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!
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
August 25, 2010 - 1:52 pm
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 TSS 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.