Overburdened Sewer Infrastructure

A total of 101 Sanitary Sewage Overflows (SSOs) were recorded from Half Moon Bay to Montara from 2011 to mid 2017, according to public records manually compiled by Resist Density. These findings raise significant questions as to whether the infrastructure can accommodate any more large development until major repairs and upgrades are made.

Executive Summary

  • The large number and volume of sanitary sewer overflows (SSOs) on the San Mateo County Midcoast from January 2011 through May 2017 are indicative of an aged and failing infrastructure lacking a preventative maintenance program. These SSOs and other system failures have reduced operational reliability of the sewage system, increased emergency costs, added financial, legal and regulatory risk and they pose an ongoing threat to environmental safety.

  • The potential for significant rainy seasons in 2018 and beyond could increase sewage flows to higher than “normal” levels, further increasing the risk of SSOs during or after heavy rains.

  • SAM’s 5-year infrastructure plan for 2017 lists 44 projects, 10 of which are priority 1. Due to budget constraints, SAM proposed funding and initiation of only 2 infrastructure projects in the 2017/18 fiscal year at a cost of ~$2M, with ~$500K of that to come from emergency reserves. All other projects will be delayed.

  • Ongoing litigation has added to SAM’s financial pressures. Litigation between SAM’s member agencies has also resulted in political infighting and ill will. This has reduced cooperation on key issues and risks timely completion of critical infrastructure projects.

  • SAM is understaffed and is challenged to deliver reliable service.



  • SAM must find the means to complete all priority 1 infrastructure projects as soon as possible and establish a robust preventative maintenance program.

  • SAM and member agencies should increase the rate of replacing aged pipes in their districts.

  • SAM staff should have more up-front involvement and input into individual member agency strategies and plans, to ensure that they are pursued in the best interests of the overall collective.

  • SAM’s next risk analysis should consider the cumulative impact of all approved and planned coastside developments over the next 5 years, including an estimate of unapproved second units in single family homes.

  • New development permits for large developments (multi-unit housing, large commercial and industrial developments) should be more critically reviewed with respect to their impact on outdated and overburdened system infrastructure.

  • A moratorium on new sewer connections for large developments should be considered until such time that all critical repairs and upgrades are completed and the risk of SSOs and system failures is reduced to an acceptable level.

  • SAM should hire 2 additional staff in 2018 to maintain reliable service, as recommended by 2 consultant reviews.

  • SAM should consider means to increase revenue, including new grants, loans, bonds and rate increases.

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