Department of
Environmental Quality

Water quality standards (WQS) adopted and submitted since May 30, 2000, are not effective for Clean Water Act (CWA) purposes until EPA approves them (see 40 CFR 131.21). This is known as the Alaska Rule.

Several sections of Idaho's water quality standards are under EPA review, and until these are acted upon, their use in CWA programs, such as National Pollutant Discharge Elimination System (NPDES) permits or Total Maximum Daily Loads (TMDLs), will not be approved by EPA. Instead, prior rules remain in effect for CWA programs. For state-adopted rules awaiting EPA action, the information presented below provides the previous rule language that is currently effective for CWA purposes. The rule section and date of publication are included in parentheses.

Toxics

Mercury - Aquatic Life

In 2005, Idaho adopted EPA's methylmercury fish tissue criterion for protection of human health. The decision was made to remove the old tissue-based aquatic life criteria and rely on the fish tissue criterion to provide protection for aquatic life as well as human health. Thus, published Idaho WQS do not have mercury water column criteria for the protection of aquatic life. While EPA approved Idaho's adoption of the fish tissue criterion in September 2005, it had withheld judgment on Idaho's removal of aquatic life criteria. On December 12, 2008, EPA disapproved Idaho's removal of the old aquatic life criteria (EPA disapproval letter). The water column criteria for total recoverable mercury summarized in the table below are effective for CWA purposes (IDAPA 58.01.02.210.01, 2004).

Cadmium - Aquatic Life

In 2006, Idaho adopted statewide site-specific aquatic life criteria for cadmium, revising the hardness-dependent criteria equations for cadmium in section 210.02 of the rules. In 2010, a rule was approved by the Idaho Legislature that lowered the cap on hardness for cadmium to 10 mg/L, which overcame EPA reservations about whether the new criteria were protective enough of aquatic life throughout Idaho. On March 9, 2011, Endangered Species Act (ESA) consultation was completed and EPA approved Idaho’s revised cadmium criteria (EPA approval letter). These approved criteria are reflected in Idaho's metals criteria calculator.

Various Compounds - Human Health

Idaho also updated the human health criteria for 88 chemicals in 2006. Until these criteria are acted on by EPA, the human health criteria published in the 2005 version of IDAPA 58.01.02.210.01 apply.

• Numeric Criteria for Toxic Substances (2005)

Temperature

Seasonal Cold

Idaho first adopted temperature criteria for the seasonal cold beneficial use (IDAPA 58.01.02.250.3) in April 2000. In 2002, Idaho revised its temperature criteria for the seasonal cold beneficial use.  These revised criteria are undergoing review at EPA.  Although the criteria adopted in 2000 have not been acted on by EPA, they were adopted by Idaho and submitted to EPA prior to May 30; therefore, these criteria are effective for CWA purposes per the Alaska Rule.  The effective temperature criteria for seasonal cold are:

Water temperatures of 27 degrees Celsius or less as a daily maximum with a daily average of no greater than twenty-four degrees Celsius.

Bull Trout

Idaho adopted bull trout temperature criteria in 1998. These criteria were revised in 2001 and the revisions are currently undergoing EPA review. Currently, the bull trout temperature criterion effective for CWA purposes is the federally promulgated temperature criterion of 10ºC (7-day average of maximum daily temperatures) for waters specified in 40CFR 131.33. For waters not listed in 40 CFR 131.33, the following 1998 criteria (IDAPA 58.01.02.250.02.f) are effective:

Water temperatures for the waters identified under Subsection 250.02.f.i shall not exceed twelve degree Celsius daily average during June, July and August for juvenile bull trout rearing, and nine degrees Celsius daily average during September and October for bull trout spawning.  For the purposes of measuring these criteria, the daily average shall be generated from a recording device with a minimum of six evenly spaced measurements in a twenty-four hour period.

i. The bull trout temperature criteria shall apply to all tributary waters, not including fifth order main stem rivers, located within areas above fourteen hundred (1400) meters elevation south of the Salmon River basin – Clearwater River basin divide, and above 600 meters elevation north of the Salmon River basin-Clearwater River basin divide, in the 59 key watersheds listed in Table 6, Appendix F of Governor Batt's State of Idaho Bull Trout Conservation Plan, 1996, or as designated under Sections 110 through 160 of this rule.

ii. No thermal discharges will be permitted to the waters described under Subsection 250.02.f.i, unless socially and economically justified as determined by the Department, and then only if the resultant increase in stream temperature is less than five-tenths degrees Celsius (0.5C).

Although these criteria were not acted on by EPA, they were adopted prior to May 30, 2000. Thus, these criteria are effective for CWA purposes, but only for a few water bodies not included in the federal rule. A list of water bodies not included in the federal rule is under development.