SS Credit 6.2: Stormwater Design: Quality Control
1 Point
Intent
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
rainfall using acceptable best management
practices (BMPs).
BMPs used to treat runoff must be capable of removing 80% of the
average annual post development total
suspended solids (TSS) load based on existing monitoring reports.
BMPs are considered to meet these criteria
if (1) they are designed in accordance with standards and
specifications from a state or local program that has
adopted these performance standards, or (2) there exists in-field
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.
Potential Technologies & Strategies
Use alternative surfaces (e.g., vegetated roofs, pervious pavement
or grid pavers) and nonstructural techniques
(e.g., rain gardens, vegetated swales, disconnection of
imperviousness, rainwater recycling) to reduce imperviousness
and promote infiltration thereby reducing pollutant loadings.
Use sustainable design strategies (e.g., Low Impact Development,
Environmentally Sensitive Design) to design
integrated natural and mechanical treatment systems such as
constructed wetlands, vegetated filters, and open
channels to treat stormwater runoff.
In the United States, there are three distinct climates that
influence the nature and amount of rainfall occurring on an annual
basis.
Humid watersheds are defined as those that receive at least 40
inches of rainfall each year, Semi-arid 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:
(a) Humid Watersheds – 1 inch of rainfall;
(b) Semi-arid Watersheds – 0.75 inches of rainfall; and
(c) Arid Watersheds – 0.5 inches of rainfall.
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