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County staff outline stormwater ordinance update to align with 2022 NPDES permit
Summary
San Mateo County sustainability staff presented a draft stormwater ordinance update May 28 that would assign shared implementation responsibility to multiple departments, add definitions and enforcement authority, and incorporate new permit provisions; no action was requested at the planning commission meeting.
San Mateo County sustainability staff briefed the Planning Commission on May 28 on a draft update to the county’s stormwater ordinance designed to align local rules with the municipal stormwater permit issued in February 2022 and to give the county authority to implement and enforce new permit provisions.
Sultan Henson, a sustainability specialist, told the commission the draft ordinance would move the county from a single‑department implementation approach (previously environmental health services) to a collaborative structure that explicitly includes the Sustainability Department, Planning and Building, Parks, Environmental Health and the Department of Public Works. Henson said the change reflects the growing complexity of permit requirements and the specialization of county departments.
The draft ordinance adds or expands definitions (including illicit discharge, responsible party and full trash capture devices), updates enforcement authority to a broader set of authorized officials, and references supporting implementation documents such as the county drainage manual and emergency response plans rather than restating technical guidance in the ordinance text. Staff said this structure allows DAF (Division of Administrative Functions / subject department) to update technical manuals without amending the ordinance itself.
Henson described key new requirements incorporated from the regional permit: trash‑reduction measures in high‑trash zones (more common on the Bay side), operations and maintenance agreements for regulated stormwater facilities such as green infrastructure, and explicit authority to stop construction where required best management practices (BMPs) are not in place. Staff reported that county review concluded the ordinance update is categorically exempt from CEQA under Class 8.
Planning and Building staff member Camille Leung explained how the ordinance interfaces with development review. She said new or replaced impervious surface thresholds trigger drainage and treatment requirements: 10,000 square feet for typical existing single‑family parcels, and 5,000 square feet for subdivisions and commercial projects. Leung said drainage controls aim to limit increases in runoff and treatment systems are required to reduce pollutant loads before discharge to receiving waters.
Commissioners asked about how frequently the ordinance is updated, what prompted the change, how the county responds to illicit discharges from older properties, and whether shared departmental responsibility would slow enforcement. Henson said the 2022 regional municipal permit prompted the current revision, that the Sustainability Department would act as the coordinating lead for complaints and response, and that environmental health will continue business‑inspection roles while Public Works and Parks manage physical infrastructure projects.
Staff outlined next steps: the draft ordinance will go to the Board of Supervisors for a first reading followed by a second reading and adoption. Staff said supporting documents and implementation guidance will be published online and can be updated as needed without an ordinance amendment.
There were no public speakers on this item during the meeting. The commission took the briefing as informational and did not act on the draft ordinance at the May 28 hearing.
