TMDL title: Total Maximum Daily Loads for the Lower Grande Ronde, Wallowa, and Imnaha Subbasins
Water Quality Limited Parameters: Temperature
Status: In development.
Schedule: DEQ will present the TMDLs for the Lower Grande Ronde, Imnaha and Wallowa Subbasins to the Environmental Quality Commission for proposed rule adoption a minimum of 30 days prior to EPA for their approval or disapproval by Dec. 4, 2028.
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The project schedule for all replacement temperature TMDLs is online.
Project Area: The project will include the Lower Grande Ronde Subbasin, Imnaha Subbasin, Wallowa Subbasin, Lower Snake-Asotin Subbasin, and Hells Canyon Subbasin.
Project summary
Monitoring data show temperatures for multiple streams in the project area watersheds are too warm for sensitive fish and do not meet Oregon's EPA approved temperature standards. As a result, the waters not meeting standards have been placed on a national list of impaired waters. The federal Clean Water Act requires states or EPA to develop a Total Maximum Daily Load, or TMDL, for each water listed as impaired. Once approved, the updated TMDL will replace the existing temperature TMDL issued by DEQ in September 2010 and approved by the United States Environmental Protection Agency on December 17, 2010.
DEQ is replacing the existing TMDL following the outcome from two court cases and related EPA actions. In response to a 2012 court decision, EPA disapproved Oregon's Natural Conditions Criterion for temperature in 2013, which had been used in most temperature TMDLs from 2003 through 2012. A 2019 court ruling then required DEQ and EPA to replace 15 TMDLs using the remaining approved parts of Oregon's temperature water quality standard.
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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 loading 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.
Quality Assurance Project Plan
A Quality Assurance Project Plan is required prior to writing the TMDL. The plan outlines the framework for developing a temperature TMDL, including defining the problem scope, key temperature-related processes and technical modeling approach. It also details the data sources, evaluation methods, potential management scenarios and project management components such as documentation and team coordination.
- Total Maximum Daily Loads for the Lower Grande Ronde, Wallowa, and Imnaha Subbasins QAPP
Rulemaking
TMDL development and implementation is a public process. DEQ will develop this TMDL by rule per Oregon Administrative Rule Chapter 340 Division 42. During a rulemaking process, DEQ seeks public involvement by holding public hearings, establishing rule advisory committee meetings for technical and policy input, and for feedback regarding potential fiscal impacts related to the rule.
DEQ will hold two rule advisory committee meetings and a public hearing. DEQ will present the draft TMDL and Water Quality Management Plan to the Environmental Quality Commission, DEQ's formal policy and rulemaking body, for adoption before submitting the TMDL to EPA for approval or disapproval.
DEQ will have a rulemaking webpage for rule advisory committee meeting dates and information, draft project documents including the TMDL, Water Quality Management Plan, Technical Support Document, and Fiscal Impact Statement, and to sign up for email updates.
Contact
Michele Martin, Project manager
Trea Nance, Basin Coordinator
Steve Mrazik, Watershed Management Manager