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Arsenic and Old Fish: Idaho Initiates Negotiated Rule Making in Response to 2016 Settlement Agreement

Posted By Johanna M. Bell, Monday, May 7, 2018
Updated: Wednesday, May 2, 2018

In 2010 Idaho adopted 10 µg/L as the numeric criteria for Arsenic for both fish
only and fish + water exposures. This value was based on the Safe Drinking Water Act (SDWA)
Maximum Contaminant Level (MCL), and was chosen, in part, because of concerns about
background levels in Idaho waters that exceed the US Environmental Protection Agency’s
(EPA’s) national recommendation for Arsenic. EPA approved the 10 µg/L criteria in 2010.

In May 2016, EPA entered into a consent decree with Northwest Environmental Advocates (NWEA) to reconsider EPA’s 2010 approval of Idaho’s human health criteria for Arsenic. In September 2016, EPA disapproved Idaho’s 10 µg/L Arsenic human health criteria 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 an Idaho submittal of revised human health criteria for Arsenic, or promulgate federal criteria, by July 15, 2019.  DEQ had been waiting for scientific updates to EPA’s “IRIS Toxicological Review of Inorganic Arsenic” in order to more accurately promulgate standards reflective of risk to human health. However, in an effort to avoid promulgation of federal Arsenic criteria for Idaho, DEQ has initiated rulemaking to revise the human health criteria for Arsenic.

Idaho’s average total Arsenic groundwater concentrations have been shown through multiple studies to be 85 to 340 times higher than the EPA-recommended national water quality criteria for Arsenic for fish only (i.e., 0.14 µg/L) and over 660 to 2,600 times higher than the criteria recommended for fish + water (i.e., 0.018 µg/L). Furthermore, Idaho Department of Water Resources studies have shown that more than 25% of drinking water samples collected in Southwest, South Central and West Central Health Districts exceed 10 µg/L Arsenic – which suggests background Arsenic levels within those basins likely far exceed EPA’s recommended criteria. 

Preliminary review of the Arsenic Settlement Agreement impacts to the Idaho NPDES (or pending IPDES) permits indicate that essentially ALL issued permits will be affected and likely out of compliance long into the future under EPA’s proposed standards.  

Idaho is a headwaters state with some of the most pristine and sought-after water resources in the world. The fact that virtually all of these world-class water resources have background concentrations of Arsenic that exceed the fish only and fish + water human health criteria proposed by EPA should provide an adequate reason for both DEQ and EPA to question the appropriateness for implementing low-level standards based on theoretical calculations. Native Americans, along with every succeeding human population in Idaho, have long been exposed to these naturally-occurring Arsenic concentrations that far exceed EPA’s proposed water quality standard.


Idaho’s update to the human health criteria for Arsenic should protect our community members, the environment, incorporate achievable and affordable water quality requirements, and be coordinated with the drinking water program.  AIC understands that universal access to safe drinking water and safe fish supports our communities’ wellbeing and economic development.  AIC believes it is important to implement a statewide approach to address the risks to human health from Arsenic, and that a successful statewide approach will take the following into consideration:
  1. In many locations in Idaho, potable ground water sources of Arsenic are greater than surface water concentrations.
  2. Removal of Arsenic from wastewater treatment/recycled water to levels several orders of magnitude less than 10 µg/L is not technically feasible.
  3. Human health exposure to Arsenic is dominated by Arsenic in drinking water sources.
  4. High Arsenic concentrations in surface water bodies that lead to measurable concentrations of Arsenic in fish tissue are likely correlated with the basin’s geologic conditions; thus, a review of the combined fish + drinking water threat to human health within these basins would likely be nearly equivalent to exposure from drinking water sources alone.

For the full set of initial AIC comments submitted, please click HERE.

Staff Contact: Johanna M. Bell

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