I am in the processing of accessing the feasibility of attaining this credit with a site that is currently 88% impervious and the proposed site is roughly 81% impervious. While i will be able to show a slight reduction in site runoff via a retention swale (+/- 4%), i am wondering if an exfiltration system would be a means of achieving the additional runoff decrease. I know this goes against the standard runoff reduction calculations, but has this credit been achieved via structured stormwater system?