R&W has designed rapid mix diffusers for several clients who were unable to meet their National Pollution Discharge Elimination System (NPDES) Whole Effluent Toxicity (WET) limit. Toxicity resulting from high dissolved solids required the design and demonstration of rapid mix diffusers in order to revise NPDES permit limits for WET. In Michigan, the demonstration requires that the proposed design complies with R 323.1082 Mixing Zones (Rule 82) specifically designed to develop a zone near the discharge which is not considered to be habitable. This uninhabitable area is defined as the area in which the velocity is greater than or equal to 5 feet per second (fps). R&W has designed systems that have resulted in revisions to NPDES permit limits from 5.0 to 7.5 TUa.
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