Dames & Moore, 1999 - USDA Forest Service

4.2.8 Potential Borrow Source Areas
Remedial strategies may require methods to improve protection From wind and stream erosion processes,
and mass inovement hazards. For example, riprap may need to be placed in specific areas due to river
rerouting, places where it is now absent but required (e.g., slope reach 1-A), or supplemented in river
reaches with present low quality riprap (see Section 4.2.7, Existing Railroad Creek Riprap). In addition,
remedial work (e.g., revegetation, recontouring, etc.) of tailings may require a local soil cover source. A
preliminary assessment of potential borrow source areas was conducted to achieve the following objectives:
4.2.8.1 Sand and Gravel
Identify potential accessible sources of riprap within the Railroad Creek drainage basin
Identify potential accessible sources of soil cover within the Railroad Creek drainage basin
Summary of Historical Findings
The gravel currently covering the tailings piles was placed during the 1991 site reclamation efforts. The
gravel reportedly originated from a gravel pit developed at "Dan's Camp" (Figure 4.2-23). Other than the
"Dan's Camp" pit utilized by the USFS previously, no onsite sources of granular borrow material were
identified during the review of historical information,
RI Findings
A borrow source evaluation to identify potential sources of sand and gravel was conducted as part of the RI.
The scope of work included the initial review of geologic maps and aerial photographs for the Railroad
Creek watershed from the Glacier Peak Wilderness boundary down to Lucerne. The objective of the
assessment was to identify a source or sources of granular borrow material as close to the Site as possible.
The gravel pit area at Dan's Camp was assessed visually and appears to be a good source of sand and gravel.
The material exposed in the gravel pit was estimated to be a gravelly sand to sandy gravel, with relatively
low percentages of silt. However, this source is approximately seven miles from the Site.
Referring to Figure 4.2-25, on September 30, 1997, six test pits were excavated in two potential source
areas: (1) three pits east of tailings pile 3 (DMTP3E-4 through DMTP3E-6), and (2) three pits along the
slopes south of the' three tailings piles (DMTP I S- I, DMTP2S- 1, AND DMTP3S- 1). A second objective of
the test pits completed south of the tailings piles was to characterize the near-surface groundwater
conditions in the native soil. The test pit logs are presented in Appendix C. Soils in the test pits were
described generally following USCS standards and were evaluated with respect to approximate grain size
distribution (i.e., percent boulders, cobbles, sands, and fines), maximum boulder size, and range of boulder
sizes.
The onsite potential borrow areas may be adequate sources for soil cover, particularly for elements of the
Site which may require siltier soils. For general tailings pile slope cover, some sorting would be necessary
to sifi out the coarse fraction (which may be suitable as a riprap supplement) and the fine fraction (to
prevent wind transport).
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17693-00Sd19Wuly 19. 1999;4:51 PM;DRAFr FINAL RI REPORT