Lower Grande Ronde, Wallowa, and Imnaha Subbasins Temperature Total Maximum Daily Loads

In 2013, the United States Environmental Protection Agency disapproved the Natural Conditions Criterion contained in Oregon's water quality standard for temperature due to the 2012 U.S. District Court decision for NWEA v. EPA, 855 F. Supp. 2d 1199 (D. Or., 2012). This portion of the temperature water quality standard was used in most temperature TMDLs issued from 2003 through 2012. On Oct. 4, 2019, the U.S. District Court issued a judgment for NWEA v. EPA, No. 3:12-cv-01751-HZ (D. Or., Oct. 4, 2019) and required DEQ and USEPA to replace 15 Oregon temperature TMDLs that were based on the Natural Conditions Criterion and to reissue the temperature TMDLs based on the remaining elements of the temperature water quality standard.

A Total Maximum Daily Load is a water quality restoration plan and the calculation of the maximum amount of a pollutant that a waterbody can receive while still meeting water quality standards for that particular pollutant. The maximum amount of a pollutant a waterbody can receive is called the loading capacity. Loading from all pollutant sources must not exceed the loading capacity of a waterbody, including an appropriate margin of safety.

The temperature TMDLs for the Lower Grande Ronde, Wallowa, and Imnaha Subbasins will be developed to address units identified as temperature impaired.  The exact extents are described in the Quality Assurance Projects Plan listed on the Total Maximum Daily Loads for the Lower Grande Ronde, Wallowa, and Imnaha Subbasins Quality Assurance Project Plan. The TMDL phasing considers the extent of the water quality models being used to support the TMDLs, requirements of the court order and DEQ's available resources.