Site Conditions - The site consists of 4.74 acres located on the north side of Ballenger Creek Drive and south of interstate 70. The majority of the site has been graded to be relatively flat with slopes of approximately 3% to 4%. Along the sites eastern boundary a large swale conveys drainage to a 4\' x 12\' concrete box culvert under Ballenger Creek Drive. The constructed portion of the site has approximately 24,000 sq. ft of paving for a parking lot. A pre-existing storm sewer system runs through the site and conveys drainage from the adjacent commercial site to the west through the site to the existing storm drain system in Ballenger Creek Drive. The site drainage from this area and the site is conveyed to a regional Stormwater management pond. The pond was designed in accordance with the MD 2000 Stormwater Management Regulations and follows the guidelines of the Maryland Stormwater Design Manual. The manual was used as a standard by USGBC when developing the requirements and guidelines for the credit. The pond was approved by the City of Frederick in 1998. This pond was designed to handle hundreds of acres in the region. Our Request - We are asking for clarification on whether or not our off-site pond and our approach qualify the project for the credit. Under the regulations in effect at that time, the 2 year, 10 year and 100 year storms were controlled for quantity within the pond. Extended detention of the 1 year storm was used in the pond for quality. All design storms are 24 hour storms. The 1 year extended detention meets the current MD 2000 Regulations for Channel Protection volume (Cpv). Our approach in meeting the requirements of this credit are through Option 1, section 2 - "Provide a narrative describing..", as we cannot get design computations for the Stormwater management pond. Water quality is addressed on site with structural BMP\'s. Although the post-development discharge from this site is higher than the pre-development discharge because it is not managed on site, we believe we meet the credits\' intent by channeling Stormwater to a detention pond, managing quality with structural BMP\'s and protecting streams from Peak discharge rates.
As noted in LEED-NC v2.2 CIR ruling dated 9/4/2006 for SSc6.2, an off-site stormwater management system in a campus (or master-planned) context can be used to achieve SSc6.2 provided that the stormwater management system meets credit requirements for all areas that it serves. The applicant will need to provide calculations demonstrating that the required rainfall amount, as described on p. 97 of the LEED CSv2.0 Reference Guide, as applied to all areas discharging to the off-site pond, receives the requisite level of treatment. In addition, the applicant will need to provide a narrative to demonstrate that it is appropriate that this project is considered in the context of the LEED-NC Application Guide for Multiple Buildings and On-Campus Building Projects (AGMBC). A comparable CIR Ruling dated 8/22/2008 for SSc6.1 LEED NCv2.2 also appears to be applicable to this project. It states, "the requirements for credit SSc6.1 can be met by demonstrating that the existing (or improved) stormwater management systems that serve the LEED Site Boundary meet the LEED requirements for all areas within the site serviced by those systems." The applicable LEED requirements for this project appears to be those outlined in Option 1-b: Stream Channel Protection, since the post-development quantity exceeds the pre-development quantity. To comply with this option, the project will have to demonstrate both quantity control strategies and stream channel protection strategies as part of the stormwater management plan. The off-site existing pond could be used as a stream channel protection strategy via rate reduction; if calculations are performed to confirm that the pond is appropriately sized for this purpose. Quantity control strategies could include on-site infiltration areas, rainwater catchment and reuse systems, etc.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.