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the pit fills, and surface drainage channels to quickly carry this flow toward Pond 16 should help dewater
<br />and stabilize the poorly compacted, saturated fill material around the unstable Pond 16 area.
<br />If possible, you, I, or a qualified representative of NWCC should observe the excavation above the
<br />existing road, in the area below the shrub plot. I have lingering concerns about the stability of
<br />excavations into the toe area of the enormous fills to the northeast and southeast of Pond 16A and the
<br />shrub plot. It would be prudent to do this work in the late fall, when water levels are at or near their
<br />annual low and strengths are likely to be higher.
<br />Stock Tank T -25 and area above Pond 017. The plan for this area includes removing the pond above
<br />the area of current instability (Stock Tank 25), and improving road drainage to reduce infiltration. Some
<br />soil from erosion or a slump has flowed into Pond 017 from below the light use access road, reducing the
<br />pond's capacity. I understand that the pond has excess capacity, so even if minor sedimentation were to
<br />continue, the pond's utility as a water quality /detention pond would be preserved.
<br />No action will be taken to repair or stabilize the other slide areas that we observed at Seneca II West,
<br />either because they occur in undisturbed areas of pre- existing instability and can be attributed to normal
<br />surface processes and geology, because no structures are threatened, or because they will be repaired in
<br />conjunction with other planned work such as road narrowing, realignment or reclamation. These include
<br />the two slides within the C and D Pits, in the vicinity of stock tanks T -18 and T -20, several slides and
<br />slumps along roads in the Pond 006 area, the very large, low -angle slide that disrupted the light use
<br />Ridgeline Access Road, The slump and surface fracture above Pond 017, and several small non - landslide
<br />scarps that can be attributed to settlement of fill placed against the highwall.
<br />References
<br />Colton, R.B., Holligan, J.A., Patterson, P.E., and Anderson, L.W., 1975, Preliminary map of landslide
<br />deposits, Craig 1 degree x 2 degrees quadrangle, Colorado: U.S. Geological Survey, Miscellaneous
<br />Field Studies Map MF -700, scale 1:250000.
<br />Madole, R.F., 1989, Surficial geologic map of the Meeker 30'x 60' quadrangle, Garfield, Moffat, Rio
<br />Blanco, and Routt Counties, Colorado: U.S. Geological Survey, Miscellaneous Investigations Series
<br />Map I -1823, scale 1:100000.
<br />Tweto, Ogden, 1976, Geologic map of the Craig 1 degree x 2 degrees quadrangle, northwestern Colorado:
<br />U.S. Geological Survey, Miscellaneous Investigations Series Map I -972, scale 1:250000).
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