Log in
LEED v2009
Core & Shell
Sustainable Sites
Stormwater Design—Quantity Control

LEED CREDIT

CS-2009 SSc6.1: Stormwater design - quantity control 1 point

See all forum discussions about this credit »

Credit achievement rate

XX%

Upgrade to LEEDuser Premium to see how many projects achieved this credit. Try it free »

LEEDuser expert

Michael DeVuono

PE, CPESC, LEED AP BD+C

Arcadis North America
Regional Stormwater Leader

LEEDuser’s viewpoint

Frank advice from LEED experts

LEED is changing all the time, and every project is unique. Even seasoned professionals can miss a critical detail and lose a credit or even a prerequisite at the last minute. Our expert advice guides our LEEDuser Premium members and saves you valuable time.

Credit language

USGBC logo

© Copyright U.S. Green Building Council, Inc. All rights reserved.

Requirements

Option 1. Design storms
Case 1. Sites with existing imperviousness 50% or less
Path 1
Implement a stormwater management plan that prevents the postdevelopment peak discharge rate and quantity from exceeding the predevelopment peak discharge rate and quantity for the 1- and 2-year 24-hour design storms. OR
Path 2
Implement a stormwater management plan that protects receiving stream channels from excessive erosion. The stormwater management plan must include stream channel protection and quantity control strategies.
Case 2. Sites with existing imperviousness greater than 50%
Implement a stormwater management plan that results in a 25% decrease in the volume of stormwater runoff from the 2-year 24-hour design storm.

OR

Option 2. Percentile rainfall events
Case 1. Non-zero lot line projects
In a manner best replicating natural site hydrology1 processes, manage onsite2 the runoff from the developed site for the 95th percentile of regional or local rainfall events using Low Impact Development (LID)3 and green infrastructure4. Use daily rainfall data and the methodology in the United States Environmental Protection Agency’s Technical Guidance on Implementing the Stormwater Runoff Requirements for Federal Projects under Section 438 of the Energy Independence and Security Act to determine the 95th percentile amount. OR
CASE 2: zero lot line projects
For zero lot line projects located in urban areas with a minimum density of 1.5 FAR (13,800 square meters per hectare net), in a manner best replicating natural site hydrology processes, manage onsite the runoff from the developed site for the 85th percentile of regional or local rainfall events using LID and green infrastructure.

1Natural Site Hydrology is defined as the natural land cover function of water occurrence, distribution, movement, and balance.

2Manage Onsite refers to capturing and retaining the specified volume of rainfall to mimic natural hydrologic function. This includes, but is not limited to, strategies that manage volume through evapotranspiration, infiltration, or capture and reuse.

3Low Impact Development (LID) is defined as 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.

4Green Infrastructure is a soil and vegetation-based approach to wet weather management that is cost-effective, sustainable, and environmentally friendly. Green infrastructure management approaches and technologies infiltrate, evapotranspire, capture and reuse stormwater to maintain or restore natural hydrologies (US EPA).

Streamlined path available
Achievement of this credit can be documented via a LEED ND v2009 submittal. For more information check out this article.
SITES-LEED Equivalency
This LEED credit (or a component of this credit) has been established as equivalent to a SITES v2 credit or component. For more information on using the equivalency as a substitution in your LEED or SITES project, see this article and guidance document.
See all forum discussions about this credit »

What does it cost?

Cost estimates for this credit

On each BD+C v4 credit, LEEDuser offers the wisdom of a team of architects, engineers, cost estimators, and LEED experts with hundreds of LEED projects between then. They analyzed the sustainable design strategies associated with each LEED credit, but also to assign actual costs to those strategies.

Our tab contains overall cost guidance, notes on what “soft costs” to expect, and a strategy-by-strategy breakdown of what to consider and what it might cost, in percentage premiums, actual costs, or both.

This information is also available in a full PDF download in The Cost of LEED v4 report.

Learn more about The Cost of LEED v4 »

Frequently asked questions

Are there special considerations for international projects?

The answer to this question is available to LEEDuser premium members. Start a free trial »

(If you're already a premium member, log in here.)

What performance threshold do I need to achieve for an Exemplary Performance point?

The answer to this question is available to LEEDuser premium members. Start a free trial »

(If you're already a premium member, log in here.)

The calculations for this credit are always a headache! While our projects are usually awarded the credit, the equations in the LEED Reference Guide are helpful mostly for sizing a reservoir or cistern, but don't help you get to the final results. Does USGBC provide any step-by-step guidance that would make submitting these credits more predictable?

The answer to this question is available to LEEDuser premium members. Start a free trial »

(If you're already a premium member, log in here.)

Why do the requirements focus on 1-year and 2-year, 24-hour storms?

The answer to this question is available to LEEDuser premium members. Start a free trial »

(If you're already a premium member, log in here.)

Why include the 1-year storm in the credit requirements? Won't management practices for the 2-year storm be effective?

The answer to this question is available to LEEDuser premium members. Start a free trial »

(If you're already a premium member, log in here.)

How can green roofs count as a stormwater control measure?

The answer to this question is available to LEEDuser premium members. Start a free trial »

(If you're already a premium member, log in here.)

How can I achieve compliance if my project's stormwater control measures are outside the LEED project boundary?

The answer to this question is available to LEEDuser premium members. Start a free trial »

(If you're already a premium member, log in here.)

I have 100-year data—how do I convert to 2-year?

The answer to this question is available to LEEDuser premium members. Start a free trial »

(If you're already a premium member, log in here.)

Is it an acceptable strategy to capture the rainwater into tanks and discharge it into the public sewers after the rainstorm reducing the peak discharge?

The answer to this question is available to LEEDuser premium members. Start a free trial »

(If you're already a premium member, log in here.)

See all forum discussions about this credit »

Addenda

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:
Change "OPTION 2" to "PATH 2"
Campus Applicable
No
Internationally Applicable:
Yes
7/6/2012Updated: 2/14/2015
Global ACP
Description of change:
Add new option title (option 1) that reads: "OPTION 1. Design Storms" below "Requirements".
Campus Applicable
No
Internationally Applicable:
Yes
7/6/2012Updated: 2/14/2015
Global ACP
Description of change:
Add the following footnotes:1. Natural Site Hydrology is defined as the natural land cover function of water occurrence, distribution, movement, and balance.2. Manage Onsite refers to capturing and retaining the specified volume of rainfall to mimic natural hydrologic function. This includes, but is not limited to, strategies that manage volume through evapotranspiration, infiltration, or capture and reuse.3. Low Impact Development (LID) is defined as 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.4. Green Infrastructure is a soil and vegetation-based approach to wet weather management that is cost-effective, sustainable, and environmentally friendly. Green infrastructure management approaches and technologies infiltrate, evapotranspire, capture and reuse stormwater to maintain or restore natural hydrologies (US EPA).
Campus Applicable
No
Internationally Applicable:
Yes
11/3/2010Updated: 2/14/2015
Reference Guide Correction
Description of change:
Insert the term "Predevelopment" in alphabetical order with the accompanying text "Predevelopment refers to before the LEED project was initiated, but not necessarily before any development or disturbance took place. Predevelopment conditions describe conditions on the date the developer acquired rights to a majority of the buildable land on the project site through purchase or option to purchase."
Campus Applicable
No
Internationally Applicable:
No
7/6/2012Updated: 2/14/2015
Global ACP
Description of change:
Change "OPTION 1" to "PATH 1"
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
7/6/2012Updated: 2/14/2015
Global ACP
Description of change:
Add the following after Case 2: OROPTION 2. Percentile Rainfall EventsCASE 1. Non-Zero Lot Line ProjectsIn a manner best replicating natural site hydrology1 processes, manage onsite2 the runoff from the developed site for the 95th percentile of regional or local rainfall events using Low Impact Development (LID)3 and green infrastructure4. Use daily rainfall data and the methodology in the United States Environmental Protection Agency\'s Technical Guidance on Implementing the Stormwater Runoff Requirements for Federal Projects under Section 438 of the Energy Independence and Security Act to determine the 95th percentile amount.ORCASE 2. Zero Lot Line ProjectsFor zero lot line projects located in urban areas with a minimum density of 1.5 FAR (13,800 square meters per hectare net), in a manner best replicating natural site hydrology processes, manage onsite the runoff from the developed site for the 85th percentile of regional or local rainfall events using LID and green infrastructure.
Campus Applicable
No
Internationally Applicable:
Yes
11/1/2011
LEED Interpretation
Inquiry:

How can a project earn exemplary performance for Stormwater Quantity and Quality?

Ruling:

The exemplary performance requirements for SSc6.1 Stormwater Quantity and SSc6.2 Stormwater Quality listed in the LEED Green Building Design & Construction Reference Guide call for (1) a comprehensive approach to capture and treat stormwater runoff and (2) demonstrated performance above and beyond the credit requirements. To expand and clarify what these two requirements refer to, the following additional guidance is provided.SSc6.1 Stormwater QuantityTo demonstrate a comprehensive approach and performance above and beyond the credit requirements, the stormwater management strategies must:1. Address runoff from the entire development footprint of the site using Low Impact Development (LID) practices. 2. Achieve the following stormwater quantity performance:a. Case 1, Option 1: Achieve a post-development peak discharge rate and quantity that is equivalent to those calculated for the natural land cover site conditions.b. Case 1, Option 2: No EP available for his compliance path.c. Case 2: Achieve a 50% reduction in the volume of runoff during the 2-year 24-hour design storm.LID is defined as an approach to managing stormwater runoff that emphasizes on-site natural features to protect water quality by replicating the natural 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, and soil amendments. These are engineered practices that may require specialized design assistance.SSc6.2 Stormwater QualityTo demonstrate a comprehensive approach and performance above and beyond the credit requirements, the best management practices employed must be non-structural, conforming to LID practices as defined above, and should be designed to remove at least 80% of the average annual total suspended solids (TSS) from twice the rainfall volume required for the base credit (i.e, runoff generated from 1 inch of rain in an arid climate, 1.5 inches of rain in a semiarid climate, and 2 inches of rain in a humid climate).To document compliance with these requirements, a detailed narrative or stormwater management plan summary should be provided that describes the exemplary performance approach and includes calculations that clearly highlight compliance with the exemplary performance requirements. As the exemplary performance requirements for these two credits overlap considerably, only one SSc6 EP point is available to projects. Applicable internationally.

Campus Applicable
No
Internationally Applicable:
Yes
5/30/2007
LEED Interpretation
Inquiry:

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

Ruling:

The most effective way to achieve SSc6.1 is to implement a stormwater management plan that prevents the post-development peak discharge rate and quantity from exceeding the pre-development peak discharge rate and quantity for a 2-year 24-hr storm. If the adjacent pond is intended to treat the runoff from the project site, and if it is sized sufficiently to store the developed site increased runoff from a 2-year 24-hr storm, then it can contribute to credit achievement. Please provide volume calculations to show what the pre and post development 2-year 24-hr storm runoff is and some volume calculations for the stormwater management pond to verify that it can store this runoff volume. Alternatively, the project team can demonstrate that receiving stream is protected from excessive erosion by implementing a stream channel protection strategy and quantity control strategies and that the 2 year runoff velocity in the stream is low enough so as not to cause stream erosion. Applicable Internationally.

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
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
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
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
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
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
See all forum discussions about this credit »

Checklists

Step by step to LEED certification

LEEDuser’s checklists walk you through the key action steps you need to earn a credit, including how to avoid common pitfalls and save money.

See all forum discussions about this credit »

Documentation toolkit

The motherlode of cheat sheets

LEEDuser’s Documentation Toolkit is loaded with calculators to help assess credit compliance, tracking spreadsheets for materials, sample templates to help guide your narratives and LEED Online submissions, and examples of actual submissions from certified LEED projects for you to check your work against. To get your plaque, start with the right toolkit.

Credit achievement rate

XX%

Upgrade to LEEDuser Premium to see how many projects achieved this credit. Try it free »

LEEDuser expert

Michael DeVuono

PE, CPESC, LEED AP BD+C

Arcadis North America
Regional Stormwater Leader

Get the inside scoop

Our editors have written a detailed analysis of nearly every LEED credit, and LEEDuser premium members get full access. We’ll tell you whether the credit is easy to accomplish or better left alone, and we provide insider tips on how to document it successfully.

USGBC logo

© Copyright U.S. Green Building Council, Inc. All rights reserved.

Requirements

Option 1. Design storms
Case 1. Sites with existing imperviousness 50% or less
Path 1
Implement a stormwater management plan that prevents the postdevelopment peak discharge rate and quantity from exceeding the predevelopment peak discharge rate and quantity for the 1- and 2-year 24-hour design storms. OR
Path 2
Implement a stormwater management plan that protects receiving stream channels from excessive erosion. The stormwater management plan must include stream channel protection and quantity control strategies.
Case 2. Sites with existing imperviousness greater than 50%
Implement a stormwater management plan that results in a 25% decrease in the volume of stormwater runoff from the 2-year 24-hour design storm.

OR

Option 2. Percentile rainfall events
Case 1. Non-zero lot line projects
In a manner best replicating natural site hydrology1 processes, manage onsite2 the runoff from the developed site for the 95th percentile of regional or local rainfall events using Low Impact Development (LID)3 and green infrastructure4. Use daily rainfall data and the methodology in the United States Environmental Protection Agency’s Technical Guidance on Implementing the Stormwater Runoff Requirements for Federal Projects under Section 438 of the Energy Independence and Security Act to determine the 95th percentile amount. OR
CASE 2: zero lot line projects
For zero lot line projects located in urban areas with a minimum density of 1.5 FAR (13,800 square meters per hectare net), in a manner best replicating natural site hydrology processes, manage onsite the runoff from the developed site for the 85th percentile of regional or local rainfall events using LID and green infrastructure.

1Natural Site Hydrology is defined as the natural land cover function of water occurrence, distribution, movement, and balance.

2Manage Onsite refers to capturing and retaining the specified volume of rainfall to mimic natural hydrologic function. This includes, but is not limited to, strategies that manage volume through evapotranspiration, infiltration, or capture and reuse.

3Low Impact Development (LID) is defined as 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.

4Green Infrastructure is a soil and vegetation-based approach to wet weather management that is cost-effective, sustainable, and environmentally friendly. Green infrastructure management approaches and technologies infiltrate, evapotranspire, capture and reuse stormwater to maintain or restore natural hydrologies (US EPA).

Streamlined path available
Achievement of this credit can be documented via a LEED ND v2009 submittal. For more information check out this article.
SITES-LEED Equivalency
This LEED credit (or a component of this credit) has been established as equivalent to a SITES v2 credit or component. For more information on using the equivalency as a substitution in your LEED or SITES project, see this article and guidance document.

XX%

Upgrade to LEEDuser Premium to see how many projects achieved this credit. Try it free »

Got the gist of SSc6.1 but not sure how to actually achieve it? LEEDuser gives step-by-step help. Premium members get:

  • Checklists covering all the key action steps you'll need to earn the credit.
  • Hot tips to give you shortcuts and avoid pitfalls.
  • Cost tips to assess what a credit will actually cost, and how to make it affordable.
  • Ideas for going beyond LEED with best practices.
  • All checklists organized by project phase.
  • On-the-fly suggestions of useful items from the Documentation Toolkit and Credit Language.

In the end, LEED is all about documentation. LEEDuser’s Documentation Toolkit, for premium members only, saves you time and helps you avoid mistakes with:

  • Calculators to help assess credit compliance.
  • Tracking spreadsheets for materials purchases.
  • Spreadsheets and forms to give to subs and other team members.
  • Guidance documents on arcane LEED issues.
  • Sample templates to help guide your narratives and LEED Online submissions.
  • Examples of actual submissions from certified LEED projects.

Are there special considerations for international projects?

The answer to this question is available to LEEDuser premium members. Start a free trial »

(If you're already a premium member, log in here.)

What performance threshold do I need to achieve for an Exemplary Performance point?

The answer to this question is available to LEEDuser premium members. Start a free trial »

(If you're already a premium member, log in here.)

The calculations for this credit are always a headache! While our projects are usually awarded the credit, the equations in the LEED Reference Guide are helpful mostly for sizing a reservoir or cistern, but don't help you get to the final results. Does USGBC provide any step-by-step guidance that would make submitting these credits more predictable?

The answer to this question is available to LEEDuser premium members. Start a free trial »

(If you're already a premium member, log in here.)

Why do the requirements focus on 1-year and 2-year, 24-hour storms?

The answer to this question is available to LEEDuser premium members. Start a free trial »

(If you're already a premium member, log in here.)

Why include the 1-year storm in the credit requirements? Won't management practices for the 2-year storm be effective?

The answer to this question is available to LEEDuser premium members. Start a free trial »

(If you're already a premium member, log in here.)

How can green roofs count as a stormwater control measure?

The answer to this question is available to LEEDuser premium members. Start a free trial »

(If you're already a premium member, log in here.)

How can I achieve compliance if my project's stormwater control measures are outside the LEED project boundary?

The answer to this question is available to LEEDuser premium members. Start a free trial »

(If you're already a premium member, log in here.)

I have 100-year data—how do I convert to 2-year?

The answer to this question is available to LEEDuser premium members. Start a free trial »

(If you're already a premium member, log in here.)

Is it an acceptable strategy to capture the rainwater into tanks and discharge it into the public sewers after the rainstorm reducing the peak discharge?

The answer to this question is available to LEEDuser premium members. Start a free trial »

(If you're already a premium member, log in here.)

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:
Change "OPTION 2" to "PATH 2"
Campus Applicable
No
Internationally Applicable:
Yes
7/6/2012Updated: 2/14/2015
Global ACP
Description of change:
Add new option title (option 1) that reads: "OPTION 1. Design Storms" below "Requirements".
Campus Applicable
No
Internationally Applicable:
Yes
7/6/2012Updated: 2/14/2015
Global ACP
Description of change:
Add the following footnotes:1. Natural Site Hydrology is defined as the natural land cover function of water occurrence, distribution, movement, and balance.2. Manage Onsite refers to capturing and retaining the specified volume of rainfall to mimic natural hydrologic function. This includes, but is not limited to, strategies that manage volume through evapotranspiration, infiltration, or capture and reuse.3. Low Impact Development (LID) is defined as 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.4. Green Infrastructure is a soil and vegetation-based approach to wet weather management that is cost-effective, sustainable, and environmentally friendly. Green infrastructure management approaches and technologies infiltrate, evapotranspire, capture and reuse stormwater to maintain or restore natural hydrologies (US EPA).
Campus Applicable
No
Internationally Applicable:
Yes
11/3/2010Updated: 2/14/2015
Reference Guide Correction
Description of change:
Insert the term "Predevelopment" in alphabetical order with the accompanying text "Predevelopment refers to before the LEED project was initiated, but not necessarily before any development or disturbance took place. Predevelopment conditions describe conditions on the date the developer acquired rights to a majority of the buildable land on the project site through purchase or option to purchase."
Campus Applicable
No
Internationally Applicable:
No
7/6/2012Updated: 2/14/2015
Global ACP
Description of change:
Change "OPTION 1" to "PATH 1"
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
7/6/2012Updated: 2/14/2015
Global ACP
Description of change:
Add the following after Case 2: OROPTION 2. Percentile Rainfall EventsCASE 1. Non-Zero Lot Line ProjectsIn a manner best replicating natural site hydrology1 processes, manage onsite2 the runoff from the developed site for the 95th percentile of regional or local rainfall events using Low Impact Development (LID)3 and green infrastructure4. Use daily rainfall data and the methodology in the United States Environmental Protection Agency\'s Technical Guidance on Implementing the Stormwater Runoff Requirements for Federal Projects under Section 438 of the Energy Independence and Security Act to determine the 95th percentile amount.ORCASE 2. Zero Lot Line ProjectsFor zero lot line projects located in urban areas with a minimum density of 1.5 FAR (13,800 square meters per hectare net), in a manner best replicating natural site hydrology processes, manage onsite the runoff from the developed site for the 85th percentile of regional or local rainfall events using LID and green infrastructure.
Campus Applicable
No
Internationally Applicable:
Yes
11/1/2011
LEED Interpretation
Inquiry:

How can a project earn exemplary performance for Stormwater Quantity and Quality?

Ruling:

The exemplary performance requirements for SSc6.1 Stormwater Quantity and SSc6.2 Stormwater Quality listed in the LEED Green Building Design & Construction Reference Guide call for (1) a comprehensive approach to capture and treat stormwater runoff and (2) demonstrated performance above and beyond the credit requirements. To expand and clarify what these two requirements refer to, the following additional guidance is provided.SSc6.1 Stormwater QuantityTo demonstrate a comprehensive approach and performance above and beyond the credit requirements, the stormwater management strategies must:1. Address runoff from the entire development footprint of the site using Low Impact Development (LID) practices. 2. Achieve the following stormwater quantity performance:a. Case 1, Option 1: Achieve a post-development peak discharge rate and quantity that is equivalent to those calculated for the natural land cover site conditions.b. Case 1, Option 2: No EP available for his compliance path.c. Case 2: Achieve a 50% reduction in the volume of runoff during the 2-year 24-hour design storm.LID is defined as an approach to managing stormwater runoff that emphasizes on-site natural features to protect water quality by replicating the natural 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, and soil amendments. These are engineered practices that may require specialized design assistance.SSc6.2 Stormwater QualityTo demonstrate a comprehensive approach and performance above and beyond the credit requirements, the best management practices employed must be non-structural, conforming to LID practices as defined above, and should be designed to remove at least 80% of the average annual total suspended solids (TSS) from twice the rainfall volume required for the base credit (i.e, runoff generated from 1 inch of rain in an arid climate, 1.5 inches of rain in a semiarid climate, and 2 inches of rain in a humid climate).To document compliance with these requirements, a detailed narrative or stormwater management plan summary should be provided that describes the exemplary performance approach and includes calculations that clearly highlight compliance with the exemplary performance requirements. As the exemplary performance requirements for these two credits overlap considerably, only one SSc6 EP point is available to projects. Applicable internationally.

Campus Applicable
No
Internationally Applicable:
Yes
5/30/2007
LEED Interpretation
Inquiry:

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

Ruling:

The most effective way to achieve SSc6.1 is to implement a stormwater management plan that prevents the post-development peak discharge rate and quantity from exceeding the pre-development peak discharge rate and quantity for a 2-year 24-hr storm. If the adjacent pond is intended to treat the runoff from the project site, and if it is sized sufficiently to store the developed site increased runoff from a 2-year 24-hr storm, then it can contribute to credit achievement. Please provide volume calculations to show what the pre and post development 2-year 24-hr storm runoff is and some volume calculations for the stormwater management pond to verify that it can store this runoff volume. Alternatively, the project team can demonstrate that receiving stream is protected from excessive erosion by implementing a stream channel protection strategy and quantity control strategies and that the 2 year runoff velocity in the stream is low enough so as not to cause stream erosion. Applicable Internationally.

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
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
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
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
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
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

LEEDuser expert

Michael DeVuono

PE, CPESC, LEED AP BD+C

Arcadis North America
Regional Stormwater Leader

See all LEEDuser forum discussions about this credit » Unsubscribe from discussions about CS-2009 SSc6.1