The proposal to delete the acute standard was based on the Division’s findings that the current state standard, which was derived from USEPA guidance, was not based on sound science. USEPA Region 4 commented on the proposed deletion and identified three options: (1) leave the current acute criterion in place and wait for release of any revisions to USEPA’s selenium criteria, (2) adopt the acute criterion from USEPA’s current national guidance, or (3) adopt an alternate criterion based on other scientifically defensible guidance.
In response, the Division conducted a survey of recent studies of selenium toxicity to aquatic species and determined that it was appropriate to develop state-specific water quality criteria for selenium. The agency is proposing an acute criterion for warmwater aquatic habitat of 258 ug/L, with an alternate calculation option depending on the sulfate concentration that is present. The proposed chronic criterion for warmwater aquatic habitat is 8.6 ug/g (dry weight) of whole fish tissue or 19.2 ug/g (dry weight) of fish egg/ovary tissue. The analysis of fish tissue is triggered when the water column concentration of selenium exceeds 5.0 ug/L. If the water column result is less than or equal to 5.0 ug/L, the water body is meeting is aquatic life uses. If the water column result is greater than 5.0 ug/L, then the next step is to determine whether the site is attaining the fish tissue or egg/ovary tissue criterion.
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