Dames & Moore, 1999 - USDA Forest Service

Robins drink only the UCL concentrations from Railroad Creek
the modeled earthworm metal concentrations were accurate
Table 7.2.4-13A shows that Robins could be at risk from cadmium in the subsurface tailings. lagoon, and
maintenance yard, and fiom zinc in the subsurface soils, tailings pile 3, the lagoon, and the maintenance
yard, and from lead in the lagoon and maintenance yard.
When robins were exposed to the median concentrations in the subsurface soils. and tailings pile 3, there
was no risk from either cadmium or zinc (Table 7.2.4-138). It is highly likely that the input parameters for
the robin vastly overestimate the actual exposure conditions because risk was also shown for robins feeding
on earthworms exposed to site background concentrations of cadmium and the risk characterization does not
account for robins relatively large forage ranges.
However, because of the limited data for the lagoon and maintenance yard soils, it was not possible to
further estimate risk in these areas. It should be noted however, that since earthworms were not observed in
the areas where metal concentrations were elevated, it is likely that there is not a complete exposure
pathways to robins in these areas.
Little Brown Bat
Hazard quotients for little brown bats feeding on emergent aquatic insects (Table 7.2.4-14) were calculated
by dividing the doses estimated in Table 7.2.3-1 8 by the TRVs in Table 7.2.3-4B. The default assumptions
were:
bats fed only on aquatic insects From Railroad Creek
bats drink only the UCL concentrations from Railroad Creek
the modeled insect metal concentrations were accurate for Railroad Creek
It is apparent that little brown bat is not at risk from consumption of emergent insects or surface waters
(Table 7.2.4-14). Therefore, there was no need to further evaluate risk to bats along Railroad Creek.
7.2.4.2 Modifying Factors
Because the most difficult aspect of risk characterization is the quantification of the effect of home range on
exposure, median exposure concentrations were used. However, is should be noted that the red-tailed hawk,
and mule deer also move seasonally. The red-tailed hawk is only a visitor during the summer months and
then migrates to Central and South America. Although the mule deer does not migrate per se, it does move
to lower elevations during the winter when snow fall exceeds its ability to reach grasses and forbs, or to
move about easily. The little brown bat is only active during the summer, and hibernates during the winter.
While mink do not migrate or hibernate, the onset of cold weather is likely to reduce the consumption of
aquatic species. This assures that none of the terrestrial ROCs will be exposed to the worst case or median
exposure conditions used for risk characterization in Section 7.2.4.1 above.
G:\~W)~\bolda1-2\n17-O.dos 7-70
17693-005-01 9Uuly 27.1999:J: 16 PMDRAFT FINAL RI REPORT