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 Method 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?
You rely on LEEDuser. Can we rely on you?
LEEDuser is supported by our premium members, not by advertisers.
Go premium for
Amy Rider
Sustainability ManagerKEMA Services
161 thumbs up
March 29, 2011 - 5:07 pm
1: Intensity or Precipitation.
First of all, the Hydrosystem Filters I have seen don't actually remove TSS 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.