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Credit language straight from USGBC
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11 Comments
Structural control and LEED boundary
Can the storm water management structural control be located outside of the LEED project boundary?
Tristan Roberts replied Editor – LEEDuser, BuildingGreen, LLC Mar 31 2010
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?
John Beeson replied Chief Mystic in Resident, betterENVIRONMENT, LLC Apr 01 2010
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.
Tristan Roberts replied Editor – LEEDuser, BuildingGreen, LLC Apr 01 2010
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.
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!
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?
Tristan Roberts replied Editor – LEEDuser, BuildingGreen, LLC Apr 13 2010
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."
Stormwater cistern
This is a project located in previously developed 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!
Amy Rider replied Sustainability Consultant, KEMA Services Aug 25 2010
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.
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
Amy Rider replied Sustainability Consultant, KEMA Services Aug 25 2010
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.
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