Overburdened Water & Sewer Infrastructure

Our local water and sewer infrastructure is old and in need of significant repairs and upgrades. Many pipes throughout both systems are over 40 years old and major assets have approached or exceeded their projected lifetimes and must be replaced. As the risk of failure increases with age, maintenance and capital improvement costs are also ever increasing, forcing the agencies to fall further behind in maintaining reliable service without significant increases in capital and maintenance costs, most of which comes from customers. Capacity of both systems is also limited, as indicated below.

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Water Supply for the Future?

MWSD’s current reliable water capacity is 758,880 gpd and they estimated in 2017 that they could support up to 1,000 new water connections (Source: MWSD 2017 Water System Master Plan, Table ES-5). If reliable system capacity is maintained, a 1% growth rate in population will not max out the system until the year 2050. However, year after year of seasonal droughts has reduced the volume of water available in local aquifers. An assessment of the Alta Vista Well (the largest water source for MWSD) in 2019 indicated a significant depletion in available water causing a drawdown in output after multiyear droughts, although the well did appear to recharge following normal rainfall seasons. Climate change has increased the likelihood and severity of droughts going forward, which also reduces the probability of finding adequate new sources of water on the Midcoast. This risks future water supply and quality and brings into question whether the system can actually support that many new connections.


Aging and failing infrastructure also jeopardizes water supply and quality. To increase the pace of needed repairs, MWSD established an annual water reliability charge of $558 per connection in July 2020, adding a significant financial burden to many coastside residents. Despite the added revenue from this charge, it covers only half of the needed capital improvement costs, meaning that risks to reliable supply will remain without additional rate increases. Water financial reserves are also below the policy requirements at present, in spite of a $500,000 transfer from Sewer Reserves in 2020.

 Our Recommendations

  • Large commercial and multi-unit residential development applications must provide a more thorough assessment of risks to ongoing water supply and quality, as well as risks of exceeding sewer capacity that threaten environmental safety and service interruptions.

  • Large commercial and multi-unit residential developments must be required to add on-site storage of fire water to reduce the burden on the community’s fire water storage and drinking water supply.

  • SAM must adopt new governance guidelines to improve working relationships among member agencies and better ensure that they meet their legal, regulatory and financial obligations in order to avoid excessive costs, agency consolidation and/or loss of local control of sewer service.

Overburdened Sewer Infrastructure

MWSD’s current sewer capacity allocation from SAM is 510,000 gpd of dry weather season flow according to the JPA. According to SAM Monthly Manager Reports, dry season flows over the last year (Jun-Sep 2019 and Jun-Jul 2020) have averaged 253,500 gpd, approximately half of MWSD’s capacity allocation. Assuming the system continues to operate at these flow rates in the dry seasons, MWSD’s capacity allocation will not be exceeded for the foreseeable future. However, wet season flows present a challenge to the sewer system due to inflow and infiltration of storm water runoff. Under such conditions, old pipes and pumps have a higher probability of failure, which can lead to sewage backup and Sanitary Sewage Overflows (SSOs).


SAM has a long history of SSOs, most of which have been directly attributable to failing infrastructure. A total of 101 SSOs occurred in the SAM service area from January 2011 to May 2017. See Midcoast ECO's SAM Status Update and SAM/MWSD Flow Analysis Report – March 7, 2018 for details.


The largest of these spills (344,000 gal) resulted in a $300,000 fine and regulatory enforcement action by the San Francisco Regional Water Quality Control Board (RWQCB) directing SAM to complete replacement of the Intertie Pipeline System (IPS) and add more sewage storage capacity by December 31, 2019 in order to reduce excessive wet weather flow into the SAM treatment plant. IPS sections 1-3 were replaced in 2018 and SAM also initiated a preventative maintenance program. However, the project to increase wet weather sewage storage capacity from 200,000 gallons to 400,000 gallons next to the Portola Pump Station started late and there have been 11 additional SSOs from June 2017 to August 2020 that have spilled a total of over 10,000 gallons of raw sewage with less than half of that volume recovered.


Although other upgrades and repairs continue, the failure rate of old pipes and equipment throughout the system continues to increase, threatening environmental safety and further increasing costs which must be paid almost exclusively by ratepayers. MWSD already raised sewer rates by 47% from 2017-2019 and has approved additional increases in sewer rate charges of 9% per year for 2020-2022. These additional increases will fund $40M in sewer operation and maintenance costs over the next 20 years, barring any catastrophic failures. The Wet Weather storage project is now scheduled to be completed by March 31, 2021. The RWQCB seems to be accepting the delay.

Overview of Local Water and Sewer Service Providers


Water service is provided by Montara Water and Sanitary District (MWSD) for Montara and Moss Beach and by Coastside County Water District (CCWD) for El Granada and Half Moon Bay (HMB). Primary sewage collection service is provided by MWSD for Montara and Moss Beach and by Granada Community Service District (GCSD) for El Granada. HMB provides primary sewage collection within its city limits.


The Sewer Authority Mid-Coastside (SAM) provides secondary sewage collection and treatment for all 3 agencies according to a Joint Powers Agreement (JPA). SAM is governed by a board of 8 directors (4 from HMB, 2 from GCSD and 2 from MWSD) and expenses are shared according to sewage volume. From August 2019 to July 2020, relative volumes averaged 58% for HMB, 21% for GCSD and 21% for MWSD.

According to a San Mateo County Sea-level Rise Vulnerability Assessment from 2018, the SAM sewage treatment plant is highly vulnerable to sea level rise and creek backup and is subject to ground water infusion in the event of flooding. Inundation would likely cause a loss of service. For these reasons, the plant’s adaptive capacity was rated as “low”.

Age of Coastside’s Only Sewage Treatment Plant Exceeds Projected Lifetime

The 42-year old SAM plant has reached the end of its projected lifetime and will need to be replaced within the next few years. A new plant could cost $100-500 million, depending on the chosen site and design criteria. Despite the fact that there are no alternatives for sewage treatment on the Coastside if SAM should fail, there are currently no plans to replace the plant.


In addition, HMB’s 4-year old lawsuit against the other SAM partner agencies and HMB’s refusal to pay their share for improvements in disputed portions of the infrastructure have disrupted the SAM partnership and delayed critically important projects. HMB’s delay of the Wet Weather Storage Project added almost 100% to the project’s budgeted cost. Such budgetary and governance issues at SAM remain significant, further jeopardizing key decisions and timely repairs, as well as adding unnecessary operational and legal expenses to the 3 partner agencies.

Undue Risk of Large Development Projects

Overall, these issues raise significant questions as to whether our local water and sewer infrastructure can accommodate new large development projects that significantly increase new connections, without added risk of water service interruptions or sewage system failure. In addition, large development projects should require additional fire water storage, rather than relying only on water storage of the overall system.