ID#1525 made on
SSc6.1 - Stormwater management - rate and quantity
LEED BD+C: New Construction, LEED O+M: Existing Buildings, LEED BD+C: Core and Shell, LEED BD+C: Schools
This inquiry relates to the stormwater management infrastructure on a remote campus of a local University. The project has been developed in phases. In Phase I, a 2.0 acre stormwater basin was constru...
This inquiry relates to the stormwater management infrastructure on a remote campus of a local University. The project has been developed in phases. In Phase I, a 2.0 acre stormwater basin was constructed. This basin exceeds the LEED quantity and quality requirements for 4.0 acres of existing impervious area that now drains to it. The existing impervious area is not part of our LEED applicant project and was previously untreated. This stormwater basin is considered part of our LEED project site and will also treat the runoff from our LEED applicant project. We are now in Phase II, and are adding 8.29 acres of impervious surface to the LEED project site. The stormwater basin constructed during Phase I is being upgraded as part of Phase II, by adding sediment collecting forebays, to increase TSS removal from both existing and new impervious areas draining to this basin. Approximately 6.0 acres (70%) of this new impervious surface will drain into the upgraded 2.0 acre stormwater basin and will be treated to LEED quality requirements. All of the remaining 2.29 acres of new impervious surface the LEED project is adding, in addition to 1.7 acres of existing untreated impervious area, will drain into a rain garden designed to remove at least 80% of the TSS and 40% of the TP in the water. The rain garden will drain into an existing County owned regional stormwater basin, not located on the LEED project site. Because we are treating 5.7 acres of existing impervious surface that is not part of our project plus 6 acres of our LEED project's impervious surface, we are hoping the USGBC will allow us to claim credit equivalence for both SSc6.1 and SSc6.2, despite the fact that 2.29 acres of our LEED project's impervious surface will ultimately drain into an off-site regional basin. Please clarify for our team whether we are likely to qualify for credit equivalence based on the scenario described above.
Based on the description provided, the project will adequately meet SSc6.2 requirements. However, the stormwater management system as designed will not meet the SSc6.1 requirement to control rate and quantity. The project is located in a campus and is utilizing a centralized stormwater basin. For campus applications like this, the LEED-NC Application Guide for Multiple Buildings & On-Campus Building Projects states that if a centralized stormwater management system is utilized, it must be comprehensive for the campus. In this case, the combined approach is somewhat comprehensive for two related phases of development. Only one phase, the current application, is a LEED project. Even if the capacity of the two-acre basin plus the rain garden handles the equivalent of the LEED project's runoff, it is borrowing from the existing capacity meant for Phase I. Capacity to handle all of Phase II's runoff would have to be added in order to achieve credit 5.1.
Update April 15, 2011: Please note that all 2009 projects in multiple building situations must follow the 2010 Application Guide for Multiple Buildings and On-Campus Building Projects, located here: https://www.usgbc.org/ShowFile.aspx?DocumentID=7987. 2009 project teams should check this document for up to date guidance on all multiple building issues. Applicable Internationally.
Related Addenda (Corrections & Interpretations)