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Home My WebLink About04.a. Receive update on Dublin San Ramon Services District -East Bay Municipal Utility District Recycled Water Authority (DERWA) requestPage 1 of 7 Item 4.a. S Central Contra Costa Sanitary District December 18, 2017 TO: REAL ESTATE, ENVIRONMENTAL AND PLANNING COMMITTEE FROM: MELODY LABELLA, RESOURCE RECOVERY PROGRAM MANAGER REVIEWED BY: JEAN -MARC PETIT, DIRECTOR OF ENGINEERING AND TECHNICAL SERVICES ROGER S. BAILEY GENERAL MANAGER SUBJECT: RECEIVE UPDATE ON DUBLIN SAN RAMON SERVICES DISTRICT -EAST BAYMUNICIPAL UTILITYDISTRICT RECYCLED WATERAUTHORITY (DERWA) REQUEST TO DEVELOP A MEMORANDUM OF UNDERSTANDING FORA PILOT PROJECT TO DIVERT RAW WASTEWATER FROM CENTRAL SAN'S SERVICE AREA FOR THE PURPOSE OF PRODUCING RECYCLED WATER TO MEET DERWA'S PEAK SUMMER IRRIGATION DEMAND Background In January2017, Central San received a letterfrom the Dublin San Ramon Services District (DSRSD) — East Bay Municipal Utility District (EBMUD) Recycled Water Authority (DERWA) requesting development of a memorandum of understanding (MOU) to explore a potential partnership and pilot project to divert a portion of the raw wastewater from Central San's San Ramon Pump Station between May and September every year. The wastewater would be diverted through DSRSD's existing collection system to DSRSD's treatment plant, for the purpose of producing and distributing recycled water to meet DERWA's peak summer irrigation demand. According to the letter, DERWA made this request due to the need for a temporary supplemental supply to help meet recycled water demands in the EBMUD and DSRSD service areas until wastewater flows increase with development and other long-term options are identified. n March 2017, staff brought this issue to the REEP Committee for discussion. At that meeting, the Committee indicated that additional information is needed to determine how to divert the water and what the impacts would be to Central San. The Committee directed staff to continue strategizing with DERWA and return with a proposed plan at a future Committee meeting. Central San staff has been working with DSRSD staff to evaluate diversion options, in addition to having internal discussions on how the potential diversions will impact Central San's operation and future recycled water projects. Staff is returning to update the Committee on these efforts. Diversion Alternatives n October 2017, DSRSD staff, with support from their consultant West Yost, presented five diversion December 18, 2017 REEP Committee Meeting Agenda Packet - Page 5 of 31 Page 2 of 7 alternatives to Central San staff, which ranged from a simple gravity diversion using the existing emergency overflow interconnection between Central San's and DSRSD's collection system, to building a DERWA pump station adjacent to Central San's. Central San and DSRSD staff worked together to narrow these five alternatives down to two gravity diversion options and further refine the interconnection and operational details for each. Central San's Engineering and Operations staff have been meeting internally to review these two alternatives, evaluate their potential impacts, and determine how the potential impacts could be mitigated. Diversion Alternative 2 would divert all the incoming dry weather wastewater flow to the San Ramon Pump Station by modifying the existing overflow interconnection between Central San's and DSRSD's collection systems. This option would involve closing the influent gate into the pump station, which has been pinned open (not exercised) since the 1990s, when a large sanitary sewer overflow to the adjacent creek occurred due to that gate failing to open fully after being temporarily closed. Diversion Alternative 4 would modify the existing emergency overflow interconnection between Central San's and DSRSD's collection system to divert approximately 1.5 million gallons per day (MGD) of dry weather flow from the west side of the San Ramon Pump Station. Schematics of the two diversion alternatives are presented in Attachments 1 and 2. An overview of the two diversion alternatives, including DERWA pros and cons and Central San operational and policy concerns, are presented in Attachment 3. Discussion While Central San is highly supportive of expanding the beneficial reuse of its wastewater, there are significant consequences that could result from allowing DERWA to divert Central San's raw wastewater supply. I n particular, staff's biggest concern is that once DERWA comes to rely on Central San's wastewater flow, it will always be reliant upon it, making it unavailable for large-scale recycled water projects at Central San's main treatment plant. For example, during dry weather drought conditions, Central San has approximately 25 MGD of wastewater available for producing additional recycled water. The Refinery Recycled Water Project demand is 20 MGD; however, 24 MGD would be needed to yield 20 MGD of recycled water due to the production efficiency of advanced treatment processes. Beyond that, Central San would need additional treated wastewater to dilute the concentrated brine created from the reverse osmosis process prior to discharge, requiring even more wastewater flow. I n other words, Central San is going to need every drop of wastewater in the summer months in order to reliably serve the full Refinery Project. When asked about the length of time DERWA would need Central San's raw wastewater supply, DSRSD staff has indicated that it would be until enough additional wastewater is generated from new development in the areas that DSRSD serves. According to DSRSD's Master Plan, it will take approximately 10 years to generate the amount of wastewater that would be diverted under Diversion Alternative 4 and even longer to replace the amount of wastewater that would be diverted under Diversion Alternative 2. Conclusion Due to the significance of the potential operational and policy -related impacts that could result from Diversion Alternatives 2 and 4, staff recommends not moving forward on any permanent infrastructure modifications to allow for the diversion of Central San's raw wastewater to DERWA. However, if the Committee wishes to pursue this request from DERWA further, a diversion pilot project could be considered. A temporary sump pump could be installed in the bottom of Central San's manhole (manhole 11) immediately upstream of the interconnection with DSRSD's collection system to lift a portion of the wastewater from Central San's collection system into DSRSD's collection system. Conducting this pilot would allow DERWA to obtain additional wastewater flow, while allowing Central Santo evaluate localized and system -wide impacts without significant investment by DERWA. Staff looks forward to discussing this updated information and receiving your direction at the December December 18, 2017 REEP Committee Meeting Agenda Packet - Page 6 of 31 Page 3 of 7 18, 2017, REEP Committee meeting. GOAL ONE: Provide Exceptional Customer Service Strategy 2 - Improve Interdepartmental Collaboration GOAL SIX: Embrace Technology, Innovation and Environmental Sustainability Strategy 1 - Augment the Region's Water Supply ATTACHMENTS: 1. Attachment A - Schematic of Diversion Alternative 2 2. Attachment B - Schematic of Diversion Alternative 4 3. Attachment C - Overview of Diversion Alternatives 2 & 4 December 18, 2017 REEP Committee Meeting Agenda Packet - Page 7 of 31 ATTACHMENT A MH 17 24" VCP I L4- Force iviain la rurue iviain Surge N Tank 101 MH --———————————————— — — — —_ _ _ _ _ 18" Sewer 11 10/17/2017 v � o J � L I L4- Force iviain la rurue iviain Surge N Tank 101 MH --———————————————— — — — —_ _ _ _ _ 18" Sewer 11 10/17/2017 ATTACHMENT B 17 24" VCP ' MH _ _ _ _ MH 18" Force Main 16 15 Oil LARWIN ' 14" Force Main PUMP STATION 12" Force Main Surge 14 O 18" Force Main Tank N 24" Force Main 00 New 1 High Existing 18" Plug Manhole 10 Level Valve L Bypass 4 DSRSD MH MH ----------------- 18" Sewer 11 � 18" Sewer —� 'A,— � -4,,— - - 11/13/2017 Page 6 of 7 Attachment C — Overview of Diversion Alternatives 2 and 4 DERWA Alternative Description Construction Requirements DERWA Pros DERWA Cons Central San Operational and Policy Concerns 2 Gravity Bypass of New high-level overflow . No new creek crossing • Poor flow control This option is not recommended by staff for further consideration due to the following Existing PS by Closing line from manhole (MH) • Does not require a new • No flow metering concerns. Inlet Gate and Raising #10 back to the pump MH Hydraulic Grade station . CCCSD can schedule Operational Concerns: maintenance activities inside pump station for An overflow at this Pump Station many years ago led to commitments made by months when gate is Central San to San Ramon's City Council to prevent future overflows. As a result, closed and risk of the Pump Station's inlet gate was pinned open at the direction of Central San's overflow is lowest management at that time. Serious concerns about closing the inlet gate and causing another overflow, should the gate not fully reopen. If a new inlet gate is proposed, there is the same concern that the gate could fail in a closed or partially closed position causing an overflow. • Unknown upstream hydraulic impacts by doing gravity diversion. We have not modeled this scenario to see the resulting hydraulic grade line (HGL). The estimated impact on the new upstream HGL rising by 5 feet was developed by DERWA's consultant and needs to be validated by Central San. • Taking all the dry weather flow would result in keeping the Pump Station offline, crippling its ability to respond quickly to a rapid increase in incoming flow should the new diversion become blocked. • Potential for deposition in the inverted siphon during low flows (night). • Potential downstream gravity sewer impacts due to less flow and possible solids deposition. • Potential forcemain odors and corrosion issues due to not being operated and no corrosion/odor control operating. Potential issues with valves on forcemain piping. • Requires extra resources (staff and materials) to address flushing and odor concerns with the forcemains and gravity sewers. Difficult to predict exactly how much until in operation. • Reduced flow creates further challenges with operating the existing wastewater treatment plant during low flow conditions and challenges with implementing future nutrient removal and recycled water facilities (less water available impacts both operation and storage needs). Policy Concerns: • Diverting this flow will reduce the volume of treated wastewater available at Central San's treatment plant, which would reduce the volume available to serve the Refinery Project and to diluting the resulting brine, making the project more expensive (due to added storage) and possibly infeasible to fully implement. • Diverting the flow reduces volume for all recycled water projects and customers and may trigger more expensive recycled water projects all around. • Possible impact on pump zone fee currently in development. • Possible long-term service area implications Page 1 of 2 December 18, 2017 REEP Committee Meeting Agenda Packet - Page 10 of 31 Page 7 of 7 Attachment C — Overview of Diversion Alternatives 2 and 4 DERWA Alternative Description Construction Requirements DERWA Pros DERWA Cons Central San Operational and Policy Concerns 4 Gravity Diversion at • New MH between MH 11 • No new creek crossing • Only flow from MH This option is not recommended by staff for further consideration due to the following MH 11 and MH 10 • Maintains ability for high- 11 is available for concerns. • New 18" sewer pipe from level gravity bypass to diversion MH 10 to DSRSD MH DSRSD in the event of a • Poor flow control Operational Concerns: • New 18" sewer pipe from failure at the Pump • No flow metering MH 10 to the new MH Station • This alternative may be technically feasible but there are many concerns that need • Fill 18" sewer between • No modifications to the to be further explored and addressed. Overall there are risks and challenges we MH 11 and new MH existing Pump Station will not be able to identify until a diversion is operational. • New gate valves in • All construction on the • This option will divert half the flow coming into the Pump Station, which would gravity sewer lines trail side of the creek require operating the existing pumps in a way that we do not currently operate. Increased wear and potential pump issues with cycling pumps with variable frequency drives that are oversized for the reduced flow. May require new pumps and controls, which there may not be enough space for. Replacing existing pump(s) with smaller ones is not acceptable because it would impact the reliable pumping capacity for the pump station. • Odors are a major concern for residents in this area. Increasing residence time in the Pump Station (due to lower flows) could increase the potential for odors. • New potential failure points (manholes and valves) being installed adjacent to a creek would raise Central San's risk of overflows in an environmentally -sensitive area. • Installation of gate valves in gravity line not ideal, and hard to maintain or access in the future. Valve access and maintenance is a concern. One risk is that we are unable to open valve at end of summer and cannot convey wet weather flows to the pump station. • Reduced flow creates further challenges with operating the existing wastewater treatment plant during low flow conditions and challenges with implementing future nutrient removal and recycled water facilities (less water available impacts both operation and storage needs). Policy Concerns: • Diverting this flow will reduce the volume of treated wastewater available at Central San's treatment plant, which would reduce the volume available to serve the Refinery Project and to diluting the resulting brine, making the project more expensive (due to added storage) and possibly infeasible to fully implement. • Diverting the flow reduces volume for all recycled water projects and customers and may trigger more expensive recycled water projects all around. • Possible impact on pump zone fee currently in development. • Possible long-term service area implications Page 2of2 December 18, 2017 REEP Committee Meeting Agenda Packet - Page 11 of 31