Increased regulatory requirements leading to more stringent effluent limitations required that this industrial user obtain additional credit for effluent dilution in the receiving water. Kleinfelder’s ability to provide a sound scientific basis for an alternative mixing zone, our understanding of the available regulatory options, and our recognized reputation with regulators made us an ideal partner for this discharger.
The dilution credit that could be applied under the standard definition of the regulatory mixing zone (RMZ) was inadequate. The discharger was previously unsuccessful in convincing regulators to apply an alternative mixing zone (AMZ) with greater dilution credit. An AMZ had only been granted on one previous occasion in the history of this agency. The discharge contained a mix of potentially toxic pollutants warranting extreme caution. Therefore, it was necessary to demonstrate that granting an AMZ was supportable under difficult conditions.
Through careful analysis of receiving water quality criteria, effluent quality characterization, and use of advanced statistical analyses for determining whether and to what extent dilution credit was needed on a pollutant by pollutant basis, Kleinfelder was able to calculate the amount of dilution necessary to avoid adverse impacts to human health and the environment. Also, Kleinfelder was able to demonstrate that the size of the AMZ needed to achieve this level of dilution was acceptably small and posed no adverse impact to the receiving water.
The mixing zone corresponding to the required effluent dilution factor was determined and formed the basis for a request for an alternative mixing zone (AMZ). The AMZ was granted and the outfall and diffuser has been constructed and is in operation.