Dames & Moore, 1999 - USDA Forest Service

- Plants
Hazard quotients for plants (Table 7.2.4-6A) were calculated by dividing the UCL of soil concentrations in
Table 7.2.3-3A by the plant toxicity benchmarks in Table 7.2.3-3A. In the case of cadmium. copper, lead
and zinc, an alternative hazard quotient is calculated based upon the field data found in Table 7.2.3-3B. The
default assumptions were:
the soils used for the plant toxicity benchmarks have the same bioavailability of metals as
the site soils
the site plants are as sensitive as the plants used to derive the benchmarks
Table 7.2.4-6A shows that plants may experience toxicity from cadmium, copper, lead. and zinc in Holden
Village and the surface soils, subsurface soils, tailings piles 1,2 and 3, the lagoon and the maintenance yard.
When compared to median soil concentrations, copper exceeded the TRVs for plants exposed to copper in
all areas, and for lead in tailings pole 3 and in dust samples (Table 7.2.4-6B) However, when compared .
against soil metals concentrations from other mining sites where plants were found growing successfully,
TRVs were exceeded only for copper in subsurface soils, the lagoon, and the maintenance yard (Table 7.2.4-
6C). When compared against median soil concentrations, no soils exceeded the field data from other mining
sites (Table 7.2.4-6D).
It is not clear that many of the sampling locations provide adequate habitat for plants, because of the
physical qualities of the substrate. This is particularly true of tailings piles which are typically devoid of
the moisture required by plants. Plants are unlikely to inhabit dry soils even if no metals were present.
Therefore, although metals concentrations in these areas may exceed the plant TRVs, it is unlikely that
there is a complete exposure pathway for the plants or herbivores.
In the Holden Village soils, metals may be less bioavailable than in bioassay soils. Janssen et al. (1997a;
1997b) have recently shown that the bioavailability of metals in soils is governed by soil pH, amorphous
iron content, organic carbon content, and temperature (Marinussen et al. 1997). Therefore, the degree of
risk from copper is likely to be lower in soils containing high levels of amorphous iron and/or organic
matter, and higher where pH is low. Therefore, since these soils come from lawns and gardens that have
been amended with organic matter, the actual risk is likely to be less than the predicted risk, which was
already relatively low.
Earthworms
Hazard quotients for earthworms (Table 7.2.4-7A) were calculated using the UCL of soil concentrations
in Table 7.2.3-3A by the worm toxicity benchmarks in Table 7.2.3-3A. The default assumptions were:
the soils for the earthworm toxicity benchmarks have the same bioavailability of metals
as the Site soils
the site earthworms are as sensitive as the earthworms used to derive the benchmarks
earthworms would have been found at the Site in the absence of elevated levels of metals
Table 7.2.4-7A shows that some TRVs for earthworms were exceeded at all locations sampled. Only the
TRV for copper was exceeded by the median copper concentration (Table 7.2.4-7B) which is a more
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17693-005-019Uuly 27.1999,5:16 PMDRAFT FINAL RI REFORT