On October4, 1999, EPA proposed an amendment to its Final Water Quality Guidance for the Great Lakes System (the "Guidance") to prohibit mixing zones for bioacccumulative chemicals of concern ("BCCs"). The proposal would phase out mixing zones for existing discharges over a period of ten years.
The EPA had proposed a similar provision on mixing zones when it first issued the Guidance in 1995. The U.S. Court of Appeals for the District of Columbia Circuit, however, vacated that provision and remanded it to EPA for further consideration. A mixing zone is the area beyond the point source outfall in which ambient concentrations of a particular pollutant are allowed to exceed the otherwise applicable water quality criterion for that pollutant. It is the area of dispersal in the receiving water where the pollutants in the effluent are not yet sufficiently diluted to meet the applicable water quality criteria. EPA claims that the elimination of mixing zones is necessary to maintain the environmental integrity of the Great Lakes basin ecosystem. It maintains that contamination by BCCs has already disrupted sport fisheries in the lakes and if BCCs are allowed to be discharged above water quality criteria, they could present a significant potential risk to human health, aquatic life and wildlife.
If the proposed rule becomes final, Great Lakes states would be required to adopt regulations consistent with the Guidance. Illinois, Indiana, Minnesota, Michigan and Wisconsin already have adopted requirements to eliminate mixing zones for BCCs that they have submitted to EPA for approval. New York, Ohio and Pennsylvania have not adopted requirements to eliminate their mixing zones. Under the proposal, these states would have 18 months after the publication of a final BCC mixing zone rule to submit their own provisions complying with the Guidance. EPA would then have six months following this mission to approve or disapprove.