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 TSS 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%. Thanks in advance.

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Michael DeVuono

Regional Stormwater Leader

Arcadis North America

LEEDuser Expert

144 thumbs up

Tue, 12/10/2013 - 18:49

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% TSS 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.

Ricardo Sá

Director of Sustainability

Edifícios Saudáveis Consultores (503 910 767)

LEEDuser Basic Member

79 thumbs up

Wed, 12/11/2013 - 10:03

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% TSS 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?

Michael DeVuono

Regional Stormwater Leader

Arcadis North America

LEEDuser Expert

144 thumbs up

Wed, 12/11/2013 - 13:20

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 TAG call today. I will let you know how this goes.

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