Dames & Moore, 1999 - USDA Forest Service

Water seepage emanates, in the spring, from the base of the northern and northwestern portions of the
tailings pile, near Railroad Creek. Cemented sand and gravel exists in the immediate area near the level of
Railroad Creek at the northwest comer of the pile.
A series of steel pipe monuments designed to protect the groundwater monitoring wells was noted across the
surface of the pile. The groundwater monitoring wells were reportedly installed by contractors to the USFS
during two separate events in 199 1 (PNL) and 1995 (USBM).
The remnant of a decant tower was observed in the southern portion of the pile, immediately east of the east
waste rock pile (Figure 4.1-5b. Grout was not observed and surface water was flowing into the feature
during spring snowmelt. Based on a review of construction drawings completed for the Forest Service
tailings rehabi~itation.~roject between 1989 and 1991, it appears that each tailings pile had decant towers
which were identified for filling with grout; however none of the drawing shows the apparent remnant of a
decant tower noted herein on tailings pile 1.
Tailings Pile 2
Tailings pile 2 is located to the east of tailings pile 1, and is estimated to be 45 acres in size. The pile is
bounded to the west by Copper Creek, to the north by Railroad Creek, and the east by a slope which leads to
tailings pile 3, and the south by a natural, conifer tree-covered slope which climbs to the south. The surface
of the pile is generally covered with rounded gravel. Relatively young coniferous vegetation are present on
the surface. Some grasses were reportedly drilled into the surface of the pile and growth appears to be
relatively successful; however, it is understood that fertilizers and lime are necessary to promote growth
(personal communication with Keith Anderson, formerly of the USFS, 1996). Some mature coniferous
trees are present near the edges of the tailings pile, near the top of the slopes leading to Copper Creek and
Railroad Creek; the trees apparently reseeded naturally. Portions of the surface are also covered with
miscellaneous woody debris in an attempt to increase the success of revegetation (PNL, 1991). Other
experimental test plots are also present.
Two interceptor ditches trend across the southern portion of the pile which drain mostly to the southeast
comer of the pile, eventually flowing into Railroad Creek after crossing the southern margin of tailings pile
3. Like the ditches on tailings pile 1, they are lined with a permeable geofabric and small rip rap; some of
the rip rap has decomposed to coarse sand. A series of steel pipe monuments associated with the
groundwater monitoring wells also exist across the surface of the pile.
The northwestern, northern and eastern margins of the pile have relatively steep slopes leading down to
Copper Creek and Railroad Creek. The maximum height is noted on Site maps to be approximately 120
feet. The maximum angle near the base of the slope is estimated to be in excess of 55 degrees near the
confluence of Railroad Creek and Copper Creek. The remainder of the slope is estimated to be on the order
of 40 to 45 degrees. The slopes steeper than 45 degree are generally not covered with gravel. An organic
matting with grass seed had been placed over portions of the slope. Grasses were observed growing out of
some of the mats.
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17693-005-019Vuly 19. 1999;4:51 PM;DRAm FINAL RI REPORT