Many project teams are reluctant to attempt this credit because conventionally engineered solutions don’t always meet LEED requirements. Don’t be deterred. The best and easiest way to improve the quality of stormwater is to let water permeate the ground through increased landscaping and reduced impervious areas. As long as your soil type has a good infiltration rate, letting stormwater seep into the ground will treat 100% of the pollutants associated with the stormwater runoff. Let natural infiltration do as much of the work possible before using more expensive mechanical methods. In urban sites, infiltration options can be very limited and a rainwater cistern or green roof might be the best approach for credit compliance.
This credit deals with the prevention of polluted runoff, and uses Total Suspended Solids (TSSTotal suspended solids (TSS) are particles that are too small or light to be removed from stormwater via gravity settling. Suspended solid concentrations are typically removed via filtration.) as the indicator of level of pollution. Nitrates and phosphates are not accounted for in the credit calculations. Projects can use biological or mechanical treatment methods for smaller and more frequent storms for credit compliance. In order to earn the credit you must be able to show your stormwater treatment system is effective at treating all rainstorms for any year up to 90% of the average annual rainfall event.
Retaining and reusing stormwater on-site can provide numerous environmental benefits, along with LEED synergies. In addition to trapping suspended solids, capturing stormwater for reuse can reduce peak runoff rate and volume, helping with SSc6.1: Stormwater Design—Quantity Control, and help with water efficiency credits WEc1, WEc2, and WEc3.
Explore low-impact development strategies such as bioretention, vegetated swales, a green roof, rainwater cisterns, and porous pavement. These strategies reduce hardscape and impervious areas, thereby reducing runoff. Some strategies such as green roofs and rainwater cisterns have space needs, so be sure to consider their requirements. The owner and civil engineer should work together to determine the feasibility and rough cost increase of including rainwater cisterns or a green roof.
The easiest way to earn this credit is through decreasing your project’s impervious area by reducing the building footprint, increasing landscaped areas, and disconnecting impervious areas—designing sidewalks, roofs, and parking areas so that the runoff is not directed to a drainage system or other hardscapes. Use natural infiltration, promoted by strategies like green roofs, downspout disconnection (disconnecting the downspouts so that runoff is directed to softscape area instead of storm drains), softscapes, bioswales, porous paving, and rain gardens.
Overlapping strategies and technologies address SSc6.1: Stormwater Design—Quantity, as well as SSc6.2. Vegetative swales, for example, can contribute to both credits—integrate the requirements of both for best results. Keep in mind, however, that each credit requires different calculations and methodologies. Reducing the quantity of stormwater runoff for SSc6.1 does not always equate to a quality improvement for SSc6.2.
Using site space for stormwater management is often a must. Architects and owners may see stormwater best management practices (BMPs) as wasting valuable land—a mentality that can make this credit difficult. It may help to stress that stormwater BMPs can act as aesthetic features that enhance the quality of the site and add value to the project. Creative, integrated approaches can even reduce space-hogging, unattractive strategies like detention ponds while adding amenities with multiple benefits, like green roofs.
Use an integrated design strategy to improve the quality of stormwater runoff. True integration requires the input and collaboration of the entire site team, including the civil engineer, landscape architect and architect. Don’t leave stormwater management solely in the hands of the civil engineer.
Make sure that all team members understand landscape and hardscape tradeoffs. All team members should know how these details affect stormwater generation, runoff, and possible capture, treatment, and reuse strategies.
Indirect benefits of stormwater systems are just as real as direct costs to the project, but can be harder to quantify. These include issues like reducing the burden on the municipal system; reducing contaminants in waterways; reducing peak runoff, making stream habitats more consistent; reducing the temperature of runoff, which improves the conditions for aquatic life; and reducing erosion. If your municipal codes are more stringent and come with higher fees, there may be a more direct cost benefit to the project from stormwater mitigation. Any additional costs in this case are likely to be for documentation purposes, although most municipalities require similar stormwater documentation.
Familiarize yourself with natural hydrology, site topography and soil infiltration rates by conducting site visits and tests. Confirm that soils are capable of infiltrating 90% of annual rainfall. If the porous site area cannot infiltrate 90% of rainfall, you will need to add structural controls or soil amendments to achieve the target.
Research local regulations on the stormwater quality requirements, as well as regulations on the collection, storage and reuse of stormwater, including water rights.
Research historical climate records to understand expected storm event frequency, intensity, and duration.
The civil engineer determines the degree of stormwater management required by LEED based on average annual rainfall. The engineer uses these calculations to determine the type and size of systems needed. Managing 90% of the average annual rainfall is equivalent to treating the amounts listed on this table.
Develop a project-wide water budget and a landscape irrigation water budget. This will help teams decide if reusing rainwater may be appropriate and where to use it—typically either in irrigation or toilet flushing.
The civil engineer can conduct a cost-benefit analysis of stormwater-reduction strategies, including cisterns, porous pavement, rain gardens, parking garages (instead of parking lots), detention ponds, green roofs, sand filters, or detention tanks. Some of these strategies may be perceived as added costs, but this analysis may show that with reduced infrastructure, these environmental strategies are cost-neutral, or better.
Depending on local regulations, this credit may be standard practice. For example, new developments following the Commonwealth of Massachusetts Stormwater Policy must provide at least 80% of TSS removal rates through BMPs. Also, any projects areas that are required to follow the U.S. Environmental Protection Agency, Section 6217(g) of the 1900 Coastal Zone Management Act Reauthorization Amendments, are required to meet these same TSS standards.
In locations where local stormwater regulations are similar to or more stringent than LEED requirements, implementation of this credit will incur minimal additional cost for documentation purposes. In locations where it goes beyond standard practice, it may require additional design and documentation costs.
Some municipalities require documented stormwater management. The documentation for LEED requirements should not represent a significant soft cost premium.
Integrating the stormwater plan into the design at an early stage and calculating the pollution reduction percentages will decrease additional costs as the landscape and building infrastructure can be designed accordingly.
Explore potential synergies and tradeoffs with other LEED credits or green building strategies. Items to discuss can include the use of parking lots vs. parking garages (SSc7.1) for stormwater management, rain gardens, trees for shading hardscapes (also SSc7.1), tress for passive solar design (EAc1), impervious surfaces, planting material (WEc1), wind-break opportunities, water reuse (WEc3), rainwater capture (WEc1) and acoustical barriers
The civil engineer calculates the minimum volume of stormwater that must be treated through infiltration, reuse or mechanical treatment to meet the 80% TSS removal rates after development. Base this calculation on the average annual rainfall for the project.
Calculate the potential for stormwater reuse and corresponding cistern sizes to accommodate stormwater reuse for irrigation or other applications like toilet flushing. Be sure to allocate proper space for rainwater cisterns.
The civil engineer develops a stormwater management plan for post-development suspended sediment loads, detailing acceptable BMPs and their associated TSS removal rates. Reference the LEED 2009 Reference Guide’s table of Effectiveness of Management Practices for Total Suspended Solids Removal from Runoff. (Also shown here.)
The civil engineer and the landscape architect design the landscape and stormwater systems to maximize infiltration and collect water where possible. These systems must be designed based on the watershed region, and the BMPs employed must in combination remove 80% of the TSS for the post-construction design. The civil engineer will need to verify that the design meets the LEED requirements.
Find TSS removal rate data in state or local best management practice manuals.
You must design any BMPs to local standards that have adopted an 80% TSS removal rate criterion, or use existing data that has monitored the TSS removal rates of different stormwater controls.
Previously existing stormwater management systems on the project site can be used towards credit compliance as long as requirements are met.
The stormwater design should reflect unique site features, attempt to minimize impacts on natural stormwater hydrology, and promote infiltration and treatment of stormwater runoff.
Treating captured stormwater to the quality standards required for this credit provides the potential for a clean water source for irrigation or toilet flushing, and a further reduction of the burden on municipal treatment facilities.
Consider contouring the land to direct stormwater to planting beds to reduce irrigation needs of potable water in locations where stormwater capture and reuse is not allowed. Parking lots and walkways can be graded to direct runoff to depressed swales or bioretention facilities with perforated pipes and other slow release infiltration mechanisms. This design offers better stormwater management than typical elevated or impervious planters.
Soil type, planting medium and plant species must be considered for their capacity to promote infiltration. For example, clay soils do not allow for good infiltration rates and an engineered soil or compost could be added to allow for better absorption.
Stormwater storage and biofiltration can be incorporated into landscape features and can also include educational elements for occupant and community benefits.
All design methods must consider the soil type and infiltration rates to show that soils are capable of treating the appropriate amount of rainfall.
In urban areas and sites with little land, use a variety of features to achieve project goals. For example, green roofs and rainwater cisterns may be effective in these situations. Capturing rainwater for irrigation will reduce the amount of stormwater runoff leaving the site as well as outdoor potable water use. Reusing captured rainwater for toilet flushing will have similar effects, in addition to reducing potable water use indoors. In some cases, cisterns with open bottoms may be effective in storing stormwater runoff and will encourage infiltration and reduce the peak flow rate discharge. These cisterns may be incorporated under parking areas or other hardscape.
Porous pavement can be incorporated into many sites and climatic conditions. Proper design, installation, and maintenance is important. Work with an experienced contractor, and verify that porous paving will work with your site’s climate and soil conditions. For example, snowplowing, sanding, and salting can damage porous paving.
Stormwater systems can range from bioswales to cisterns to green roof systems, and range greatly in cost and effectiveness depending on the application. Certain on-site stormwater treatment technologies can be costly but serve additional environmental purposes and may contribute to various other LEED credits related to open space and heat island effect. See ‘Related Credits.’ These strategies should be considered and designed for multiple purposes.
Stormwater features such as constructed wetlands, green roofs, and bioswales can be designed as a site asset (aesthetic, habitat, etc.) and provide valuable amenities. Including these features can also increase property value.
The most cost-effective stormwater management strategies are those that preserve or restore natural site features and promote natural infiltration: reducing hardscapes, designing a smaller building footprint, increasing landscaping area, using porous paving materials, natural swales, and other low impact development strategies. Natural infiltration may also decrease the cost of maintenance compared to other structural and packaged stormwater control systems.
Bioinfiltration strategies on streets and parking lots, such as vegetated filter strips and grass swales, are alternatives to typical curb and gutter design that allow for infiltration of stormwater, as opposed to conveying the runoff to storm drains. Reducing the number of curbs, storm drains, and piping systems can substantially reduce construction costs.
Installing a green roof is one successful way to control and treat stormwater. Different types of green roofs provide varying levels of stormwater management, amenity, benefits and maintenance requirements. While green roofs can be expensive, they can often reduce the costs of traditional stormwater systems for a net savings.
Stormwater collection, storage and reuse equipment will increase costs, but will reduce the expenses of potable water.
There are fewer codes and associated costs for collecting and reusing stormwater for irrigation than for interior water reuse. Captured stormwater can often be reused for irrigation without much treatment. Reuse for toilet flushing and cooling tower make-up usually requires treatment.
The civil engineer runs final calculations for the project’s stormwater design. Be sure to address all value engineered items and the finalized design.
The civil engineer verifies that TSS removal and infiltration rate goals are met.
The civil engineer includes all stormwater treatment strategies on the project plans.
The civil engineer fills out the LEED documentation including a list of the BMPs used, descriptions of their function, expected annual percentage of rainfall infiltrated by each and a list of the structural controls used, descriptions of TSS removal performance, and expected annual percentage of rainfall treated by each. The civil engineer should also provide a copy of the project plans with designated stormwater strategies, detailing where the BMPs or structural controls are located along with the area the serve. It’s helpful to include an optional narrative naming the local standard that the stormwater system is designed to match or surpass.
Stormwater quality control systems require a maintenance plan for proper functioning. Ideally this is developed by the civil engineer shortly after design completion.
Commissioning water reuse systems will help ensure they operate as designed. This step can be incorporated EAp1: Fundamental Commissioning, or EAc3: Enhanced Commissioning.
Compacted soil from high vehicle traffic prior to or during construction can severely limit natural infiltration of stormwater. Avoid site compaction during construction as much as possible—this will also help compliance with SSc5.1: Site Development—Protect or Restore Habitat. Aerating soils is not a substitute for avoiding compaction, but can be used to improve infiltration rates.
Provide maintenance personnel with plans and operations manuals for the operation of all structural control systems.
Implement a maintenance plan to ensure ongoing, as-designed performance of stormwater systems and equipment. Doing so will also contribute to LEED-EBOM SSc6: Stormwater Management credit compliance.
If using porous paving, implement a plan to maintain its porosity. Vehicle use, sand and organic matter, and snowplowing can all damage or reduce the effectiveness of porous paving.
If relying on natural infiltration in landscaped areas, keep the plants in those areas healthy and avoid soil compaction from vehicle use.
Maintenance will be required for most stormwater systems. If the project uses structural controls, check with the product manufacturer, designer, and engineer for details on additional cost for maintenance requirements. If the project uses non-structural controls, have the designer confirm the associated maintenance practices for facility manager or additional contracts required. Maintenance costs will vary depending on the strategies employed.
Excerpted from LEED for New Construction and Major Renovations Version 2.2
Limit disruption and pollution of natural water flows by managing stormwater runoff.
Implement a stormwater management plan that reduces impervious cover, promotes infiltration, and captures and treats the stormwater runoff from 90% of the average annual rainfall using acceptable best management practices (BMPs).
BMPs used to treat runoff must be capable of removing 80% of the average annual post development total suspended solids (TSSTotal suspended solids (TSS) are particles that are too small or light to be removed from stormwater via gravity settling. Suspended solid concentrations are typically removed via filtration.) load based on existing monitoring reports. BMPs are considered to meet these criteria if (1) they are designed in accordance with standards and specifications from a state or local program that has
adopted these performance standards, or (2) there exists in-field performance monitoring data demonstrating compliance with the criteria. Data must conform to accepted protocol (e.g., Technology Acceptance Reciprocity Partnership [TARP], Washington State Department of Ecology) for BMP monitoring.
Use alternative surfaces (e.g., vegetated roofs, pervious pavement or grid pavers) and nonstructural techniques (e.g., rain gardens, vegetated swales, disconnection of imperviousnessResistance to penetration by a liquid and is calculated as the percentage of area covered by a paving system that does not allow moisture to soak into the ground., rainwater recycling) to reduce impervious- ness and promote infiltration thereby reducing pollutant loadings.
Use sustainable design strategies (e.g., Low Impact Development, Environmentally Sensitive Design) to design integrated natural and mechanical treatment systems such as constructed wetlands, vegetated filters, and open channels to treat stormwater runoff.
This guide provides design strategies and techniques on incorporating biofilters in projects.
This website gives designers and planners information on the appropriate application of bioretention areas.
This report describes low-impact development approaches to stormwater management for big-box stores.
Technical manuals on stormwater BMP’s as they relate to Denver and surrounding counties.
This design manual provides stormwater information specific to semi-arid climates, including Denver, Colorado.
This design manual provides stormwater information specific to Denver, Colorado.
This portion of the EPA’s website provides general information on stormwater, including technical information specific to NPEDS.
This website provides stormwater information specific to the Portland, Oregon area.
A guide to low-impact development for residences.
This design manual provides stormwater information specific to Maryland.
This website provides stormwater information specific to Massachusetts.
This technical manual from the U.S. EPA contains background on documenting stormwater requirements through capturing the 95th percentile storm using onsite management practices.
Features a database of over 500 BMPBest Management Practice studies, performance analysis results, tools for use in BMP performance studies, monitoring guidance and other study-related publications.
This database provides studies and analysis on BMPs and is intended to improve design.
This website provides information on the performance of technologies in a number of states across the U.S.
Online magazine for stormwater professionals.
This online research center for civil engineers of all backgrounds includes stormwater information.
This website provides a comprehensive overview of LID strategies including design manuals and case studies.
A stormwater management and drainage report covering both SSc6.1 and SSc6.2 can document all aspects of credit compliance.
Create documentation quantifying stormwater volume and peak rate mitigation strategy.
Provide narrative documentation like this to demonstrate structural and non-structural stormwater control measures.
This template is the flattened, public version of the dynamic template for this credit that is used within LEED-Online v2 by registered project teams. This and other public versions of LEED credit templates come from the USGBC website, and are posted on LEEDuser with USGBC's permission. You'll need to fill out the live version of this template on LEED Online to document this credit.
Documentation for this credit can be part of a Design Phase submittal.
I would like to know what determines the site boundary for capturing the 90% anual rainfall total. Does the treatment area have to be the entire site boundary?
Yes, you have to consider the entire LEED boundary to perform your calculations. You have to take into account what kind of surfaces are there in your site and their runoff coefficients, and make your calculations in proportion to the area covered by each type of surface.
Can anyone provide any insight into slow-release fertilizer requirements?
Stantec, can you provide any more specifics in your question—what kind of insight you're looking for, and what you see it applying to?
In CaGBC CIRCredit Interpretation Ruling. Used by design team members experiencing difficulties in the application of a LEED prerequisite or credit to a project. Typically, difficulties arise when specific issues are not directly addressed by LEED information/guide #854, the Final Ruling states "provided that no surface-applied fertilizers (greater than 1% phosphorous) are used, fertilizers may be applied around the plant root zone in the soil at the time of planting and not be in violation of the phosphorous management plan for ongoing operational management of phosphorous to meet SSc6.2."
My interpretation of this is that if slow-release fertilizer was used at the time of planting it would be exempt from the minimum 1% phosphorous requirement - would you agree with my assumption?
Yes, I agree with your reading of this CIRCredit Interpretation Ruling. Used by design team members experiencing difficulties in the application of a LEED prerequisite or credit to a project. Typically, difficulties arise when specific issues are not directly addressed by LEED information/guide on phosphorous.
Our project located in Guadalajara-Mx is applying for EP on SScr2. After few tests on site, we detected that the terrain doesn´t have any capacity of infiltration. Due to municipal laws, if you are not able to built absorption well in your terrain, you´ll have to build it somewhere else.
Could this alternative help for earning SScr6.1/6.2 and WEcr2, whether designed correctly depending on credits calculations?
Even though, a system for capturing rainwater is also being planned. This captured rainwater will be used for irrigation purposes, however it may not have all capacity for accomplishing those credits.
Johanna, I don't see any reason that you couldn't apply this strategy to earning those credits.
In this case mentioned by Johanna, would it be a problem with earning this credit whether excesses from filtered captured rain water, used for irrigation purposes, are conducted into municipal drainage? Considering the terrain doesn´t have capacity of infiltration.
I'm not sure I understand your question. If you're using captured rainwater for irrigation, unless you're over watering, you shouldn't have any runoff...
Thanks for your response. I reckon I haven´t explained all the situation. Captured rainwater will be used for irrigation, however the garden is above a parking so this water will recirculate, thus at some point, it will occur excesses and, these excesses, even being naturally filtered due irrigation, will be conducted into municipal drainage.
Nadia, I don't know how to answer that question—I think you'd need to work with your civil engineer on that.
Part of our stormwater management strategies is to collect and treat stormwater. The treated water will then be used for flushing and irrigation purposes. The Stormwater collection and treatment scheme has been designed in accordance to the International Plumbing Code (IPCInternational Plumbing Code), which is commonly used in the region (Middle East). H
My questions are:
1) Is it an issue if the IPC does not specifically refer to the 80% of TSSTotal suspended solids (TSS) are particles that are too small or light to be removed from stormwater via gravity settling. Suspended solid concentrations are typically removed via filtration. removal criterion ?
2) Should I submit calculations showing what will theTSS (in ppmParts per million.) be following the filtration process ?
George, reducing the quantity of stormwater through collection and use is a common and effective strategy for achieving this credit. I don't think you need to pay close attention to documenting how the collected water will be filtered for this credit, but any water that is not collected will need this documentation.
The civil engineer on my project is having trouble finding a source for exactly how the annual rainfall volume is supposed to be calculated. Can anyone point me (us) to an example or resource that will clarify this? The reference guide mentions it, but doesn't actually spell out how it is to be calculated.
Jeremy, have you checked out our tips above under Bird's Eye View, Checklists, Resources, and Doc Toolkit? Since your question is fairly broad, I would point you there to begin with. Let us know if you have further questions.
I have the same question as Jeremy, but I'm not sure where to find the sources you mentioned - Bird's Eye View, Checklists, Resources, Doc Toolkit...could please post links to them?
The sources Tristan mentioned are at the top of this page. Scroll up to see them.
We are pursuing this credit for a new building on an existing corporate campus, Initial review came back and said we had to demonstrate treatment for entire campus flows, not just project site flows. Has anyone else had this interpretation?
The LEED application guide for campuses states that:
"A master planning approach to storm water management and overall impervious surface management that is campus-wide or based on the local watershed is preferred over stormwater management planning limited to one project site at a time."
I can't speak to whether reviewers are always asking for this, but it does seem to be a clear policy preference for LEED.
Tristan - Thanks for the insight. I did find a case where Harvard was able to get this credit via an alternative compliance path, demonstrating that while they did not meet the strict interpretation of the criteria for the entire campus, they achieve the improvements in each of the desired areas:
- reducing impervious cover,
- increasing on-site infiltration,
- eliminating sources of contaminants, and
- removing pollutants from stormwater
Here's the link to their credit submittal:
Robert Peccia & Associates
Many of the efforts used to control stormwater quality also improve stormwater quantity. Promoting infiltration is one way to contribute to both credits.
Capturing and reusing stormwater for irrigation purposes will also reduce the quantity of potable water used on the site for irrigation. Bioswales with native plantings will help with stormwater control without needing irrigation.
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