Many project teams are reluctant to attempt this credit because conventionally engineered solutions don’t always meet LEED requirements. Don’t be deterred. The best and easiest way to improve the quality of stormwater is to let water permeate the ground through increased landscaping and reduced impervious areas. As long as your soil type has a good infiltration rate, letting stormwater seep into the ground will treat 100% of the pollutants associated with the stormwater runoff. Let natural infiltration do as much of the work possible before using more expensive mechanical methods. In urban sites, infiltration options can be very limited and a rainwater cistern or green roof might be the best approach for credit compliance.
This credit deals with the prevention of polluted runoff, and uses Total Suspended Solids (TSSTotal suspended solids (TSS) are particles that are too small or light to be removed from stormwater via gravity settling. Suspended solid concentrations are typically removed via filtration.) as the indicator of level of pollution. Nitrates and phosphates are not accounted for in the credit calculations. Projects can use biological or mechanical treatment methods for smaller and more frequent storms for credit compliance. In order to earn the credit you must be able to show your stormwater treatment system is effective at treating all rainstorms for any year up to 90% of the average annual rainfall event.
Retaining and reusing stormwater on-site can provide numerous environmental benefits, along with LEED synergies. In addition to trapping suspended solids, capturing stormwater for reuse can reduce peak runoff rate and volume, helping with SSc6.1: Stormwater Design—Quantity Control, and help with water efficiency credits WEc1, WEc2, and WEc3.
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.
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."
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.
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.
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.
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
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.
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.
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.
Explore low-impact development strategies such as bioretention, vegetated swales, a green roof, rainwater cisterns, and porous pavement. These strategies reduce hardscape and impervious areas, thereby reducing runoff. Some strategies such as green roofs and rainwater cisterns have space needs, so be sure to consider their requirements. The owner and civil engineer should work together to determine the feasibility and rough cost increase of including rainwater cisterns or a green roof.
The easiest way to earn this credit is through decreasing your project’s impervious area by reducing the building footprint, increasing landscaped areas, and disconnecting impervious areas—designing sidewalks, roofs, and parking areas so that the runoff is not directed to a drainage system or other hardscapes. Use natural infiltration, promoted by strategies like green roofs, downspout disconnection (disconnecting the downspouts so that runoff is directed to softscape area instead of storm drains), softscapes, bioswales, porous paving, and rain gardens.
Overlapping strategies and technologies address SSc6.1: Stormwater Design—Quantity, as well as SSc6.2. Vegetative swales, for example, can contribute to both credits—integrate the requirements of both for best results. Keep in mind, however, that each credit requires different calculations and methodologies. Reducing the quantity of stormwater runoff for SSc6.1 does not always equate to a quality improvement for SSc6.2.
Using site space for stormwater management is often a must. Architects and owners may see stormwater best management practices (BMPs) as wasting valuable land—a mentality that can make this credit difficult. It may help to stress that stormwater BMPs can act as aesthetic features that enhance the quality of the site and add value to the project. Creative, integrated approaches can even reduce space-hogging, unattractive strategies like detention ponds while adding amenities with multiple benefits, like green roofs.
Use an integrated design strategy to improve the quality of stormwater runoff. True integration requires the input and collaboration of the entire site team, including the civil engineer, landscape architect and architect. Don’t leave stormwater management solely in the hands of the civil engineer.
Make sure that all team members understand landscape and hardscape tradeoffs. All team members should know how these details affect stormwater generation, runoff, and possible capture, treatment, and reuse strategies.
Indirect benefits of stormwater systems are just as real as direct costs to the project, but can be harder to quantify. These include issues like reducing the burden on the municipal system; reducing contaminants in waterways; reducing peak runoff, making stream habitats more consistent; reducing the temperature of runoff, which improves the conditions for aquatic life; and reducing erosion. If your municipal codes are more stringent and come with higher fees, there may be a more direct cost benefit to the project from stormwater mitigation. Any additional costs in this case are likely to be for documentation purposes, although most municipalities require similar stormwater documentation.
Familiarize yourself with natural hydrology, site topography and soil infiltration rates by conducting site visits and tests. Confirm that soils are capable of infiltrating 90% of annual rainfall. If the porous site area cannot infiltrate 90% of rainfall, you will need to add structural controls or soil amendments to achieve the target.
Research local regulations on the stormwater quality requirements, as well as regulations on the collection, storage and reuse of stormwater, including water rights.
Research historical climate records to understand expected storm event frequency, intensity, and duration.
The civil engineer determines the degree of stormwater management required by LEED based on average annual rainfall. The engineer uses these calculations to determine the type and size of systems needed. Managing 90% of the average annual rainfall is equivalent to treating the amounts listed on this table.
Develop a project-wide water budget and a landscape irrigation water budget. This will help teams decide if reusing rainwater may be appropriate and where to use it—typically either in irrigation or toilet flushing.
The civil engineer can conduct a cost-benefit analysis of stormwater-reduction strategies, including cisterns, porous pavement, rain gardens, parking garages (instead of parking lots), detention ponds, green roofs, sand filters, or detention tanks. Some of these strategies may be perceived as added costs, but this analysis may show that with reduced infrastructure, these environmental strategies are cost-neutral, or better.
Depending on local regulations, this credit may be standard practice. For example, new developments following the Commonwealth of Massachusetts Stormwater Policy must provide at least 80% of TSS removal rates through BMPs. Also, any projects areas that are required to follow the U.S. Environmental Protection Agency, Section 6217(g) of the 1900 Coastal Zone Management Act Reauthorization Amendments, are required to meet these same TSS standards.
In locations where local stormwater regulations are similar to or more stringent than LEED requirements, implementation of this credit will incur minimal additional cost for documentation purposes. In locations where it goes beyond standard practice, it may require additional design and documentation costs.
Some municipalities require documented stormwater management. The documentation for LEED requirements should not represent a significant soft cost premium.
Integrating the stormwater plan into the design at an early stage and calculating the pollution reduction percentages will decrease additional costs as the landscape and building infrastructure can be designed accordingly.
Explore potential synergies and tradeoffs with other LEED credits or green building strategies. Items to discuss can include the use of parking lots vs. parking garages (SSc7.1) for stormwater management, rain gardens, trees for shading hardscapes (also SSc7.1), tress for passive solar design (EAc1), impervious surfaces, planting material (WEc1), wind-break opportunities, water reuse (WEc3), rainwater capture (WEc1) and acoustical barriers
The civil engineer calculates the minimum volume of stormwater that must be treated through infiltration, reuse or mechanical treatment to meet the 80% TSS removal rates after development. Base this calculation on the average annual rainfall for the project.
Calculate the potential for stormwater reuse and corresponding cistern sizes to accommodate stormwater reuse for irrigation or other applications like toilet flushing. Be sure to allocate proper space for rainwater cisterns.
The civil engineer develops a stormwater management plan for post-development suspended sediment loads, detailing acceptable BMPs and their associated TSS removal rates. Reference the LEED 2009 Reference Guide’s table of Effectiveness of Management Practices for Total Suspended Solids Removal from Runoff. (Also shown here.)
The civil engineer and the landscape architect design the landscape and stormwater systems to maximize infiltration and collect water where possible. These systems must be designed based on the watershed region, and the BMPs employed must in combination remove 80% of the TSS for the post-construction design. The civil engineer will need to verify that the design meets the LEED requirements.
Find TSS removal rate data in state or local best management practice manuals.
You must design any BMPs to local standards that have adopted an 80% TSS removal rate criterion, or use existing data that has monitored the TSS removal rates of different stormwater controls.
Previously existing stormwater management systems on the project site can be used towards credit compliance as long as requirements are met.
The stormwater design should reflect unique site features, attempt to minimize impacts on natural stormwater hydrology, and promote infiltration and treatment of stormwater runoff.
Treating captured stormwater to the quality standards required for this credit provides the potential for a clean water source for irrigation or toilet flushing, and a further reduction of the burden on municipal treatment facilities.
Consider contouring the land to direct stormwater to planting beds to reduce irrigation needs of potable water in locations where stormwater capture and reuse is not allowed. Parking lots and walkways can be graded to direct runoff to depressed swales or bioretention facilities with perforated pipes and other slow release infiltration mechanisms. This design offers better stormwater management than typical elevated or impervious planters.
Soil type, planting medium and plant species must be considered for their capacity to promote infiltration. For example, clay soils do not allow for good infiltration rates and an engineered soil or compost could be added to allow for better absorption.
Stormwater storage and biofiltration can be incorporated into landscape features and can also include educational elements for occupant and community benefits.
All design methods must consider the soil type and infiltration rates to show that soils are capable of treating the appropriate amount of rainfall.
In urban areas and sites with little land, use a variety of features to achieve project goals. For example, green roofs and rainwater cisterns may be effective in these situations. Capturing rainwater for irrigation will reduce the amount of stormwater runoff leaving the site as well as outdoor potable water use. Reusing captured rainwater for toilet flushing will have similar effects, in addition to reducing potable water use indoors. In some cases, cisterns with open bottoms may be effective in storing stormwater runoff and will encourage infiltration and reduce the peak flow rate discharge. These cisterns may be incorporated under parking areas or other hardscape.
Porous pavement can be incorporated into many sites and climatic conditions. Proper design, installation, and maintenance is important. Work with an experienced contractor, and verify that porous paving will work with your site’s climate and soil conditions. For example, snowplowing, sanding, and salting can damage porous paving.
Stormwater systems can range from bioswales to cisterns to green roof systems, and range greatly in cost and effectiveness depending on the application. Certain on-site stormwater treatment technologies can be costly but serve additional environmental purposes and may contribute to various other LEED credits related to open space and heat island effect. See ‘Related Credits.’ These strategies should be considered and designed for multiple purposes.
Stormwater features such as constructed wetlands, green roofs, and bioswales can be designed as a site asset (aesthetic, habitat, etc.) and provide valuable amenities. Including these features can also increase property value.
The most cost-effective stormwater management strategies are those that preserve or restore natural site features and promote natural infiltration: reducing hardscapes, designing a smaller building footprint, increasing landscaping area, using porous paving materials, natural swales, and other low impact development strategies. Natural infiltration may also decrease the cost of maintenance compared to other structural and packaged stormwater control systems.
Bioinfiltration strategies on streets and parking lots, such as vegetated filter strips and grass swales, are alternatives to typical curb and gutter design that allow for infiltration of stormwater, as opposed to conveying the runoff to storm drains. Reducing the number of curbs, storm drains, and piping systems can substantially reduce construction costs.
Installing a green roof is one successful way to control and treat stormwater. Different types of green roofs provide varying levels of stormwater management, amenity, benefits and maintenance requirements. While green roofs can be expensive, they can often reduce the costs of traditional stormwater systems for a net savings.
Stormwater collection, storage and reuse equipment will increase costs, but will reduce the expenses of potable water.
There are fewer codes and associated costs for collecting and reusing stormwater for irrigation than for interior water reuse. Captured stormwater can often be reused for irrigation without much treatment. Reuse for toilet flushing and cooling tower make-up usually requires treatment.
The civil engineer runs final calculations for the project’s stormwater design. Be sure to address all value engineered items and the finalized design.
The civil engineer verifies that TSS removal and infiltration rate goals are met.
The civil engineer includes all stormwater treatment strategies on the project plans.
The civil engineer fills out the LEED documentation including a list of the BMPs used, descriptions of their function, expected annual percentage of rainfall infiltrated by each and a list of the structural controls used, descriptions of TSS removal performance, and expected annual percentage of rainfall treated by each. The civil engineer should also provide a copy of the project plans with designated stormwater strategies, detailing where the BMPs or structural controls are located along with the area the serve. It’s helpful to include an optional narrative naming the local standard that the stormwater system is designed to match or surpass.
Stormwater quality control systems require a maintenance plan for proper functioning. Ideally this is developed by the civil engineer shortly after design completion.
Commissioning water reuse systems will help ensure they operate as designed. This step can be incorporated EAp1: Fundamental Commissioning, or EAc3: Enhanced Commissioning.
Compacted soil from high vehicle traffic prior to or during construction can severely limit natural infiltration of stormwater. Avoid site compaction during construction as much as possible—this will also help compliance with SSc5.1: Site Development—Protect or Restore Habitat. Aerating soils is not a substitute for avoiding compaction, but can be used to improve infiltration rates.
Provide maintenance personnel with plans and operations manuals for the operation of all structural control systems.
Implement a maintenance plan to ensure ongoing, as-designed performance of stormwater systems and equipment. Doing so will also contribute to LEED-EBOM SSc6: Stormwater Management credit compliance.
If using porous paving, implement a plan to maintain its porosity. Vehicle use, sand and organic matter, and snowplowing can all damage or reduce the effectiveness of porous paving.
If relying on natural infiltration in landscaped areas, keep the plants in those areas healthy and avoid soil compaction from vehicle use.
Maintenance will be required for most stormwater systems. If the project uses structural controls, check with the product manufacturer, designer, and engineer for details on additional cost for maintenance requirements. If the project uses non-structural controls, have the designer confirm the associated maintenance practices for facility manager or additional contracts required. Maintenance costs will vary depending on the strategies employed.
Excerpted from LEED 2009 for New Construction and Major Renovations
To limit disruption and pollution of natural water flows by managing stormwater runoff.
Implement a stormwater management plan that reduces impervious cover, promotes infiltration and captures and treats the stormwater runoff from 90% of the average annual 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:
This LEED credit (or a component of this credit) has been established as equivalent to a SITES v2 credit or component. For more information on using the equivalency as a substitution in your LEED or SITES project, see this article and guidance document.
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.
This guide provides design strategies and techniques on incorporating biofilters in projects.
This website gives designers and planners information on the appropriate application of bioretention areas.
This report describes low-impact development approaches to stormwater management for big-box stores.
Technical manuals on stormwater BMP’s as they relate to Denver and surrounding counties.
This design manual provides stormwater information specific to semi-arid climates, including Denver, Colorado.
This design manual provides stormwater information specific to Denver, Colorado.
This portion of the EPA’s website provides general information on stormwater, including technical information specific to NPEDS.
This website provides stormwater information specific to the Portland, Oregon area.
A guide to low-impact development for residences.
This design manual provides stormwater information specific to Maryland.
This website provides stormwater information specific to Massachusetts.
This technical manual from the U.S. EPA contains background on documenting stormwater requirements through capturing the 95th percentile storm using onsite management practices.
Features a database of over 500 BMPBest Management Practice studies, performance analysis results, tools for use in BMP performance studies, monitoring guidance and other study-related publications.
This database provides studies and analysis on BMPs and is intended to improve design.
This tool is very useful for determining the percentile for rainfall information for a site. However, it should be used for planning purposes only, and should not be a substitute for a site-specific hydrology study performed by a qualified civil engineer or stormwater professional.
This website provides information on the performance of technologies in a number of states across the U.S.
Online magazine for stormwater professionals.
This online research center for civil engineers of all backgrounds includes stormwater information.
This website provides a comprehensive overview of LID strategies including design manuals and case studies.
Provide narrative documentation like this to demonstrate structural and non-structural stormwater control measures.
A stormwater management and drainage report covering both SSc6.1 and SSc6.2 can document all aspects of credit compliance.
Documentation for this credit can be part of a Design Phase submittal.
Sample LEED Online forms for all rating systems and versions are available on the USGBC website.
If local requirements are not as stringent as LEED requirements, are we still required to meet LEED requirements beyond local standards? My project is following the State of California San Francisco BayA bay is a component of a standard, rectilinear building design. It is the open area defined by a building element such as columns or a window. Typically, there are multiple identical bays in succession. Regional Water Quality Control Board Municipal Regional Permit (MRP). The MRP directs that the “first flush” of runoff be treated. In Santa Clara County, the first flush is generally defined as 10% of the 2 year storm or 0.2 inches. The LEED criteria for arid watersheds (defined as those receiving less than 20 inches of rainfall per year) defines 90% of the annual rainfall as 0.5 inches (see below). Using the LEED criteria, the stormwater treatment controls would need to be 250% larger than that required under the MRP. Therefore, this LEED credit will not be attained.
The architect spoke with another civil engineer and his interpretation is that we are treating 100% based on the C.3 requirements of State of California San Francisco Bay Regional Water Quality Control Board Municipal Regional Permit (MRP). His interpretation is that there are two approaches. One meet the standards which are established the State of California San Francisco Bay Regional Water Quality Control Board Municipal Regional Permit (MRP) and if there are no standards than meet the minimum requirements established by LEED.
Can someone help verify the correct approach? Thank you.
I've never heard of any credit deferring to local regulations as a compliance path. The requirements for this credit are pretty clear, treat 0.5" rainfall 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.
LEED isn't about simply complying with local regs, it's going above and beyond in some cases.
Perhaps for your area they have pinpointed a more accurate 90% rainfall amount, and someone has submitted 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.
use of lead metal downspouts in stormwater systems
does LEED NC v2009 (v3) prohibit the use of lead based metals? this application would be for use in a downspout for stormwater into the city sewer.
I would like to get confirmation on whether the following approach of demonstrating compliance with LEED requirements could be accepted or not. We are only applying for credit SSc6.2.
In our building, we have designed ONE retention tank collecting water from roof and landscaping areas around the building. There are 2 different inlets to the tank, one for rainwater from roof and one for the rainwater from landscaped areas.
We have planned to install Biovitor filters inside the tank for each inlet, however due to tank size issues, now we would like to install ONLY one filter in the inlet for the rainwater from landscaped areas.
Tank inlet for water collected from roof – NO FILTER
Tank inlet for water collected from landscaped areas – WITH FILTER
Water runoff from roof is approx. 75% of total site runoff. Biovitor filters have more than 90% of TSSTotal suspended solids (TSS) are particles that are too small or light to be removed from stormwater via gravity settling. Suspended solid concentrations are typically removed via filtration. removal efficiency.
Since runoff from roof is practically not polluted we would like to focus on eliminating TSS from landscaped areas runoff. We believe that if we are able to demonstrate that
TSS concentration in water tank using filter < 20% of the TSS concentration in water tank if no filter used
then it would mean that we have removed more than 80% of the TSS.
There is no other water mixed in the process which could reduce TSS concentrations.
Would this approach be accepted? Is it possible to demonstrate compliance using TSS concentrations estimated but not measured with any water test?
Thank you in advance.
The credit calls for you to remove 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 need to do the math and prove that you do this. The credit does not dictate how you do this. I would, however, disagree with your assumption that roof runoff is "practically not polluted" and would not recommend that you completely leave 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. out of the math.
You need to develop a total poundage of TSS for your site, and remove 80% of the poundage.
Typical roof poundage is around 21 EMC mg/l which works out to about 9.6 lbs/ac
I would recommend implementing some form of dead storage in the roof tank, and make the case that the TSS settles out and you have 100% removal efficiency.
Thank you Michael for the reply.
We have developed calculations showing 2 cases:
CASE 1: without any 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 solution:
TSS in water coming from roof: 455 mg
TSS in water coming from green areas: 2734 mg
TSS in water from hardscaped areas: 12273 mg
total: 15462 TSS mg
CASE 2: with filter installed in inlet for runoff from land/hardscaped areas:
TSS in water coming from roof: 455 mg
TSS TSS in water coming from green areas (filtered): 410 mg
TSS in water from hardscaped areas (filtered): 1841 mg
total: 2706 TSS mg.
if we show this type of calculation, would it be enough for demonstrating compliance?
We have used the following TSS concentration values taken from the NY State Stormwater Management Design Manual annex A:
Commercial roof: 9mg/l
Green area (lawn): 602mg/l
Hardscaped areas: 468 mg/l
Are the values above fine? they are given as general values for those areas.
a concentration of 21mg/l in water from seems to be closer to residential roofs than to commercial roofs.
would it be correct to use 9mg/l for roofs?
I think you are taking the correct approach with this now. By all means, if 9 mg/l is coming from a BMPBest Management Practice Manual that regulates the area your where your project is being constructed, use that.
You just need to be able to defend your calculations, with a straight face.
I think you are well on your way. Good luck!
thanks again for your response.
We will try to follow this approach, however my only concern is whether 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. concentrations given in the manual will be accepted for our project. Our project is located in Europe, however the TSS concentrations I have taken are coming from the NY state manual and I am afraid the reviewer might have comments on this. Any experience on using data from a different location than where the project is? I wonder that if we are not able to find TSS concentration data from local source, we might be risking the credit.
You need to pass the straight face test. I'd compile several sources, and make an educated judgment.
I cant find clear cut for Stormwater Management Plan definition, i mean is it using both structural and non structural plans to achieve stormwater quality control?
It is asking what your concept/design strategy is for removing 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. from the runoff generated by the 90% average rainfall.
You can use both structural and non-structural methods as stand alone, or a combination of the two.
We have site that is located about 600m from the sea, hence the stormwater will be discharged to the sea instead going to municipal infrastructure. Hence the quantity and quality for stormwater that going to municipal infrastructure will not receive any negative impact. Can we eligible to score for this point by adopting this strategy?
No. The credit does not allow for direct discharges.
We have designed a rainwater storage tank for dirty rainwater, with a bigger capacity than required. The water, after being storaged for a while, is pumped to the local sewerage system.
I have read in this forum different approaches for this and is not clear to me. Can we then confirm that a bigger storage tank is enough to settle 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.? or should we add any additional treatment?
I don't know that your idea of capturing and pumping this out to the local storm sewers passes the smell test.
In theory, this water is reused for gardening, landscaping etc. The majority of the solids do settle out in the cistern, and anything pumped out through the reuse process is filtered by the mulch beds, etc.
If you have a pump, that will likely be drawing from the bottom of the cistern, at face value to me it seems like you're only storing the solids before dumping them back into the local storm drains.
I'd definitely want more information on the pump, and what kind of filtration it provides, if any. To me this seems to be the key part of your question.
Finally we have decided to install an additional treatment before the water reaches the local storm drains because we are afraid that GBCIThe Green Building Certification Institute (GBCI) manages Leadership in Energy and Environmental Design (LEED) building certification and professional accreditation processes. It was established in 2008 with support from the U.S. Green Building Council (USGBC). will not accept the removal only via settling.
In the same building we have also a tank capturing water from the roof. We have filters removing 90% 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 then the water is reused mostly for flushing toilets. Can we assume a final 100% TSS removal even if the reuse is only for flushing?
I have a project where we are promoting infiltration by installing permeable pavers for a portion of the pavement, and we are capturing and treating runoff from 90% of the average annual rainfall event, however we are increasing the total impervious area from the existing conditions. Can I still meet this credit? We are removing 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. for all runoff from the site.
In short yes, you are good. Reducing impervious surface is one of the ways to improve water quality, but not an actual requirement for this credit. Just calculate a runoff volume using the 90% annual rainfall event, treat that volume 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.
We are planning to have Sedum Roofing, partly to recieve credit 6.1.
I have read a lot about vegetated roofing also to pursue credit 6.2. I wonder what can be expected from sedum roofing when it comes to the quality of the stormwater running through it. I assume that the water has no 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 it when falling onto the roof.
My question is:
- What TSS inhold can be expected to be added to stormwater that runs through Sedum?
The intent with my question is to answer the following follow up question:
- What filtering solution is suitible for filtering these TSS?
Thanks in advance
We have a Sieve analysis for the sedum soil constituents, meaning that the dimensions of the soil particles that would, worst case, be released from the sedum itself - are known.
Would it, in fact, be possible to argue that no 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 the Sedum would be added to the stormwater after a short period for the Sedum to reach "steady state"? And that only bird excrement and such would factor as the TSS that is being added to the water?
we have a tank in our project that will store rainwater. because our landscape theoretically doesn't require irrigation, it seems this cistern would only serve the purpose of SSc6.1
I understand storing and slowly releasing rainwater isn't the same as treating it - but im wondering if there is any kind of tried and true simple (cheaper) method of treating from the cistern? (ex: filters, etc?).
if so, anyone have product info I could have our civil engineer reference?
I would look into the feasibility of Snoit inlet filters on your inflow pipes.
unless im misunderstanding - the snoit filters I found on website are catch basin filters? our civil engineer seems to think this might not be acceptable for the Stormwater quality ordinances in Houston area. So it might satisfy LEED but not Houston (?). I wouldn't know...
civil engineer is checking on that, but in mean time im wondering if there is anything that can be used at the cistern. my understanding is that the cistern alone doesn't treat anything (even if suspended solids "settle" etc). so eventually overflow/excess cistern water will be slowly let out into storm sewers - "untreated". (?). I guess im just wondering if there is some kind of feature/add-ons to cisterns that might accomplish this?
You are correct, a cistern does not treat anything, and if you are releasing the water from the invert of the cistern, and solids that settle will be let out as well.
I would look at means to treat upstream of the cistern, so that water that enters the cistern is already treated. If snouts aren't acceptable (hard for me to believe) then look at alternate means, veggie swales, raingardens, disconnected roof leaders, street sweeping .....
I'm not understanding the purpose of the cistern. If you're not using it for water reuse, then what is it doing? Are you not allowed to use infiltrators? For water quality, have you considered hydrodynamic separators such as Vortech or StormFilter from Contech?
I am working on a project which plans to use the Downstream Defender by Hydro International to achieve 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. of stormwater. The literature with the product says it treats 50% of TSS. Other literature by Washington Dept of Ecology states it treats 80% of all TSS over 125 microns. Per LEED credit language, 'infield performance monitoring data demonstrating compliance with the criteria' can be used. Data must conform to accepted protocol (e.g., Technology Acceptance Reciprocity Partnership [TARP], Washington State Department of Ecology) for BMPBest Management Practice monitoring." I am assuming we will be able to meet the credit requirements, but just wanted to confirm. Anyone have experience with these units for LEED projects?
Submit all independent 3rd party testing data that you have for the product.
Question one. We are in a semi-arid watershedWatershed that receives less than 20 inches of rainfall per year.. In the calculations, we count on 0,75 inch rainfall during 24 hours?
We are planning to clean the rainwater from the roof. Is this credit meant to be for this kind of water or is it only from parking spaces and similar?
Our plan is to put a small sand filter infiltration basin by every well on the roof. Do you think this will work? Do anyone have another suggestion how to clean the water without having some kind of storage volume? We have one well per 100 square meters and the flow will be quite low if we count with a 0,75 in, 24 hour rainfall.
Thanks in advance,
Hi Victor, Question 1 has been the source of much confusion, and I have received some guidance on this:
The intention was not to ask teams to calculate the 90th percentile storm but the average annual precipitation (then 90% of that amount). They also said those 3 amounts- 1in, 0.75in, and 0.5in- were intended for projects to use if they choose based on which “distinct climate” they fall into (U.S. only. An equivalent would be allowed for projects outside the U.S., but the project would have to show equivalency). So essentially projects could calculate their specific amount or use the applicable one in the footnote.
The intent of the credit is to treat all surface runoff to 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. standard, I think your approach is viable, have your CE show the treatment in his/her calculations.
For table SSC6.2-1, we dont know how to describe BMPBest Management Practice neither its 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, because the rain water from the parking is directed and collected to be sent to a vegetated site outside the leed boundary. What should i put in those spaces?
IMO, the description should be just what you wrote above "rain water from parking is collected to vegetated site". You can find 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. rates in literature such as the NJ Stormwater Best Management Practices Manual: http://www.nj.gov/dep/stormwater/bmp_manual2.htm
I hope this helps.
Is that the pre-development runoff rate or post-development runoff rate?
It is the 90th percentile runoff depth which is used to calculate the pre and post runoff rate and volume.
Jamison, it is the 90th percentile RAINFALL event (depth in inches), which is the same for both pre- and post-development conditions. This has to do with weather, independent of site conditions.
I've recently discovered that the EPA National Stormwater Calculator provides percentile rain depths in the calculation outputs. This is much easier than calculating it yourself, if it is not already provided by a local agency.
But as you pointed out a few weekes ago, and which I agree, this is not the 90th percentile storm at all. We are really talking about 1.0, 0.75, and 0.50-inch design storms.
I forgot to bring this up on our last 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, I don't know that we go and correct this now, as v4 is very clear. But if the reference guide is going to give you the design depth, it is not technically the 90th percentile. The 90th percentile storm in my area is 2.04 inches.
Agreed. I mostly wanted to point out to Jamison that the design event is independent of site condition, and it RAINFALL, not RUNOFF. And thanks again for confirming my understanding to use the 0.5" rain (for arid watersheds) instead of the 90th percentile event. I guess my comment about Natl. Stormwater Calculator would be helpful for EISA Section 438 compliance, but not LEED SSc6.2.
By the way, has the SS TAGLEED Technical Advisory Group (TAG): Subcommittees that consist of industry experts who assist in developing credit interpretations and technical improvements to the LEED system. considered any requirements for treating snowmelt for areas where snowmelt runoff is greater than runoff from the 2-yr. storm? That is the case for most of Alaska, and it is very difficult to calculate the volume and rate of runoff from snowmelt. It is even more difficult to treat the runoff with Green Infrastructure since the ground is still frozen at the time.
Can you contact me through my profile? I'd like to discuss offline if you do not mind.
Hi, for international projects, the 0.5/0.75/1" rainfall data can still be used, right? no need for getting local 90% rainfall data - or?
I am going to go with yes. As discussed above, it looks like the ref guide actually specifies the design storm to be used. The terminology in this is not correct, you need to use the 1/.75/ or .5 inch design storm (whichever fits your climate). These are not necessarily the 90th percentile storm.
The intention was NOT to ask teams to calculate the 90th percentile (all events over a 10 or 30 year period, like EPA 438 in v4), but the average annual precipitation (then 90% of that amount). They also said those 3 amounts- 1in, 0.75in, and 0.5in- were intended for projects to use if they choose based on which “distinct climate” they fall into (U.S. only. An equivalent would be allowed for projects outside the U.S., but the project would have to show equivalency). So essentially projects could calculate their specific amount or use the applicable one in the footnote.
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 GBCIThe Green Building Certification Institute (GBCI) manages Leadership in Energy and Environmental Design (LEED) building certification and professional accreditation processes. It was established in 2008 with support from the U.S. Green Building Council (USGBC). 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.
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%.
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.
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?
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.
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.
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.
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?
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.
I have received a reply back from the GBCIThe Green Building Certification Institute (GBCI) manages Leadership in Energy and Environmental Design (LEED) building certification and professional accreditation processes. It was established in 2008 with support from the U.S. Green Building Council (USGBC). 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??
Would you mind posting the response. This does not compute.
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'.
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.
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 GBCIThe Green Building Certification Institute (GBCI) manages Leadership in Energy and Environmental Design (LEED) building certification and professional accreditation processes. It was established in 2008 with support from the U.S. Green Building Council (USGBC).; the project has not been reviewed yet but we wanted to double check this approach was fine.
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.
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..
You're preaching to the choir here. Those GBCIThe Green Building Certification Institute (GBCI) manages Leadership in Energy and Environmental Design (LEED) building certification and professional accreditation processes. It was established in 2008 with support from the U.S. Green Building Council (USGBC). 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.
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.?
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.
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.
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.
You should be good with that approach.
so just to reiterate...if we have to, our stormwater mitigation can be outside of our project LEED boundary then, correct? We have no room on site and are looking to put an underground system underneath a nearby parking area.
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?
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.
So if we capture rainwater and reuse, do we need to show any type of filtering or will this automatically acquire the credit?
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.
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?
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!
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.
Green roofs help retain stormwater and reduce peak flow.
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