(1) For Lake Koocanusa and the Kootenai River mainstem, the standards specified in (6) and (7) supersede the otherwise applicable water quality standards found elsewhere in state law.
(2) Numeric selenium standards for Lake Koocanusa and the Kootenai River mainstem from the US-Canada international boundary to the Montana-Idaho border are expressed as both fish tissue and water column concentrations. When the aquatic ecosystem is in steady state and selenium data is available for both fish tissue and the water column, the fish tissue standards supersede the water column standard. When the aquatic ecosystem is in non-steady state, both the fish tissue and water column standards apply. The numeric selenium standards apply to the lake, to the river, or to both, as provided in this rule.
(3) As of December 25, 2020, Lake Koocanusa and the Kootenai River aquatic ecosystems are in non-steady state. The department will reassess the status of these aquatic systems triennially and amend this rule to reflect any change.
(4) The water column standards are derived from modeling selenium bioaccumulation in fish tissue and reflect criteria that protect the aquatic life beneficial use. Permit conditions and limits developed from the water column standards comply with the fish tissue standards.
(5) No person may violate the numeric water quality standards in (6) through (7).
(6) Fish tissue standards will be instantaneous measurements not to be exceeded. Fish tissue sample results shall be reported as a single value representing an average of individual fish samples or a composite sample, each option requiring a minimum number of five individuals from the same species. Fish tissue standards are applicable to tissues of fish in Lake Koocanusa from the US-Canada international boundary to the Libby Dam and in the mainstem Kootenai River from the outflow below the Libby Dam to the Montana-Idaho border. Egg/ovary tissue standards supersede any muscle or whole-body standards, as well as the water column standards in (7), when fish egg/ovary samples are available and when the aquatic ecosystem is in steady state. When fish egg/ovary samples are unavailable, and the aquatic ecosystem is in steady state, fish muscle or whole-body standards supersede the water column standards in (7).
15.1 mg/kg dry weight (dw)
11.3 mg/kg dw
8.5 mg/kg dw
(7) Water column standards are the numeric standards for total dissolved selenium computed as a 30-day average, and shall not be exceeded more than once in 3 years, on average.
(a) Lake Koocanusa from the US-Canada international boundary to the Libby Dam: 0.8 µg/L.
(b) Kootenai River mainstem from the outflow below the Libby Dam to the Montana-Idaho border: 3.1 µg/L.