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ORSANCO Proposes to Delay Mixing Zone Ban on Bioaccumulative Chemicals of Concern


July 11, 2013, the Ohio River Valley Sanitation Commission (ORSANCO) announced that it was proposing to revise its mixing zone regulations to delay the date by two years after which mixing zones are not authorized or available for bioaccumulative chemicals of concern (BCCs).  Currently, ORSANCO’s pollution control standards provide the BCC mixing zone prohibition takes effect October 16, 2013.  Under ORSANCO’s pollution control standards, BCCs include mercury, PCBs, dioxin, and various pesticides and other chemicals that have been determined to bioaccumulate in fish tissue.

Of particular concern with respect to the mixing zone ban is ORSANCO’s 12 part per trillion water quality standard for mercury, which is more stringent than Kentucky’s water quality standard.  Both the Kentucky and ORSANCO standards are derived from EPA’s recommended standard for mercury in fish tissue of 0.3 mg/kg methyl mercury.  Recent newspaper articles have focused attention on the potentially broad scope of industrial and municipal wastewater sources that may contain mercury.

ORSANCO has noted on its website that it has undertaken a study, which has not yet been completed, to evaluate the relationship between mercury in wastewater discharges and the levels of methyl mercury in fish tissue.  ORSANCO has explained that its mercury limit is a “not to be exceeded” standard whereas the criteria adopted to prevent long term effects from mercury discharges are typically expressed as mean or average concentrations at a particular stream flow.  ORSANCO also notes that questions have also been raised as to whether the ban of mixing zones for BCCs is an appropriate approach for a flowing river system, such as the Ohio River.

ORSANCO will initiate a formal review of its pollution control standards in March 2014, which presents an opportunity to review these concerns with respect to the mercury standard and the ultimate ban on mixing zones for BCCs.  Comments may be submitted on ORSANCO’s proposed changes to the effective date of the ban on mixing zones for BCCs until September 12, 2013.  A public hearing has been scheduled on the proposed changes for August 13, 2013 at the Cincinnati Airport Holiday Inn.

To view a complete PDF of the May/June 2013 issue of the Environmental Letter, click HERE.

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