Mobility and Infrastructure Committee Memorandum
TO: MOBILITY & INFRASTRUCTURE COMMITTEE DATE: MARCH 12, 2026 FROM: PUBLIC WORKS DEPARTMENT WARDS: ALL
SUBJECT: TOTAL DISSOLVED SOLIDS MANAGEMENT PLAN AGREEMENT BETWEEN THE CITY OF RIVERSIDE AND RUBIDOUX COMMUNITY SERVICES DISTRICT ISSUE:
Receive an update on the Total Dissolved Solids (TDS) Management Plan Agreement Between the City of Riverside, Regional Water Quality Control Plant and Rubidoux Community Services District.
RECOMMENDATIONS:
That the Mobility & Infrastructure Committee:
Receive and file an update on the TDS Management Plan Agreement between the Regional Water Quality Control Plant and Rubidoux Community Services District; and Recommend that the City Council approve the TDS Management Plan Agreement Between the City of Riverside, Regional Water Quality Control Plant and the Rubidoux Community Services District.
BACKGROUND:
The City of Riverside Public Works Department, Wastewater Division, is responsible for the collection, conveyance, and treatment of wastewater for over 93,000 customers within City limits. The facilities include over 800 miles of gravity sewers, 400 miles of City laterals, 19 wastewater lift stations, 16,000 sewer manholes. The Riverside Regional Water Quality Control Plant (RWQCP) has a treatment capacity of 46 million gallons per day (MGD). Additionally, under agreements with the city, the RWQCP provides wastewater treatment services for the Edgemont, Jurupa, and Rubidoux Community Services Districts (RCSD) and the unincorporated community of Highgrove.
Through the wastewater treatment process, the RWQCP removes organic and inorganic matter from the waste stream to ensure compliance with water quality standards before discharging to the Santa Ana River or reusing it as recycled water. The RWQCP water quality requirements are outlined under the National Pollutant Discharge Elimination System (NPDES) No. CA 0105350, Order No. R8-2013-0016. As part of the requirement, the effluent limit for Total Dissolved Solids (TDS) is set at a 12-month flow weighted average not to exceed 650 mg/l.
RCSD, under various agreements dating back to 1978, has acquired 3.055MGD of treatment and disposal rights from the RWQCP. Historically, RCSD’s influent flows have average 1.7 MGD a day with a TDS concentration of 790 mg/l.
In 2019, RCSD proposed an annexation to the Riverside Local Agency Formation Commission (LAFCO) for the Rio Vista Specific Plan, which included 1,697 dwelling units, approximately 2.7 million square feet of light industrial and business facilities, and a new public school. However, the City of Riverside opposed the annexation due to RCSD’s continued high TDS concentrations in wastewater discharged to RWQCP; pending RCSD’s TDS Management Plan completion to manage high concentrations in untreated sewage.
In February 2024, RCSD submitted its draft TDS Management Plan for review. Following multiple discussions with RWQCP, the RCSD Board of Directors approved the final TDS Management Plan in April 2025.
DISCUSSION:
The RWQCP remains compliant with all NPDES effluent limitations, including the 12-month rolling TDS average of 590 mg/l. The agreement with RCSD ensures continued compliance with RWQCP effluent limits by including triggers that RCSD must follow if effluent TDS encroaches the 650 mg/l limit or when 750 equivalent dwelling units (EDU) are connected to sewer service.
RCSD commitments include:
A condition in the Plan of Service and Environmental Impact Report for the Rio Vista Project requiring construction of a physical potable water supply intertie with West Valley Water District, capable of moving up to 2,000 AFY of low TDS concentration water.
If 750 equivalent dwelling units (“EDU”), defined as ¾ inch water meter connection, are connected to sewer service within the district’s current or expanded service area before the Rio Vista Project build the physical intertie with West Valley Water District, the District will construct the physical intertie itself within 12 months of the 750th EDU connection. The count on the future 750 EDUs will start on the date the last Party executes this Agreement.
Purchase low TDS potable water through the intertie with West Valley Water District to blend with the District’s groundwater supply in sufficient volumes to enable the District’s TDS concentration in sewage delivered to the Riverside WWTP to be 650 mg/L or less in the event the TDS concentration in tertiary treated water discharged from the Riverside WWTP reaches the a 12-month average of 620 mg or compliance triggers in future NPDES permits.
These Triggering TDS Concentrations have been determined based on the current NPDES permit TDS compliance calculation and the anticipated compliance calculation of a forthcoming NPDES permit. The Triggering TDS Concentrations may be adjusted to reflect future controlling NPDES permits that use a compliance calculation different from the current and anticipated compliance calculation utilized herein.
If TDS conditions in sewage are delivered to the Riverside WWTP change, the district may request that Riverside reevaluate and/or amend the Triggering TDS Concentrations, which may include discontinuing the purchase of water through the intertie. Any reevaluation and/or amendment of the Triggering TDS Concentrations requested by the district, including the discontinuation of water purchases, shall be at the sole discretion of Riverside.
If the District successfully implements groundwater treatment solutions, such as a Reverse Osmosis plant, that eliminates the need for imported water and allows independent compliance with the NPDES permit, it may discontinue purchasing water through the intertie.
RWQCP commitments include:
Notify LAFCO within thirty (30) calendar days of the execution of this Agreement that Riverside has approved the District’s TDS Management Plan and no longer objects to annexations of the new service areas currently proposed, including the Rio Vista Project, into the district for sewer service.
Provide the District with prompt written notice if and/or when the Riverside, Regional Water Quality Control Plant discharge reaches the Triggering TDS Concentration, as defined in section 5 (c) of the Agreement (Attachment 1).
FISCAL IMPACT:
There is no fiscal impact associated with the TDS Management Plan Agreement Between the City of Riverside, Regional Water Quality Control Plant (RWQCP) and the Rubidoux Community Services District (RCSD).
Prepared by: Robert Eland, Technical and Compliance Manager Approved by: Nathan Mustafa, Interim Public Works Director Certified as to
availability of funds: Julie Nemes, Interim Finance Director Approved by: Kris Martinez, Assistant City Manager
Approved as to form: Rebecca McKee-Reimbold, Interim City Attorney Attachment:
Presentation
Total Dissolved Solids Management ● Page 1