Stormwater Ordinance

The County of San Mateo Stormwater Ordinance is a local regulation for the unincorporated county area that implements a state-mandated program aimed at protecting and enhancing watercourses, wetlands, the San Francisco Bay, and the 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. 

State Mandates and NPDES Permit

The County of San Mateo is subject to a Municipal Regional Stormwater National Pollutant Discharge Elimination System (NPDES) permit issued by the State Water Resources Control Board. This permit is a critical component of state-level efforts to manage stormwater runoff and pollution. The NPDES permit is periodically updated, covering multiple cities, counties, water, and flood control districts within the Bay Area. 

Recent Update

The most recent comprehensive update of the NPDES permit occurred in May 2022. This update prompted the revision of the County’s Stormwater Ordinance to ensure continued compliance with new state mandates. 

Ordinance Update 

History of the Ordinance

• February 14, 1995: Adoption of Storm Water Management and Discharge Control Ordinance (Ordinance 3633). 

• Recent Update: The proposed Ordinance update is the first comprehensive update since the initial adoption. 

Collaboration

County staff from the following departments have collaborated to revise the Stormwater Ordinance: 

• Sustainability Department 

• Department of Public Works 

• Planning and Building 

• County Parks 

• Environmental Health Services 

Purpose of the Update

The primary goal of the ordinance update is to: 

• Align the County’s ordinance with state-mandated changes. 

• Provide legal authority to implement and enforce new provisions of the NPDES permit. 

• Reflect the shared responsibility across multiple County departments for stormwater management and regulatory compliance. 

Supporting Documents & Updated Documents

In addition to the Stormwater Ordinance itself, the County has updated several key supporting documents to help guide implementation. These documents are incorporated by reference into the Stormwater Ordinance and may be revised as needed by County staff: 

• County Drainage Manual: Provides guidance on drainage systems and water management. 

• Stormwater Enforcement Response Plans (ERPs) Updated for specific areas:  

• • Commercial and Industrial Business Inspection ERP 

• • Illicit Discharge ERP 

• • Construction Site Control ERP 

Document Access

Links to each of these documents (PDF download) are provided above for public access. 

Other Key Documents  

• Basin Plan 

• Ocean Plan 

• National Pollutant Discharge Elimination System (NPDES) Stormwater Permit 

Summary of Changes

The updated Stormwater Ordinance includes several significant revisions, such as: 

• Incorporation of New Permit Provisions: Updated NPDES permit provisions have been integrated into the Ordinance to ensure continued regulatory compliance. 

• Legal Authority to Enforce: The updated ordinance ensures the County has the authority to enforce new state mandates, including trash control and pollutant inspections on private properties. 

• New Definitions: Expanded definitions have been added, including Areas of Special Biological Significance. Additionally, the scope of authorized enforcement officials has been expanded to include additional County departments. 
• Department Coordination Lead: The Sustainability Department will now lead the coordination efforts across multiple departments to ensure effective stormwater management.