1. CREDIT ISSUE Our project is seeking clarification on LEED for New Construction Sustainable Sites Credit 6.1, Quantity Control. Our project treats and manages stormwater directly across the street from the project, using a stormwater management (SWM) pond. This pond was designed as a regional facility specifically to handle this site and other adjacent sites as part of a regional SWM plan. It was always the intention for this pond to handle quality and quantity control for this site. The question is whether or not our stormwater management measures, which are directly adjacent to the project, will qualify for this credit since they are off-site? 2. STRATEGY Our approach is to use the credit\'s Option 1, which requires "a plan to protect the receiving stream from excessive erosion by implementing a stream channel protection strategy and quantity control strategies." Using cross section analysis we can demonstrate that the receiving stream for the SWM pond has adequate capacity, it means that the 10 yr runoff is contained in the bed and banks of the stream. At the same time the cross section analysis will give us velocity for the 2 year runoff that should be equal or less than the allowed velocity for the ground cover of the stream that is specified by State law. 3. INTENT In addition to meeting the technical requirements, we also believe we meet the credit\'s intent, which is to "limit disruption of natural hydrology." By channeling stormwater to a detention and treatment pond we are protecting streams from peak discharge rates, thus maintaining natural hydrology. Furthermore, the design team has placed emphasis on maintaining vegetated open space on the project site. The project exceeds the local zoning\'s open space requirement by 92%, thus improving on-site infiltration and retaining natural functions of the site.
The most effective way to achieve SSc6.1 is to implement a stormwater management plan that prevents the post-development peak discharge rate and quantity from exceeding the pre-development peak discharge rate and quantity for a 2-year 24-hr storm. If the adjacent pond is intended to treat the runoff from the project site, and if it is sized sufficiently to store the developed site increased runoff from a 2-year 24-hr storm, then it can contribute to credit achievement. Please provide volume calculations to show what the pre and post development 2-year 24-hr storm runoff is and some volume calculations for the stormwater management pond to verify that it can store this runoff volume. Alternatively, the project team can demonstrate that receiving stream is protected from excessive erosion by implementing a stream channel protection strategy and quantity control strategies and that the 2 year runoff velocity in the stream is low enough so as not to cause stream erosion. Applicable Internationally.