The Ohio River Valley Water Sanitation Compact (ORSANCO) has approved changes to its Pollution Control Standards at a meeting held late last week. They include specification of design flows to be used for setting permit limits to protect human health criteria (the 7Q10 for noncarcinogens; the harmonic mean flow for carcinogens), and a provision to allow consideration of variances to mixing zone requirements. This latter was in response to requests by industry for relief from ORSANCO’s prohibition of mixing zones for bioaccumulatives, such as mercury, which resulted in discharge limits that were more stringent than could be met with current technology.
The proposed adoption of a total dissolved solids criterion of 500 ppm was deferred until additional information on occurrence and sources can be obtained. That matter will be reconsidered at the Commission’s February meeting.
You can see a press release from ORSANCO at http://www.orsanco.org/images/stories/files/pressreleases/2010standardsrelease.pdf
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