hi there, here's what will probably be an easy question for you but is stumping me, as this is my first time documenting this credit. the form calls for each BMP documentation to input the percentage of site that is being treated. do I need to account for the entirety of the LEED project site, in terms of each BMP treating a percentage thereof? or do I only need to account for the portion of the site that contains impervious surface? the development site for our project will be made up of landscaping and pervious paving, with the only impervious surface being the roof. The roof runoff is all being treated in rain garden(s). If I do need to account for all of the landscaped and pervious paving areas on the form, is it safe to assume they are removing 100% of TSS? The Hydrologic Soil Type for the site is "C", which has me worried. Thanks!

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Michael DeVuono

Regional Stormwater Leader

Arcadis North America

LEEDuser Expert

144 thumbs up

Thu, 08/08/2013 - 11:57

Hi Patricia, you need to treat the 90th percentil runoff volume with a BMP (or BMPs) that remove at least 80% TSS. You can route the entire site through one BMP that does this, or route a portion of the site through a BMP with higher efficiency. This is essentially a math problem. You must use your entire site for the runoff calculation, this is what produces the runoff volume, but like I said above, you do not necessarily need to treat the entire site if you over-compensate in other areas. As to your other question, even lawn and landscaped areas produce polluted runoff (in some cases more than the roof, which is essentially clean water), so no you can not net these areas out of your calcs.

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