Dames & Moore, 1999 - USDA Forest Service

- Soil
Surficial materials at the Site south of Railroad Creek, except for the tailings and waste rock piles, are
primarily either soil or a mixture of soil and man-made fill material. Soil is composed of relatively
loose/sofi fine-grained material originating from weathered local bedrock and organic material. Fill is
composed of local soil plus rock, branches, stumps, and manmade artifacts which have been placed in
..;:conjunction with historic earthworks. Based on the results of borings (Appendix B) and test pit excavations
(Appendices C and E), the thickness of the soil unit varies from less than one foot to approximately 10 feet.
Colluvium
Colluvium is material deposited by gravity. Grain-sizes present in colluvium range from silt and sand
through cobbles and boulders. Colluvial deposits comprise the majority of surficial material in Holden
Village and much of the north bank of Railroad Creek opposite the tailings piles. Based on the borings
(Appendix B) and test pit excavations (Appendices C and E), colluvial deposits appear to underlie the
southern portion of tailings pile 3, as well as beneath Holden Village and the Winston home sites area. The
soil is noted as a mixture of low to moderate density, fine-grained soil with angular rock. The thickness of
the colluvium may be in excess of 20 to 30 feet in isolated locations.
Alluvium
Alluvium is material moved and deposited by the action of moving water. Material size ranges from silt- to
cobble- and boulder-size, and grains are usually rounded to subrounded. The density of the material
normally ranges from loose to moderately dense. Alluvium (as differentiated from alluvium/reworked till
described later) is limited in extent to areas beneath and adjacent to the current and recent channels of
Railroad Creek.
ail inns Materials
Tailings are fine-grained materials and are the by-product of the milling/processing operation. The tailings
are distributed along the south side of Railroad Creek in tailings piles 1, 2, and 3. The thickness of tailings
pile 1 appears to range from less than 10 feet near the southern edge of the pile to about 60 feet at the TPI-2
location. Tailings materials within the three piles are relatively loose to moderately dense mixtures of silt to
fine sand. The thickness of tailings pile 2 appears to range from 15 feet near the southern edge of the pile to
about 120 feet at the northern edge. The thickness of tailings pile 3 appears to range from 10 feet or less near
the southern boundary of the pile to approximately 70 feet along the northern edge. Tailings thicknesses are
based on boring logs (Appendices C and E) and interpretation of geophysical survey data (Appendix A).
The engineering properties of the materials were investigated by Hart Crowser in 1975, and by Dames &
Moore for the RI. The grain size of the material ranged from a silt (90 percent passing the No. 200 sieve;
0.075 mm) to a silty fine sand (approximately 40 percent passing the No. 200 sieve). The dry unit density is
approximately 11 0 to 11 5 pounds per cubic foot. The relative density based on the Standard Penetration
Test (SPT) conducted during the drilling and sampling completed by Hart Crowser was "medium dense."
The densities noted in test pits completed by Dames & Moore were qualitatively determined to range
between "loose" to "moderately compact." The moisture contents ranged from 15 to 30 percent. The shear
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