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LEED v2009
Existing Building Operations
Sustainable Sites
Stormwater Quantity Control

LEED CREDIT

EBOM-2009 SSc6: Stormwater Quantity Control 1 point

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Requirements

Option 1
During the performance period, implement a stormwater management plan that infiltrates, collects and reuses runoff or evapotranspirates runoff from at least 15% of the precipitation falling on the whole project site both for an average weather year and for the 2-year, 24-hour design storm. Implement an annual inspection program of all stormwater management facilities to confirm continued performance. Maintain documentation of inspection, including identification of areas of erosion, maintenance needs and repairs. Perform all routine required maintenance, necessary repairs or stabilization within 60 days of inspection.

OR

Option 2
Use Low Impact Development (LID)1 practices to capture and treat water from 25% of the impervious surfaces for the 95th percentile of regional or local rainfall events. Implement an annual inspection program of all stormwater management facilities to confirm continued performance. Maintain documentation of inspection, including identification of areas of erosion, maintenance needs and repairs. Perform all routine required maintenance, necessary repairs or stabilization within 60 days of inspection.
1Low impact development (LID) is an approach to managing stormwater runoff that emphasizes on-site natural features to protect water quality by replicating the natural land cover hydrologic regime of watersheds and addressing runoff close to its source. Examples include better site design principles such as minimizing land disturbance, preserving vegetation, minimizing impervious cover, and design practices like rain gardens, vegetated swales and buffers, permeable pavement, rainwater harvesting, and soil amendments. These are engineered practices that may require specialized design assistance.

Alternative Compliance Paths (ACPs)

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Frequently asked questions

Where do I find information about the 2-year 24-hour storm for my location?

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What is the best way to determine the slope of vegetated areas?

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What value should we use for the runoff coefficient for our pervious paving?

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We have an international project and don’t know where to find data for the 2-year 24-hour storm. Where can we find this information?

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What is the runoff coefficient for water bodies like pools and ponds onsite?

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Addenda

1/8/2010Updated: 2/14/2015
Reference Guide Correction
Description of change:
Replace the text in the second paragraph titled "Volume Captured via Collection Facilities" with the following:For less complex sites without detention facilities, teams can perform awater balance to determine if a proposed reduction in impervious areaand/or rain capture systems will result in the required reduction in siterunoff. However, in order to determine the discharge rate and quantityfrom a site with a wet or dry detention facility, project teams should makea detailed analysis of the stage-storage relationship of the detentionfacility, coupled with an analysis of any control structures used toregulate discharge. Drawdown rates due to infiltration and thereforegeotechnical conditions will also need to be considered. While it ispossible to perform these types of calculations by hand, a computersimulation model is more typically used and recommended.
Campus Applicable
No
Internationally Applicable:
No
7/6/2012Updated: 2/14/2015
Rating System Correction
Description of change:
Add the following footnotes to the bottom of the page:1.The baseline condition is the site condition prior to LEED registration.2. low impact development (LID) is an approach to managing stormwater runoff that emphasizes on-site natural features to protect water quality by replicating the natural land cover hydrologic regime of watersheds and addressing runoff close to its source. Examples include better site design principles such as minimizing land disturbance, preserving vegetation, minimizing impervious cover, and design practices like rain gardens, vegetated swales and buffers, permeable pavement, rainwater harvesting, and soil amendments. These are engineered practices that may require specialized design assistance.
Campus Applicable
No
Internationally Applicable:
No
7/6/2012Updated: 2/14/2015
Global ACP
Description of change:
Add "OPTION 1" before first paragraph
Campus Applicable
No
Internationally Applicable:
Yes
2/22/2010Updated: 2/14/2015
Reference Guide Correction
Description of change:
Replace the text in the third paragraph titled "Volume Captured viaRetention Facilities" with the following:"For less complex sites without detention facilities, teams can perform awater balance to determine if a proposed reduction in impervious areaand/or rain capture systems will result in the required reduction in siterunoff. However, in order to determine the discharge rate and quantityfrom a site with a wet or dry detention facility, project teams should makea detailed analysis of the stage-storage relationship of the detentionfacility, coupled with an analysis of any control structures used toregulate discharge. Drawdown rates due to infiltration and thereforegeotechnical conditions will also need to be considered. While it ispossible to perform these types of calculations by hand, a computersimulation model is more typically used and recommended."
Campus Applicable
No
Internationally Applicable:
No
11/1/2011Updated: 2/14/2015
Reference Guide Correction
Description of change:
Revise the third equation box to:Qr = (800 cf / 259,200 sec) = (0.003 cfs or 1.35 gpm)
Campus Applicable
No
Internationally Applicable:
No
7/6/2012Updated: 2/14/2015
Global ACP
Description of change:
Add the following after the second paragraph:OROPTION 2Use Low Impact Development (LID) practices to capture and treat water from 25% of the impervious surfaces for the 95th percentile of regional or local rainfall events.Implement an annual inspection program of all stormwater management facilities to confirm continued performance. Maintain documentation of inspection, including identification of areas of erosion, maintenance needs and repairs. Perform all routine required maintenance, necessary repairs or stabilization within 60 days of inspection.
Campus Applicable
No
Internationally Applicable:
Yes
7/6/2012Updated: 2/14/2015
Global ACP
Description of change:
Delete the Alternative Compliance Path for Projects Outside the U.S.
Campus Applicable
No
Internationally Applicable:
Yes
5/23/2008
LEED Interpretation
Inquiry:

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?

Ruling:

The project has reduced impervious area by 38% and seeks compliance with SSc6.1 on this basis. Peak flow rates and volume do have a relationship with impervious area. However, if a reduction in impervious area will result in compliance with the requirements of SSc6.1, than it is the responsibility of the project team to perform calculations of the pre- and post-development runoff volumes as described in the LEED-NC v2.2 Reference Guide to demonstrate that compliance. Applicable Internationally.

Campus Applicable
No
Internationally Applicable:
Yes
8/22/2008
LEED Interpretation
Inquiry:

Using LEED-NC 2.2 & applying the on-campus application guide for a new building in an existing campus setting, can credits 6.1 & 6.2 be met by an analysis of an existing on-campus detention pond constructed at the time of original campus construction (1970\'s), provided that the pond meets or is upgraded to meet these requirements? If not isn\'t LEED punishing the institutions that had the foresight to plan effectively and implement appropriate storm drainage practices before it was the popular thing to do? The proposed approach would use the native lands prior to 1970 as the pre-development site condition (imperviousness less than 50%) and require that post-campus construction storm water (including all existing & future planned buildings / improvements) meet the requirements of 6.1 & 6.2. Should the existing pond prove adequate to meet the requirements then the project could count the credits, if not then improvements to the existing pond could be made to meet the requirements and achieve the credits.

Ruling:

For the purposes of SSc6.1, the applicant would like to base the pre-development conditions for a university campus on those conditions that existed prior to initial construction in the 1970\'s. The intent of this credit is to limit disruption of natural hydrology and therefore it is acceptable to consider the pre-development conditions as those that existed prior to initial construction. Similar to the campus compliance option outlined in LEED-NC v2.2 SSc6.2 CIR ruling dated 9/4/2006, 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. Applicable Internationally.

Campus Applicable
No
Internationally Applicable:
Yes
2/26/2009
LEED Interpretation
Inquiry:

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?

Ruling:

The project team is requesting whether their efforts to reduce the post-development stormwater discharge rate and quantity from their low permeability site meets the intent of the credit, even though they are still above the pre-development levels. Based on the description provided, the project does not meet the intent of the credit. However, if the stormwater management plan was expanded to include additional on-site quantity control strategies (such as a rain catchment system), AND stream channel protection strategies, then the project could pursue the Option 1B compliance path in the NCv2.2 Reference Guide. Applicable Internationally.

Campus Applicable
No
Internationally Applicable:
Yes
9/4/2006
LEED Interpretation
Inquiry:

The intent of SSc6.2, interpreted from the manual and subsequent CIRs, is to minimize the disruption and pollution of natural water bodies by contaminated stormwater. To meet the Credit Intent, the Requirements specify active TSS treatment of stormwater, using BMPs that reduce the percentage of contaminants in the runoff. The project site is 5.24 acres and has 3 acres of impervious surfaces. The site is part of an overall 75 acre master plan that empties it\'s stormwater into Tributary A, North Buffalo Creek. There is an existing retention pond in the middle of the Park that is adjacent and just North of the Site (not located within the project site for LEED). The drainage area to the pond is +/- 44 acres of highly developed office and commercial property and 70% of this area is impervious. The project site is included within these 44 acres. The pond drain is an open pipe with headwall. The outlet pipe runs underground through the Site and empties upstream of the proposed building into Tributary A, North Buffalo Creek. The Site has an existing storm sewer outflow system designed and sized for future development of this site plus the upper buildings and parking lots (approximately 9 acres). This system empties directly into Buffalo Creek downstream of the proposed LEED building. We propose to modify the spillway of the existing pond to treat approximately 110,000 C.F. of stormwater for the extended acreage in lieu of treating stormwater only for the project site. Of the overall 75 acre master plan, +/- 44 acres runoff into the pond and contain untreated water, entering and exiting the pond without allowing pollutants and suspended solids to be removed. Given the existing stormwater system, it does not make sense to treat stormwater on the project site, but rather to treat all of the stormwater from the larger 44 acre site. We believe that treating the 44 acres will meet and exceed the intent of the credit for the following reasons: 1) We will create a new spillway with an orifice that stores the first inch of runoff for the entire 44 acres, which will achieve 85% TSS removal based on existing monitoring and will be constructed in accordance with the Greensboro Stormwater Design Manual. 2) The project site is part of a 75 acre master plan and by creating the spillway we will be maximizing the positive impact on the overall water quality entering Tributary A, North Buffalo Creek for an area that is 25 times the project site\'s size. The spillway will also resolve any associated stormwater system issues that were previously designed and constructed in a less environmentally friendly manner. We believe that we meet and exceed the intent of SSc6.2 because we are aiding in the overall water quality improvement and pollution minimization for the Buffalo Creek through stormwater quality control and therefore will earn this credit. Please confirm that achieving the treatment requirements for the larger 44 acre site will enable the project to earn the credit and perhaps be eligible for an exemplary performance ID credit. Also please confirm that we will be able to earn this credit by treating the Stormwater outside the project site as defined for the LEED submission.

Ruling:

Yes, achieving the TSS removal requirements for the larger 44 acre site as described will warrant the award of SS Credit 6.2. In accordance with the LEED-NC Application Guide for Multiple Buildings and On-Campus Building Projects (AGMBC), a centralized approach to stormwater management is acceptable. Submittal documentation will require the project team to demonstrate that the centralized BMP adheres to the credit requirements for all current development within the site serviced by the BMP. However, the project will not be awarded an Innovation in Design credit for Exemplary Performance of SSc6.2 as a result of these efforts. The approach of modifying the spillway to treat the stormwater for the extended acreage requires the BMP to be able to treat all current and future development. Therefore, the proposed BMP meets, but not exceed the requirements of this credit. Furthermore, page 85 of the LEED-NC v2.2 Reference Guide states that there is no exemplary performance point available for this credit.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.

Campus Applicable
No
Internationally Applicable:
Yes
7/10/2001
LEED Interpretation
Inquiry:

The existing imperviousness of the project\'s urban site is 74%, mostly due to surface asphalt parking lots. A portion of the stormwater runs offsite while the remainder is piped to drywells. The new development will have a net imperviousness of approximately 62%, most of which will be a building roof and pedestrian plaza. This represents a reduction of 17%. All of the stormwater runoff from the new development will be directed to new drywells dispersed around the site, recharging groundwater. Stormwater from the minimal remaining surface parking will be piped to a water quality swale and discharged into drywells. The intent of Credit 6 is to "Limit disruption of natural water flows by minimizing stormwater runoff, increasing on-site infiltration and reducing contaminates." Credit 6.1 addresses the first two of these intents, while Credit 6.2 addresses the third, reducing contaminates. Credit 6.1 states "if existing imperviousness is greater than 50%, implement a stormwater management plan that results in a 25% decrease in the rate or quantity of stormwater runoff." Although the net imperviousness of site surfaces will be reduced by only 17%, rather than the stated 25%, we feel this project will meet the intent of the credit because 100% of the stormwater will remain on-site and be directed to drywells, thus infiltrating and recharging ground water. Run-off leaving the site will be eliminated, impervious surface area will be significantly reduced and on-site water flows will more closely resemble the natural flows that existed before the existing surface parking lot was constructed. Do you agree that the proposed stormwater management meets the intent of Credit 6.1?

Ruling:

As all of the storm water is being infiltrated on site, the proposed storm water management meets the intent of Credit 6.1. Provide a narrative and calculations describing the approach in the LEED Application. Applicable Internationally.

Campus Applicable
No
Internationally Applicable:
Yes
3/15/2007
LEED Interpretation
Inquiry:

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.

Ruling:

In this instance, to achieve this credit without intercepting stormwater from the natural landscape, the submittal must demonstrate that stormwater runoff from the site\'s development footprint is fully treated to meet the requirements of this credit AND that the remaining natural landscape does not contribute to suspended solids or phosphorous runoff. In addition to the required documentation, please provide the entire site plan, including topography, that highlights the area of natural landscape. Applicable Internationally.

Campus Applicable
No
Internationally Applicable:
Yes
8/22/2008
LEED Interpretation
Inquiry:

The intent of this credit is to reduce or eliminate water pollution by eliminating sources of contaminants and removing pollutants from stormwater runoff. To achieve this, a stormwater management plan must be implemented that captures and treats the stormwater runoff from 90% of the average annual rainfall (1-inch, part of a humid watershed) for the entire LEED Boundary using acceptable best management practices (BMPs) that are capable of removing 80% of the average annual post-development total suspended solids (TSS) load. The proposed site is part of a university located in an urban area and is approximately 6.75 acres with a building footprint of 5.94 acres. The project consists of a parking garage and mechanical space that are entirely underground, and four buildings at the surface. The four buildings that emerge at the surface are connected by the subsurface portion of the building and support both green and conventional roofs. Pedestrian walkways, landscaped open space and a water quality swale make up the balance of the site at the surface. The majority of the stormwater runoff from the site is treated by the large water quality swale at the southern end of the site and water quality units before being reused for irrigation on site. There is a proposed infiltration system in the southwest corner of the site, located in the small portion of the site not directly over the building footprint. Portions of the conventional roof areas (approximately 10% of the site area) cannot be directed towards the water quality swale or the infiltration system due to their location on site. Therefore these roof drains are proposed to be directly discharged to the city stormwater system north of the site. Sources of TSS are generally from automobiles, oil, grease, salt, sediment and debris. The major sources of TSS are paved areas and parking lots where the materials listed above are found. The Massachusetts Stormwater Policy from the Massachusetts DEP considers roof runoff clean, since roofs are presumed to be free of sediment and debris and therefore relatively free of pollutants or TSS. The Massachusetts DEP does not require treatment of roof runoff because it is expected to generate close to zero pounds of TSS. Thus, the 80% removal requirement is not applicable. It is understood that the USGBC requires stormwater runoff from the entire LEED Boundary to be treated, although the Massachusetts DEP allows roof runoff to be discharged directly without treatment. This project does meet the credit intent without treating roof runoff since the relatively clean roof runoff would not contribute to water pollution downstream. Previous LEED certified projects for this university have achieved a point for this credit while not treating roof runoff and stating that roof runoff is considered clean by the State of Massachusetts. We would like to confirm that this is the position that all USGBC reviewers will take when awarding this credit.

Ruling:

Roof runoff is not exempt from the treatment requirements of this credit. See previous CIR ruling dated 11/01/2004. In addition, previous LEED reviews are not precedent setting. Applicable Internationally.

Campus Applicable
No
Internationally Applicable:
Yes
2/11/2009
LEED Interpretation
Inquiry:

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?

Ruling:

The approach of demonstrating credit compliance through Option 1a: Discharge Rate and Quantity for some drainage basins and Option 1b: Stream Channel Protection for the other drainage basins is acceptable. Please note that in addition to stream channel protection strategies, Option 1b requires the project to pursue stormwater quantity control strategies. Such strategies could include reduced impervious areas, infiltration systems, stormwater harvest for reuse, etc. 1. Please fill out the submittal template using the site-wide pre/post runoff rates and quantities. In the narrative section, describe in detail the approach that is taken for each sub-catchment area. 2. Although not stated directly on the submittal template, the 2-year 24-hour storm runoff values should be input. The 1-year 24-hour storm runoff values should also be provided; either in the template narrative or uploaded as a separate attachment. 3. The stream channel restoration activities, as described in the CIR, can either be included or excluded from the LEED project boundary, provided the boundary is consistent for all credits. 4. Achievement of this credit will depend on whether the project team can demonstrate that they have met the requirements of this credit. 5. Please provide a site map clearly defining the sub-catchment areas and provide pre/post stormwater discharge calculations for each area. Please provide details regarding the stream channel restoration activities. Consult SSc5.1 CIR ruling dated 6/5/07 for implications related to including the restored stream sections in the LEED project boundary. Finally, please provide a narrative describing the quantity control strategies implemented by the project, particularly within the sub-catchments that will not achieve the Option 1a requirements.

Campus Applicable
No
Internationally Applicable:
No
7/24/2006
LEED Interpretation
Inquiry:

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.

Ruling:

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.

Campus Applicable
No
Internationally Applicable:
Yes
6/18/2009
LEED Interpretation
Inquiry:

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?

Ruling:

The project is seeking clarification on whether required stormwater management systems can be located outside of the LEED site boundary, and whether 100% infiltration meets the credit requirements. If the project cannot meet the credit requirements based on the LEED site boundary (referred to as "LEED project footprint" in the CIR), which needs to be applied consistently across all credits, there may be the option to achieve this credit on a campus level as described in the LEED-NC Application Guide for Multiple Buildings & On-Campus Building Projects. As supported by the LEED-NC v2.2 CIR Rulings dated 8/22/08 and 5/23/08, "the requirements for credit SSc6.1 can be met by demonstrating that the existing stormwater management systems that serve the LEED Site Boundary meet the LEED requirements for all areas within the site serviced by those systems." In the case of 100% infiltration, both the requirements for SSc6.1 and SSc6.2 are met.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; Middle East; Oman.

Campus Applicable
No
Internationally Applicable:
Yes
1/27/2007
LEED Interpretation
Inquiry:

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.

Ruling:

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.

Campus Applicable
No
Internationally Applicable:
No
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Requirements

Option 1
During the performance period, implement a stormwater management plan that infiltrates, collects and reuses runoff or evapotranspirates runoff from at least 15% of the precipitation falling on the whole project site both for an average weather year and for the 2-year, 24-hour design storm. Implement an annual inspection program of all stormwater management facilities to confirm continued performance. Maintain documentation of inspection, including identification of areas of erosion, maintenance needs and repairs. Perform all routine required maintenance, necessary repairs or stabilization within 60 days of inspection.

OR

Option 2
Use Low Impact Development (LID)1 practices to capture and treat water from 25% of the impervious surfaces for the 95th percentile of regional or local rainfall events. Implement an annual inspection program of all stormwater management facilities to confirm continued performance. Maintain documentation of inspection, including identification of areas of erosion, maintenance needs and repairs. Perform all routine required maintenance, necessary repairs or stabilization within 60 days of inspection.
1Low impact development (LID) is an approach to managing stormwater runoff that emphasizes on-site natural features to protect water quality by replicating the natural land cover hydrologic regime of watersheds and addressing runoff close to its source. Examples include better site design principles such as minimizing land disturbance, preserving vegetation, minimizing impervious cover, and design practices like rain gardens, vegetated swales and buffers, permeable pavement, rainwater harvesting, and soil amendments. These are engineered practices that may require specialized design assistance.

Alternative Compliance Paths (ACPs)

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1/8/2010Updated: 2/14/2015
Reference Guide Correction
Description of change:
Replace the text in the second paragraph titled "Volume Captured via Collection Facilities" with the following:For less complex sites without detention facilities, teams can perform awater balance to determine if a proposed reduction in impervious areaand/or rain capture systems will result in the required reduction in siterunoff. However, in order to determine the discharge rate and quantityfrom a site with a wet or dry detention facility, project teams should makea detailed analysis of the stage-storage relationship of the detentionfacility, coupled with an analysis of any control structures used toregulate discharge. Drawdown rates due to infiltration and thereforegeotechnical conditions will also need to be considered. While it ispossible to perform these types of calculations by hand, a computersimulation model is more typically used and recommended.
Campus Applicable
No
Internationally Applicable:
No
7/6/2012Updated: 2/14/2015
Rating System Correction
Description of change:
Add the following footnotes to the bottom of the page:1.The baseline condition is the site condition prior to LEED registration.2. low impact development (LID) is an approach to managing stormwater runoff that emphasizes on-site natural features to protect water quality by replicating the natural land cover hydrologic regime of watersheds and addressing runoff close to its source. Examples include better site design principles such as minimizing land disturbance, preserving vegetation, minimizing impervious cover, and design practices like rain gardens, vegetated swales and buffers, permeable pavement, rainwater harvesting, and soil amendments. These are engineered practices that may require specialized design assistance.
Campus Applicable
No
Internationally Applicable:
No
7/6/2012Updated: 2/14/2015
Global ACP
Description of change:
Add "OPTION 1" before first paragraph
Campus Applicable
No
Internationally Applicable:
Yes
2/22/2010Updated: 2/14/2015
Reference Guide Correction
Description of change:
Replace the text in the third paragraph titled "Volume Captured viaRetention Facilities" with the following:"For less complex sites without detention facilities, teams can perform awater balance to determine if a proposed reduction in impervious areaand/or rain capture systems will result in the required reduction in siterunoff. However, in order to determine the discharge rate and quantityfrom a site with a wet or dry detention facility, project teams should makea detailed analysis of the stage-storage relationship of the detentionfacility, coupled with an analysis of any control structures used toregulate discharge. Drawdown rates due to infiltration and thereforegeotechnical conditions will also need to be considered. While it ispossible to perform these types of calculations by hand, a computersimulation model is more typically used and recommended."
Campus Applicable
No
Internationally Applicable:
No
11/1/2011Updated: 2/14/2015
Reference Guide Correction
Description of change:
Revise the third equation box to:Qr = (800 cf / 259,200 sec) = (0.003 cfs or 1.35 gpm)
Campus Applicable
No
Internationally Applicable:
No
7/6/2012Updated: 2/14/2015
Global ACP
Description of change:
Add the following after the second paragraph:OROPTION 2Use Low Impact Development (LID) practices to capture and treat water from 25% of the impervious surfaces for the 95th percentile of regional or local rainfall events.Implement an annual inspection program of all stormwater management facilities to confirm continued performance. Maintain documentation of inspection, including identification of areas of erosion, maintenance needs and repairs. Perform all routine required maintenance, necessary repairs or stabilization within 60 days of inspection.
Campus Applicable
No
Internationally Applicable:
Yes
7/6/2012Updated: 2/14/2015
Global ACP
Description of change:
Delete the Alternative Compliance Path for Projects Outside the U.S.
Campus Applicable
No
Internationally Applicable:
Yes
5/23/2008
LEED Interpretation
Inquiry:

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?

Ruling:

The project has reduced impervious area by 38% and seeks compliance with SSc6.1 on this basis. Peak flow rates and volume do have a relationship with impervious area. However, if a reduction in impervious area will result in compliance with the requirements of SSc6.1, than it is the responsibility of the project team to perform calculations of the pre- and post-development runoff volumes as described in the LEED-NC v2.2 Reference Guide to demonstrate that compliance. Applicable Internationally.

Campus Applicable
No
Internationally Applicable:
Yes
8/22/2008
LEED Interpretation
Inquiry:

Using LEED-NC 2.2 & applying the on-campus application guide for a new building in an existing campus setting, can credits 6.1 & 6.2 be met by an analysis of an existing on-campus detention pond constructed at the time of original campus construction (1970\'s), provided that the pond meets or is upgraded to meet these requirements? If not isn\'t LEED punishing the institutions that had the foresight to plan effectively and implement appropriate storm drainage practices before it was the popular thing to do? The proposed approach would use the native lands prior to 1970 as the pre-development site condition (imperviousness less than 50%) and require that post-campus construction storm water (including all existing & future planned buildings / improvements) meet the requirements of 6.1 & 6.2. Should the existing pond prove adequate to meet the requirements then the project could count the credits, if not then improvements to the existing pond could be made to meet the requirements and achieve the credits.

Ruling:

For the purposes of SSc6.1, the applicant would like to base the pre-development conditions for a university campus on those conditions that existed prior to initial construction in the 1970\'s. The intent of this credit is to limit disruption of natural hydrology and therefore it is acceptable to consider the pre-development conditions as those that existed prior to initial construction. Similar to the campus compliance option outlined in LEED-NC v2.2 SSc6.2 CIR ruling dated 9/4/2006, 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. Applicable Internationally.

Campus Applicable
No
Internationally Applicable:
Yes
2/26/2009
LEED Interpretation
Inquiry:

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?

Ruling:

The project team is requesting whether their efforts to reduce the post-development stormwater discharge rate and quantity from their low permeability site meets the intent of the credit, even though they are still above the pre-development levels. Based on the description provided, the project does not meet the intent of the credit. However, if the stormwater management plan was expanded to include additional on-site quantity control strategies (such as a rain catchment system), AND stream channel protection strategies, then the project could pursue the Option 1B compliance path in the NCv2.2 Reference Guide. Applicable Internationally.

Campus Applicable
No
Internationally Applicable:
Yes
9/4/2006
LEED Interpretation
Inquiry:

The intent of SSc6.2, interpreted from the manual and subsequent CIRs, is to minimize the disruption and pollution of natural water bodies by contaminated stormwater. To meet the Credit Intent, the Requirements specify active TSS treatment of stormwater, using BMPs that reduce the percentage of contaminants in the runoff. The project site is 5.24 acres and has 3 acres of impervious surfaces. The site is part of an overall 75 acre master plan that empties it\'s stormwater into Tributary A, North Buffalo Creek. There is an existing retention pond in the middle of the Park that is adjacent and just North of the Site (not located within the project site for LEED). The drainage area to the pond is +/- 44 acres of highly developed office and commercial property and 70% of this area is impervious. The project site is included within these 44 acres. The pond drain is an open pipe with headwall. The outlet pipe runs underground through the Site and empties upstream of the proposed building into Tributary A, North Buffalo Creek. The Site has an existing storm sewer outflow system designed and sized for future development of this site plus the upper buildings and parking lots (approximately 9 acres). This system empties directly into Buffalo Creek downstream of the proposed LEED building. We propose to modify the spillway of the existing pond to treat approximately 110,000 C.F. of stormwater for the extended acreage in lieu of treating stormwater only for the project site. Of the overall 75 acre master plan, +/- 44 acres runoff into the pond and contain untreated water, entering and exiting the pond without allowing pollutants and suspended solids to be removed. Given the existing stormwater system, it does not make sense to treat stormwater on the project site, but rather to treat all of the stormwater from the larger 44 acre site. We believe that treating the 44 acres will meet and exceed the intent of the credit for the following reasons: 1) We will create a new spillway with an orifice that stores the first inch of runoff for the entire 44 acres, which will achieve 85% TSS removal based on existing monitoring and will be constructed in accordance with the Greensboro Stormwater Design Manual. 2) The project site is part of a 75 acre master plan and by creating the spillway we will be maximizing the positive impact on the overall water quality entering Tributary A, North Buffalo Creek for an area that is 25 times the project site\'s size. The spillway will also resolve any associated stormwater system issues that were previously designed and constructed in a less environmentally friendly manner. We believe that we meet and exceed the intent of SSc6.2 because we are aiding in the overall water quality improvement and pollution minimization for the Buffalo Creek through stormwater quality control and therefore will earn this credit. Please confirm that achieving the treatment requirements for the larger 44 acre site will enable the project to earn the credit and perhaps be eligible for an exemplary performance ID credit. Also please confirm that we will be able to earn this credit by treating the Stormwater outside the project site as defined for the LEED submission.

Ruling:

Yes, achieving the TSS removal requirements for the larger 44 acre site as described will warrant the award of SS Credit 6.2. In accordance with the LEED-NC Application Guide for Multiple Buildings and On-Campus Building Projects (AGMBC), a centralized approach to stormwater management is acceptable. Submittal documentation will require the project team to demonstrate that the centralized BMP adheres to the credit requirements for all current development within the site serviced by the BMP. However, the project will not be awarded an Innovation in Design credit for Exemplary Performance of SSc6.2 as a result of these efforts. The approach of modifying the spillway to treat the stormwater for the extended acreage requires the BMP to be able to treat all current and future development. Therefore, the proposed BMP meets, but not exceed the requirements of this credit. Furthermore, page 85 of the LEED-NC v2.2 Reference Guide states that there is no exemplary performance point available for this credit.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.

Campus Applicable
No
Internationally Applicable:
Yes
7/10/2001
LEED Interpretation
Inquiry:

The existing imperviousness of the project\'s urban site is 74%, mostly due to surface asphalt parking lots. A portion of the stormwater runs offsite while the remainder is piped to drywells. The new development will have a net imperviousness of approximately 62%, most of which will be a building roof and pedestrian plaza. This represents a reduction of 17%. All of the stormwater runoff from the new development will be directed to new drywells dispersed around the site, recharging groundwater. Stormwater from the minimal remaining surface parking will be piped to a water quality swale and discharged into drywells. The intent of Credit 6 is to "Limit disruption of natural water flows by minimizing stormwater runoff, increasing on-site infiltration and reducing contaminates." Credit 6.1 addresses the first two of these intents, while Credit 6.2 addresses the third, reducing contaminates. Credit 6.1 states "if existing imperviousness is greater than 50%, implement a stormwater management plan that results in a 25% decrease in the rate or quantity of stormwater runoff." Although the net imperviousness of site surfaces will be reduced by only 17%, rather than the stated 25%, we feel this project will meet the intent of the credit because 100% of the stormwater will remain on-site and be directed to drywells, thus infiltrating and recharging ground water. Run-off leaving the site will be eliminated, impervious surface area will be significantly reduced and on-site water flows will more closely resemble the natural flows that existed before the existing surface parking lot was constructed. Do you agree that the proposed stormwater management meets the intent of Credit 6.1?

Ruling:

As all of the storm water is being infiltrated on site, the proposed storm water management meets the intent of Credit 6.1. Provide a narrative and calculations describing the approach in the LEED Application. Applicable Internationally.

Campus Applicable
No
Internationally Applicable:
Yes
3/15/2007
LEED Interpretation
Inquiry:

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.

Ruling:

In this instance, to achieve this credit without intercepting stormwater from the natural landscape, the submittal must demonstrate that stormwater runoff from the site\'s development footprint is fully treated to meet the requirements of this credit AND that the remaining natural landscape does not contribute to suspended solids or phosphorous runoff. In addition to the required documentation, please provide the entire site plan, including topography, that highlights the area of natural landscape. Applicable Internationally.

Campus Applicable
No
Internationally Applicable:
Yes
8/22/2008
LEED Interpretation
Inquiry:

The intent of this credit is to reduce or eliminate water pollution by eliminating sources of contaminants and removing pollutants from stormwater runoff. To achieve this, a stormwater management plan must be implemented that captures and treats the stormwater runoff from 90% of the average annual rainfall (1-inch, part of a humid watershed) for the entire LEED Boundary using acceptable best management practices (BMPs) that are capable of removing 80% of the average annual post-development total suspended solids (TSS) load. The proposed site is part of a university located in an urban area and is approximately 6.75 acres with a building footprint of 5.94 acres. The project consists of a parking garage and mechanical space that are entirely underground, and four buildings at the surface. The four buildings that emerge at the surface are connected by the subsurface portion of the building and support both green and conventional roofs. Pedestrian walkways, landscaped open space and a water quality swale make up the balance of the site at the surface. The majority of the stormwater runoff from the site is treated by the large water quality swale at the southern end of the site and water quality units before being reused for irrigation on site. There is a proposed infiltration system in the southwest corner of the site, located in the small portion of the site not directly over the building footprint. Portions of the conventional roof areas (approximately 10% of the site area) cannot be directed towards the water quality swale or the infiltration system due to their location on site. Therefore these roof drains are proposed to be directly discharged to the city stormwater system north of the site. Sources of TSS are generally from automobiles, oil, grease, salt, sediment and debris. The major sources of TSS are paved areas and parking lots where the materials listed above are found. The Massachusetts Stormwater Policy from the Massachusetts DEP considers roof runoff clean, since roofs are presumed to be free of sediment and debris and therefore relatively free of pollutants or TSS. The Massachusetts DEP does not require treatment of roof runoff because it is expected to generate close to zero pounds of TSS. Thus, the 80% removal requirement is not applicable. It is understood that the USGBC requires stormwater runoff from the entire LEED Boundary to be treated, although the Massachusetts DEP allows roof runoff to be discharged directly without treatment. This project does meet the credit intent without treating roof runoff since the relatively clean roof runoff would not contribute to water pollution downstream. Previous LEED certified projects for this university have achieved a point for this credit while not treating roof runoff and stating that roof runoff is considered clean by the State of Massachusetts. We would like to confirm that this is the position that all USGBC reviewers will take when awarding this credit.

Ruling:

Roof runoff is not exempt from the treatment requirements of this credit. See previous CIR ruling dated 11/01/2004. In addition, previous LEED reviews are not precedent setting. Applicable Internationally.

Campus Applicable
No
Internationally Applicable:
Yes
2/11/2009
LEED Interpretation
Inquiry:

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?

Ruling:

The approach of demonstrating credit compliance through Option 1a: Discharge Rate and Quantity for some drainage basins and Option 1b: Stream Channel Protection for the other drainage basins is acceptable. Please note that in addition to stream channel protection strategies, Option 1b requires the project to pursue stormwater quantity control strategies. Such strategies could include reduced impervious areas, infiltration systems, stormwater harvest for reuse, etc. 1. Please fill out the submittal template using the site-wide pre/post runoff rates and quantities. In the narrative section, describe in detail the approach that is taken for each sub-catchment area. 2. Although not stated directly on the submittal template, the 2-year 24-hour storm runoff values should be input. The 1-year 24-hour storm runoff values should also be provided; either in the template narrative or uploaded as a separate attachment. 3. The stream channel restoration activities, as described in the CIR, can either be included or excluded from the LEED project boundary, provided the boundary is consistent for all credits. 4. Achievement of this credit will depend on whether the project team can demonstrate that they have met the requirements of this credit. 5. Please provide a site map clearly defining the sub-catchment areas and provide pre/post stormwater discharge calculations for each area. Please provide details regarding the stream channel restoration activities. Consult SSc5.1 CIR ruling dated 6/5/07 for implications related to including the restored stream sections in the LEED project boundary. Finally, please provide a narrative describing the quantity control strategies implemented by the project, particularly within the sub-catchments that will not achieve the Option 1a requirements.

Campus Applicable
No
Internationally Applicable:
No
7/24/2006
LEED Interpretation
Inquiry:

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.

Ruling:

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.

Campus Applicable
No
Internationally Applicable:
Yes
6/18/2009
LEED Interpretation
Inquiry:

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?

Ruling:

The project is seeking clarification on whether required stormwater management systems can be located outside of the LEED site boundary, and whether 100% infiltration meets the credit requirements. If the project cannot meet the credit requirements based on the LEED site boundary (referred to as "LEED project footprint" in the CIR), which needs to be applied consistently across all credits, there may be the option to achieve this credit on a campus level as described in the LEED-NC Application Guide for Multiple Buildings & On-Campus Building Projects. As supported by the LEED-NC v2.2 CIR Rulings dated 8/22/08 and 5/23/08, "the requirements for credit SSc6.1 can be met by demonstrating that the existing stormwater management systems that serve the LEED Site Boundary meet the LEED requirements for all areas within the site serviced by those systems." In the case of 100% infiltration, both the requirements for SSc6.1 and SSc6.2 are met.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; Middle East; Oman.

Campus Applicable
No
Internationally Applicable:
Yes
1/27/2007
LEED Interpretation
Inquiry:

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.

Ruling:

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.

Campus Applicable
No
Internationally Applicable:
No

LEEDuser expert

Ashwini Arun

WSP
Senior Sustainability Manager

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