Optimizing Regional Treatment Solutions with Septic to Sewer and Recycled Water Opportunities

Presentation Description: The North Coast Regional Water Board recently established a Total Maximum Daily Load (TMDL) for pathogens in the Russian River, following the river’s listing as impaired for water contact recreation. The TMDL documentation lists potential pathogen sources that include treated municipal wastewater, untreated sewage from collection system and onsite wastewater treatment systems (OWTS), i.e. septic systems.
As part of an effort to meet TMDL requirements and reduce pathogen concentrations in the Russian River, the Russian River County Sanitation District (RRCSD) and Sonoma Water have worked with West Yost to evaluate the feasibility of regional wastewater solutions for the western Sonoma County (West County) area.

This area is served by four small wastewater treatment plants (WWTPs), and about 5,000 unsewered parcels rely on OWTSs. Each WWTP serves between 500 and 1,000 users, including disadvantaged communities (DACs). A regional solution could improve treatment efficiency, facilitate septic-to-sewer conversions, and help advance California’s goal of providing adequate sanitation for all residents.

Key study tasks include:
-Comparing regionalization alternatives that address existing system deficiencies and capture economies of scale.
-Conducting a risk-based GIS analysis to prioritize unsewered parcels for regional service.
-Evaluating opportunities to expand recycled water use to offset existing potable and groundwater usage for agriculture and nearby quarries.
-Assessing climate change resiliency by analyzing how expanding floodplains may affect unsewered parcels under future scenarios.

A Feasibility Study Report will identify the most viable regional strategies and an implementation plan to guide decision makers as projects are implemented, as well as support applications for grant funding to facilitate project implementation. The study will demonstrate how regional solutions and incorporating unsewered areas can benefit all stakeholders. While focused on Sonoma County, the approaches used are broadly transferable and can inform other communities facing septic reliance, regulatory challenges and equity concerns.

The presentation will draw on a broad range of perspectives: regulatory, agency and consultant.