Stormwater Ordinance

The County of San Mateo Stormwater Ordinance is a local regulation for the unincorporated county area that implements a state-mandated program to protect and enhance watercourses, wetlands, the San Francisco Bay and Pacific Ocean by reducing pollutants and eliminating non-stormwater discharges into the county storm drain system. In most cases, stormwater entering storm drains is untreated and can carry pollutants and sediment directly to watercourses and waterbodies.

Ordinance Update

The County of San Mateo is subject to a Municipal Regional Stormwater National Pollutant Discharge Elimination System (NPDES) permit that is issued by the State Water Resources Control Board. The State Board’s permit is updated periodically and covers multiple cities, counties, water and flood control districts within the Bay Area. The latest comprehensive update of the NPDES permit occurred in May 2022, prompting this Stormwater Ordinance update.

History of the Ordinance

February 14, 1995: Adoption of the Stormwater Managment and Discharge Control Ordinance (Ordinance 3633)
San Mateo County Ordinance, current: Chapter 4.100 Stormwater Managment and Discharge Control
Drafted Update: The proposed Ordinance update is the first comprehensive updates since the initial adoption.

Collaboration

County staff from the Sustainability Department, Department of Public Works, Planning and Building, Parks, and Environmental Health Services have collaborated to revise the County’s Stormwater Ordinance.

Purpose

The purpose of the Ordinance update is to align with state-mandated changes, provide authority to implement and enforce new NPDES permit provisions, and reflect the shared responsibility across county departments for coordination and compliance.

In addition, the County has updated the County Drainage Manual and three Stormwater Enforcement Response Plans (ERP), linked below. These supporting documents help implement the Ordinance by providing guidance to county staff and the public regarding new development, redevelopment, and enforcement. These documents are incorporated by reference in the Ordinance and may be revised as needed by county staff.

Comparison of Changes

Incorporation of New Permit Provisions: Updated NPDES permit provisions have been integrated into the Ordinance to ensure regulatory compliance.
Legal Authority to Enforce: The ordinance ensures the County maintains the authority to enforce new state mandates, including trash control and pollutant inspections on private properties.
New Definitions: Expanded definitions including Areas of Special Biological Significance and expanding the scope of Authorized Enforcement Officials to additional departments.
Department Coordination Lead: The ordinance now reflects the shared stormwater management responsibilities across multiple County departments with the Sustainability Department leading coordination efforts.
Incorporated by Reference: For a more streamlined, navigable, and comprehensive ordinance, key supporting documents are incorporated by reference rather than direct inclusion. These documents include the following: Basin Plan, Drainage Manual, Commercial and Industrial Business Inspection ERP, Illicit Discharge ERP, and Construction Site Control ERP.