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Dames & Moore, 1999 - USDA Forest Service

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Sediment<br />

Railroad Creek and Site<br />

Historical and 1997 sediment data were segregated to represent sediments in Railroad Creek within the area<br />

of influence from the mine, sediments in Railroad Creek downgradient of the Site, and sediments within<br />

Copper Creek. There was insufficient data to calculate area background concentrations for sediment in<br />

Railroad and Copper Creeks; however, background ranges are presented in the screening tables for<br />

comparison purposes. It should be noted that analytical data from the various sampling events are not<br />

always comparable. The detection limits and range of detection appear inconsistent for some events. even<br />

though the samples were presumably analyzed by the same method. However, for the purposes of<br />

screening, all sample data were combined. It should also be noted that screening criteria for soil ingestion<br />

were applied to sediment data due to a lack of sediment cleanup levels. The exposure assumptions used in<br />

the soil ingestion cleanup levels (i.e., ingestion of 100 mg/day) are expected to significantly overestimate the<br />

potential risks based on ingestion of sediment.<br />

Railroad Creek Adiacent to Site<br />

The results of the screening for this exposure area are presented in Table 7.1-23. Based on the screening,<br />

aluminum, arsenic, beryllium, chromium, manganese, and molybdenum were selected as IHSs. However,<br />

aluminum, beryllium, chromium and manganese were within the range of background concentrations<br />

measured in Railroad Creek.<br />

Railroad Creek Downmdient of Site<br />

The results of the screening for this exposure area are presented in Table 7.1-24. Based on the screening,<br />

aluminum, beryllium, chromium and manganese were selected as IHSs. However, beryllium and<br />

manganese were within the range of background concentrations measured in Railroad Creek.<br />

Couwr Creek<br />

The results of the screening for this exposure area are presented in Table 7.1-25. Based on the screening,<br />

beryllium, chromium and manganese were selected as IHSs. However, concentrations of all of these<br />

constituents were within the range of background concentrations measured in Copper Creek.<br />

Comer Creek Diversion<br />

The results of the screening for this exposure area are presented in Table 7.1-26. Based on the screening,<br />

only chromium was selected as an IHS. However, the concentration of chromium was below the range of<br />

background concentrations measured in Copper Creek.<br />

Surface Water and Fish<br />

As with sediment, historical and 1997 surface water data were segregated to represent conditions in Railroad<br />

Creek within the area of influence from the mine, Railroad Creek downgradient of the site, and Copper<br />

Creek. Area background concentrations of total metals in surface water were statistically derived in Section<br />

5. For the purposes of the screening, analytical results for total metals were evaluated because total metals<br />

content is more appropriate for evaluating health risks than filtered (dissolved) metals content.<br />

~.\~pd.n~m~\rrpofi\h01do~2~\7-0<br />

doc 7-2 1 DAMES & MOORE<br />

17693-005-0 19Uuly 27,<strong>1999</strong>;s: 16 PMDRAFT FINAL RI REPORT

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