Post Stormwater Treatment TSS Monitoring
Post Stormwater Treatment TSS Monitoring
(OP)
I'm currently reviewing post-construction monitoring data for stormwater treatment of TSS. The removal efficiency goal is 80%, however the average removal efficiency measure for the site is 62%. The average TSS leaving the site is under 20 mg/l with a few hits just below 30 mg/l. Is there any literature that defines a reasonable limit for TSS in stormwater? Based on the data the site is showing 80-90% removal efficiency at some discharge points where the incoming waters were loaded above 100 mg/l, while the incoming waters with lower TSS concentrations did not show as significant a removal efficiency. Any ideas welcomed. thanks ahead of time.





RE: Post Stormwater Treatment TSS Monitoring
Perhaps your regulating agency can give you a real number to shoot for rather than 80% of the incoming flow. Other influencing factors include quality of the receiving stream, volume of runoff, etc. Under 20 mg/L sounds about as good as you can get without extensive treatment. Read the article about SeaTac Airport in the September 2006 Stormwater Magazine to see how extensive treatment can get.
RE: Post Stormwater Treatment TSS Monitoring
He pointed out that if he had to prove 80% removal, he would have a ruck dump a load of soil at the inlet of a practice and could probably get the % removal easily...and conversly...one would have a lot of trouble getting 80% TSS removal from tap water.
There is a great need for more real scientific studies related to stormwater. There are a lot of regulations based on very limited science. The regulations seem to be based on beliefs that change from year to year...even to contradict themselves in a short period of time.
RE: Post Stormwater Treatment TSS Monitoring
Verify your state water quality regs. The reason you are treating is to achieve a water quality criteria on the discharge. So if your discharge complies with the criteria, who cares if it's 62% or 80% or 5% efficient - you are complying.
In Washington (where turbidity is regulated, not TSS concentration) the turbidity regs are written that you are allowed a certain exceedance over background. If background is less than 50, you are allowed a 5 NTU increase. If over 50, you are limited to a 10% increase. Again, no word on treatment efficiency.
So maybe there's room for reintepreting the site discharge as applies directly to the reg, rather than the stormwater manual. If you built the BMP per the stormwater manual, and can achieve the water quality regs, you should be able to make the case that your site is compliant.