TMDL Title: Walla Walla Subbasin temperature TMDL
Water Quality Limited Parameters: Temperature
Schedule: DEQ will convene a TMDL rule advisory committee with the first meeting occurring in summer 2028. The TMDL will be submitted to EPA in 2029. EPA must take action to approve or disapprove the TMDL by Nov. 29, 2029, as required by court order.
Project area: Walla Walla Subbasin (HUC 17070102)
The project schedule for all replacement temperature TMDLs can be found on the Temperature Replacement Project page.
Project summary
Monitoring data show stream temperatures in the Walla Walla Subbasin are too warm for sensitive fish and exceed Oregon's EPA approved temperature standards. As a result, some waters in the Walla Walla Subbasin have been placed on Oregon's Section 303(d) 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 2005 Walla Walla Subbasin Stream Temperature TMDL and Water Quality Management Plan.
DEQ is replacing the 2005 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, which had been used in most temperature TMDLs up to that point. A 2019 court ruling then required DEQ and EPA to replace 15 temperature TMDLs using the remaining approved parts of Oregon's temperature water quality standard.
A modeling Quality Assurance Project Plan (QAPP) is required prior to writing the TMDL. The plan outlines the framework for the temperature TMDL analysis, 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.
Modeling Quality Assurance Project Plan for Walla Walla Subbasin Temperature TMDL
Public participation
TMDL development and implementation is a public process which includes the establishing of a local advisory group, holding informational webinars and a public comment period.
Rule Advisory Committee
DEQ seeks public involvement by establishing a Rule Advisory Committee, which provides technical input to DEQ. The Rule Advisory Committee meetings are public and community members and organizations may attend. DEQ will convene a TMDL Rule Advisory Committee with the first meeting occurring in 2028. Please visit the rulemaking page for details and information on how to participate.
Public webinar, hearing and comments
DEQ will also hold an informational webinar and a public hearing and comment period, where anyone can provide comments on the draft TMDL. DEQ makes responses available to the public following the comment period. Please visit the rulemaking page for details and information on how to participate.
Contact
Michele Martin
Project manager
Steve Mrazik
Watershed Management Manager
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