Dames & Moore, 1999 - USDA Forest Service

utilizing a "Schmidt" hammer, or a hammer which applies energy to the rock and measures relative
resistance. The results of the evaluation are presented in Section 4.2.8.
3.1.5 Geologic Hazards Assessment
Referring to Figure 3.1-7, this task included the collection of field data for the evaluation of seismic, slope
stability and erosion potential, and a riprap investigation.
3.1.5.1 Seismic Potential Assessment
As noted above, a total of nine trackhoe excavations were completed to assess the engineering
characteristics of the Site soils and tailings materials. The results were utilized to analyze the potential for
liquefaction and slope instability of the tailings materials during a seismic event (earthquake). The data
collected from the excavations included the relative density of the material and grain size, as well as the
presence or absence of saturated conditions within the tailings materials completed both on top and near
the toes of the tailings piles.
Data from geotechnical engineering-related laboratory testing (grain size and moisture content per ASTM
Method D2216-92 and D422-63) of soil samples collected in the field, downhole geophysical surveys
conducted by a subcontractor to Dames & Moore (Northwest Geophysical Associates, Inc.) in selected
wells (TPI-4A, PZ-2A, and PZ-SA), as well as data generated by others (Hart Crowser, 1975) were
analyzed for use in computer analysis of liquefaction potential, as described in Section 3.1 1.1.1. The
results of the assessment are presented in Section 4.2.4.1.
3.1.5.2 Tailings Pile Slope Stability
Referring to Figure 3.1-7, the slopes of the tailings piles facing Railroad Creek were evaluated in'the field
in terms of their potential for mass movement. The methods utilized were generally consistent with the
guidelines established in the Mass Wasting Module of the Washington State Department of Natural
Resources (WDNR) Watershed Analysis Manual (version 3.1) for Level 2 analysis. The field program
focused on evaluating the slopes adjacent to Railroad Creek. The field program included the
documentation and mapping of slope angles, soil types, consistency of soil surface, and indications of
slope instabilities. In addition, a cursory evaluation of the avalanche chute south of tailings pile 3 was
conducted using the same methodologies. The field findings were analyzed in conjunction with computer
slope stability analyses which also incorporated field and laboratory data collected by others, as described
in Section 3.1 1 .I .2 (Hart Crowser, 1975). A summary of field findings and slope stability analyses are
presented in Section 4.2.4.2.
3.1.5.3 Erosion Potential Assessment
The slopes of the tailings piles facing Railroad Creek were also evaluated in the field in terms of their
erosion potential. The methods utilized were generally consistent with the guidelines established i the
Surface Erosion Module of the Washington State Department of Natural Resources (WDNR) Watershed
Analysis Manual (version 3.1) for Level 2 hillslope erosion analysis. The field program focused on the
evaluation of slopes adjacent to Railroad Creek. The field program included completing backhoe test
trench excavations (noted above under Section 3.1.3) and the documentation and mapping of slope
angles, soil types, consistency of soil surface, and indications of hillslope erosion. The field findings
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