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

    COPYRIGHT © 2009 BY THE U.S. GREEN BUILDING COUNCIL, INC. ALL RIGHTS RESERVED

    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."

104 Comments

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Albert Sagrera Architect Societat Organica
Apr 22 2013
LEEDuser Member
216 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 216 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
216 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 T&M Associates Apr 19 2013 LEEDuser Expert 345 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

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 T&M Associates Mar 12 2013 LEEDuser Expert 345 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
216 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 T&M Associates Mar 06 2013 LEEDuser Expert 345 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 216 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
Feb 27 2013
Guest
3 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 T&M Associates Feb 28 2013 LEEDuser Expert 345 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 T&M Associates Jan 30 2013 LEEDuser Expert 345 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
995 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 T&M Associates Jan 23 2013 LEEDuser Expert 345 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 995 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 T&M Associates Jan 23 2013 LEEDuser Expert 345 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 995 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 T&M Associates Jan 24 2013 LEEDuser Expert 345 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 24 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 T&M Associates Jan 29 2013 LEEDuser Expert 345 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
47 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 T&M Associates Jan 07 2013 LEEDuser Expert 345 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
LEEDuser Member

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 T&M Associates Dec 11 2012 LEEDuser Expert 345 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 LEEDuser Member

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
216 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 T&M Associates Nov 12 2012 LEEDuser Expert 345 Thumbs Up

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

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Albert Sagrera Architect, Societat Organica Nov 12 2012 LEEDuser Member 216 Thumbs Up

Thanks Michael!
We are trying and pushing for manufacturers to give us this information, but it is not easy. Could you send us a technical catalog of filters, where appers this information from the percentage of 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.? Just to have a model, because we've never seen one .. in order to explain and give an example to manufacturers. My email is "pserra@societatorganica.com" thanks!!

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Lucie Sancova
Nov 06 2012
LEEDuser Member
54 Thumbs Up

Cistern volume

I work on the project where it is impossible to design non-structural measures because soil can´t infiltrate almost any water. All of the rainfall is collected in the cistern and discharges to the public sewer through filter with 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. efficiency. To meet the intent of this credit is it necessary to size the volume of the cistern to store all water from average annual rainfall? LEED reference guide requires capturing, treating (p. 101) and accommodating (p.104) 90% of the annual rainwater volume. The credit form requires only treating 90% of the annual rainwater volume.

If it is not necessary to store this amount of water, does following solution meet this credit requirement? I must for example capture 900 cu ft of water that represents 90% annual rainwater volume. Water flow to the cistern with the volume of 300 cu ft. Water is discharged to the public sewer in 8 hours and ready to capture another 300 cu ft of water. The volume of 900 cu ft is discharged in 24 h, the requirement of 80 % TSS efficiency is fulfilled. Is this cistern design sufficient to meet the credit intent?

Thanks a lot!

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Michael DeVuono T&M Associates Nov 07 2012 LEEDuser Expert 345 Thumbs Up

Provided that your runoff calculations are correct (dependent on your watershed climate), you must treat 90% of the actual runoff volume. Keep in mind, that even on impervious surfacesSurfaces that promote runoff of precipitation volumes instead of infiltration into the subsurface. The imperviousness or degree of runoff potential can be estimated for different surface materials., you do not get 100% runoff.

If all that is worked out, and you can demonstrate that your "filter" (I'm assuming this is a snout of some sort?) actually treats 90% of that runoff volume, I would run with it.

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Lucie Sancova
Nov 06 2012
LEEDuser Member
54 Thumbs Up

90 % of the average annual rainfall

Could anyone give me an advice which of the following interpretation complies with the credit language? There are two possibilities how to construe this requirement:

a) 90% of the average annual rainfall is equivalent to 1/0.75/0,5 inches based on climate as states in LEED Reference Guide. As explains Gregory Hurst down here (Aug 26 2011), this is the depth of rain that equates to 90% of the daily rainfall amounts, 90% of the days will have rainfall amounts under the calculated value. From this point of view 90% determines only the rainfall depth.

For example if I have 1000 sq ft of absolutely 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. site in humid climate, I must capture and treat 900 cu ft of rainfall (1000 sq ft * 1 in) to meet the credit intent.

b) The numbers of rainfall depth 1/0.75/0,5 inches represent the average annual rainfall and 90% of the calculated runoff must be treated and captured. This interpretation conforms to the possibility to calculate 90% rainfall compliance based on areas (see Simon S., Nov 29 2011).

In this case if I have 1000 sq ft of absolutely imperviousness site in humid climate, I must capture and treat only 810 cu ft of rainfall (0.9 * 1000 sq ft * 1 in) to meet the credit intent.

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Michael DeVuono T&M Associates Nov 07 2012 LEEDuser Expert 345 Thumbs Up

Check your math.
1 inch of rainfall over 1000 sf is 83cf

(1/12 ft)(1000 ft^2) = 83.3 ft^3

Now typically, when agencies say they want "1 inch of runoff" I use a depth of 1.2" rainfall to account for evaporation, evatranspiration, etc.

So...

(1.2/12ft)((1000ft^2) = (100 ft^3)(.90) = 90 ft^3

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Melissa Wrolstad
Oct 05 2012
Guest
972 Thumbs Up

Accounting for Forested Areas

I have a project with a LEED site boundary that includes some undisturbed naturally forested area. How do I account for this area in stormwater quality calculations?

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Michael DeVuono T&M Associates Oct 07 2012 LEEDuser Expert 345 Thumbs Up

Does it route through a BMPBest Management Practice?

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Melissa Wrolstad Oct 16 2012 Guest 972 Thumbs Up

No. It accounts for more than 50% of the LEED project site and naturally infiltrates water because it is undisturbed.

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Michael DeVuono T&M Associates Oct 16 2012 LEEDuser Expert 345 Thumbs Up

Tough to say without seeing this first hand, but, this credit leaves a lot up to the discretion of your CE, with the catch all that the approach should be acceptable within the locality. If I were working on this project, I would totally net out the undisturbed areas, and route only the disturbed area through the a BMPBest Management Practice with 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.

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ADRIENN GELESZ LEED AP ABUD Engineering Ltd.
Sep 14 2012
LEEDuser Member
187 Thumbs Up

percentage versus actual TSS number

Hi!
Does anyone know how to convert remaining g/l data into percentage data? If there is a oil separator where this data is given (e.g.what is the maximum 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. content of water after cleaning), how can we assign a % to it from the LEED table?

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Michael DeVuono T&M Associates Sep 14 2012 LEEDuser Expert 345 Thumbs Up

What method are you using for treatment?

You need to calc the pollutant load based in the cover type the water flows over.

Each cover type has an EMC, Event Mean Concentration, which is produced per volume of runoff.

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Matthieu Bouadana
Jul 18 2012
Guest
12 Thumbs Up

LEED SS Credit 6.2 - NYC building, Tight Fit

Hoping someone could help me out - I'm looking for a Stormwater Management system which will be going under a NYC building to fulfill LEED SS Credit 6.2. All the strormwater management systems I've looked at (Stormcepter, Contech) all need pump trucks to drain the sediment from the system. The idea is this system will be under the building and only accessible through the basement where trucks will not be able to go. Does anyone know a system where a pump truck is NOT required for maintenance?

Thanks!

Matt

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Michael DeVuono T&M Associates Jul 18 2012 LEEDuser Expert 345 Thumbs Up

I think you're barking up he wrong tree. You need to find a portable vacuum to clean this out.

How do other systems in NYC work? I've never heard of putting these under a building, but in NYC you make due right?

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Rebekah Burke Director of Sustainable Design Clark Nexsen
May 08 2012
LEEDuser Member
230 Thumbs Up

Alternative Compliance-High Infiltration

Site is located in western Wasington state. We are using the western Washignton Hyraulic model #3 to size the underground detention. The infiltration rate for the site is 50"/hour. Using the LEED volume calculation, which requires 90% of the average annual rainfall to be captured, requiring the underground detention to double in size. Becasue of the high infiltarion rate is it possible to use an alternative compliance method to show the LEED volume calculation is onerous as the water will infiltrate, and the size isn't necessary.

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Michael DeVuono T&M Associates May 15 2012 LEEDuser Expert 345 Thumbs Up

You don't need to "store" any volume of water with this credit, you need to treat it.

Is 90% of your site not routed through the basin? If not, i would simply model your ground cover as a "pseudo-infiltration practice." Does 90% of your site hit areas with 50"/hr infiltration rate?

I would caution against using such a high number, unless that is something typically used in Washington. (I'm not familiar at all with the Left Coast). I would get laughed at around here if I tried to submit any kind of calc using 50"/hr.

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Divjot Singh LEED AP BD+C May 18 2012 Guest 100 Thumbs Up

I might be wrong, but as I see, it seems that the intention of this credit is to minimize polluted storm runoff getting into stormwater lines. So if we minimize this runoff thats one strategy and the runoff which is still going into stormwater lines, it has to be treated to 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. and its second strategy.
We can store water for other purposes but polluted stormwater runoff should be prevented from entering municipal storm water lines, thats what I think.

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Justin Jones via Greengrade LEED Management Software
May 08 2012
Guest
147 Thumbs Up

Impervious Area

Am I correct in assuming that even though our total impervious area on the site will increase, we can achieve this credit by implementing treatment strategies that capture 90% of the storm water run off and remove 80% 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.?

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Michael DeVuono T&M Associates May 15 2012 LEEDuser Expert 345 Thumbs Up

yes

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Patricia Missawa CTE - Centro de Tecnologia de Edificações
Apr 23 2012
Guest
69 Thumbs Up

Vegetated areas

I’m having some doubts on how to define the stormwater volume treated by different types of vegetated areas since in Brazil we don’t have any study related to it.
1- If my project has a flat vegetated area, can I consider that 90% of the stormwater will be treated by infiltration (considering this area has a 0.1 runoff coefficient) and that 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. of the infiltrated volume will be removed?
2- If my project has a green roof (4-8 inches), can I considerer that 70% of the stormwater will infiltrate and that 100% of TSS of the infiltrated volume will be removed, even if this volume will not be retained in this area, i.e., the volume infiltrated will be drained to public sewers after the soil saturation?

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Tristan Roberts LEED AP BD+C, Editorial Director – LEEDuser, BuildingGreen, Inc. Aug 30 2012 LEEDuser Moderator

Patricia, on item 1 I agree with your calcuations. On item 2, it gets more complicated since all green roofs are different—I think you could use some input from a civil engineer on that.

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ADRIENN GELESZ LEED AP, ABUD Engineering Ltd. Oct 10 2012 LEEDuser Member 187 Thumbs Up

Hi,
two questions that came to my mind when reading the above comment:
1 -when calculating the treated run-off, do you include the water volume in the calculation that infiltrates into the ground/evaporates and also the volume that leaves the area? I mean, in case of a vegetated area where runoff coefficient is 0.1, do you get the credit without any additional BMPBest Management Practice, saying that the 90% is treated with 100% efficiency, equaling a 90% average; or do you only get the credit if the actual runoff (10% of total rainfall) flows through a BMP of 80% efficiency before leaving the site?
2 - What is the difference between the removal efficiency of the flat vegetated area and i.e. a grass swale? Grass swale should capture water and infiltrate it into the ground - however, average efficiency is only 60% according to EPA. Can water infiltrating into the ground really be considered to remove 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.?

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Michael DeVuono T&M Associates Oct 10 2012 LEEDuser Expert 345 Thumbs Up

1.The curve number used to generate a runoff volume already takes into account the volume that infiltrates. A higher CN produces a higher runoff volume.

2. Your question regarding removal efficiencies is a long-standing argument with any regulatory agency. 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. is typically what I see/use with any type of vegetated BMPBest Management Practice. Definitely not 100% with any type of open-channel flow.

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ADRIENN GELESZ LEED AP, ABUD Engineering Ltd. Oct 10 2012 LEEDuser Member 187 Thumbs Up

Thanks Michael,
So you say that in question 1 that you do have to treat the volume of runoff, even if the infiltration is around 90%?

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Michael DeVuono T&M Associates Oct 10 2012 LEEDuser Expert 345 Thumbs Up

If you are infiltrating 90% of the sites runoff, through a BMPBest Management Practice with 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, you are good.

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Joel Cesare
Mar 09 2012
Guest
58 Thumbs Up

City Stormwater Filtration

Most of the stormwater runoff on our site will be directed to the city drain intake, which reportedly is equipped with enhanced filtration. Can this be used for BMPBest Management Practice?

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Amy Rider Sustainability Manager, KEMA Services Mar 16 2012 LEEDuser Expert 1358 Thumbs Up

In general, if the project itself is not taking action the measure cannot count toward credit achievment. However, I do recommend finding out what they mean by "enhanced filtration" so that your project approach can complement the city system.

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Maria C C
Feb 28 2012
Guest
170 Thumbs Up

Default percentage for removal of TSS by dislodging in a lagoon

Hello to all. Hope you can help me with this one.

The Municipal Entity of my project requires us to discharge 100% of the stormwater into the City´s Lagoon "Laguna de Terminos"
The reason is that there is no sewage system since the water table is at less than a meter from the surface.
The project is located in Ciudad del Carmen, in the Yucatan Republic, Mexico.
We are doing what is asked by this Entity (sending the water through pipelines and soak ways into the lagoon) and have their approval for the design.

My question is: Is there a default rate 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 through natural sedimentation in a lagoon? I know you can check it with municipal entities in order to know the exact amount, but we have asked them and they don't have the data.

Thank you for your help. Regards

Maria

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Michael DeVuono T&M Associates Mar 03 2012 LEEDuser Expert 345 Thumbs Up

Define lagoon. A pond of standing water? Or do you have high and low marsh areas? Plantings?

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Maria C C Mar 05 2012 Guest 170 Thumbs Up

The Laguna de Terminos is a tropical lagoon estuarine system in the southern Gulf of Mexico, with an area of 1 742 acres, (705 ha).

The river Usumascinta flows into this lagoon. The lagoon system is the largest of the country. Including the continental fresh water marine platform, it has also the connections to the sea, freshwater ponds, salt marine estuarie areas, submerged grasses, wetlands and surrounding mangrove forests.

Vegetation: Mainly marsh areas with species such as Thalia geniculate where the water stagnation is higher and the Thypa latifolia and Cyperus articulatum in the rest of the lagoon. You can also find Pistia stratiotes and Nymphaea.

It is a protected area by the National Institute of Ecology and therefore the quality of water runoff to this lagoon is highly protected.

Hope this clears your question Mike. Thanks for your help.

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Michael DeVuono T&M Associates Mar 05 2012 LEEDuser Expert 345 Thumbs Up

Oh, i understand now . you need to remove 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. from your sites runoff before it gets to the lagoon. You can not use the body of water you are discharging into as the BMPBest Management Practice. The idea is not to further pollute the receiving body.

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Lauren Ford Project Architect Cooper Carry
Feb 14 2012
Guest
504 Thumbs Up

Reducing Impervious a requirement or a strategy?

If we are increasing the total impervious area on the site, but treating the stormwater to reduce 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., do we still meet the intent of the credit? Is reducing impervious area a requirement or a recommended strategy?

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Tristan Roberts LEED AP BD+C, Editorial Director – LEEDuser, BuildingGreen, Inc. Feb 15 2012 LEEDuser Moderator

Lauren, reducing total impervious area is a recommended strategy, but not a requirement of SSc6. You can pursue other strategies to counterbalance any increases.

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Udana Ratnayake
Jan 19 2012
Guest
657 Thumbs Up

Rainwater Harvesting

Our project is harvesting and reusing rainwater for flushing. rainwater that falls on the roof is collected in a 10cubic meter sump. during a heavy rain the sump is allowed to over flow and the excess rainwater would flow through the drainage system. how should we calculate the following.

1) Percent site treated by implementing rainwater harvesting
2) 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 system

Thanks

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Amy Rider Sustainability Manager, KEMA Services Feb 22 2012 LEEDuser Expert 1358 Thumbs Up

1. The percent of site treated via rainwater harvesting (for the roof alone, you'll need to account for the rest of the site separately) will be a result of the storage volume compared to the anticipated rainfall across the roof areaRoof area is the area of the uppermost surface of the building which covers enclosed Gross Floor Area, as measured when projected onto a flat, horizontal surface (i.e. as seen in Roof Plan view). ‘Roofs’, or portions of roofs, covering unenclosed areas (e.g. roofs over porches and open covered parking structures) are not included in the areas used to evaluate compliance with SSc7.2, though they may be applicable to SSc7.1..
2. The captured rainfall that is reused for toilet flushing has a 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%.

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Chi-Chung Sue Steven Leach International Asia Inc. Taiwan Branch
Nov 29 2011
LEEDuser Member
3401 Thumbs Up

Calculating 90% rainfall compliance

We're currently working on a high-rise commercial building, and hope someone could shed some lights on the following questions:

1. Is it ok to calculate the % of rainfall captured and treated based on areas? Say, the total site area represents 100% rainfall, and there's 50% of building footprintBuilding footprint is the area on a project site used by the building structure, defined by the perimeter of the building plan. Parking lots, parking garages, landscapes, and other nonbuilding facilities are not included in the building footprint. collecting rainwater and treating all that's collected, with another 40% of landscape able to capture all rainwater within the area. Can we assume that 90% of the rainwater within the site is captured and treated?

2. In this case, the high-rise building will not only be able to collect rainwater from the horizontal surface on the rooftop, but also the vertical surface which blocks some of the rainfalls and leads them to a mid-level gutter system. Does the vertical surface also contribute to the 90% rainfall calculation?

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Amy Rider Sustainability Manager, KEMA Services Dec 06 2011 LEEDuser Expert 1358 Thumbs Up

While I have never seen it done this way, it seems like a reasonable approach to showing % rainfall quantity captured, especially if you can demonstrate that you are collecting that which hits the vertical surfaces on-site as well.

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Kash Boodjeh
Aug 22 2011
Guest
197 Thumbs Up

% of annual rainfall treated?

The reference guide states that "90% of the avg annual rainfall is equivalent to treating the runoff from 1" of rainfall for a Humid WatershedWatershed that receives at least 40 inches of rainfall each year. (at least 40")." I don't understand how they arrived at 1".

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Gregory Hurst Office Manager, Robert Peccia & Associates Aug 26 2011 LEEDuser Expert 851 Thumbs Up

Calculating the actual number of inches that equates to 90% of the average annual rainfall is a long and data intensive process. We have done it by collecting up to 50 years worth of daily rainfall data and determining the average depth of rainfall for each day of the year. Then we calculate the depth of rain that equates to 90% of the daily rainfall amounts. 10% of the days will have average rainfall amounts over your calculated value, and 90% of the days will have rainfall amounts under your calculated value.

Since this is difficult to do, LEED has chosen to provide some reasonable guidance with an estimated depth of rainfall that should be treated for arid, semi-arid and humid areas.

There may be better explanations or approaches to this question, but his is the approach we have used.

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Renaud Gay Shanghai Pacific Energy Center
Aug 07 2011
Guest
48 Thumbs Up

Project with large natural green areas.

I am a little bit confused by this project and would like to have your advise. Many thanks in advance!

I work for resort in China made of small houses in a previously undeveloped natural environment, surrounded by forest, undertaking LEED NC 2.2. The green area is around 90%, only 10% is being developed in small roads and houses.
The topography of the site is made of hills with forested areas and houses are included in that landscape; and a valley with a water stream leading to an artificial water reservoir, holding rain water for rice fields, in the vicinity of the project.
Rain water from roads and roofs are directly conveyed in the water stream and the reservoir.

1. My first wonder is related to 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. definition in this project. Since in this resort small roads will only be used for electric golf cars or bicycles and that is area is far for urban areas, we can expect the TSS concentration to be quite low. How to take into account this aspect in this credit?

2. The credit requires to treat run-offs from all surfaces. We have 90% of green areas on steep slopes. Run-offs from those areas will be important and naturally directed in the reservoir. When not used as BMPs, should the TSS treatment in such areas be considered as 100%?

3. As mentioned, the reservoir was previously existing with function to supply water to the rice fields, just 30 ft far from the site. Is it possible to integrate the TSS efficiency of the rice fields (that would be used as a combination of non-structural measures? I guess that the previous MPR guidance replies to that question...

Thanks again, i realize it is a long message.

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Amy Rider Sustainability Manager, KEMA Services Dec 19 2011 LEEDuser Expert 1358 Thumbs Up

It indeed seems like your project site is a bit unusual, but I hope I can shed some light.

1. Even though you may not have a large source of pollution on site you still need to treat the site's stormwater. Please note that 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 not defined by its chemical property, but just whether or not it will settle.

2 and 3. The TSS removal efficiency of the reservoir depends on a number of factors including detention time, but if water is not retained it is typically not seen as treating TSS. If the stormwater goes to the rice fields and stays there you should be able to claim those areas as your permanent retention ponds.

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