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Ask the Expert Question-and-Answer Archive (Wastewater Treatment)

by Mike McGinness, EcoShield Environmental Systems, Inc.
May, 2006

Dilution, Excessive Rinsing

Q. I've seen some movement among the agencies to define excessive rinsewater use as dilution. In CA there have been several cases where EPA prosecuted plating shops for running rinsewater when there were no parts in the tank.

A. I have not personally seen any of these cases yet. If you have any details on the ones you heard about I would like to know more about them. I would think their cases would be weak if the plating operations have design and test data justifying the water overflow rates to meet part cleaning specs and or QA/ QC requirements for part cleanliness after part rinsing. Continuous airborne dust fallout in the rinse tanks might be a reason for some continuous overflow between part rinsing. Also a TDS probe with a QA/QC set point limit might run long after a batch of parts were rinsed off and the TDS setting could be based on a reasonable QA/QC rinse water contaminate limit specification for the part application.

On the other hand if they can not justify the rinse water flow rates for any reason other than to meet the discharge permit limits I would think the EPA could prove their case.

In summary, I would agree that excessive rinse water use IS dilution and therefore illegal according to EPA regulations for the Electroplating and Metal Finishing waste water category! However, the problem is in defining excessive rinse water use and getting a judge or jury to accept that definition as it is not spelled out, or defined in the CFR in a measurable way as to just what is and is not dilution! Therefore, it is all a matter of how the plater has justified, or failed to justify his rinse water flow rates!

One possibility is to make a comparison between 2 or more shops doing the same work, with the same equipment and same processes. If one shop is using ten times as much rinse water as another shop, and has no treatment system (since he has diluted his way into compliance with the discharge permit limits) and his competitor is doing the same parts with the same equipment and is using the same process, but uses 1/10th as much rinse water and has a waste water treatment system to treat and meet the same discharge limits, then the EPA should be able to make a dilution claim stick in court.



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