I am fielding a question for our civil engineer. We are trying to determine if the existing conditions (previously developed) are actually hurting us on this credit, and if there's any alternative way we'd be able to meet requirements and document our situation. Here is his breakdown:

The stormwater drainage design for the project collects and treats 98% of the runoff generated from the site. The existing site soils are environmentally impacted and per the environmental consultant, based on the soils conditions, areas of concentrated infiltration into the subsurface is not feasible. This is a hardship for the project as the proposed design for stormwater outflow from the site cannot be reduced for the 1 and 2 year storm events to be at or below predevelopment conditions. Further, the site historically was previously developed and included industrial/manufacturing uses on the site, which we understand included a significant amount of impervious area on the site. However, detailed record plan information is not available to confirm the exact limits and runoff that was once generated from the site.

Any suggestions for meeting compliance? We will be performing site mitigation based on the previous industrial uses, and extensive mitigation to a waterfront on one side of the project site, including restoration to shorelines and shellfish beds, among other aspects.