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Water Quality: Docket No. 58-0102-1803

Rulemaking initiated to allow de minimis additions of heat in waters that exceed applicable temperature criteria.

Status of Rulemaking

Pending rule approved by the Idaho Legislature. Final and effective April 11, 2019. Final rule package submitted to EPA for approval April 15, 2019.

Final Rule Package Submitted to EPA

For more information, go to

This submittal also includes documents that exist as part of the rulemaking record and posted below.


This rulemaking has been initiated to allow de minimis additions of heat when waters exceed applicable temperature criteria due to man-made causes. Currently, Idaho’s point source treatment requirements allow point sources of heat to raise receiving water temperatures up to 0.3°C only when the receiving water is naturally warmer than numeric criteria. There is not an allowance for any increase, however small, when it cannot be shown receiving water temperatures are naturally warmer than criteria.

Idaho has many very small point sources. All add some heat to the waters to which they discharge. And, in most cases, the water bodies to which they discharge are warmer than Idaho’s numeric temperature criteria set to protect aquatic life for a portion of each year. Heat is a non-conservative pollutant, and the sources of heat can be relatively small. This rulemaking proposes allowing NPDES/IPDES regulated human sources of heat loading to cause no more than a de minimis 0.3°C increase in receiving water temperatures. This would allow a 0.3°C increase to waters that are exceeding the numeric temperature criteria upstream for the designated aquatic life use even in cases where the exceedance of numeric criteria is not due to natural conditions.

Negotiated Rulemaking Meeting Schedule

No additional meetings are scheduled.

Method for Participating and Submitting Comments

Those interested in participating in the negotiated rulemaking process are encouraged to attend the scheduled meeting via telephone and video conferencing. Individuals interested in participating by telephone and video conferencing should contact Paula Wilson.

For those who cannot participate by attending the meeting, public comment opportunities will be made available throughout the rulemaking process.

Submit all written comments by mail, fax or email to:

Paula Wilson
Idaho Department of Environmental Quality
1410 N. Hilton, Boise, ID 83706
Fax: (208) 373-0481
Paula Wilson

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Negotiated Rule Documents and Meeting Presentations Date Posted Date of Meeting Discussion Written Comment Deadline
Draft No. 2 08/27/18 N/A DEQ is not requesting public comments on this draft. The next comment period will commence upon publication of the proposed rule in the September 5, 2018, issue of the Idaho Administrative Bulletin. The proposed rule comment deadline is October 5, 2018.
Preliminary Draft (Draft No. 1) De Minimus Heat Additions – Discussion Paper #1 De Minimus Heat Additions  – DEQ PowerPoint Presentation 06/25/18 07/20/18 07/20/18 07/20/18 07/30/18
Public CommentsSubmitted ByDate Received
Comment on Proposed RuleU.S. EPA Region 1010/11/18
Comment on Proposed RuleIdaho Conservation League (ICL)10/5/18
Comment on Proposed RuleCity of Nampa10/4/18
Comment on Draft No. 1Ron Harriman07/20/18
Comment on Draft No. 1Hubert Osborne07/23/18
Comment on Draft No. 1Idaho Conservation League (ICL)07/30/18
Comment on Draft No. 1City of Boise07/30/18
Comment on Draft No. 1Association of Idaho Cities (AIC)07/30/18
Comment on Draft No. 1City of Meridian07/30/18
Comment on Draft No. 1U.S. EPA Region 1007/31/18

April 11, 2019

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