Intent
To limit disruption and pollution of natural water flows by managing stormwater runoff.
Requirements
Implement a stormwater management plan that reduces impervious cover, promotes infiltration and captures and treats the stormwater runoff from 90% of the average annual rainfall1 using acceptable best management practices (BMPs).
BMPs used to treat runoff must be capable of removing 80% of the average annual postdevelopment total suspended solids (TSS) load based on existing monitoring reports. BMPs are considered to meet these criteria if:
- They are designed in accordance with standards and specifications from a state or local program that has adopted these performance standards.
OR
- There exists infield performance monitoring data demonstrating compliance with the criteria. Data must conform to accepted protocol (e.g., Technology Acceptance Reciprocity Partnership [TARP], Washington State Department of Ecology) for BMP monitoring.
1 There are 3 distinct climates in the United States that influence the nature and amount of annual rainfall. Humid watershed are defined as those that receive at least 40 inches of rainfall each year, Semiarid watersheds receive between 20 and 40 inches of rainfall per year, and arid watersheds receive less than 20 inches of rainfall per year. For this credit, 90% of the average annual rainfall is equivalent to treating the runoff from the following (based on climate): Humid Watershed - 1 inch of rainfall Semiarid Watersheds - 0.75 inches of rainfall Arid Watersheds - 0.5 inches of rainfall.
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