Determining Retention Requirements

Hi Nadia, my apologies for the super delayed response! The answer is yes. We were able to use the full stormwater volume captured within our LEED boundary. Our team ended up consulting multiple LEED Coaches to get to the bottom of this issue. Per their responses: "For the purposes of LEED calculation, we do allow different calculation methodology (outlined in the EPA's Technical Guide for Federal Projects). LEED does not require the project team to cap the bioretention management volume, but we do expect the calculated infiltration rates and biorention volume to make sense per the site design, the medium, and regional soils. Projects must be able to demonstrate via calculation that the site is designed to retain onsite, the required volume from the 90th percentile storm event.""The credit does not set a limit for the amount of infiltration that can be achieved by a particular measure. If professional engineering judgement indicates a specific level of performance can be achieved, the LEED credit does not limit that. As mentioned in the v4 Reference Guide > Further Explanation (https://www.usgbc.org/credits/new-construction-core-and-shell-schools-new-construction-retail-new-construction-data-8?view=guide&return=/credits/New%20Construction/v4/Sustainable%20sites#Further_explanation):The project team may choose the runoff volume calculation methodology most appropriate for the project, provided sufficient documentation and justification to demonstrate that the intent of the credit is being met.We asked a follow up question to verify if the LEED Coaches were using "Biorention" and "Infiltration" interchangeably. "I think the answer depends on how you are defining "Bioretention." If your system is only delaying the release of runoff to moderate the volume and speed of runoff, then it would not be meeting the credit. The intent is to manage, by infiltration, evapotranspiration or reuse, the total volume of runoff from the 24-hour storm being analyzed, within the LEED project boundary."With this combination of responses, we submitted documentation that included the full stormwater bioretention volume and successfully appealed the credit for 3 points + 1 Regional Priority point!