The Town of Discovery Bay Community Services District Wastewater Treatment Plant Master Plan

1. The Town of Discovery Bay Community Services District Wastewater Treatment Plant Master Plan NOVEMBER 9, 2011

2. Master Plan Purpose • Assessment of existing facilities • Analysis of future needs • Road map for improvements

3. Master Plan Organization • Section 1: Introduction • Section 2: Executive Summary • Section 3: Existing and Future Land Use • Section 4: Collection System Pump Stations • Section 5: Wastewater Flows and Loads • Section 6: Overview of Wastewater Treatment Plant • Section 7: Plant Hydraulic Capacity Analysis • Section 8: Waste Discharge and Treatment Requirements • Section 9: Influent Pump Station • Section 10: Headworks • Section 11: Secondary Treatment • Section 12: Secondary Effluent Lift Station • Section 13: Tertiary Filtration • Section 14: UV Disinfection • Section 15: Salinity Reduction • Section 16: Emergency Storage • Section 17: Solids Handling • Section 18: SCADA System • Section 19: Summary of Future Improvements

4. Projected Growth within TDBCSD

5. Collection System Pump Station Improvements • Total budgeting cost for improvements to all pump stations is $650,000 as shown in Table 2-2. • It is recommended that the District establish priorities for this work and then budget to accomplish certain portions of the work each year until completed.

6. Existing and Future Flows and Loads

7. Existing Wastewater Treatment Plant(s) Figure 6-1Flow Diagram

8. Plant Hydraulic Analysis • Existing and future peak flows modeled • Existing facilities can accommodate future peak flows with suitable modifications to: • Influent pump station • Secondary effluent lift station • Export pump station

9. Key NPDES Permit Requirements

10. Influent Pump Station • Current issues with the Influent Pump Station include: • Pump ragging • Lack of flow splitting controls • Lack of sump mixing that results in different wastewater characteristics for Plants 1 and 2 • Inability to take the pump station out of service for needed repairs • Recommended improvements to the Influent Pump Station include: • Structural rehabilitation • Replacement of all pumps • Piping modifications • Installation of a sump mixer • Improved flow splitting controls • Re-activate Pump Station “W” to allow Influent PS to be taken out of service and to allow pumping raw sewage to emergency storage basin • The total estimated capital cost for these improvements is about $1 million.

11. Headworks • One at each plant with: • Flow measurement flume • Screen to remove rags, large solids • Influent sampler (Plant 2 only) • Screen capacity • 6.2 Mgal/d, each • No expansion needed • Influent sampling improvements recommended

12. Existing Secondary Treatment Facilities • Basin sizes good for 2.0 Mgal/d AAF(currently at 90 percent capacity) • One additional brush rotor (or equivalent) recommended in each ditch for reliability • Can take a clarifier out of service in dry weather • Cannot take either ditch out of service

13. Existing Secondary Treatment Facilities (con’t) • Add one new ditch and one new clarifier at Plant 2 • Add standby floating aerator in each existing ditch • with future design flows, will be able to: • Take any clarifier out of service at any time of the year • Take any ditch out of service during dry weather flows

14. Secondary Treatment System Expansion Cost Estimate

15. Secondary Effluent Lift Station • If no future filters, future peak flows can be accommodated by “over-speeding” existing pumps • If filters are added, pump lift would increase, requiring new impellers, motors, VFDs • Cost: $250,000

16. Tertiary Filtration • May be needed for • Improved UV disinfection • Reclamation • Future discharge requirements • Provide flow equalization ahead of filters

17. UV Disinfection • Three scenarios: • Scenario 1: 23 MPN/100 mL without filters (existing conditions) • Scenario 2: 23 MPN/100 mL with filters. • Scenario 3: 2.2 MPN with filters (possible future requirement) • Scenarios 1 and 3 require conversion of the existing UV3000 channel to UV3000Plus Capital cost = $1.2 million. • Scenario 2 requires only flow splitting weir improvements • On-site viral bioassay testing needed to confirm capacity

18. Salinity Reduction • 1,000 µmhos/cm desired by state, but not currently required • To meet 1,000 µmhos/cm: • Microfiltration • Reverse osmosis • Brine concentration • Concentrated brine disposal • Capital cost = $15.7 million • Annual cost = $2.12 million • Improved source control recommended to reduce salinity

19. Emergency Storage • Existing 5 Mgal earthen basin at Plant 1 not usable • Improvements required include: • Re-activate Pump Station “W” • New Return pump station for draining basin • Cost = $243,000

20. Wetlands Treatment Potential • 2007 demonstration project to evaluate metals removal, mainly copper • Wetlands demonstration removed 90 percent copper • Alternative copper compliance methods eliminated the need for treatment • Possible future potential for metals and refractory organics

21. Solids Handling • Sludge lagoons are full or nearly full • Belt press capacity limits use of solar dryers • Future improvements: • Phase 1 • 2 belt presses • 2 solar dryers • Cost = $4.65 million • Phase 2 • 1 solar dryer • Cost = $2.03 million

22. SCADA System • Existing system and previous recommendations reviewed • Recommended improvements: • Redundant master RTU at Plant 2 • Improved features for monitoring and control sewage lift stations • Begin long-term replacement of obsolete PLCs on a priority basis • Total cost = $350,000

23. Summary of Improvements • A list of all the recommended improvements developed in this Master Plan is presented in the handout Table 2-14. • A site plan indicating where the future improvements could be located is shown is the handout Figure 20-1.