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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...
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54 Comments
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
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?
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.
Exemplary Performance Guidance
Noticed a ruling 11/01/2011 (#10109 & 10108) gives useful guidance on Exemplary PerformanceIn LEED, certain credits have established thresholds beyond basic credit achievement. Meeting these thresholds can earn additional points through Innovation in Design (ID) or Innovation in Operations (IO) points. As a general rule of thumb, ID credits for exemplary performance are awarded for doubling the credit requirements and/or achieving the next incremental percentage threshold. However, this rule varies on a case by case basis, so check the credit requirements. point requirements for c6 Quality & Quantity ... worth checking out! https://www.usgbc.org/leedinterpretations/LISearch.aspx?liaccessid=10109
% 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".
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.
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.
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.
TSS removal efficiency % table?
What is the best resource for finding 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 for various BMPs? Is there a table or reference to base our #s off of since we don't have calculations or on-site monitoring?
Kash, there is a table showing sample documentation 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. efficiencies in the LEED Reference Guide, page 104.
Deviation from Default TSS Removal Efficiency
I am working on a project in Germany that is using multiple buffer strips to remove 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 runoff before it reaches a small drainage channel. Rain water from the roof of the building is collected in a cistern for toilet flushing. Rainwater falling on the asphalt parking (2% slope) area flows (sheet flow) across a 10 ft long grass buffer strip (1% slope) and then across a 70 ft long forested (large pine trees, small other trees, underbrush) buffer strip (3% slope) before reaching a small drainage channel. Because of the dual buffer strip combined with the relatively low slopes and long distance to the drainage channel, I think that the actual TSS removal is higher than the default 65% taken from the EPA’s Guidance Specifying Management Measures for Sources of Nonpoint Pollution in Coastal Waters manual. I think that the TSS removal of the bufferstrip should be closer to the 80-90% range but I do not have a local resource or a good equation to use that would justify this. Is there a way to claim greater TSS removal efficiency than the default 65% removal efficiency for my case that would be acceptable to GBCI reviewers?
Rich,
I would agree that, based on your description of the system, you are achieving higher 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 rates. While a local resource that shows higher TSS removal rates will always make your case stronger don't forget about the magnification effect of using multiple BMPs in series.
Remember that while not a perfect indicator of removal efficiency, you can assume that each of the filter strips is removing a percentage of the TSS present, for a combined removal efficiency for all of the water that passes through both filter strips. Assuming the first removes 65% of the TSS and the second removes 65% of what remains the combined efficiency should be 87% (65% + 35% x 65%).
Don't forget to also give yourself credit for the rainwater that is captured and reused.
Thank you Amy. I'll try the combination approach. Much appreciated.
Rich
May I include native landscape restored as a BMPBest Management Practice? What would be the average TS removal?
Can you explain in detail the combined removal efficiency?
LEED Documentation - is it required for this point
Our project approach to this point is pretty straightforward. We are using a water quality structure with a sand filter for the entire site. Is there further documentation required for this point beyond just filling in the table SSc6.2-1 and checking the box that the BMPBest Management Practice's treat runoff from 90% of the average annual rainfall? ? I was thinking that they might want to see what WQ system is being used, proof of 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, some calculations, etc.
Kelley, it does appear that that is the extent of the documentation requirements. Because you probably need to complete the other documentation you mentioned in order to make sure the strategy will work, I would have that on hand in case it's needed as well.
green roof
We will install an extensive green roof in our project. Does anyone know what the runoff rarte is and how 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. are captured by 2.7 inches of substrate?
Emmanuel, I am not a stormwater expert so I wouldn't be able to tell you how to get this value. However, I would be cautious about assuming standard values for green roofs. This article in Environmental Building News shared some interesting data on this: Green Roof Study Finds Big Variation in Stormwater Retention.
Removal % in LEED reference guide table.
If I understand correclty, we can use the table in the reference guide with several BMPs to determine the removal efficiency. In this table however there are 2 values : average TS removal % and Probalb Range 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 which is a range. Which value do we work with. e.g. if we have a wet pond, do we use 60%?
The 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 efficiency (i.e. 60% for wet ponds) should be used unless you have a local resource to reference that lists a higher removal efficiency.
Where can I find this table? I'm not finding it in the LEEDOnline Forms, or in the Reference Guide.
It's on page 104 of my LEED BD+C 2009 edition reference guide. It's labeled "Table 2. Management Practices for Removing Total Suspended Solids from Runoff". Make sure you're not using the free abridged version. It's only in the version you purchase.
Determining compliance
I’m working on a Project in Portugal, which consists in a 13.400m2 site, with 6000m2 rooftop (harvests rain), 2500m2 green roof, 2735m2 of gardens, 306 m2 of planters and 1840m2 of impermeable pavements.
First of all I am considering the use a hydrosystem filter to remove the 80%SST from the runoff, and so I must determine the flow rate that my drainage areas are producing.
However I am not sure which model to use in order to determine this flow rate, since the Rational MethodA formula that can be used for calculating stormwater flow rates. Q = CIA, where C represents a coefficient for physical drainage area, I is the rainfall intensity, and A is area. The method is suitable for watersheds smaller than 300 acres in size. asks for a rainfall intensity and the NRSCS model asks for a Precipitation, which in fact will be equal to the 90% of the average annual rainfall (1’’, 0.75’’ or 0.5’’). So, if i use an intensity, will the 2year 24h event allow to treat the 90% of the average annual rainfall? I’m quite confused in this.
One other question relies on the following. I’m collecting from a 6000m2 rooftop to a 125m3 tank which will only supply WC’s and irrigation, does this rain water filling the tank need to respect the 80% SST removal, once it is not directly discharged in the draining system? I was only considering treating the First Flush and the overflow of the tank..is it suitable for credit compliance?
And one more thing, the rainfall that hit the garden area is considered as 100% treated?
1: Intensity or Precipitation.
First of all, the Hydrosystem Filters I have seen don't actually remove 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. so be sure your product has a documented TSS removal efficiency to provide as a reference.
In general, this credit looks only at average annual precipitation so the NRCS model should be fine. If you are pursuing SSc6.1 you will need to account for rainfall intensity.
2: Treatment of Captured Rainwater.
Since you plan to reuse some of the rainwater captured on-site that water is considered treated and counts toward your 90% of average annual rainfall total. Likely some treatment (or at least filtration) will be needed to reuse this water. See SSc6.1 in the Reference Guide for additional calculation guidance for rainwater harvesting systems.
3: Infiltration as Treatment.
If 100% of the stormwater that makes it to the "garden area" does not leave the site and will be infiltrated into the soil there then yes, 100% of it is considered treated.
6.1 or 6.2 - Exemplary Performance
I realize this is a long question but it is complicated and requires some context. Please bear with me!
I'm working on a project that will include large amounts of pervious pavement as well as rain gardens and other Low Impact Development (LID) techniques. The project was awarded a grant from the State of Washington to pay for the construction and monitoring of various LID stormwater facilities. Originally, the project was not pursuing LEED so we designed the storm system per State standards. The client would now like to pursue LEED certification for the building (in the middle of construction) so we are trying to determine if SSC6.1 or 6.2 are feasible.
We're fairly certain that we can't achieve 6.1 because the site soils do not infiltrate (the design rate is 0.006 in/hour). Additionally, little flow control has been provided since the site discharges directly to the Puget Sound.
SSC6.2 is perhaps a bit more hopeful. We're treating all stormwater runoff from pollution-generating surfaces through rain gardens and pervious pavement. In many cases runoff passes through the pervious pavement, is collected by an under drain, and is then sent to a rain garden where it is treated again. However, the State of Washington doesn't require treating roof runoff if the roof is not constructed of leachable materials so in our design all runoff from the roof bypasses treatment. Because of this I don't think we can achieve 6.2.
Here's my question: Can we pursue an innovative design point for the pervious pavement and extra-treatment measures on the site if we don't first achieve 6.1 or 6.2 first? Does a team need to achieve the standard credit before it can pursue an innovative design point related to that credit?
If not, any ideas how we might be able to achieve 6.1 or 6.2? Runoff from a building roof needs to be treated per LEED, correct?
Thanks!
There is a general rule within LEED that innovation credits will not be awarded for design elements already covered by the LEED system, so you are correct that an innovation credit won't work in this case.
As for how to achieve these credits, I don't see any way based on your description short of treating the roof water (unless your roof surface is only 10% of your site!). On-site capture and reuse is often a good way to go when adjacent to a water body but I imagine that would be entirely cost prohibitive (and probably illogical) at this stage of the project.
TSS vs. SSC
Our client has installed a stormwater treatment technology that removes (per EPA testing) over 80% SSC (suspended solids concentration). Can I use SSC in lieu 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. given that both SSC and TSS are analytical parameters that measure sediment concentrations in water?
Based on the results of this USGS Water Resources Investigation Report comparison between the two methodologies (http://water.usgs.gov/osw/pubs/WRIR00-4191.pdf), I'd say yes.
That being said, as always, the final decision comes down to your reviewer. I highly recommend citing this report (or something similar) in your documentation.
Please let us know the results.
Discharge to the sea
Is there any stormwater treatment required for compliance with SS Credit 6.2 when all collected stormwater will discharge into the sea/Harbour which unlikely to cause pollution to water flow likes watercourses/river.
All of the same requirements apply to stormwater discharge that is going into the sea/harbour. The intent of the credit is to reduce pollution eminating from the site.
define what is non-structural control and structural control 6.2
In doing our templete, I would like clarity of what each component is and some examples of each. Our company provided the landscaping portion for a green addition and remodel for an office building. Within the landscaped area, I designed 3 rain gardens and selected all native plants that survive in storm water collected areas as well as plants for the high dry sites. Also used various sizes of gravel and rock, a small hardscape area with gravel between joints and pitch to 3 sides of raingarden and to planting bed. If I structured the components of the new landscape & the rain gardens based on many site visit studies during heavy rains prior to construction to best retain stormwater and utilize all water runoff to provide for plant material and nature, is it a structural control or not by LEED definition? One of the rain gardens run parallel to the building and was designed to 'appear' as a dry stream bed collecting water from the higher elevation, the other 2 collect from disconnected downspouts. The entire landscape design and installation was to save all runoff water 100%, utilize and filter it with plant material and coarse wood chip mulch and it proved to be highly successful as my calculation proved in 6.1 template of 99.78% I am just not sure how to complete 6.2 Thank you
Carol Palansky Nature's Way Inc Land Care Chesterland Ohio
Hi Carol,
Rain gardens and similar plant based stormwater treatment and infiltration zones are generally considered non-structural.
For what it is worth, the two categories aren't weighed differently on the LEED Form, so when in doubt as to which category is appropriate, guessing should not change the outcome.
Thank you, Amy, for your reply. I get mixed answers on this as our local soil and water engineer thought it to be structural items since a small hardscape is within the rain garden area. Good to know not weighed on exact catagory on this particular section.
calculations
Is there a more clear way that the calculations can be done. Or any more examples. Can you hire a civil engineer to show how to do the calcs on this site.
Parker, that's kind of a vague question... what do you have in mind as far as a more clear way? There is some sample documentation in the Doc Toolkit tab above, and pointers in the Checklists tab.
I would definitely delegate this credit to a civil engineer, why not?
Trist,
Why don't you take all that money your are being paid, and answer my question. Why don't you create some BETTER documentation, so I don't have to hire a civil engineer. You should hire a civil engineer and not tell me to do so. It can't be that hard. Go the extra mile for me,,,there is a huge gap in information on this credit, fill it in. I am good at LEED, I have complex questions, answer them for me. How many users are there on this site anyways?
Parker, if you aren't getting your money's worth on this site just ask and we'll give you a full refund.
If you look around this site you can see that I and other members of the LEEDuser community are happy to help—all the way through that extra mile. We simply need a bit more information to go on from your end. Where are you getting stuck in your calcs? What is about them that isn't clear to you? It doesn't make sense for us to invest in creating more samples if we don't know that they're addressing the questions of yourself and others.
In many cases with LEED a consultant and his or her specialized know-how is a smart investment. I know LEED very well but I wouldn't hire me to do an energy model for EAc1 or write a stormwater management plan for SSc6. The guidance on a site like this simply can't and doesn't try to anticipate all the possible site conditions that would lead to different SSc6 calcs.
I like the site, just seems like the examples aren't very clear examples.
Okay, just help us out a bit and be more specific about what's not clear. I would love to try to provide more samples but I would want to select them based on what's needed.
Tristan, for the record, we are very happy with LEED User! We understand that the website is a collaboration amongst professionals and are excited by the opportunity to work together to decipher the requirements for each of our projects. Thank you for your hard work in setting this up and answering our many questions!
SSC6.2 removal eficiency
Dear Leeduser
I am working on a project which has a huge retention pond within the site boundary. The calculation by our civil engineer indicated that the pond is able to treat 100% of annual rainfall and achieve 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 eficiency. However, once I added 100% to both "TSS Removal Efficiency" and "% of Annual Rainfall Treated by BMPBest Management Practice" on the LEED Template, the Weighted Average TSS Removal Efficiency became 111.11. Is this correct? Please let me know. Thanks.
Are you using LEED Online v2 for an NC v2.2 project?
I plugged the same numbers into the new LEED Online for NC 2009 and got the same result, so I think there must be some logic making that correct, though I don't know what it is, to be perfectly honest. The tipoff is the "weighted" average. There is a similar weighting for SSc7.2 which results in percentages over 100.
Strategies to filter TSS
The project is located in Italy and the project team is able to treat the 90 % of the average annual rainfall using some systems in series. The water comes from the roofs and all the hardscape in the site area (there is also vegetation where water is considered 100 % treated). The water coming from 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. flows through the drainage basin and then is collected in a sedimentation tank; after that it flows through some filters and then goes to the sewage systems. According to table 2 Reference Guide LEED NC v3 (page 104) I assumed that the sedimentation tank has 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 15% (oil grit separator).
Question 1) I don't know which is the average TSS removal for the drainage basin and for the filters. Do you have any suggestion ?
Question 2) Is there any comparative table where I can find the correlation between the filter mesh and the average TSS removal ?
Question 3) Once I have all the average TSS removal percentages (for each system), how can I count them together? I don't think a solution is to sum the TSS removal percetages for each system...
Thanks
1. Drainage basins don't typically remove 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. by themselves. For the filters you'll need to confirm the TSS removal rates with the manufacturer and get documentation from them showing the infield performance data.
2. I don't know of any table that correlates filter mesh with TSS removal rates. I think there a lot of factors that come into play outside of just the mesh size. Again the best bet is to contact the manufacturers as they generally conduct their own tests.
3. You describe a train of treatment devices. Here is the approach we recommend:
TSS x (1- % removal efficiency) = A
A x (1- % removal efficiency) = B
B x (1- % removal efficiency) = C ...
A is the TSS remaining after that BMPBest Management Practice. B is the TSS remaining after that BMP plus the measure that achieved A, and so on...
One item of note, although the table on page 104 of the Reference Guide states that an oil/grit separator removes 15% of the TSS on average, you should confirm this again (sorry for being so repetitious) with the design and manufacturer. Remember that the Ref. Guide also defines TSS as those particles too small or light to be removed via gravity settling.
Stormwater cistern
This is a project located in previously developedPreviously developed sites are those altered by paving, construction, and/or land use that would typically have required regulatory permitting to have been initiated (alterations may exist now or in the past). Previously developed land includes a platted lot on which a building was constructed if the lot is no more than 1 acre; previous development on lots larger than 1 acre is defined as the development footprint and land alterations associated with the footprint. Land that is not previously developed and altered landscapes resulting from current or historical clearing or filling, agricultural or forestry use, or preserved natural area use are considered undeveloped land. The date of previous development permit issuance constitutes the date of previous development, but permit issuance in itself does not constitute previous development." urban area. We have a cistern capable of receiving 100% of the site's runoff, however, only a small amount of this water will be reused in flushing fixtures and landscape irrigation while the remaining water will be pumped to the municipal sewage (after the storm event has stopped). This is mainly to empty the cistern in order to be ready for the next storm. Water pumped to municipal system will not be filtered. It is expected that solids will sediment at the cistern. How is this strategy enough for this credit compliance? If it's not enough, what should we add to it? Thanks!
Jana, when you say the cistern is capable of receiving 100% of the site's runoff, I assume that the cistern is sized to hold a certain volume of water based on a certain storm event (e.g. 1-year, 10-year, 50-year, etc.). You mention a small amount of water will be reused in flushing fixtures and for irrigation, so I'm also assuming that the cistern does not get completely emptied when the pumps to the municipal system kick on. I would suggest you verify with the engineers how much water will be held and reused for flushing and irrigation. If that volume is equal to or greater than volume calculated using the Runoff Treatment Equivalents in the LEED Reference Guide, I think you can make a convincing case that 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. from the average annual storm is treated and removed on-site. There are also some best practices that should be considered, such as pretreatment and screening (before the runoff enters the cistern) to prevent debris and sediment from building up in the cistern and entering the toilet and irrigation lines. If the pretreatment system is a hydro-dynamic treatment device, it may well be capable of removing 80% of the TSS from 90% of the average annual rainfall itself. You just need to make sure it's sized properly.
EP points
The summary graphic indicates that SSc6.1 and SSc6.2 qualify for a EP point. The LEED forms do not show this being an option. Can you clarify if an EP point is available, and if it is available then what are the requirements?
Dimitris, the LEED Reference Guide says the following:
"No standardized exemplary performanceIn LEED, certain credits have established thresholds beyond basic credit achievement. Meeting these thresholds can earn additional points through Innovation in Design (ID) or Innovation in Operations (IO) points. As a general rule of thumb, ID credits for exemplary performance are awarded for doubling the credit requirements and/or achieving the next incremental percentage threshold. However, this rule varies on a case by case basis, so check the credit requirements. option has been established for this credit. However, project teams may apply for exemplary performance by documenting a comprehensive approach to capture and treat stormwater runoff and demonstrating performance above and beyond the credit requirements. Only 1 exemplary performance credit may be achieved for SS Credit 6.1, Stormwater Design—Quantity Control, and SS Credit 6.2, Stormwater Design—Quality Control."
LEED Project Boundaries and stormwater credits
This is in response to a recent question on this subject. The MPR Supplemental Guidance (located here: http://www.usgbc.org/ShowFile.aspx?DocumentID=6473 ) states on page 14:
"The nature of storm water calculations often necessitates that land outside the LEED project boundary be considered when determining compliance for these credits. Also, it may be necessary to discharge site runoff to a regional or master stormwater management system, such as a retention pond. This additional real property does not need to be included in the LEED project boundary or be considered for prerequisite, other credit, or other MPR compliance."
I hope this solves the problem!
We had seen this guidance which helped us to understand that our retention facility, which is outside our LEED boundary, can be used to show compliance with this credit. However, we are unsure whether we then run the calcs for the entire stormwater area or if we have to run the calcs for only the area within the LEED boundary. We're assuming that we would use the whole stormwater area which includes land outside our LEED Boundary.
Structural control and LEED boundary
Can the storm water management structural control be located outside of the LEED project boundary?
I don't have experience with this but it seems as though logically speaking it would make sense to allow this. Some structural controls might simply not fit within a site, especially a tight one.
Could you provide a little more context?
The LEED project boundary is defined but the structural control is outside of that boundary and within a different LEED project boundary for another project. The Structural control handles portions of both LEED projects.
John, we're having some trouble displaying the comments on this credit. Our expert on this, Greg Hurst, wasn't able to respond directly, but he sent me this comment:
LEED SSc6.2 says that a stormwater management plan must be developed that captures and treats stormwater. It does not specifically state that the treatment has to exist “on site”, i.e. within the LEED defined boundary.
I think that a clarification may have been posted on USGBC site on this. I have not checked it as I respond to this question. I recall the documentation to achieve this credit has to show that the treatment BMPs have been designed to account for the LEED property in question and must demonstrate that all other properties using the same treatment train must also be accommodated in the calculations. In other words, you cannot double count the BMP’s, and you have to provide calculations that show that all properties using the treatment train can be treated simultaneously.
It is a bit like a master treatment plan where the total treatment train construction is apportioned out to the properties.
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