Forum discussion
NC-2009 SSc6.2: Stormwater Design—Quality Control
If we capture rainwater and reuse it for irrigation, do we need to show any type of filtering or will this automatically acquire the credit?
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Why do the requirements focus on 1-year and 2-year, 24-hour storms?
How can green roofs count as a stormwater control measure?
I have 100-year data—how do I convert to 2-year?
Are there special considerations for international projects?
What performance threshold do I need to achieve for an Exemplary Performance point?
Michael DeVuono
Regional Stormwater LeaderArcadis North America
LEEDuser Expert
187 thumbs up
October 22, 2013 - 12:08 pm
I'd take 100% TSS credit for it ... no filtrations.
Mike D
56 thumbs up
October 29, 2013 - 5:52 am
Thanks Michael,
I have received a reply back from the GBCI saying the water that is reused does not count...I'm confused now. If we are reusing all the water for irrigation, can the credit not be achieved??
Michael DeVuono
Regional Stormwater LeaderArcadis North America
LEEDuser Expert
187 thumbs up
October 29, 2013 - 6:08 am
Would you mind posting the response. This does not compute.
Mike D
56 thumbs up
October 29, 2013 - 6:10 am
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'.
Michael DeVuono
Regional Stormwater LeaderArcadis North America
LEEDuser Expert
187 thumbs up
October 29, 2013 - 7:54 am
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 TAG 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 TSS 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.
Mike D
56 thumbs up
October 29, 2013 - 8:24 am
Thanks for this. Yes, the water is being reused for irrigation and toilet flushing so we all assumed it was 100% TSS removal.
Just as a note, the comment received was by contacting GBCI; the project has not been reviewed yet but we wanted to double check this approach was fine.
Michael DeVuono
Regional Stormwater LeaderArcadis North America
LEEDuser Expert
187 thumbs up
October 29, 2013 - 8:44 am
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.
Mike D
56 thumbs up
October 29, 2013 - 9:49 am
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..
Michael DeVuono
Regional Stormwater LeaderArcadis North America
LEEDuser Expert
187 thumbs up
October 29, 2013 - 10:29 am
You're preaching to the choir here. Those GBCI responses aren't "official" so you're reviewer may agree with your approach. This is the first I have ever heard of this not counting, and we have recommended this approach on this site for quite some time. To be safe, if you follow the creative wording above, I think you will be okay. Goo dluck, and keep us posted.
Mike D
56 thumbs up
October 30, 2013 - 11:58 am
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 TSS?
Michael DeVuono
Regional Stormwater LeaderArcadis North America
LEEDuser Expert
187 thumbs up
October 30, 2013 - 12:17 pm
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.
Michael DeVuono
Regional Stormwater LeaderArcadis North America
LEEDuser Expert
187 thumbs up
November 13, 2013 - 2:36 pm
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.