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by David Mittelman
As it turns out, San Mateo County has the most restrictive septic ordinance in the Bay Area. It is constraining the development in rural areas of more housing, ironically where there is the space to do so, perpetuating unsafe living conditions for farmers, publicized in the aftermath of the shootings in Half Moon Bay in 2023.
Some background first. What is a septic system, and why does this matter regarding housing?
Where there is no access to centralized sewer systems, a septic system consisting of a septic tank and a drain field is used. The septic tank separates solids and liquids. The treated liquid is then dispersed into the drain field, where the soil further filters it before reaching groundwater. Sometimes, there is a requirement for a dual system: a primary and a secondary field. The secondary field is a backup to the primary field, ideally allowing alternating use between the fields to allow each field time to “rest” and recover between uses. Finally, a “reserve” refers to an area of land set aside for potential future use in case the existing septic system needs to be expanded or replaced.
Septic systems are sized based on the number of bedrooms planned. Conversely, the size of the system dictates the number of bedrooms possible. The EPA assumes that an average person uses roughly 75 gallons of water daily. San Mateo County assumes two people will be in every bedroom, or 150 gallons of water per day per bedroom. However, the County does not have a legal definition of a bedroom. Often, it comes down to the discretion of the local planning department to determine what is or is not a bedroom based on, among other things, the width of the door or proximity to a bathroom.
San Mateo County alone requires BOTH a dual system and then 100% reserve for primary and secondary fields, essentially creating a 300% reserve requirement. The next highest reserve requirement is Sonoma County, at only 200%. Additionally, San Mateo County is the only county that requires a property owner to plan and prove a conventional system before planning an alternative. This has the effect of reducing the number of bedrooms possible on a site. Traditional systems require vastly more space than alternative systems that utilize newer technologies. Theoretically, a lot might support a conventional system sized for a three-bedroom home. However, an alternative system in the same space could support 11 bedrooms across a three-bedroom primary residence and four two-bedroom ADUs (accessory dwelling units). However, because of the way San Mateo County has written its ordinance, it doesn’t matter. That property could only be built as a three-bedroom home.
Santa Cruz County has no dual system requirement; it is just a reserve field. Put another way, the same land area used for a conventional system could support twice the bedrooms in Santa Cruz County over San Mateo County. In Contra Costa County, you only need your primary field! That equates to four times the bedrooms of an identical lot in San Mateo County. Also, Sonoma County is the only county with provisions for incinerating toilets, which is a fantastic, time-proven way to avoid the entire problem of septic drain fields altogether.
How can San Mateo County fix its septic policies to create more housing opportunities?
1. Create a legal definition of a bedroom. Sonoma County has a definition, and so should San Mateo County.
2. Remove the requirement to plan a conventional system before planning an alternative one. The current language in the Onsite Wastewater Treatment Systems Manual effectively binds the size of the alternative system to that of a conventional one.
3. Expand the types of systems allowed in San Mateo County to align with the rest of the bay, including recirculating sand filters, mounted beds, at-grade systems/raised sand beds, and pre-approved proprietary treatment technologies. Additionally, San Mateo County should join other counties in allowing alternative systems to support subdivisions.
4. Allow for composting/incinerator toilets in agricultural settings and parks.
5. Remove the dual system requirement.
6. Remove the reserve requirement, or at the very least, allow a secondary field to count as the reserve.
7. For proprietary systems, adopt third-party standards and accept any system that meets/exceeds them. The county should adopt the following standards, requiring any system to meet the requirements of at least one of these certifications: NSF/ANSI 40 and 245, EN 12566.
8. Maintain a list of proprietary systems that pass muster to facilitate adoption and permitting.
Woodside could support many more ADUs than are being pursued; however, many property owners cannot construct them because they cannot expand their septic systems. It is time for San Mateo County to support Woodside and other rural communities by aligning its septic ordinance with the rest of the Bay Area.
This op-ed has a clickbait headline.
The first paragraph attempts to link restrictive septic ordinances with the horrific mass shooting in Half Moon Bay – which is a stretch worthy of any number of national politicians.
The needlessly long middle of the article is a deep dive into septic, alternatives, and a list of demands on San Mateo County.
And finally in the final paragraph the author mentions Woodside and support for ADU’s.
What, if any, was the purpose of this article?
It seems the author wanted to lay out exactly WHAT the current septic ordinance is, what it is based on, in order to demonstrate the ridiculously excessive requirements per San Mateo County that inhibit the construction of more housing, specifically more ADUs in Woodside. Should the County revise its septic system requirements to be in line with other Bay Area housing jurisdictions, it would likely lead to better sanitary facilities for farm workers and the ability to develop housing to meet Regional Housing numbers, as required by the State.
There has been little appetite for change from the County. The rationale is that the money of many would be spent on the needs of few. Eg it isn’t worth it to spend thousands on an Environmental Impact Report to analyze and allow alternate systems, since those who would benefit from these efforts are those comparative few who live in rural areas.
Alluded to in the article was the abhorrent conditions of farm worker housing in Half Moom Bay. Sanitary facilities at many farms have not been upgraded, some because of an inability to do so due to restrictive septic rules. The space requirements to bring systems up to code, expanding fields, etc are just too onerous, encroach on or take away from valuable farm land.
Vulnerable agricultural workers live in substandard conditions. Willing homeowners cannot create more housing opportunities. And Woodside may get heavily penalized for not meeting its housing element goal. All because San Mateo County isn’t motivated to make needed changes to its septic ordinance to bring it into the 21st century.