Division of Water Proposes Changes to Water Quality Standards for Selenium

The Energy and Environment Cabinet is in the process of conducting a Triennial Review of Kentucky’s water quality standards. The cabinet’s proposed changes to the Kentucky water quality standards were published in the Administrative Register of Kentucky on Sept. 1, 2012. The cabinet received public comment on these standards through Oct. 1, 2012; a public hearing was held on Sept. 27, 2012.

Among the initial proposed amendments to the Kentucky water quality standards, the cabinet proposed to withdraw the acute water quality criterion for selenium. This action was based on the cabinet’s concern that Kentucky’s current acute criterion derived from U.S. EPA guidance is not scientifically sound or defensible. The cabinet proposed this change after evaluating relevant litigation, the EPA (2004) proposed draft national recommended selenium criteria, which was not finalized, and a substantial body of scientific studies of the toxicity of selenium to aquatic life which conducted after the cabinet adopted its current selenium criteria in 1990. The studies establish that the current acute selenium criterion in Kentucky is out of date with current knowledge and is in need of reconsideration.

EPA Region IV submitted comments regarding the withdrawal of the acute selenium aquatic life criterion and recommended the following three options to the cabinet:

  1. Leave Kentucky’s current acute criterion in place and wait for the release of any revisions to U.S. EPA’s criteria guidance;
  2. Adopt the acute criterion from U.S. EPA’s current national §304(a) recommended guidance; or
  3. Adopt an alternate criterion based on other scientifically defensible information.

The cabinet submitted a Statement of Consideration (SOC) to the Legislative Research Commission (LRC) on Nov. 14, 2012 responding to comments received regarding the water quality standards. In its SOC for 401 KAR 10:031, the cabinet left open the possibility of adopting the current national recommended acute criterion for selenium, or, alternatively, developing a state-specific criterion based on other scientifically defensible information, as suggested by EPA.

The cabinet subsequently conducted an evaluation of recent studies of selenium toxicity to aquatic species following which the cabinet determined it appropriate to develop state-specific water quality criteria. Therefore, the cabinet is proposing to amend the existing Kentucky water quality criteria for selenium. This action is responsive to public comments received, in particular U.S. EPA’s recommended option to “adopt an alternate criteria (sic) based on other scientifically defensible information.”

The cabinet is proposing a revised acute criterion for selenium consistent with the EPA (2004) proposed selenium criteria. The proposed Kentucky Water Quality Acute Criterion for Warm Water Aquatic Habitat for Selenium is 258 µg/L (footnote 1).

Footnote 1:  If the concentration of sulfate is less than forty-four (44) mg/L, the alternate acute water quality standard for selenium may be obtained by calculating the Criterion Maximum Concentration (CMC) using the concentrations of selenite and selenate as follows: CMC = 1/[f1/CMC1) + (f2/CMC2)], where CMC1 is 258 µg/L for selenite and CMC2 is e(0.5812 [ln (sulfate)] + 3.357) µg/L for selenate, and f1 is the fraction of total selenium that is selenite and f2 is the fraction of total selenium that is selenate.

With regard to the chronic criterion for selenium, the available data indicate that the mode of chronic toxicity effects on fishes is based primarily on dietary uptake rather than aqueous concentration. Therefore the cabinet’s proposed chronic criteria are based on exposure of fishes to selenium through diet. The cabinet is proposing a tissue-based chronic criteria, adopting the option to assess whole-body fish tissue or, alternatively, to assess fish egg/ovary tissue. The cabinet incorporated studies with data derived from taxa native or naturalized to Kentucky and taxa that serve as surrogates to native species. The chronic criteria will be implemented via a threshold water column concentration of total selenium of 5.0 µg/L, which is the current Kentucky and USEPA chronic criteria for selenium.

The proposed Kentucky Water Quality Chronic Criteria for Warm Water Aquatic Habitat for Selenium* is 8.6 µg/g (footnote 2,3) or 19.2 µg/g (footnote 4).

Footnote 2: This value is the concentration in µg/g (dry weight) of whole fish tissue.
Footnote 3: A concentration of 5.0 µg/L or greater selenium in the water column shall trigger further sampling and analysis of whole-body fish tissue or alternately of fish egg/ovary tissue.
Footnote 4: This value is the concentration in µg/g (dry weight) of fish egg/ovary tissue.
*These proposed values are derived based on species native or naturalized to Kentucky waters or which serve as appropriate surrogates for native fish species.

The cabinet provided a proposed agency amendment to LRC on Feb. 5, 2013 which amends 401 KAR 10:031 to incorporate these new Kentucky water quality criteria for selenium. The letter to LRC explaining the background for this amendment and a technical document detailing the technical rationale for the amendments to the Kentucky water quality criteria can be found at: http://water.ky.gov/waterquality/Pages/WaterQualityStandards.aspx

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