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NC-2009 SSc6.1:Stormwater Design—Quantity Control

Underground Storage Chambers

To reduce runoff peak and quantity our project team used an embedded underground chambers system. In this practice, the only chambers waterflow outlet is water exfiltration on surrounding soil. As far as you know, Is the underground Exfiltration cosidered as runoff, or as a water management system to reduce and prevent it?

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Profile picture for user Mike Dee
Michael DeVuono
Regional Stormwater Leader
Arcadis North America
LEEDuser Expert
144 thumbs up

Mon, 02/08/2016 - 13:35

According to your scenario, whatever gets into the underground chambers is infiltrated, and therefore, is not considered runoff. The only runoff you would have on your site is that which bypasses your system, if any.

Mon, 02/08/2016 - 14:47

Thanks Michael. From the data i modeled on Hydrocad, it results that the soil is so pervious ( 2,880 mm/h - 0,0008 m/s ) that water don't even storage into chambers but directly infiltrates underground. Is it possible to achive a zero runoff in a teorethical model as the runoff calculation? I think GBCI is gonna reject it.. How can i do to demonstrate compliance?
Profile picture for user Mike Dee
Michael DeVuono
Regional Stormwater Leader
Arcadis North America
LEEDuser Expert
144 thumbs up

Mon, 02/08/2016 - 14:59

That infiltration rate doesn't seem realistic for any soil that is suitable for construction. I would check that rate first. While LEED doesn't require it, I never use more than 10-15 in/hr as an infiltration rate, and always apply a FOS=2. But to answer your question: "Is it possible to achive a zero runoff in a teorethical model as the runoff calculation?" Yes, you just did it.

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