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The calculations for this credit are always a headache! While our projects are usually awarded the credit, the equations in the LEED Reference Guide are helpful mostly for sizing a reservoir or cistern, but don't help you get to the final results. Does US

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NC-2009 SSc6.2:Stormwater Design—Quality Control

Which type of water needs to be filtered?

Dear all, Please confirm this assumption - our interpretation of this credit is that it only applies to runoff, not to roof captured water. Is this correct? I'm asking because the client is harvesting rainwater for irrigation and janitorial cleaning but there will be more rainwater than needed. this excess water will be filtered to 80% TSS removal. Would that comply with the credit intent? Or we also/only have to filter the runoff from the ground?? Is the credit aimed to runoff from the groundfloor? Thanks

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Michael DeVuono
Regional Stormwater Leader
Arcadis North America
LEEDuser Expert
144 thumbs up

Wed, 01/23/2013 - 16:04

Yes, you are treating the capture/reuse water at 100% TSS removal, and the remaining at 80%

Wed, 01/23/2013 - 16:17

Hi Michael, Just to confirm - we are talking about 3 different types of water: - the harvested water from the roof that will be reused; - the excess water from the roof that will not be reused and will have to infilter in the soil; - and the runoff from the ground. You mean that if I filter the roof water that wil be reused, the excess roof water but not treat the runoff from the ground I will be complying?
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Michael DeVuono
Regional Stormwater Leader
Arcadis North America
LEEDuser Expert
144 thumbs up

Wed, 01/23/2013 - 18:45

Capture and reuse = 100% TSS removal. Whatever is not "captured and reused" must be treated via a BMP that removes at least 80% TSS. You need to treat the 90 percentile rainfall, regardless of cover type. The cover type is what produces the runoff volume. Roof = 98% runoff = more volume to treat. Lawn Areas = Around 60% runoff = less volume to treat but you still need to treat what runs off.

Thu, 01/24/2013 - 13:51

In our case, the groundcover is essentially crushed stone, because the project consists on a subway station. Not sure how to capture the water from the ground floor covered by crushed stone and filter it...I understand if we can't capture and filter we won't be able to comply, right? thanks
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Michael DeVuono
Regional Stormwater Leader
Arcadis North America
LEEDuser Expert
144 thumbs up

Thu, 01/24/2013 - 13:55

Do you obtain complete infiltration of what hits the crushed stone? If you do not have runoff, there is nothing to treat. If you capture what would have run off in your cistern, you are well on your way to this credit. You need to evaluate the runoff over the crushed stone. You could always underdrain that area, and route through a pre-fab water quality unit.

Mon, 01/28/2013 - 21:29

Marcio, as far as I understand, you need to calculate if the excess water captured and used exceeds the 90% rainfall. If that's not the case, you need to treat the excess to 80% TSS removal. That applies to the ground runoff as well. If you infiltrate it you're fine, but if your infiltration rate is low you may need to treat the excess water as well through any strategies you may devise (store and infiltrate, or filtrate). You must do an infiltration/percolation test to evaluate this. All this must be evaluated in terms of the total amount generated inside your LEED boundary, that is, the total figure must comply with the credit, and not only the excess water from the cistern, or whatever structure you're dealing with. Michael, pls correct me if I'm wrong. Um abração,
Profile picture for user Mike Dee
Michael DeVuono
Regional Stormwater Leader
Arcadis North America
LEEDuser Expert
144 thumbs up

Tue, 01/29/2013 - 12:47

Correct, you are working towards a volume total. If you can get that total into the cistern, and use it, is the main point. Without knowing specifics I'm going leave you with that.

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