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EPA Issues Final Decision on Missouri’s 303(d) List of Impaired Waters

On November 13, 2012, EPA Region 7 issued its final decision on the Missouri Department of Natural Resources’ (MDNR) list of impaired waters, bringing the total number of impaired waters on the Missouri 2012 303(d) list to 258.

In July 2012, EPA partially disapproved Missouri’s 303(d) list, proposing to restore 11 waterbodies/pollutants that had been slated for removal from the list. EPA’s final decision restores eight water bodies to the 303(d) list of impaired waters.

Section 303(d) of the Clean Water Act requires states to submit to EPA every two years a list of those waterbodies that are not attaining water quality standards. The 303(d) list of impaired waters, in turn, triggers the development of a total maximum daily load (TMDL) for the waterbody. A TMDL is a calculation of the maximum amount of a pollutant that a waterbody can receive and still meet water quality standards, and an allocation of that load among the various sources of that pollutant.

The listing of impaired waters and development of TMDLs can have significant impacts for facilities that currently operate under NPDES discharge permits, or seek re-issuance of those NPDES permits in the future, as those final permit limits are derived in light of allocations of waste loads and related mixing zone considerations that incorporate flow and beneficial use designations, among other water quality and technical considerations. Understanding how MDNR and EPA apply these factors in developing final permit limits is crucial in evaluating whether a facility’s NPDES permit limits were properly derived.

The Final 2012 Missouri 303(d) List is enclosed.