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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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