Dames & Moore, 1999 - USDA Forest Service

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Creek was documented on a Howe Sound map dated 1937; however, the previous location of the streambed
in the area of tailings piles 2 and 3 is unknown. Each tailings pile was built by sequentially constructing a
perimeter dike, then discharging tailings slurry inside the perimeter dike (Figures 4.1-4 and 4.1-5). The dike
was constructed with "thickened" tailings, or waste rock material, recovered after mill processing, from
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which the majority of the extremely fine-grained fraction had been removed. This material was relatively
angular and allowed for the construction of slopes in excess of 50 degrees (ORB, 1975).
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The slurry that was not thickened was placed behind the perimeter dikes. Solids settled from the slurry, and
water was discharged from concrete decant towers in the southern portion of the impoundment. The drains
from the bottoms of the decant towers flowed through the tailings piles to Railroad Creek. When an
impoundment filled with sediment, the process was repeated so that the piles were raised sequentially.
Deposition of tailings for tailings piles 1 and 2 below the 3,200-foot contour was accomplished by gravity
flow from the mill facility. However, beginning in 1942, tailings required pumping from an installation near
the southwest comer of tailings pile 2. The pumping method for deposition was reportedly utilized for the
portions of tailings piles 2 and 3 above the 3,200-foot contour.
A discussion of each of the tailings piles is presented hereafter. A discussion of the chemistry is presented
in Sections 5 and 6.
Tailings Pile 1
Tailings pile 1 is located to the northeast of the mill facility and is estimated to cover an area of 25 acres.
The pile is bounded to the north by Railroad Creek, to the east by Copper Creek, and to the south by the east
waste rock pile and a natural, conifer tree-covered slope which climbs to the south. The surface of tailings
pile 1 is generally covered with rounded gravel. However, the southeastern and northwestern portions of the
pile are uncovered. The areas are apparently not covered with gravel due to the relatively steep slope angles
and the inability of the gravel to remain in place.
The tailings pile area is partially covered with plots of coniferous trees, some of which were reportedly
established in the 1960s and are estimated to be more than 10 feet tali. Some of the plots have been irrigated
and fertilized by USFS Forest Sciences Laboratory personnel (communications with George Shearer, USFS,
1997). Portions of the surface are also covered with miscellaneous woody debris in an attempt to increase
the success of revegetation (PNL, 1992).
Several swales or ditches are present across the pile. The swales were installed in the surfaces of all three
piles to limit surface water infiltration as part of the reclamation efforts completed by the USFS in 1989
through 1991. The swales are lined with a permeable geofabric and relatively small "rip rap" (rock used to
protect areas from surface erosion). Some of the rip rap has decomposed to a coarse sand.
The northern and eastern margins of the pile have relatively steep slopes leading down to Railroad Creek.
Site maps provided by the USFS indicate the maximum height to be approximately 40 to 50 feet. The angle
near the top of slope was approximately 45 degrees, with isolated slope segments approaching vertical. The
remainder of the slope is estimated to be less than 40 degrees. The slopes not covered with gravel are
estimated to be in excess of 45 degrees. An organic matting with grass seed has been placed over portions
of the slope for erosion protection. Grasses are growing out of some of the mats.
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17693-005-019Vuly 19. 1999:4:5 1 PM,DRAFT FINAL RI REPORT