NC-2009 SSc6.2: Stormwater Design—Quality Control

  • NC CS Schools SSc6.2 Credit req's diagram
  • Use natural infiltration

    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.

    Pollution Prevention

    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. 

    Numerous environmental benefits

    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.

  • FAQs for SSc6.1 and SSc6.2

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

    The 2-year, 24-hour design stormA 2-year, 24-hour design storm is a nationally accepted rate that represents the largest amount of rainfall expected over a 24-hour period during a 2-year interval. The rate is the basis for planning and designing stormwater management facilities and features. is a storm that has a high probability of happening and contributing to stormwater pollution. A 2-year storm has a 50% chance of happening in a given year, whereas a 1-year storm has a 100% chance.

    It should be noted that most state or local programs only require projects to meet regulatory requirements related to flooding and/or water quality.  This type of stormwater management program is designed to control the large, infrequent storm events that cause flooding, but not to manage smaller storm events that we now know cause the majority of the overall erosion and quality concerns because of their much higher frequency. The criteria of SSc6.1 are designed to ensure that both concerns are addressed in LEED projects that achieve this credit.

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

    It depends on how you look at it. Here's how LEEDuser Expert Michael DeVuono describes it: Think about it in terms of a simple pre>post analysis. Your one year "pre" number will be smaller than your 2-year "pre" number. Sometimes that 1-year number is so small that you have to choke back a lot of water, to ensure the "post" 1-year is smaller. This raises the required storage volume for the BMPBest Management Practice. So if you're looking at both the 1- and 2-year events, you may have a greater storage need than if you simply looked at the 2-year event. The 2-year "pre" number will be bigger, so you can let more out in the "post."

    How can green roofs count as a stormwater control measure?

    There are different approaches to this. One approach is to ensure that green roof soil depth and retention capacity allows for the 2-year, 24-hour design storm.

    However, simply taking a “CN credit” for a green roof is usually beneficial enough. (The Curve Number or CN provides a number characterizing the runoff properties for a particular soil and ground cover.) Instead of the roof being modeled as impervious (with a CN of 98 which produces a high rate of runoff) some projects with extensive green roofs have used a lawn CN—usually around 61. In the calculations this results in a lower overall rate of runoff for the site, and is usually a more feasible option that providing stormwater storage in the roof media itself. If you can model your site so there is less runoff, there is less runoff volume that needs to be stored.

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

    Projects with stormwater control measures outside the LEED project boundary may be accepted if the measures appropriately take into account neighboring facilities by demonstrating that the existing stormwater management systems that serve the LEED project boundary meet the LEED requirements for all areas within the site serviced by those systems. LEED 2009 campus projects are required to reference USGBC's AGMBC guidance, which has specific guidelines for stormwater. For more on this see, for example, LI#2275 from 08/22/2008.

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

    Storm intervals don’t convert. These numbers represent specific storm event probability. A 100-year storm has a 1% chance of happening in a given year, while a 2-year storm has a 50% chance of happening in a given year. The best resource for rainfall intensity data is NOAA’s Hydrometeorological Design Studies Center Precipitation Frequency Data Server. Further guidance on interpolating 2-year, 24-hour storm event can be found in LEEDuser's EBOM SSc6 Guidance.

    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?

    This is a common strategy for reducing peak rate, which will help you comply with SSc6.1, but you'll need to add onsite reuse or infiltration to meet SSc6.2 requirements.

    A sample graph illustrating the 95th percentile rainfall event

    Are there special considerations for international projects?

    In 2012, an additional compliance option was added to SSc6.1 that was specifically written with international projects in mind. This can be found in the credit language, and is fully supported on the most recent LEED Online forms. Projects in some countries can have trouble finding the stormwater data they're looking for. Some useful sites are posted in LEEDuser's Resources tab.

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

    LEED Interpretation #10108 dated 11/01/2011 gives guidance in achieving Exemplary Performance. Achievement of the exemplary performance point encompasses both quantity and quality measures, and includes a comprehensive approach to capture and treat stormwater runoff.

    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?

    No. USGBC has indicated that providing step-by-step instructions for this entire calculation process within the context of LEED reference documents is not possible. Various methods and computer-based software programs are available to estimate stormwater runoff rates and volumes, and the exact methods used for a particular project will depend upon the data available for a given site and the preferences of the qualified professional (typically a civil engineer) performing the calculations.

    LEEDuser has heard from LEED project teams that the LEED expert on the project is sometimes expected to do the calculations for these credits, even if that person isn't a stormwater expert. We recommend a more integrated process in which the civil engineer documents this credit.

Legend

  • Best Practices
  • Gotcha
  • Action Steps
  • Cost Tip

Pre-Design

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  • 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.

Schematic Design

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  • 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.


  • Runoff Treatment EquivalentsThe 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.

Design Development

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  • 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.)

    Management practices for removing TSS


  • 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.

Construction Documents

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  • 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.

Construction

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  • 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.

Operations & Maintenance

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  • 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.

  • USGBC

    Excerpted from LEED 2009 for New Construction and Major Renovations

    SS Credit 6.2: Stormwater design - quality control

    1 Point

    Intent

    To limit disruption and pollution of natural water flows by managing stormwater runoff.

    Requirements

    Implement a stormwater management plan that reduces impervious cover, promotes infiltration and captures and treats the stormwater runoff from 90% of the average annual rainfall1 using acceptable best management practices (BMPs).

    BMPs used to treat runoff must be capable of removing 80% of the average annual postdevelopment 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:

    • They are designed in accordance with standards and specifications from a state or local program that has adopted these performance standards.

    OR

    • There exists infield 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.
    1 There are 3 distinct climates in the United States that influence the nature and amount of annual rainfall. Humid watershedWatershed that receives at least 40 inches of rainfall each year. are defined as those that receive at least 40 inches of rainfall each year, Semiarid watersheds receive between 20 and 40 inches of rainfall per year, and arid watersheds receive less than 20 inches of rainfall per year. For this credit, 90% of the average annual rainfall is equivalent to treating the runoff from the following (based on climate): Humid Watershed - 1 inch of rainfall Semiarid Watersheds - 0.75 inches of rainfall Arid Watersheds - 0.5 inches of rainfall.

    Potential Technologies & Strategies

    Use alternative surfaces (e.g., vegetated roofs, pervious pavement, 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 imperviousness and promote infiltration and thereby reduce pollutant loadings.

    Use sustainable design strategies (e.g., low-impact development, environmentally sensitive design) to create integrated natural and mechanical treatment systems such as constructed wetlands, vegetated filters and open channels to treat stormwater runoff.

Technical Guides

Stormwater Best Management Practices Design Guide, Vegetated Biofilters (EPA/600/R-04/121A)

This guide provides design strategies and techniques on incorporating biofilters in projects.


Bioretention (Rain Gardens) – EPA’s Stormwater Menu of BMPs

This website gives designers and planners information on the appropriate application of bioretention areas.


Model Low Impact Development Strategies for Big Box Retail Stores

This report describes low-impact development approaches to stormwater management for big-box stores.


Urban Drainage and Flood Control District

Technical manuals on stormwater BMP’s as they relate to Denver and surrounding counties.


Clean Water Ways, Stormwater Implementation BMP Guidelines

http://www.cleanwaterways.org/professionals/index.html


Effectiveness of Urban Stormwater BMPs in Semi-Arid Climates

This design manual provides stormwater information specific to semi-arid climates, including Denver, Colorado.


Denver Water Quality Management Plan, Stormwater Quality BMP Implementation Guidelines, Chapter 6

This design manual provides stormwater information specific to Denver, Colorado.


City and County of Denver, Department of Public Works Wastewater Management Division Storm Drainage Design and Technical Criteria

This design manual provides stormwater information specific to Denver, Colorado.


EPA’s National Pollutant Discharge Elimination System (NPDES) Overview

This portion of the EPA’s website provides general information on stormwater, including technical information specific to NPEDS.


Stormwater Best Management Practices Design Guide, Vegetated Biofilters (EPA/600/R-04/121A)

This guide provides design strategies and techniques on incorporating biofilters in projects.


Stormwater Management Manual (Portland Bureau of Environmental Services)

This website provides stormwater information specific to the Portland, Oregon area.


Rain Garden Handbook for Western Washington Homeowners: Designing your Landscape to Protect our Streams, Lakes, Bays and Wetlands

A guide to low-impact development for residences.


Maryland Stormwater Design Manual

This design manual provides stormwater information specific to Maryland.


Massachusetts Stormwater Technology Evaluation Project

This website provides stormwater information specific to Massachusetts.


Technical Guidance on Implementing the Stormwater Runoff Requirements for Federal Projects under Section 438 of the Energy Independence and Security Act

This technical manual from the U.S. EPA contains background on documenting stormwater requirements through capturing the 95th percentile storm using onsite management practices.


International Stormwater Best Management Practices (BMP) Database

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.

Web Tools

International Stormwater Management Best Practices Database

This database provides studies and analysis on BMPs and is intended to improve design.


Technology Acceptance and Reciprocity Partnership

This website provides information on the performance of technologies in a number of states across the U.S.

Publications

Stormwater — A Journal for Surface Water Quality Professionals

Online magazine for stormwater professionals.


Storm Water Solutions

Online magazine for stormwater professionals.


American Society of Civil Engineers Online Research Library

This online research center for civil engineers of all backgrounds includes stormwater information.

Organizations

Low Impact Development Center

This website provides a comprehensive overview of LID strategies including design manuals and case studies.

Stormwater Quality Narrative

Provide narrative documentation like this to demonstrate structural and non-structural stormwater control measures.

Stormwater Management Report

All Options

A stormwater management and drainage report covering both SSc6.1 and SSc6.2 can document all aspects of credit compliance.

Design Submittal

PencilDocumentation for this credit can be part of a Design Phase submittal.

LEED Online Forms: NC-2009 SS

The following links take you to the public, informational versions of the dynamic LEED Online forms for each NC-2009 SS credit. You'll need to fill out the live versions of these forms on LEED Online for each credit you hope to earn.

Version 4 forms: (newest)

Version 3 forms:

These links are posted by LEEDuser with USGBC's permission. USGBC has certain usage restrictions on these forms; for more information, visit LEED Online and click "Sample Forms Download."

144 Comments

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Jamison Hill Energy Engineer/LEED Consultant Community Environmental Center
Mar 07 2014
LEEDuser Member
19 Thumbs Up

90% of average annual runoff

Is that the pre-development runoff rate or post-development runoff rate?

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Michael DeVuono Senior Staff Designer, T&M Associates Mar 07 2014 LEEDuser Expert 1918 Thumbs Up

It is the 90th percentile runoff depth which is used to calculate the pre and post runoff rate and volume.

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Rob Watson CEO ECON Group
Dec 23 2013
LEEDuser Member
1582 Thumbs Up

Approval of BMPs not fully installed

We have a client in a far northern climate that wants to achieve additional credit by installing rain gardens to handle runoff during the summer rainy season. They will not be able to begin construction until spring. The building is already complete and in soft opening mode and they want to submit for certification before the work on the rain gardens is complete.

Has anyone had experience with GBCI accepting plans, contracts, etc. (along with the requisite calcs) as 'evidence' that these measures fulfill the requirements of SSc6 (plus contributions to WEc1, etc.)

Thanks in advance.

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Pedro Ribeiro Director of Sustainability Edifícios Saudáveis Consultores
Dec 09 2013
LEEDuser Member
500 Thumbs Up

Doubt related with calculation procedure

I have some doubts related with this credit in a specific project with the following characteristics:

- The majority of the site area collect run-off water to one lake installed on-site, and also to a storage tank ;

- The lake is connected to the municipal drainage system, to ensure that whenever full, the excess water is drained off-site. Also, the lake has the capacity to be totally discharged 24 hours after the storm events.

- The lake is used to feed the irrigation system and also the WC flushes.

- The remaining areas, drain directly to the municipal drainage system.

In order to achieve compliance, please tell me if the following procedure is correct:
1) Determine the rainfall event associated with the percentile 90, and considering the total area, calculate the total amount of water that falls over the site;
2) Consider that the water that infiltrates in the vegetated areas (around 90%) and the water that is reused for irrigation and WC flushes have an average 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 of 100%. Now, how shall I calculate the amount of reused water? The problem is that all this calculations are made on a daily basis, but the water can be reused on different days... what's the best way of solving this?
3) Consider that the water run-off from the areas that do not collect water to the tank is all drained out of site, without any kind of treatment;
4) Consider that, if there remains any water in the tank and lake, it have an average TSS removal of 80%.

Thanks in advance.

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Michael DeVuono Senior Staff Designer, T&M Associates Dec 10 2013 LEEDuser Expert 1918 Thumbs Up

I'm sorry, I am having a difficult time following your post, but i will give it a shot.

90 percentile rainfall is just that. This is the depth you use in your stormwater model.

Use that depth in your runoff calculations, SCS methodology, to determine what actually runs off the site. Areas that are infiltrated will be taken care of in this model, either by the corresponding CN or the pracitce modelled as a biofiltration, raingarden, etc.

What runs off the site needs to be treated for 80% 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. Infiltration facilities will not give you 100% TSS removal, more like 60-85% depending on what the practice is that you propose.

Please post a follow up question, and we can go from there.

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Pedro Ribeiro Director of Sustainability, Edifícios Saudáveis Consultores Dec 11 2013 LEEDuser Member 500 Thumbs Up

I apologize if I've not been clear enough.

My fundamental question is related on how shall I estimated the amount of collected water that is reused (and then have 100% 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. removed).

The calculations are made considering the dailly precipitation equivalent to the one from the 90th percentile. However, the water that was collected in that particular day, can be stored and then reused later. Imagine that after doing the calculations, we determine that the amount of water that need to be treated for 80% TSS removal is 100 cf and the irrigation water needs + flush discharges sum up 20 cf / day. Is it reasonable to assume that the collected water will be all reused? Or we can only consider the reused water on that particular day?

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Michael DeVuono Senior Staff Designer, T&M Associates Dec 11 2013 LEEDuser Expert 1918 Thumbs Up

OK, you need to develop a water budget. This many flushes per day, 1 gallon per flush (or whatever your fixture is), setup an irrigation plan, this many gpm's per day/week/whatever....go from there.

Ideally if you are trying to say you are reuisng all runoff, you want to show a defecit in a available reuse water, this way there is no doubt as to you using it all. Look at some past posts to see how this was handled.

We are going to have some discussion regarding reuse on the TAGLEED Technical Advisory Group (TAG): Subcommittees that consist of industry experts who assist in developing credit interpretations and technical improvements to the LEED system. call today. I will let you know how this goes.

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Sheryl Swartzle LEED administration TLC Engineering for Architecture
Nov 12 2013
LEEDuser Member
537 Thumbs Up

SSc6.2 Civil Engineer's comment

The civil engineer on our project made the following comment : "Item 6.2, quality control: all exfiltrationExfiltration is air leakage through cracks and interstices and through the ceilings, floors, and walls. trenches accepting rainwater discharge are "dry" and that is considered as pretreatment for quality control, best management practice in Dade County. Water not discharging to trenches will infiltrate in landscaped areas. In the past we have gotten this credit. HOWEVER, we can provide no evidence of removing 80% of suspended solids and there are no monitoring reports. If that's really required, it's a no go."
Not being a civil engineer myself, I am looking for feedback on this please.

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Michael DeVuono Senior Staff Designer, T&M Associates Nov 12 2013 LEEDuser Expert 1918 Thumbs Up

Tell him to cite the appropriate local BMPBest Management Practice Manual, I'm sure they offer quidance on water quality. For instance, in PA, infiltration trench = 85% 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.

The reference manual also offers suggested removal rates, but this credit ultimately defers to the CE. Have him write up a report that details the removal efficiencies of the various BMPs. If he is comfortable with it, you should be fine.

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Sheryl Swartzle LEED administration, TLC Engineering for Architecture Nov 12 2013 LEEDuser Member 537 Thumbs Up

Thanks so much.

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MM K
Oct 02 2013
Guest
898 Thumbs Up

Filtering requirements

If we capture rainwater and reuse it for irrigation, do we need to show any type of filtering or will this automatically acquire the credit?

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Michael DeVuono Senior Staff Designer, T&M Associates Oct 22 2013 LEEDuser Expert 1918 Thumbs Up

I'd take 100% 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. credit for it ... no filtrations.

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MM K Oct 29 2013 Guest 898 Thumbs Up

Thanks Michael,

I have received a reply back from the GBCI saying the water that is reused does not count...I'm confused now. If we are reusing all the water for irrigation, can the credit not be achieved??

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Michael DeVuono Senior Staff Designer, T&M Associates Oct 29 2013 LEEDuser Expert 1918 Thumbs Up

Would you mind posting the response. This does not compute.

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MM K Oct 29 2013 Guest 898 Thumbs Up

For SSc6.2, water that is being stored for reuse is not considered - only that being discharged from the site. If some of that is from the vegetated roof, your civil engineer can determine the correct removal rate; examples are in Table 2 on page 104 of the 2009 LEED Reference Guide for Green Building Design & Construction, June 2010 edition. The probable rate would most likely be in the range of 'grass swale'.

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Michael DeVuono Senior Staff Designer, T&M Associates Oct 29 2013 LEEDuser Expert 1918 Thumbs Up

This is a shame, the reviewer is simply reading from a book and missing the entire point of this, IMO. I will bring this up at the next TAGLEED Technical Advisory Group (TAG): Subcommittees that consist of industry experts who assist in developing credit interpretations and technical improvements to the LEED system. meeting, but not sure if it will help you by the time anything gets addressed.

From the BD+C manual ... "Implement a stormwater management plan the ..... promotes infiltration, and captures and treats runoff from 90% .... "

OK...so you are using this for irrigation, of landscaping, outdoors .... we need to reword this somewhow, and this is going to be tough without seeing the plan.

I would consider the areas you "irrigate" as infiltration "zones." It's what they are, you are putting the water back in the acquifer through these zones. To be conservative I would say that the sites discharge is held in a "stormwater vault" where 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. settle at the bottom and are not discharged...(again conservative, take 75% TSS removal even though we know it is 100%. Then the stormwater vault discharges to the vegetated "infiltration zone" which provides another 65% TSS removal.

Now lets do the math...and you're probably going to need your engineer to do these calcs, and supplement local EMC rates, but an example for a hypothetical 1 acre lawn.

1 acre lawn with a TSS EMC of 180 mg/l produces an approximate runoff volume of 0.28 acre-feet which in turn produces 133.7 lbs of TSS.

Our target removal: 133.7 lbs(0.80) = 106.96 lbs

First flush through our "vault" = 133.7(.80) = 100.28 lbs removed

33.425 lbs remain

We then route through the "infiltration zone" 33.425(0.60) = 20.055 lbs removed

Total removal = 120.33 lbs = 90% TSS removal

Or something like that.

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MM K Oct 29 2013 Guest 898 Thumbs Up

Thanks for this. Yes, the water is being reused for irrigation and toilet flushing so we all assumed it was 100% 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.
Just as a note, the comment received was by contacting GBCI; the project has not been reviewed yet but we wanted to double check this approach was fine.

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Michael DeVuono Senior Staff Designer, T&M Associates Oct 29 2013 LEEDuser Expert 1918 Thumbs Up

The toilet flushing thing, I can see their point. But I would not use the toilet water as part of my runoff number. If they aren't considering that runoff, then don't use that as part of your numbers.

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MM K Oct 29 2013 Guest 898 Thumbs Up

Yes, I won't use this number. But I am puzzled about why we cannot use the rest of the water as irrigation for the green roof. The project is a zero lot line and no water would be discharged.. I would think this achieves the credit..

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Michael DeVuono Senior Staff Designer, T&M Associates Oct 29 2013 LEEDuser Expert 1918 Thumbs Up

You're preaching to the choir here. Those GBCI responses aren't "official" so you're reviewer may agree with your approach. This is the first I have ever heard of this not counting, and we have recommended this approach on this site for quite some time. To be safe, if you follow the creative wording above, I think you will be okay. Goo dluck, and keep us posted.

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MM K Oct 30 2013 Guest 898 Thumbs Up

Many thanks for your help Michael much appreciated.
In another project, the team would like to install a filter but is not sure which size of the filter to choose. They are thinking of 15 microns. Is that ok?
What would be the typical size 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.?

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Michael DeVuono Senior Staff Designer, T&M Associates Oct 30 2013 LEEDuser Expert 1918 Thumbs Up

I would consult with the manufacturer and have them specify the product that achieves the desired results. A suspended solid is anything from a soda can to a fleck of dust.

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Michael DeVuono Senior Staff Designer, T&M Associates Nov 13 2013 LEEDuser Expert 1918 Thumbs Up

Not to drudge up an older topic, but the BD+C reference manual, page 103, under "Structural Measures" specifically deals with what you are proposing.

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Muhammad Faisal Azizullah Jaffar Sustainability Consultant Ramboll
Oct 02 2013
Guest
67 Thumbs Up

Storm water quality within LEED Boundary

Hello

I am currently working on a Golf course community within the middle east and in regards to the various strategies employed on site , there are vagetated filter strips, oil spearators, wet pond /lakes, wadi / grass swales and extended retention dry pond but some of this extendeds beyond the LEED boundary, but still remains within the site boundary of the project. Is that acceptable or we have to be within the LEED boundary. Or possibly extended the LEED boundary, but we would have to rework on other credits. please clarify.

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Michael DeVuono Senior Staff Designer, T&M Associates Oct 02 2013 LEEDuser Expert 1918 Thumbs Up

You should be good with that approach.

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MM K
Sep 27 2013
Guest
898 Thumbs Up

Rainwater cistern and greenroof

Our project will capture rainwater for the irrigation of the green roof and for the flushing of WCs in the building.
What can we consider the 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 efficiency of the rainwater capturing?
If we are reusing this water to irrigate and for flushing, does this achieve the credit without needing to achieve 80% TSS removal?
Also, the greenroof is mostly composed of sedum, What would be a typiucal removal efficiency for those types of green roofs?

Thank you!

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Michael DeVuono Senior Staff Designer, T&M Associates Sep 27 2013 LEEDuser Expert 1918 Thumbs Up

Capture and reuse will give you 100% 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, or very close to it.

Green roofs, depending on the layout, I treat more like a vegetated filter strip, 35-50% TSS depending on the size, but this needs to actually treat something .... green around the edges, treating the interior mechanicals and such that drain outwards.

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MM K Sep 27 2013 Guest 898 Thumbs Up

So if we capture rainwater and reuse, do we need to show any type of filtering or will this automatically acquire the credit?

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Jiri Dobias
Sep 09 2013
LEEDuser Member
1050 Thumbs Up

Retention Tank

Dear Leedusers,
our project will install a retention tank which will collect storm water from the whole LEED area. The retention tank will provide water for flushing toilets and watering greenery. Even though the size of the tank is about 240 m3 (8500 cf) it is possible that during 2-year 24 hour design storm some of storm water will be drained to the municipal drainage system.
According the LEEDonline it seems that all BMPBest Management Practice's contain WC flushing and it would be 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 rate of 100%. I don''t think that we can state 100% total weighted average TSS removal efficency when some of the stromwater could be drained to the municipal system during some non-standard storms.
I would be grateful for any suggestions or experiences.
Jiri

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Michael DeVuono Senior Staff Designer, T&M Associates Sep 09 2013 LEEDuser Expert 1918 Thumbs Up

How will the stormwater bypass the tank when it is full?

I think your best bet, and easiest to quanify and demonstrate, would be to provide some type of treatment BMPBest Management Practice that gets you the 80% 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 on the bypass water. I wouldn't even want to begin trying to quantify a geometric mean weighting of the 100% in the tank, and the byapss with a lower removal rate, as you will always have varying amounts of water stored in the tank, therefore, varying amounts of water bypassing the tank.

All this being said, I am assuming the 8500 cf is less than your 90% runoff volume, correct?

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Patricia Weber
Aug 07 2013
Guest
8 Thumbs Up

beginner question about site area to be treated

hi there, here's what will probably be an easy question for you but is stumping me, as this is my first time documenting this credit. the form calls for each BMPBest Management Practice documentation to input the percentage of site that is being treated.

do I need to account for the entirety of the LEED project site, in terms of each BMP treating a percentage thereof? or do I only need to account for the portion of the site that contains impervious surface?

the development site for our project will be made up of landscaping and pervious paving, with the only impervious surface being the roof. The roof runoff is all being treated in rain garden(s). If I do need to account for all of the landscaped and pervious paving areas on the form, is it safe to assume they are removing 100% 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.? The Hydrologic Soil Type for the site is "C", which has me worried. Thanks!

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Michael DeVuono Senior Staff Designer, T&M Associates Aug 08 2013 LEEDuser Expert 1918 Thumbs Up

Hi Patricia, you need to treat the 90th percentil runoff volume with a BMPBest Management Practice (or BMPs) that remove at least 80% 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.. You can route the entire site through one BMP that does this, or route a portion of the site through a BMP with higher efficiency. This is essentially a math problem.

You must use your entire site for the runoff calculation, this is what produces the runoff volume, but like I said above, you do not necessarily need to treat the entire site if you over-compensate in other areas.

As to your other question, even lawn and landscaped areas produce polluted runoff (in some cases more than the roof, which is essentially clean water), so no you can not net these areas out of your calcs.

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Juliane Muench
Jun 30 2013
LEEDuser Member
564 Thumbs Up

Stormwater to public rainwater channel that is connected to sea

Our building is connected to a public rainwater channel which is placed out of the LEED boundary, the rainwater channel is connected to the sea. Buildings in this area are connected to this public channel and are supposed according to the local authorities. Our project is a new construction office building and not on a campus project. I came across this definition "Projects with stormwater control measures outside the LEED project boundary may be accepted if the measures appropriately take into account neighboring facilities by demonstrating that the existing stormwater management systems that serve the LEED project boundary meet the LEED requirements for all areas within the site serviced by those systems. "
I am not sure weather that means that the whole area needs to comply with 90% rainwater treatment and remove 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., it could also mean that the channel shall have enough capacity to take all the rainwater from all the buildings that are connected to it.
As our project boundary does not include the public rainwater channel and we are not talking about a campus project, we do not have any chance to influence how the other buildings that are already connected to the system treat the rainwater before it is discharged into the channel.
Would we compliant with the credit when we discharge our rainwater into the public channel?

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Michael DeVuono Senior Staff Designer, T&M Associates Jul 01 2013 LEEDuser Expert 1918 Thumbs Up

You need to treat the runoff from your site, before it leaves your site and hits the conveyance channel. You do not need to treat the runoff from existing development outside your project.

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ADRIENN GELESZ LEED AP ABUD Engineering Ltd.
Jun 19 2013
LEEDuser Member
715 Thumbs Up

retention basin and infiltration on site

I am a little confused: The reference guide states that average 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 of an infiltration basin is 75% (50-100%). However, from several comments and the sample uploaded I get the feeling that if you infiltrate all rainwater on site then 100% removal can be achieved.
Can someone help with this issue? If using a basin that collects and infiltrates all rainwater, can you use the 100%?

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Michael DeVuono Senior Staff Designer, T&M Associates Jul 01 2013 LEEDuser Expert 1918 Thumbs Up

I think 100% may be a bit of a stretch, you are enver going to filter out all the solids. But if you have a unique situation, by all means, justify it in your application and go for it.

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Panupant Phapant SCG Cement - Building Materials Co.,Ltd.
Jun 11 2013
LEEDuser Member
62 Thumbs Up

Capturing rainwater and discharge to the public sewer

The FAQ of SSc6.2 (http://www.leeduser.com/credit/NC-2009/SSc6.2#sthash.3UFoAJvd.dpuf) suggests that capturing the rainwater into tanks and discharging it into the public sewers after the rainstorm is acceptable way for meeting SS6.2 requirements as follows:

“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?
This is a common strategy for reducing peak rate, which will help you comply with SSc6.1, but you'll need to add onsite reuse or infiltration to meet SSc6.2 requirements.”

However considering the credit’s intent, i.e. “To limit disruption of natural hydrology by reducing impervious cover, increasing on-site infiltration, reducing or eliminating pollution from stormwater runoff and eliminating comtaminants, we feel that the mention strategy does not reduce the runoff but only delay the runoff to the latter time and the pollutions collected by the runoff still be released to the public sewer which should not meet the credit’s intent.

In fact, We are interested to deploy this strategy for our project in order to comply with SSc6.1 but we still have some doubt. Could anyone affirm that this strategy help meet the SSc6.1 requirements.

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Michael DeVuono Senior Staff Designer, T&M Associates Jun 11 2013 LEEDuser Expert 1918 Thumbs Up

Slow release of stormwater will put you on your way to solving 6.1, but you will need to do some form of treatment in order to meet 6.2. You will need to implement some form of volume control as well. The slow release solves peak rate only, not volume.

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Panupant Phapant SCG Cement - Building Materials Co.,Ltd. Jun 11 2013 LEEDuser Member 62 Thumbs Up

Hi Michael,
Thank you for the clarification. Please advise whether I am correct that the intent of SSc6.1 is to reduce the "Peak" discharge to natural hydrology and public sewer, not the total volume discharge. Therefore, the capturing and slow releasing can help achieve the credit requirement.

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Michael DeVuono Senior Staff Designer, T&M Associates Jun 12 2013 LEEDuser Expert 1918 Thumbs Up

That is a fancy way of saying your post-development runoff can not exceed the pre-development runoff. 6.1 deals with both peak rate AND volume. You need to reduce the rate of runoff (a slow release), and reduce the volume (the quantity), through infiltration, reuse, or some other means.

You are heading in the reight direction with the peak rate, you now need to manage volume. If you have decent infiltration rates, you can do some sort of pre-fab arch system (StormTech, Cultec, etc) which will allow for infiltration into the soil below the system.

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Albert Sagrera Architect Societat Organica
Apr 22 2013
LEEDuser Member
538 Thumbs Up

Upload Documentation

How can we upload documentation justifying this credit? Calculations on 90% average annual rainfall, 80% 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, and other documentation?

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Tristan Roberts LEED AP BD+C, Editorial Director – LEEDuser, BuildingGreen, Inc. Apr 22 2013 LEEDuser Moderator

Albert, can you clarify your question? Is there any difficulty in using the LEED Online form and uploads?

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Albert Sagrera Architect, Societat Organica Apr 23 2013 LEEDuser Member 538 Thumbs Up

Hi Tristan, my cuestion is that in ssc6_2 form there is no place to upload documentation, only if we select the alternative compliance the form allows uploading.

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Tristan Roberts LEED AP BD+C, Editorial Director – LEEDuser, BuildingGreen, Inc. Apr 23 2013 LEEDuser Moderator

Albert, if the LEED forum does not ask you to upload something, you do not need to upload it. In this case, if the upload is not requested, you have to provide accurate information on your BMPs, etc., but you do not have to upload justification, nless there are special circumstances leading you to use the alternative compliance path.

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Albert Sagrera Architect Societat Organica
Apr 19 2013
LEEDuser Member
538 Thumbs Up

TSS efficiency values

Hi!
Where can we find accepted values for 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 efficiency of a meadow or other tipes of vegetation?

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Michael DeVuono Senior Staff Designer, T&M Associates Apr 19 2013 LEEDuser Expert 1918 Thumbs Up

This is something that will vary considerably due to your unique site conditions. If you are looking for a simple table that says this bush removes this much 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., you're not going to find it.

Start with the Table in the manual....vegetated filter strip, or grass swale. and adjust per your site. Coordinate with the civil engineer, see what he/she is doing.

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Anthony Venafro
Mar 07 2013
Guest
12 Thumbs Up

Site Area as it relates to 6.2

Can we eliminate site area to be dedicated for the computations for 1" of rainfall? i.e. existing site area is 5 acres witih a 1" volume of 14,000 cf. 0.5 acres will be dedicated to state use for roads. Can I assume if we capture the 1" (12,000 cf) from the resultant area of 4.5 acres we are ok?

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Michael DeVuono Senior Staff Designer, T&M Associates Mar 12 2013 LEEDuser Expert 1918 Thumbs Up

I do not have an answer for this. Perhaps someone else know definitively.

Can you take this area out of your LEED project boundary all together?

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Albert Sagrera Architect Societat Organica
Mar 06 2013
LEEDuser Member
538 Thumbs Up

some doubts

Hi, in our project we have a 60% of the site vegetated, planted with meadow, we have a small impervious surface near the building, and the building itself. We understand that the vegetated area treats 100% of the 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, then the water from the roof and from the impervious area is guided to a rainwater cistern and this water reused (to irrigation, lavatory faucets and wash machines), this should be also counted as 100% of TSS removal?
Then another question is that although we have a 135m3 rainwater cistern, in a stormwater event is probable that the cistern is full and than the water would have to be guided to a near water body without passing trough the cistern. Since we cannot achieve information about the filters that we also have, how could we justify the credit? Can we propose a sistem where in the event of a stormwater, in advance, we empty the rainwater cistern so we can capture al the stormwater? Thanks in advance

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Michael DeVuono Senior Staff Designer, T&M Associates Mar 06 2013 LEEDuser Expert 1918 Thumbs Up

I question your 100% 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 for routing through a planted area. Where are you getting that number from? 60-65% seems more the norm, but perhaps you have more information to back up your assumption.

As for your cistern, any cistern design should take into account back to back storms, and you total water budget. You need to actually be using the water you are storing. Proper sizing will help to reduce the risk that the cistern is full in the event of a back to back storm (less than 3% chance of happening with the 2-year event).

Can you not bypass the cistern and route through the meadow you have?

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Albert Sagrera Architect, Societat Organica Mar 06 2013 LEEDuser Member 538 Thumbs Up

Thanks for the quick answer!! Well the 100% 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 for the vegetated area, i assumed that this kind of pavement would be what LEED considers a soil with good infiltatation rate "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." But then maybe in this planted area, as a semi compacted soil, might be reasonable reduce the efectivity, thanks for the data!! The cistern capacity was calculated tacking into account the climate profile of Barcelona, it occurs that we have a highly variable rainfall regime, so we dimension de cistern so it can provide all the water we need in summer (when we have a high demand and almost no rain). The stormwater events generaly occur in october...

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Nicole Kimoto Architects Pacific, Inc.
Feb 27 2013
LEEDuser Member
285 Thumbs Up

Treating stormwater only?

Could this credit be achieved if it were only proposed to treat the storm water runoff with a structural measure and not capture? It would also need to accommodate at least 90% of the annual rainfall volume AND remove 80% of the avg annual postdevelopment load 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.? Is that correct?
thanks, NK

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Michael DeVuono Senior Staff Designer, T&M Associates Feb 28 2013 LEEDuser Expert 1918 Thumbs Up

Like a CDS or other hydro-dynamic separator?

Sure, as long as the appropriate runoff volume is treated at 80% 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. or above.

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Tristan Roberts LEED AP BD+C, Editorial Director – LEEDuser BuildingGreen, Inc.
Jan 30 2013
LEEDuser Moderator

BMPs in series

I heard a comment from a LEED user that GBCI reviewers do not understand the application of Best Management Practices in series.

Has anyone seen this on LEED reviews, and how have you dealt with it?

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Michael DeVuono Senior Staff Designer, T&M Associates Jan 30 2013 LEEDuser Expert 1918 Thumbs Up

I have not heard this, but I can emphasize that a train of 50% removal>30% removal will not satisfy this credit.

Hypothetical ... sinple drainage area (this get very complex with multiple areas)

100 lbs 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. generated by our runoff volume.
We need to remove 80 lbs of TSS.

Runoff volume routed through BMPBest Management Practice with 50% removal efficiency.
50 lbs removed, 50 lbs remain.

Next in series is a BMP with 30% removal efficiency
15 lbs of the remaining 50 lbs is removed.

65 lbs<80 lbs

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Marcio Alberto Casado Pereira
Jan 23 2013
LEEDuser Member
2425 Thumbs Up

Which type of water needs to be filtered?

Dear all,

Please confirm this assumption - our interpretation of this credit is that it only applies to runoff, not to roof captured water. Is this correct? I'm asking because the client is harvesting rainwater for irrigation and janitorial cleaning but there will be more rainwater than needed. this excess water will be filtered to 80% 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. Would that comply with the credit intent? Or we also/only have to filter the runoff from the ground?? Is the credit aimed to runoff from the groundfloor?

Thanks

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Michael DeVuono Senior Staff Designer, T&M Associates Jan 23 2013 LEEDuser Expert 1918 Thumbs Up

Yes, you are treating the capture/reuse water at 100% 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, and the remaining at 80%

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Marcio Alberto Casado Pereira Jan 23 2013 LEEDuser Member 2425 Thumbs Up

Hi Michael,

Just to confirm - we are talking about 3 different types of water:

- the harvested water from the roof that will be reused;
- the excess water from the roof that will not be reused and will have to infilter in the soil;
- and the runoff from the ground.

You mean that if I filter the roof water that wil be reused, the excess roof water but not treat the runoff from the ground I will be complying?

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Michael DeVuono Senior Staff Designer, T&M Associates Jan 23 2013 LEEDuser Expert 1918 Thumbs Up

Capture and reuse = 100% 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.

Whatever is not "captured and reused" must be treated via a BMPBest Management Practice that removes at least 80% TSS.

You need to treat the 90 percentile rainfall, regardless of cover type. The cover type is what produces the runoff volume.

Roof = 98% runoff = more volume to treat.
Lawn Areas = Around 60% runoff = less volume to treat but you still need to treat what runs off.

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Marcio Alberto Casado Pereira Jan 24 2013 LEEDuser Member 2425 Thumbs Up

In our case, the groundcover is essentially crushed stone, because the project consists on a subway station. Not sure how to capture the water from the ground floor covered by crushed stone and filter it...I understand if we can't capture and filter we won't be able to comply, right?

thanks

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Michael DeVuono Senior Staff Designer, T&M Associates Jan 24 2013 LEEDuser Expert 1918 Thumbs Up

Do you obtain complete infiltration of what hits the crushed stone? If you do not have runoff, there is nothing to treat. If you capture what would have run off in your cistern, you are well on your way to this credit.

You need to evaluate the runoff over the crushed stone. You could always underdrain that area, and route through a pre-fab water quality unit.

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Guilherme Castagna Fluxus Design Ecológico Jan 28 2013 Guest 62 Thumbs Up

Marcio, as far as I understand, you need to calculate if the excess water captured and used exceeds the 90% rainfall. If that's not the case, you need to treat the excess to 80% 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. That applies to the ground runoff as well. If you infiltrate it you're fine, but if your infiltration rate is low you may need to treat the excess water as well through any strategies you may devise (store and infiltrate, or filtrate). You must do an infiltration/percolation test to evaluate this. All this must be evaluated in terms of the total amount generated inside your LEED boundary, that is, the total figure must comply with the credit, and not only the excess water from the cistern, or whatever structure you're dealing with. Michael, pls correct me if I'm wrong.

Um abração,

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Michael DeVuono Senior Staff Designer, T&M Associates Jan 29 2013 LEEDuser Expert 1918 Thumbs Up

Correct, you are working towards a volume total. If you can get that total into the cistern, and use it, is the main point. Without knowing specifics I'm going leave you with that.

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Elizabeth Floyd Senior Project Manager Sustainable Design Consulting LLC
Dec 19 2012
LEEDuser Member
71 Thumbs Up

TSS removal with veg. roof, cistern and reuse - but no filter

The Design Team for an urban office bldg. proposes to collect water from roof and terraces as well as mech. condensate for reuse (in irrigation and cooling tower make-up water). The project also has an area of vegetated roof. At least 90% of the average annual rainfall within the LEED boundary will be collected and stored in a sub-grade cistern. Calculations show that there is more demand for the reuse than the amount collected/stored so, theoretically, the collected stormwater will not be discharged to the sewar. Without a filter, will the veg. roof and sufficiently sized cistern be sufficient BMPs to meet the 80% 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 and LEED criteria (without maintenance to remove sediment from the cistern)?

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Michael DeVuono Senior Staff Designer, T&M Associates Jan 07 2013 LEEDuser Expert 1918 Thumbs Up

Most state BMPBest Management Practice manuals will allow you to assume 100% 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 for capture/reuse. I would absolutely do the same if this were my project.

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Cara Sloat GENIVAR
Dec 11 2012
Guest
19 Thumbs Up

Combination Campus / On-site approach?

I'm working on a Canadian, CAGBC LEED NC 2009 project that is located with a business park. The business park's water treatment system, a constructed wetland, preceded by two vortex separators, was intended to be designed to meet LEED standards for quality and quantity control. However, there was limited space available for the pond and facilities, and the development was allowed to go forward with a system designed to achieve 77% removal 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..

My client's site incorporates a rainwater harvesting system and bioswales, such that the overall treatment of water coming from their site will be significantly above the required 80% removal of TSS. Installing further on-site treatment is not an affordable option and would duplicate the downstream treatment being provided by the campus facilities already installed.

However, in all the credit interpretation requests I can find in the US or Canadian system, it seems that either 1) all the treatment must be done on site, or; 2) the entire campus must be treated to the 80% removal rate.

There is no policy in place at the campus level requiring each developer to make up the additional 3% TSS treatment on their site; it would be up to each developer to make the choice to do so.

Does anyone have any experience with this kind of a situation? Is it worth submitting a 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 to determine if this combined approach to treatment is acceptable?

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Michael DeVuono Senior Staff Designer, T&M Associates Dec 11 2012 LEEDuser Expert 1918 Thumbs Up

Put a snout (google it) on your discharge pipe.

85% 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, will treat everything that leaves your site, costs a few hundred dollars.

We could get into how we approach a regional stormwater system, such as yours, but I think the snout is the way to go. Especially if there is on-site maintenance. You could probably lose the vortechs things too, I'm surprised they are still being spec'd.

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Cara Sloat GENIVAR Dec 14 2012 Guest 19 Thumbs Up

Thank you for your comment. I'll check in with the stormwater system designers and see if that will work.

(I can't lose the vortexes, they were installed in 2007 when the almost-adequate treatment pond went in.)

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Albert Sagrera Architect Societat Organica
Nov 12 2012
LEEDuser Member
538 Thumbs Up

TSS RETENTION

Hello!
We are having a hard time justifying the 80% retention 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.. In Europe the manufacturers of filters do not have this information in their technical catalogs, the efficiency of a filter is measured by the size of the net, in microns or millimeters. Our question is - is there a way to turn the filter dimension in TSS removal efficiency percentage?

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Michael DeVuono Senior Staff Designer, T&M Associates Nov 12 2012 LEEDuser Expert 1918 Thumbs Up

This is something I would put back on the product manufacturer, and have them provide an efficiency rating.

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