EBOM-2009 SSc6: Stormwater Quantity Control 1 point

Some LEED projects sites might include areas which the owner desires to not graded, and plans to restore with landscaping and dedicate as open space. If the project owner decides to do the following items listed below can the space be excluded from the stormwater treatment requirements of this credit? (1) The part of their site is not developed or graded, and was not mass graded by a prior owner. (2) The part of their site is dedicated as open space, and restored if necessary. (3) The part of their site is dedicated as open space, and directly connects to other natural open space thereby increasing native habitat areas. (4) Stormwater runoff from the developed part of the site is fully treated to meet the requirements of this credit. If the above is not enough, what other measures would the project need to undertake to avoid intercepting stormwater from a natural, dedicated open space area simply to treat it to earn this LEED point? Intercepting storm water from such an area as the one described simply to treat it and earn this LEED point would be very harmful to the intent of increasing biodiversity by dedicating and restoring natural open space. If treatment must occur in such spaces then owners would be more likely to develop the area than to dedicate and restore it.

The project site is 60 acres with major components including a hospital campus, parking garages, central utility plant and requisite parking lots and access roadways. We are applying LEED NC Version v2.2. There are 6 outfall points where stormwater leaves the 60 acre site - these are identified as outfall points 1, 2, 3, 4, 5, and 6. Outfall points 1 and 6 discharge into existing drainage channel \'A\'; outfall points 2 and 4 discharge into existing drainage channel \'B\'; outfall point 5 discharges into existing drainage channel \'C\'; and, outfall point 3 discharges into an existing storm sewer system. Existing drainage channels \'A\' and \'B\' are inadequate for capacity and velocity and reflect erosion. Channels \'A\' and \'B\' have been redesigned using Natural Channel Design techniques to provide structurally stable and aesthetically pleasing stream restoration corridors. No stream restoration is proposed downstream of outfall points 3 and 5. The existing imperviousness of the 60 acre site (i.e. current project LEED site boundary) is less than 50%. In our opinion, SSc61 credit compliance cannot be demonstrated under Option 1a (Discharge Rate and Quantity)for outfall points 1 and 6; or outfall points 2 and 4 but can be demonstrated under Option 1b (Stream Channel Protection) whereby the aforementioned stream restoration projects are proposed for existing drainage channels \'A\' and \'B\'. This leaves outfall points 3 and 5. It is our opinion that SSc61 credit compliance can be demonstrated under Option 1a (Discharge Rate and Quantity) for outfall points 3 and 5. Questions 1. The LEED-NC 2.2 submittal template for SSc6.1 is set up to receive Option 1a OR Option 1b. How is the submittal template filled out if certain outfall points from the LEED site boundary comply with Option 1a while the others comply with Option 1b as described in our case here? 2. Under Option 1A of the submittal template for SSc6.1, is the pre/post site runoff rate/quantity filled out based on the 1-yr 24-hr storm or the 2-yr 24-hr storm? The reference guide says to compute both the 1-yr and 2-yr storms but the template only provides room for one storm. 3. Currently we are reflecting 60 acres as our LEED site boundary. This area does not include the aforementioned stream restoration projects proposed for channels \'A\' and \'B\'. Does the 60 acre LEED site boundary have to include the adjacent stream restoration project areas? We are not proposing any new impervious surface in the stream restoration project areas. Are there any potential implications to adding or removing the stream restoration project areas from our current 60 acre LEED site boundary that could impact our LEED approach for this project? 4. What is the likely outcome of obtaining credit SSc6.1 for this project based on this CIR? 5. What additional information would be required to demonstrate SSc6.1 compliance for this project?

Oman Botanic Garden is a broad scale botanic reserve in Muscat, Oman. We are preparing a design submission for our 3 LEED nominated buildings and associated landscape areas. The LEED project footprint is within a much larger general project area of some 550 hectares. The total project area includes large natural landscapes comprising wadis or dry river beds. We have calculated the specified pre and post runoff volumes (SS6.1) and storm event volumes using the Arid Watershed specifications (SS6.2) as per the LEED requirements and have designed detention facilities to meet these requirements. We are proposing to use a traditional water capture and treatment process implemented in Oman known as a recharge dam. Surface water is detained behind a small dam constructed of natural materials in the existing wadi bed. It is then allowed to infiltrate back into the groundwater aquifers. This practice is widely used in arid areas of the Middle East and allows effective recharging of valuable groundwater resources. In order to minimize impact to the landscape the current drainage lines will be used, those being the existing wadis. These wadi areas are located nearby the proposed LEED footprint but not within them. All surface water flowing from the LEED Project will flow to one of two proposed recharge dams within the wadis where infiltration will occur. All detention and infiltration will occur completely within the project site. We are requesting whether the proposed treatment dams can be located outside of the specified LEED footprint but still within the project boundary and requesting confirmation that our assumption of 100% treatment for on site infiltration through this process is correct?

For this project, the proposed condition reduces the existing impervious area by 38% below the existing condition, therefore the project received a waiver for storm water management, quantity control. Stormwater management requirements were met by reducing the existing impervious area on site. The "2000 Maryland Stormwater Management Design Manual" requires a reduction on 20% of existing impervious to meet stormwater management requirements and, in this project, an impervious area reduction of 38% was achieved. If by reducing the existing impervious area by 38%, does our project meet the requirement of the credit?

The NRUCFC Headquarters project is located in the NRUCFC Campus, which is within the Dulles Town Center project in Loudoun County, Virginia. Dulles Town Center is a 540-acre high density mixed used development. When Dulles Town Center was originally planned for stormwater management in the early 1990s, it was done on a regional basis using regional stormwater management facilities. These facilities were designed and constructed to accommodate the future tenants and uses within Dulles Town Center, which includes the NRUCFC Campus. Due to the presence of shallow rock and the low permeability of the existing soils, infiltration measures were not feasible options as stormwater management facilities within Dulles Town Center. The NRUCFC Campus, currently an undeveloped parcel, is planned to be developed as an office park, with the NRUCFC Headquarters project being the 1st building. The NRUCFC Campus drains an on-site regional pond identified as BMP (Dry Pond) Facility at Ramp C (CPAP 1994-0081). Runoff to this facility is detained in a dry pond and discharged directly into a major floodplain downstream. This pond was designed, approved and built in accordance with County BMP standards at the time, which were based on the Occoquan Method in the document entitled, Northern Virginia BMP Handbook - A Guide to Planning and Designing Best Management Practices in Northern Virginia, 1992. LEED stormwater management criteria were not in existence at the time. Today, meeting LEED stormwater management criteria is not required within Loudoun County. However, to meet the intent of SSc6.1 (existing imperviousness of <=50%), additional BMP measures have been provided above those required by State and County regulations for the NRUCFC Headquarters project. These additional measures include enhanced extended detention dry pond, manufactured BMP device (Stormfilter) and two bioretention basins (with underdrain systems). All together, the increase in peak runoff rates for the NRUCFC Campus site is minor: -- 1-year 24-hour storm peak runoff rate (design case): 4.73% increase -- 2-year 24-hour storm peak runoff rate (design case): 3.69% increase The stormwater management plan for the existing pond assumed an impervious coverage of 72% for Dulles Town Center (including the NRUCFC Campus site). However, to minimize runoff leaving the site, the NRUCFC Campus as proposed has reduced this impervious coverage to 39% for the NRUCFC Headquarters project area and to 15% for the NRUCFC Campus area. By significantly reducing impervious area beyond that originally planned, keeping extensive existing tree stands and buffers on-site, proposing extensive landscape plantings, and utilizing existing stormwater management facility, we believe the NRUCFC Campus, and by extension, the NRUCFC Headquarters project, have met the intent of reducing post-development runoff volume (i.e. quantity) from this site. -- 1-year storm runoff volume (design case): 4.30% increase -- 1-year storm runoff volume (with NRUCFC parcel as originally designed): 7.56% increase -- 2-year storm runoff volume (design case): 3.97% increase -- 2-year storm runoff volume (with NRUCFC parcel as originally designed): 7.09% increase While we recognize the importance of reducing post-development runoff volume back to pre-development conditions, it isn\'t always feasible if existing site geology restricts the ability to infiltrate, such as is the case here. In these situations it is more practical to preserve more open space than originally planned and propose additional landscaping to achieve less runoff. Though the project does not reduce the post-development runoff volume back to pre-development conditions, the increases in the runoff rates and in the runoff volumes are minimized. Had the project honored the originally planned 72% impervious coverage, the increase in peak flows and the total runoff volumes would be much higher. Does this approach satisfy the credit intent of SSc6.1?