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The Napa County Stormwater Program is implemented to comply with federal stormwater management requirements to improve the health of our creeks, streams and the surrounding environment.  This is accomplished through education and regulation of construction and development practices in Napa County. By discovering new ways to apply Low Impact Development (LID) and implement construction Best Management Practices (BMPs), we can work together to improve the quality of our communities.

The Stormwater section of Engineering Services Division is charged with upholding the regulations set forth by the Clean Water Act (CWA) and the National Pollutant Discharge Elimination System (NPDES) Programs as they relate to construction-site activities.  These regulations are implemented at a local level in Chapter 16.28 of the Napa County Code. 


Construction Appendix A                                                                Post-Construction Appendix A 
Construction Appendix B                                                                Post-Construction Appendix B
Construction Appendix C                                                                Post-Construction Appendix C 


Stormwater Quality Management Plan (SQMP) Example                   County Stormwater Ordinance
Napa County Construction Site Runoff Control Requirements        General Construction Permit
Post Construction Site Runoff Control Requirements                      BMP providers list 
Construction Site Runoff Control Requirements Brochure              Rain Event Action Plan


Napa County Stormwater Pollution Prevention Program
Napa Valley Regional Rainfall and Stream Monitoring System
California State Water Resources Control Board
Fishery Network of the Central California Coastal Counties
California Stormwater Quality Association (CASQA): Main 
California Stormwater Quality Association (CASQA): Stormwater Best Management Practices Handbook

Construction Site Runoff Control Requirements
In order to protect the quality of our waterways, Napa County has established requirements regarding the runoff from construction sites and new development. County Code requires that construction sites implement best management practices (BMPs) during construction in order to protect our water resources. BMPs can vary from the scheduling of construction activities to hydroseeding exposed soils. In all cases the goal is to prevent pollutants from mixing with stormwater runoff. For more information regarding Best Management Practices please read the California Stormwater Quality Association’s BMP Handbook (link above). For more information regarding Napa County Stormwater Regulations please read the Napa County Construction Site Runoff Control Requirements and Napa County Code Chapter 16.28 (link above).
All applicants for construction permits in the unincorporated area of Napa County must conform to these Stormwater Regulations. The Public Works Department will issue a Grading Permit only after the applicant has provided plans that demonstrate compliance with these requirements. Specifically, a Stormwater Quality Management Plan (SQMP) is required for grading projects which involve:
• Slopes of 15% or greater
• Soil disturbance of 10,000 square feet or greater
• Soil disturbance within 50 feet of a Stormwater conveyance system
• Earthmoving of 50 cubic yards or greater
The SQMP must include a site map that identifies all potential pollutants and incorporates BMPs appropriate for site conditions. Appendix C of the Construction Site Runoff Control Requirements provides a checklist to guide applicants in preparing an SQMP. In developing project plans, early consideration of the protection of nearby waterways and sensitive areas is encouraged, and will help avoid delays in the plan review stage. Fees for review of Stormwater plans are based on actual time spent reviewing the plans and conducting site inspections.

In addition to County Stormwater requirements any project that disturbs more than one acre is subject to National Pollution Discharge Elimination System (NPDES) Requirements and must submit a Notice of Intent (NOI) to the State Water Resources Control Board (SWRCB) as well as develop and implement a Stormwater Pollution Prevention Plan (SWPPP). For more information regarding NPDES and State requirements related to stormwater discharges associated with construction activity please read the General Construction Permit and visit the SWRCB Web site.
Post Construction Runoff Management Requirements
Every stream, river, and reservoir is part of a watershed. A watershed is the area of land that captures rainfall and concentrates it into a stream or other drainage. The rain that falls onto a watershed may be infiltrated and recharged into the groundwater, absorbed and transpired by plants, or concentrated into stormwater runoff and discharged into a stream. When buildings, roads, parking lots, and other impervious surfaces are created they change the quantity and quality of stormwater runoff discharged into receiving waters. These impervious surfaces can have a significant impact on water quality and degrade the beneficial uses of receiving waters. These impacts may include increased bank erosion and downstream flooding, siltation of fish spawning grounds, and excessive algae growth.

To minimize the impacts of impervious surfaces, BMPs have been designed to control the runoff rate and quality of stormwater discharged from development projects in an effort maximize water quality protection and minimize construction costs, Post- Construction BMPs emphasize the use of site design and source control measures to reduce the amount of directly connected impervious surfaces and minimize stormwater contact with pollutants. To determine if your project is subject to Post Construction Requirements please complete the Post Construction Appendix A Form. For more information regarding Napa County’s Post Construction Requirements please read the Post Construction Runoff Management Requirements (link above).
Illicit Discharge Reporting
In Napa County it is illegal for anyone to discharge anything to a stormwater conveyance (i.e. stream, ditch, channel, and swale) anything that is not composed entirely of stormwater. In addition, it is prohibited to store, deposit, or place material in a manner that may result in a discharge to a stormwater conveyance. If you witness any of these activities taking place and it is an emergency please call 911, but otherwise please contact the Napa County Stormwater Hotline at (707) 299-1799 or Department of Public Works (707) 253-4351.