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Copyrighted by SANTA CLARA COUNTY CODE & Municipal Code Corporation, 1998.

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Sec. B11 1/2-18. Design and Selection of Best Management Practices.

A. Storm water quality best management practices shall be selected and designed to the satisfaction of the Manager of the Development Services Office or designee in accordance with the requirements contained in the most recent versions of the following documents:

1. NPDES Municipal Storm Water Discharge Permit issued to the County of Santa Clara by the San Francisco Bay Regional Water Quality Control Board;

2. Santa Clara Valley Urban Runoff Pollution Prevention Program (SCVURPPP.) "Guidance for Implementing Storm Water Regulations for New and Redevelopment Projects";

3. California BMP Handbooks developed by the California Storm Water Quality Agencies Association (CASQA);

4. "Start at the Source" Design Guidance Manual developed by the Bay Area Storm Water Management Agencies Association (BASMAA) ;

5. Bay Area Storm water Management Agencies Association "Using Site Design Standards to Meet Development Standards for Storm Water Quality - A Companion Document to Start at the Source"; and

6. The SCVURPPP Hydromodification Management Plan, as approved by the San Francisco Bay Regional Water Quality Control Board.

B. Numeric sizing criteria used to design storm water treatment systems shall be in accordance with the County's NPDES Municipal Storm Water Discharge Permit.

1. Storm water treatment measures depending on volume capacity, such as detention/retention units or infiltration structures, shall be designed to treat storm water runoff equal to:

a. The maximized storm water quality capture volume for the area, based on historical rainfall records, determined using the formula and volume capture coefficients set forth in Urban Runoff Quality Management, WEF Manual of Practice No. 23/ASCE Manual of Practice No. 87, (1998), pages 175-178 (e.g. approximately the 85th percentile 24-hour storm runoff event); or

b. The volume of annual runoff required to achieve 80 percent or more capture, determined in accordance with the methodology set forth in Appendix D of the California Storm water Best Management Practices Handbook for New Development and Redevelopment (2003), using local rainfall data.

2. Storm water treatment measures whose primary mode of action depends on flow capacity, such as swales, sand filters, or wetlands, shall be sized to treat:

a. Ten percent of the 50-year peak flow rate; or

b. The flow of runoff produced by rain equal to at least two times the 85th percentile hourly rainfall intensity for the applicable area, based on historical records of hourly rainfall; or

c. The flow of runoff resulting from rain equal to at least 0.2 inches per hour intensity.

(Ord. No. NS-517.74, § 1, 10-17-06)

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