Dames & Moore, 1999 - USDA Forest Service

Wind-Blown Tailings
The approximate extent of wind-blown tailings material downwind and adjacent to the tailings piles was
mapped by utilizing relatively low altitude aerial photographs (USFS, 1997) and ground truthing. Five
surface soil samples (DMSS-20 through -24) were collected in areas outside of Holden Village but within
the borders of wind-blown tailings material (Figure 3.1-4). Four of the samples were collected
exclusively of the apparent tailings materials based on visual evidence of color and texture. One sample
was collected immediately below the layer of apparent tailings material to a depth of 5 inches below the
ground surface. The samples were all collected for metals analyses as presented on Table 3.1-1. The
results of the mapping of the wind-blown tailings are presented in Section 4.2.6. The results of laboratory
analyses are presented in Section 5.2.7.
3.1.2 Seismic Refraction Survey
Referring to Figure 3.1-2 and Table 3.0- 1 (under "Geophysical Survey Lines"), seismic refraction surveys
were performed by Northwest Geophysical Associates, Inc., subcontracted by Dames & Moore, to
determine the thickness of tailings materials, as well as the depth to bedrock. The location and orientation
of several of the seismic lines were changed to accommodate field conditions as compared to lines
specified in the SAP. A total of seven seismic lines were completed.
The seismic refraction lines were conducted in a generally north-south orientation across all three tailings
piles, as well as to the west of tailings pile 1, and east of tailings pile 3. One seismic line was performed
across the waste rock pile to the east of the abandoned mill facility. One seismic line was also completed
in a generally north-south orientation between tailings piles 1 and 2, adjacent to Copper Creek.
One seismic line was completed parallel to Railroad Creek adjacent to tailings piles 2 and 3. Three of the
lines (the westemmost, center, and easternmost lines) extended across Railroad Creek to the north. The
lines were extended upslope and downslope of the tailings piles when possible. Each of the lines was
surveyed in the field by a subcontractor (Erlandsen & Associates) to Dames & Moore. The results of the
seismic refraction survey are presented in Section 4.2.3.1 and Appendix A.
3.1.3 Exploratory Test Pits and Sampling
3.1.3.1 Tailings Piles
The primary purpose of the exploratory test pits was to visually characterize the conditions of the tailings
piles near the base and tops of slopes to support seismic and slope stability analyses. The SAP outlined a
program of three test pits on the tops of each tailings pile, a test pit at the toe of the northwest comer of
tailings pile 1, and a test pit at the toe of the northeast comer of tailings pile 3. Test pit locations are
shown on Figure 3.1-2. Due to access restrictions, the test pit intended for completion on the northwest
comer of tailings pile 1 (DMTPI-I) was not completed. Three test pits were completed on tailings pile 1
(DMTPI-2, DMTPI-3, and DMTPI-4) for geotechnical evaluation. Test pits on tailings pile 2 (DMTP2-
1 and 2) and tailings pile 3 (DMTP3-I through DMTP3-4) were completed for geotechnical evaluation as
well. The results of the geotechnical laboratory analyses are discussed throughout Sections 4.2.3 and
4.2.4.
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17693-005-019Uuly 19.1999;2:07 PM;DRAFT FINAL RI REPORT