Water Quality: Docket No. 58-0102-1801

This rulemaking has been initiated to update Idaho’s human health criteria for arsenic.

In May 2016, EPA entered into a consent decree with Northwest Environmental Advocates to reconsider EPA’s 2010 approval of Idaho’s human health criteria for arsenic. In September 2016, EPA disapproved Idaho’s human health criteria of 10 µg/L arsenic for both consumption of fish only and consumption of fish & water. The consent decree requires that EPA propose new human health criteria for arsenic by November 15, 2018, and that EPA either approve Idaho’s submittal of revised human health criteria for arsenic or promulgate federal criteria by July 15, 2019. In June 2018, EPA requested the court modify the dates in the 2016 consent decree. The court granted the request. The new dates are November 15, 2022, for EPA to propose and November 15, 2023, for EPA to finalize federal criteria for Idaho in absence of EPA approval of a criterion adopted by Idaho. This rulemaking will enable Idaho to adopt human health criteria for arsenic under state rulemaking and may prevent federal promulgation of criteria for Idaho by EPA.

The text of the rule will be drafted by DEQ in conjunction with a negotiating committee made up of persons having an interest in the development of this rule. DEQ will explore the use of updated arsenic toxicity information and bioaccumulation factors to derive human health criteria for consumption of fish only and consumption of fish & water using Idaho specific inputs for cancer risk factor and fish consumption rates. In addition, DEQ will collect ambient water quality data to determine background concentrations of arsenic in Idaho waters and potential feasibility of achieving ambient water quality criteria derived for arsenic. Idahoans that recreate in, drink from, or fish Idaho’s surface waters and all who discharge pollutants to those same waters may be interested in participating in this rulemaking

Upon conclusion of negotiations, DEQ intends to publish a proposed rule for public comment in the fall of 2022 and then present the final proposal to the Idaho Board of Environmental Quality (Board) in November 2022 for adoption of a pending rule. If adopted by the Board, the rule will be reviewed by the 2023 Idaho Legislature.