The goal of Provision C.3 is for the municipalities regulated by the NPDES permit, including the County of San Mateo, to use their planning authorities to include appropriate source control, site design, and stormwater treatment measures in new development and redevelopment projects to address both soluble and insoluble stormwater runoff pollutant discharges and prevent increases in runoff flows from new development and redevelopment projects. This goal is to be accomplished primarily through the implementation of low impact development (LID) techniques.
Not withstanding exceptions listed in Provisions C.3.d and C.3.e of the NPDES Permit, all Regulated Projects are required to implement LID source control, site design, and stormwater treatment onsite. Regulated Projects are defined in the following categories:
Special Land Use Categories: New or redeveloped Auto Service Facilities, Retail Gasoline Outlets, Restaurants, or Uncovered Parking Lots, as defined in Provision C.3.b., that are stand-alone or part of any other development project, that create and/or replace 10,000 square feet or more of impervious surface (collectively over the entire project site).
New development or redevelopment projects that create or replace 5,000 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. Detached single-family home projects that are not part of a larger plan of development are specifically excluded.
Road Projects: Types of road and trail projects as specified in Provision C.3.b. that create 10,000 square feet or more of newly constructed contiguous impervious surface.
LID Treatment Measures
LID treatment measures are harvesting and re-use, infiltration, evapotranspiration, or biotreatment. Require each Regulated Project to treat 100% of the amount of runoff identified in Provision C.3.d for the Regulated Project’s drainage area with LID treatment measures onsite or with LID treatment measures at a joint stormwater treatment facility. A properly engineered and maintained biotreatment system may be considered only if it is infeasible to implement harvesting and re-use, infiltration, or evapotranspiration at a project site. Conditions which may result in infeasibility to implement LID treatment measures are detailed in Provision C.3.c.
|NPDES Provision C.3 Forms, Checklists & Worksheets|
|Infiltration Feasibility Worksheet||Required for C.3 Regulated Projects with onsite soils suitable for infiltration.|
|Rainwater Harvesting and Use Feasibility Worksheet||Required for C.3 Regulated Projects with non-potable water demand that exceeds the screening thresholds in the Project Applicant Stormwater Checklist.|
|Special Projects Worksheet||Required for transit oriented, high density, and/or infill projects that may meet the MRP criteria for Special Projects.|
|Hydromodification Management Appicability Form||The HM applicability form should be completed by municipal staff for projects that create and/or replace 43,560 sq. ft. or more of impervious surface, in order to determine whether the HM requirements apply.|
|C.3 Stormwater Technical Guidance||The Handbook for developers, builders, and project sponsors regarding post-construction stormwater controls for regulated projects, in order to meet local municipal requirements.|
|Stormwater Review Process Flowchart||Flowchart prepared by Regional Stormwater Program outlining the process of determining treatment requirements for C.3 regulated projects.|
|Flow Chart of County NPDES Review (County of San Mateo only)||Flowchart outlining permitting process for Regulated Projects for projects located in the Unincorporated areas of San Mateo County.|
|Operation & Maintenance Documents|
|Operation & Maintenance (O&M) Template Agreement (County of San Mateo only)||Applicant shall customize Template Agreement (using tracked changes) for County review and execution prior to final of the building permit for a Regulated Project.|
|Other NPDES Forms, Checklists & Worksheets|
|Stormwater Treatment Measure Maintenance Plan Templates||The O&M Agreement template requires the applicant to attach Maintenance Plan Template(s) for the appropriate Stormwater Treatment Measure. A variety of Maintenance Plan Template(s) are available in Appendix G of the C.3. Technical Guidance (link as provided).|