Has anyone ever utilized a bio-retention basin with an underdrain that eventually slowly releases the filtered runoff and discharges to a stormdrain system instead of infiltrating naturally to the subgrade to achieve the requirements of this credit? Our site is a greenfield, so we fall within the less than 50% impervious category. It is located in the southwest and the soil conditions do not allow for adequate infiltration on site; mostly limestone. There are no stream channels that the storm water will directly drain to, so option 2 does not seem feasible. Does anyone have an opinion on if this credit is able to be achieved if all stormwater is not being retained, infiltrated, evapotranspired, or reused on site?