Dames & Moore, 1999 - USDA Forest Service

elevated metals based on field screening methods, and the vehicle bridge north of the former mill facility.
The second EM line (EM-2) was completed in the western portion of the Site upslope from the valley
bottom and proceeded west to merge with the lower line.
The second area evaluated utilizing the EM survey methods was immediately east of tailings pile 3. The
EM line (EM-3) was nearly north-south in orientation, paralleling the seismic line E-E'. The results of the
EM survey are presented in Section 4.4.3.3 (under "Groundwater Flow in Native Materials" and
"Groundwater Flow in Western Portion of Site") and Appendix A.
3.3.1.7 Tailings Pile Surface Percolation Testing
Percolation tests were performed at three locations on tailings pile 2 to evaluate the infiltration rates of
water at the surface of the tailings piles. The three tests were located near or on seismic line C-C',
situated in a north-south direction west of the center of the tailings pile (Figure 3.3-2). One of the tests
was performed in the bottom of the surface water interceptor trench (installed by the USFS as part of the
tailings pile rehabilitation project) located in the southern portion of the tailings pile (DMTP-3). The
remaining two tests were conducted within the surface of the tailings piles (DMTP-1 and DMTP-2). Six-
inch-diameter steel pipes were placed vertically within the surface materials and falling head methods
were utilized. Constant head methods were 'not used due to difficulties in accessing a water supply
sufficient to provide a constant head. The results of the percolation tests completed by Dames & Moore
are presented in Section 4.4.3.1 under "Tailings Materials" and Appendix G. The results of percolation
tests completed by Hart Crowser in 1975 are presented 'in Appendix E.
3.4 TASK 4 - FLOCCULENT AND SEDIMENT
3.4.1 Railroad Creek and Lake Chelan Sediment
3.4.1.1 Railroad Creek i
Referring to Figures 3.4-1 and 3.4-2, the sediments within Railroad Creek have been evaluated by others
within the recent past (Johnson, et al, 1997; Huntamer, 1997; USGS, 1994). The data collected from
these studies were agreed upon by the Holden Mine RIIFS Technical Advisory Group to be sufficient and
of adequate data quality for use in RI characterization of Railroad Creek, and to preclude additional
sampling during the RI field programs.
3.4.1.2 Lake Chelan I
Sediment near the mouth of Railroad Creek, within Lake Chelan was evaluated by others in 1989
(Patmont, et al.).
Referring to Figures 3.0-1, 3.4-3 and 3.4-4, and Tables 3.0-1 (under "Sediment") and 3.2-5, sediment
samples were also collected by Parametrix, Inc., under subcontract to Dames & Moore in 1998 within the
Lucerne Bar portion of Lake Chelan, near the mouth of Railroad Creek, and at a reference location at
Stehekin (at the north end of Lake Chelan) to further evaluate sediment quality associated with sediment
transport from Railroad Creek. Twelve discrete samples (1-1 through 5-1) were collected at Lucerne Bar
(Figure 3.4-3). Seven of the samples were collected approximately 50 feet below the surface of the lake.
The remaining five samples were collected approximately 150 feet below the surface of the lake. The
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