Folks:

We have a project (existing imperviousness > 50%) where we have calculated that through a combination of green roof, pervious pavers, landscaped open space, and a rainwater cistern we can reduce the peak discharge rate and quantity by 25% per LEED reqs for SSc6.1. Based on rainfall patterns, we assume that we need to draw down the cistern in 2 days to accommodate potential back-to-back storms. It's really unclear to us whether or not it is acceptable to draw down the cistern by draining into the storm sewer or whether we must infiltrate, evapotranspire, or otherwise reuse all of the water on site. We'll use the cistern for irrigation in summer, but otherwise it is effectively serving as a detention tank.

Is detaining stormwater and then discharging it to the stormwater acceptable, provided you reduce the peak 24 hr discharge rate per LEED requirements? This certainly has benefits (we are in a CSO area) but does not seem to meet the full intent. My confusion is compounded by the language on LEED User (above):

"Is it an acceptable strategy to capture the rainwater into tanks and discharge it into the public sewers after the rainstorm reducing the peak discharge?

This is a common strategy for reducing peak rate, which will help you comply with SSc6.1, but you'll need to add onsite reuse or infiltration to meet SSc6.2 requirements."

I don't see why onsite reuse or infiltration are required to meet SSc6.2 (other methods remove TSS), and so it makes me think that this should say "you'll need to addd... to meet SSc6.1 requirements."

Thanks for your help,

Michael