You bring up a good discussion. Typically when SSc6.1 is evlauated, you can use the Rational Method to determine the peak rate and volume of runoff for the 1 and 2-year, 24 hour storms or the NRCS method is used for volume of runoff. Both of these methods consider infiltration in developing their respective results, NRCS through soli types, and Rational Method through the runoff coefficient.

However, your question seems to imply that you would like to consider the use of a BMP or LID strategy to help meet the peak flow and volume reduction criteria in your discharge calculations. Certainly, the soil infiltration will have an effect on how effective these BMP's are in minigating the flow and volume; if the soil is a clay that does not infiltrate, the BMP will still be mostly full when the next storm hits and the BMP will not be effective in reducing the flow or volme. On the other hand, if the soil allows stormwater to infiltrate quickly, it will be very effective. Many times, the soil can be modified to provide greater infiltration.

The end result is that the only way that I know to determine the iniltration rate for a BMP is to have a permeability test completed using standard procedures. Our experience is that even this approach may only be useful during the early life of the BMP, and the permeability of the soil may change basee on the sediment that the BMP is collecting. Maintenance is the key to long term BMP effectiveness.