in PWWFs as the collection systems continue to age. The results of the rehabilitation evaluations should be coordinated with the proposed projects for the City s wastewater facilities including relief sewers, Dale Avenue PS and force main, and storage facilities at the WWTP. Satellite Collection Systems Agreements The City should review the agreements with its satellite collection systems to ensure that appropriate limits on PWWFs are included. PWWFs are the primary criteria for sizing collection system facilities including pipes and pump stations. Wet weather flows are also a significant cause of overflows in the City s collection system. Responsibilities for limiting, conveying, and paying for PWWFs should be clearly delineated. Satellite collection systems should have active programs to control and reduce RDI/I that include identifying and disconnecting inflow sources, rigorous private lateral inspection and rehabilitation programs, and periodic monitoring and evaluation of wet weather flows. Screening and Grit Removal The WWTP does not have influent screening or grit removal, and floatables are observed on the water surface of the primary and secondary clarifiers. Influent screening may improve the performance of process units and reduce maintenance associated with debris removal. Screening and grit removal should be considered at the WWTP headworks or remote locations such as Dale Avenue PS. No Blending Conditions The City s current NPDES Permit allows the WWTP to blend when the wastewater flows exceed 40 mgd, which is the hydraulic capacity of the WWTP s secondary treatment system. Under the blending operating mode, wastewater flow in excess of 60 mgd will be diverted to storage and flows up to 60 mgd will receive primary level treatment. Flows between 40 mgd and 60 mgd bypass the secondary treatment facilities and are recombined with the 40 mgd flow that receives secondary treatment for disinfection and disposal through the City s outfall, which has a capacity of 60 mgd. ES-8

13 If at some time in the future, the City can no longer blend, a new secondary clarifier with polymer addition facilities can be constructed at the WWTP to increase the capacity of the secondary treatment facilities to 60 mgd. The City should consider reserving space adjacent to the existing secondary clarifier for an additional secondary clarifier and chemical addition facilities ES-9

14 . ve 7 TBa ys ho. k WWTP On-Site Storage Facility j Bl vd. T-2 LPS-4 SA * Dale Ave. PS WWTP TSA S- LPS-7 2 Y9 0 HW Y 6 T-. Delaware St T-2 7 T- HW LP T- 6 TSN LPS-5.F W e Av re 4 T- h i ft TSN SN na lto Ti SN 2 TN S 3 TSN T-5 SN LP S3 4 T LPS-6-8 T 3 T- T- T-5 S-032 Rehab T-5 T-9 T0 T- S-03 Rehab 2 3 T2 T-6-4 T HW Y 9 LPS-8 0 T-7 µ Miles LEGEND CITY OF SAN MATEO WET WEATHER CAPACITY ANALYSIS AND ALTERNATIVES EVALUATION Pump Station Upgrade k j Wet Weather Storage Facility Relief Sewer DRAFT Figure - Capital Improvement Projects Force Main * WWTP Upgrades Subbasins Collection System Rehabilitation P:\34000\ San Mateo Wet Weather Capacity Analysis\GIS\mxd\BC Figures\TechMemos\Draft Report\Projects.mxd