Page 94 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

LEED Sustainable Sites 75

Special Considerations and Exemplary Performance
There was no EP point available as related to this credit in LEED 2.2. LEED 2009 allows
for an exemplary performance point to be earned if the project team develops a strategy
to control both stormwater quantity (SSc6.1) and stormwater quality (SSc6.2) substantially
beyond the associated credit criteria.

SS Credit 6.2: Stormwater Management—Quality Control

USGBC Rating System
SSc6.2 is worth one point in LEED 2009 and was worth one point in LEED 2.2. LEED-
NC 2.2 lists the Intent, Requirements, and Potential Technologies and Strategies for this
credit as follows, and is similar for LEED 2009

Intent
Reduce or eliminate water pollution by reducing impervious cover, increasing on-site
infiltration, eliminating sources of contaminants, and removing pollutants from 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 percent 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 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 and Strategies
Use alternative surfaces (e.g., vegetated roofs, pervious pavement or grid pavers) and
nonstructural techniques (e.g., rain gardens, vegetated swales, disconnected imperviousness,
rainwater recycling) to reduce imperviousness and promote infiltration, thereby reducing
pollutant loadings.
Use sustainable design strategies (e.g., Low Impact Development, Environmentally
Sensitive Designs) to design integrated natural and mechanical treatment systems such as
constructed wetlands, vegetated filters, and open channels to treat stormwater runoff.

Calculations and Considerations
In LEED-NC 2.2 and 2009 the requirements for this credit have been simplified, are easily
understood, and are different for different climate zones in the United States. The climate
zone criteria for this differentiation are based on the average annual rainfall rates, and
the zones have been divided into three watershed categories: humid, semiarid, and arid.
By the LEED-NC 2.2 and 2009 definition, humid watersheds receive on average at least
40 in of rainfall per year, semiarid watersheds receive more than 20 and less than 40 in,
and arid zones receive less than 20 in of rain annually.