Plankton and Periphyton Assessments. In-Stream Assessment of Fish Population. Bio-accumulation Studies. Site Specific Studies. Stormwater Sampling and Analyses. Alternate Species Studies. PMN Testing for Chemical Manufacturs. OECD Testing. Water Effect Ratio (WER) & Recalculation Procedure. How does the WER works?

Using an EPA approved method, parallel toxicity tests are conducted to compare the toxicity of a metal in laboratory water to the toxicity of the same metal in site downstream water. Of course the toxicity in downstream water is the real life situation. Copper (Cu) may be toxic at 10 ppb in laboratory water and 50 ppb in site downstream water. This gives a ratio of 50/10=5.0 which is used to adjust your effluent limit for the metal in your permit.

Your old permit limit=20 ppb

Your new permit limit= 100 ppb

We have successfully modified many of our client’s NPDES permit metal limits based on Site Specific Studies. The limits are raised, but the receiving streams are still protected!

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