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Public Alerts and Notifications

Blending and Bypass History

SASM EntranceBlending
During wet weather, inflow and infiltration into the sanitary sewer collection systems cause high influent flows to the treatment plant. These collection systems are owned by SASM and its member agencies: City of Mill Valley, Richardson Bay Sanitary District, Almonte Sanitary District, Alto Sanitary District, Homestead Valley Sanitary District and the Kay Park region of Tamalpais Community Services District. During these high flow conditions, primary treated effluent may blend with fully treated secondary effluent prior to chlorination, dechlorination, and discharge into Raccoon Straight in Central San Francisco Bay.

If the wet weather is extreme, minimally treated sewage may bypass the remainder of the treatment process and overflow the 3.3 Million Gallon equalization (holding) ponds designed to manage peak wet weather flows, and flow directly into the Pickleweed Inlet in Richardson Bay. In this case the Marin County Health Department will be notified and the shoreline posted.

Current Status
When the Wastewater Treatment Plant experiences a blending event, City staff will update this webpage with information, including the approximate volume and duration of the event.


The Sewerage Agency of Southern Marin is conducting an urgent maintenance project as follows:

The Sycamore Avenue Sewer Maintenance Project will occur between December 22-24, and 29-31st.  The timing of this project takes advantage of the school holiday break and lighter traffic flow.  The goal is to complete the removal of debris that is backing up the sewer and creating potential blockages.  After this concerted effort, maintenance will be greatly reduced to a biennial frequency and much shorter in duration.

Traffic impacts will be minimized as much as possible.  Single lane restriction at the intersection of Sycamore Avenue and Nelson will be facilitated by traffic flaggers, cones and warning signage.  Operating hours will be between 9:00 AM and 3:00 PM.

If you have questions or concerns: Call (415) 388-2402

DATE Start time    End Time   Duration   Estimated Volume
February 9, 2014   1:19 am 9:46 pm 20h27m 2.6 M gal.

Last updated: 12/17/2014 12:33:00 PM