The goal of Provision C.3 of the Municipal Regional Stormwater Permit (MRP) is to include appropriate source control, site design, and stormwater treatment measures in new development and redevelopment projects. These measures are intended to address both soluble and insoluble stormwater runoff pollutant discharges and prevent increases in runoff flows from new and redevelopment projects. The C.3 goal is to be accomplished primarily through the implementation of low impact development (LID) techniques. 

The C.3 Stormwater Technical Guidance (updated March 22, 2023) document provides guidance on Low Impact Development (LID) Requirements, numeric sizing calculations, using site design measures, and the hydromodification management (HM) standard.  

MRP Regulated Projects are defined in the following categories:

Small Projects and Detached Single-Family Home Projects

Projects that create and/or replace at least 2,500 square feet, but less than 10,000 square feet, of impervious surface, and individual single-family homes that create and/or replace 2,500 square feet or more of impervious surface must include at least one of the following site design measures: 

• Direct roof runoff into cisterns or rain barrels for use and/or onto vegetated areas 
• Direct runoff from sidewalks, walkways, and/or patios onto vegetated areas 
• Direct runoff from driveways/uncovered parking lots onto vegetated areas 
• Construct sidewalks, walkways, and/or patios with permeable surfaces 
• Construct bike lanes, driveways, and/or uncovered parking lots with permeable surfaces 

Submittal Documents and Resources for Small Development Projects: 

Small Projects and Single-Family Home Projects, as defined by section C.3 of the MRP, are required to complete the Stormwater Requirements Checklist Form for Small Projects and Construction Best Management Practices Plan Sheet (BMPS). The project contractor is required to implement the applicable BMPS on the plan sheet. 

Regulated Development and Redevelopment Projects

New development and redevelopment projects that create 10,000 square feet or more of impervious surface (collectively over the entire project site) including commercial, industrial, residential housing subdivisions (i.e., detached single-family home subdivisions, multi-family attached subdivisions (town homes), condominiums, and apartments), mixed-use, and public projects are required to treat the permit-specified amount of stormwater runoff with Low Impact Development (LID) methods. 

Click here for an Overview of the Stormwater Quality Control Requirements 

As of December 1, 2011, stormwater treatment requirements must be met using evapotranspiration, infiltration, and/or rainwater harvesting and reuse. Where this is infeasible, landscape-based treatment measures with underdrains may be used. 

The Stormwater Management Plan Content (currently under development) contains all necessary information that must be provided on the Stormwater Management Plan (SWMP) sheet when submitting plans for entitlement or building permit review. 

A “Stormwater Treatment Measures Maintenance Agreement” (O&M Agreement) is required for all projects incorporating stormwater treatment or hydromodification management measures.  

Sample Maintenance Plans and Inspection Checklists for Reference: 

• Extended Detention Basin Inspection Checklist
• Extended Detention Basin Maintenance Plan
• Pump System Inspection Checklist
• Pump System Maintenance Plan
• Vegetated Buffer Strip Inspection Checklist
• Vegetated Buffer Strip Maintenance Plan

 Special Land Use Categories

Projects that create and/or replace 5,000 square feet or more of impervious surface related to the following categories of land use will be required to provide LID stormwater treatment: 

• Auto service facilities
• Retail gasoline outlets
• Restaurants, and/or
• Uncovered surface parking (This applies to stand-alone parking, or parking included as part of any other development project. It also applies to the top uncovered portion of a parking structure, unless drainage from the uncovered portion is connected to the sanitary sewer.) 

Special Land Use Category Projects and Other Development and Redevelopment Projects, as defined by provision C.3 of the MRP, are required to complete the Stormwater Requirements Checklist Form. This form will assist both the project applicant and City staff through the planning/permitting process and will help identify the pertinent stormwater requirements. 
 

Special Projects

When considered at the watershed scale, certain land development projects characterized as smart growth, high density, or transit-oriented development can either reduce existing impervious surfaces or create less “accessory” impervious areas and automobile-related pollutant impacts. Incentive LID Treatment Reduction Credits approved by the Water Board may be applied to these Special Projects, which are Regulated Projects that meet the specific criteria. 

Submittal Documents and Resources for C.3 Special Projects: 

Complete the Special Projects Worksheet to assist in determining whether a project meets Special Project criteria, and the percentage of low impact development (LID) treatment reduction credit. Special Projects that implement less than 100% LID treatment must provide a narrative discussion of the feasibility or infeasibility of 100% LID treatment.