Southeast Idaho Phosphate Mining Resource Area - Agency for ...

growing on overburden dumps were greater than 4.0 mg/kg, which MW (1999c) used as the
preliminary risk-base benchmark for the potential development of chronic selenium in livestock.
Results of the vegetation and soil sampling done in 1998 were summarized in the 1998 Regional
Investigation Report (MW 1999c). The data suggest that waste rock dump seeps, french drains
below waste rock dumps, mine pits ponds, tailings ponds, sedimentation ponds and stock ponds
built from, or on top of, waste rock generally contained elevated selenium concentrations. Soil
and vegetation samples from waste rock dump seeps had elevated selenium concentrations (MW
1998). These data are being used by the Selenium Working Group for assessing ecological risk.
3). Animal Studies
A preliminary human health risk assessment, based on data collected during 1998, was
conducted by MW and was described in Chapter 5 and Appendix H of the final 1998 Regional
Investigation Report B Southeast Idaho Phosphate Resource Area Selenium Project (MW 1999c).
The assessment included risk statements about consumption of beef and fish. The assessment is
summarized in Attachment B. The report concluded, Athere is no substantial and immediate risk
to Y human Y health.@ Federal agencies responded with a disclaimer letter stating that they did
not agree with MW=s conclusions.
Several studies on wildlife are being done to help assess ecological risk. Some selenium
concentration data for elk and cutthroat trout are available and are summarized in this health
consultation (Table 1.0). Data on selenium concentrations in moose, deer, birds and other wild
game are not available. The Blackfoot River Basin is used extensively by resident populations of
moose, mule deer and elk year around. The migration patterns of the elk and deer are generally
east-west with winter range in the lower interior mountain valleys and summer range in the
upper drainages (BLM 1999). It may be that elk have higher concentrations of selenium than
other animals, and so provide a good basis for assessing risk from wild game. Unlike elk, moose
do not concentrate in specific wintering areas and are more widely dispersed in aspen and conifer
forest year-round (BLM 1999). Mule deer and moose live in the Resource Area but data on
selenium concentrations in muscle tissues have not been collected.
The preliminary ecological risk assessment in MW=s Remedial Investigation (1999c) suggests
that mallard ducks and moose are not affected by selenium in the area. However, fish, snipe,
muskrat, redwing blackbirds, sheep, horses and cattle may be at potential risk of being affected
by selenium. The United States Fish and Wildlife Service (USFWS) has expressed concerns that
selenium in Mabey Creek and Dry Valley Creek may pose a health risk to waterfowl and
shorebirds (BLM 1999).
Beef, elk and trout data were assessed for this health consultation because monitoring data for
these are available and their consumption would probably contribute the most to overall
exposure.
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