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Sewer agency outlines options and costs to meet 2035 nitrogen limits
Summary
Mark Newman of the Sewer Agency of Southern Marin told the Mill Valley council the agency treats roughly 800 million to 1 billion gallons a year, described recent capital work funded by a 2015 bond, and said a regional water‑board order requiring a 50% nitrogen cut by 2035 will force multimillion‑dollar choices including trade credits, multi‑benefit projects or new treatment processes.
Mark Newman, general manager of the Sewer Agency of Southern Marin (SASM), told the Mill Valley City Council that SASM operates the Mill Valley plant and treats roughly 800 million to 1 billion gallons of wastewater a year while serving a mix of local sanitary districts and the City of Mill Valley.
“After the 2022 algal bloom in San Francisco Bay…they ordered that all wastewater treatment plants will reduce their nitrogen output by 50% starting in 2035,” Newman said, describing a regional mandate that he called costly and uncertain. He said SASM has contracted Black & Veatch for initial cost estimates and is evaluating five paths to comply, from trading credits to multi‑benefit habitat projects to established treatment upgrades such as moving‑bed biofilm reactors.
Newman reviewed recent work completed under a 2015 bond — headworks and clarifier rehabilitation, replacement of trickling‑filter media, digester repairs and the odor‑control tower commissioned in 2019 that he said cut H2S emissions dramatically. He said SASM is operated under a JPA and owns roughly nine miles of collection piping, six pump stations and a six‑mile effluent line that discharges in Raccoon Strait.
Council members pressed Newman on the near‑term rate impacts to Mill Valley residents. Councilmember Bruce Carmel summarized staff numbers in the presentation and asked whether city charges from SASM would increase at about 4% annually; Newman confirmed that figure was the current model’s projected annual growth for member agency charges. Newman also described pilot work on covering primary clarifiers as a possible further odor mitigation step if the pilot proves successful.
Newman framed trading credits as a regional compliance tool under study but cautioned it is not a one‑to‑one match with Chesapeake Bay programs because agricultural sellers are not covered in the Bay order for San Francisco Bay. He said the Bay Area Clean Water Agencies (BACWA) is developing a cost framework for any exchange, and that Black & Veatch will deliver more detailed cost options in 2026. Newman said construction for full treatment upgrades would not be expected to come online before 2035 and added that operating costs and annual budgets would increase under certain technical options.
The council did not take action on SASM’s report but asked staff to return with further financial modeling and to continue coordination with county and regional partners.
