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Hi all, my firm was hired to study the possibility of developing a former shopping mall into a mixed-use residential, commercial, and office "Town Center"-type facility. The existing public sewer infrastructure has available capacity, but not enough for the anticipated peak diurnal flows (1.6 MGD) to enter the system all at once.
We would like to explore the possibility of using an attenuation tank, similar to the type used by large stadiums, to throttle the flow leaving the site and spread out its downstream impact over several hours. As the junior engineer on this project, I have been scouring the internet for any sort of precedent for this. So far, the only relevant example I have found is from a four-dwelling development in New Zealand, so not exactly an apples-to-apples comparison.
Has anyone ever encountered this approach of using in-line storage to reduce peak flows, not for wet weather SSO/CSO prevention, but just for "business as usual" wastewater flows? We understand that there may be myriad concerns such as odor, hydrogen sulfide creation, etc, but we would still like to run down every possibility for the owner and not dismiss anything prematurely.
Thanks very much for your thoughts!
Sounds like an interesting project. I will start by saying I am not an expert in design or construction so I'm sorry if this is a very limited suggestion. However, this does seem similar to what one would do when trying to size a wet weather tank. If you know the targeted flow limit leaving the site, and if you know the peak flow at the site, you should be able to determine how much storage is required. Not sure if pumping is required or if a different pump is needed for wastewater vs stormwater.
Thanks so much for your response. I agree, the principles for sizing wet wells, equalization tanks, and stormwater tanks are instructive and well-established, so we are glad to hear that idea sounds at least initially plausible to other engineers.
I have used tanks in this way several times and seen them used by others in multiple states (both public and private). I don't believe there's much of a concern from an engineering perspective as much as there is from a maintenance/future cost perspective. Among the concerns you listed, I would add buildup of solids over time that reduces storage capacity. If you can design the tank to be easily cleaned or flushed automatically, that could be worth the added costs. Most clients want to avoid tanks because of the added cost/maintenance, but as long as they understand the drawbacks, I wouldn't have any issue proceeding with a tank.