Protecting Public Health and the Environment.

Site-Specific Water Quality Criteria

DEQ's water quality criteria may not always reflect the toxicity of a pollutant in a specific water body. Therefore, DEQ has found it may be prudent to develop new water quality criteria or modify existing criteria that will effectively protect designated and existing beneficial uses in certain water bodies as a result of site-specific analyses.

Site-specific criteria are allowed by regulation and, as with all criteria, are subject to EPA review and approval. As with all water quality criteria, site-specific criteria must be based on sound scientific principles to protect the beneficial use.

The following are acceptable conditions for developing site-specific criteria:

  • Resident species of a water body are more or less sensitive than those species used to develop a water quality criterion.
  • Biological availability and/or toxicity of a pollutant have been altered due to differences between the physicochemical characteristics of the water in a water body and the laboratory water used in developing a water quality criterion (e.g., hardness, temperature, or pH).
  • Seasonal changes to the physicochemical characteristics of a water body affect the biological availability and/or toxicity of a pollutant (seasonally dependent site-specific criteria).
  • Existing ambient water quality is not protected with statewide water quality criteria.
  • Other factors or combinations of factors that may warrant modifications to the criteria.

DEQ's procedures to derive site-specific criteria can be found in Idaho's water quality standards (IDAPA

Some site-specific criteria have been established for specific Idaho water bodies to reflect local environmental conditions.

South Fork Coeur d'Alene River Subbasin

Site-specific criteria have been established for cadmium, lead, and zinc in the South Fork Coeur d'Alene River (SFCDA) subbasin. The SFCDA subbasin site-specific criteria were developed using EPA's "resident species" approach that involved testing the toxicity of cadmium, lead, and zinc in actual site water near the headwaters of the SFCDA (upstream of pollution from mining activities) using native species that occur in the subbasin. The studies included toxicity tests with 14 species, including Westslope Cutthroat Trout, Shorthead Sculpin, mayflies, stoneflies, caddisflies, other insects, and snails.

The following DEQ technical documents describe the criteria derivation for cadmium, lead, and zinc and evaluate whether criteria developed for cadmium, lead, and zinc using species and water from the headwater reaches of the SFCDA subbasin are appropriate to apply to the lower SFCDA and tributaries.

Boise River

Site-specific criteria have been established for copper and lead in the Boise River. The Boise River site-specific criteria were developed using EPA's “water-effect ratio” (WER) approach that involved comparing the relative toxicity of copper and lead in river water and in lab water that was intended to represent the typical lab waters used by EPA to develop national criteria guidance. The WER studies used standard aquatic test organisms (Fathead Minnows and the water flea Ceriodaphnia dubia) in side-by-side comparisons in actual site (river) water and lab water. The following document describes this project in detail.

Snake River

On November 14, 2003, Idaho adopted a site-specific temperature criterion to protect fall Chinook Salmon spawning in the reach of the Snake River from Hells Canyon Dam to the Salmon River. That criterion is a maximum weekly maximum temperature of 13 °C, based on the EPA Region 10 recommendation to protect salmonid spawning, and applies from October 23 through April 15 of each year. EPA, after consultation with National Oceanic and Atmospheric Administration Fisheries, approved this criterion on July 20, 2004. 

In 2011, DEQ initiated rulemaking to revise Idaho’s water quality standards to modify the existing site-specific temperature criterion. The rule, which was approved by the Board of Environmental Quality and adopted by the Idaho legislature, established site-specific criteria of a maximum weekly maximum temperature of 14.5 °C from October 23 through November 6 and 13 °C from November 7 through April 15. Learn more.

Selenium Site-Specific Criterion Proposal for Streams Draining the Smoky Canyon Mine

On January 30, 2012, Simplot Corporation delivered to DEQ for the agency’s consideration a proposal for a site-specific selenium criterion and supporting technical documents. The proposal is for a fish egg/ovary criterion—with translation to whole-body tissue and water selenium concentrations as well—and would apply to certain streams draining Simplot’s Smoky Canyon Mine in southeast Idaho.

DEQ is reviewing the proposal and its supporting documents, after which, DEQ will make a decision to either proceed with rulemaking to adopt the selenium site-specific criterion as proposed, modify the proposal and then proceed, or request further information from Simplot before proceeding. DEQ's decision is currently pending EPA's release of their review of Simplot's Brown Trout toxicity testing and a national revision of selenium criteria.

If DEQ proceeds with rulemaking, at least one negotiated rulemaking meeting will be held. This meeting will be announced in Idaho’s Administrative Bulletin and will be open to the public. Based on the negotiations, DEQ could publish a proposed rule and take formal public comments or end the process.

The opportunities for public comment during rulemaking include the following steps:

  • Negotiated rulemaking meeting
  • Written public comments during the public comment period as announced in the Administrative Bulletin
  • Board of Environmental Quality rule review meeting
  • Before the legislative germane committees

All final water quality rules must be submitted to EPA for approval. Only with EPA approval would the site-specific criterion be effective for purposes such as §303(d) listing decisions, total maximum daily loads, or National Pollutant Discharge Elimination System permitting under the Clean Water Act.

Each step—initiation of negotiated rulemaking, proposed rule, pending rule, and final rule—is published in the Idaho Administrative Bulletin. DEQ also tracks the process on its website. Check back for further developments.


Staff Contacts

Water Quality Standards Lead
DEQ State Office
Water Quality Division
1410 N. Hilton
Boise, ID 83706
(208) 373-0502