My question is regarding Stormwater Quality Control. We are working closely with the Maryland Department of the Environment (MDE) to meet or exceed their requirements for water quality (as well as quantity) management measures. We are using BMPs such as bio-retention, wet swales, sand filters, green roofs, etc. All of the phases of construction are reviewed, approved, and inspected by MDE for sediment control and stormwater management measures. MDE\'s stormwater quality requirements for a re-development site are different than for previously undeveloped land. MDE requires that a minimum of 20% of the pre-existing impervious acreage, and 100% of the new impervious area (area that exceeds the previous amount of impervious acreage) be treated with water quality BMPs. During the seminar we were told that when questions such as this arise, it is important to look at the Intent of the credit. Credit 6.2 Intent states: "Reduce or eliminate water pollution by reducing impervious cover, increasing on-site infiltration, eliminating sources of contaminants, and removing pollutants from stormwater runoff". I believe without a doubt that we are fulfilling that stated intent on this project. In reading the requirements for SS 6.2 it is not clear to me whether USGBC will accept the same type of "philosophy" as MDE for water quality treatment for a re-development site or whether the entire impervious area for the site would have to be treated by BMPs in order to receive this credit.
While the intent of the MDE is laudable, the requirements cannot be considered directly equivalent to LEED requirements. In particular, LEED does not distinguish between pre-existing impervious areas and new impervious areas; the entire impervious area must be considered. To demonstrate credit compliance the project should submit calculations demonstrating that the required TSS and TP removal rates as outlined in the LEED-NC v2.1 Reference Guide are met for the entire site.