I was hoping I could get some advice on obtaining the quantity requirement of SS CR 6.1. We are trying to obtain this credit on an approximate 19 acre site. The site was originally a multi-office complex that will be removed and replaced with a much larger building. The impervious area of the site will be increased slightly (69% to 71%) but we are increasing the quality of the landscaping so the runoff curve number is actually lower than the existing conditions (CN 89 to 87). To achieve this credit the volume of runoff must be 25% lower than the existing conditions for the 2-yr 24hr storm event, which we determined will be 155,347 gal of runoff to remain on-site. There will be 2 underground rainwater cisterns on-site; a 20,000 gal tank to be re-used as graywater within the building and a 105,000 gal tank to be re-used for irrigation purposes. My first question is when calculating the volume for the underground tank, can I only use the total (125,000 gal) or can I determine a draw down and get some additional volume. Secondly, due to the volume shortage we are proposing to create a constructed wetland with enough storage volume to achieve this credit. Unfortunately the soil conditions are not great and we can only expect an infiltration rate around 0.04 in/hr. Although, with the wetland we will see some evaporation and evapotranspiration rates that would increase the volume of removed from the wetland. Will this rate need to be quantified for this credit, if so is there some documentation out there to help determine this. Also, in general do you think what we are proposing will satisfy the intent of the credit or do you think we are out of luck, other than adding more pervious surface? Thanks