GENERAL48692

• Permit No: C1981019
• IBM Index Class Name: General Documents
• Doc Name: Proposed Decision & Findings of Compliance
• Permit Index Doc Type: General Correspondence
• Media Type: D
• Archive: No

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Description of the Environment
The mine site is located in an upland area at an average elevation of
7,300 feet. Land use in the permit and adjacent area is primarily rangeland-
and wildlife habitat. There is some dryland farming on level uplands,
and small areas of irrigated pasture and hayland along stream courses
in the general area, Rangeland on the permit area is characterized as good
condition sagebrush and mountain shrub range that, in the past, was variously
grazed by either sheep or cattle during the spring, summer, or fall. The
rangeland also supports substantial populations of mule deer, elk, sage
grouse and numerous other wildlife species at various time throughout the
year.
The site lies just west of the northward flowing Good Spring Creek, which
is paralleled by Colorado Highway 13. The area is a gently sloping upland
ranging from about 7,640 feet near the southwest corner, to 6,560 feet near
the northeast corner. Valleys that cut into the surface are generally narrow,
v-shaped, and about 250 to 500 feet deep with valley wall gradients of
40 to Z00 percent. North of the proposed mine site, the topographic surface
is dominated by two ridgelines about two miles long, trending north-northeast,
bounded by Good Spring, Taylor and Wilson Creeks.
The permit area lies about six miles south of the axis of the Axial Basin
Anticline, a Large west-northwesterly-trending fold. The axis of a parallel
subsidiary fold, the Co1Zom Syncline, trends southeasterly through the
northeast part of the permit area. Bedding orientation generally has an
east-west strike and is characterized by dips from nearly horizontal to as
much as 20 degrees to the north. Overburden material consists of a mixture
of shales, claystones, siltstones, and sandstones.
Coal seams mined at Colowyo are in the Williams Fork Formation of the Mesa
Verde Group. The Williams Fork Formation consists of alternating beds of
sandstone, sandy shale, carbonaceous shale, and coal. The geology section
of the permit application describes ten coal seams in a 392 foot interval
of the formation which are recoverable by surface mining techniques. The
Williams Fork Formation has been estimated to be 1600 feet thick in the
vicinity, and is underlain by the ridge-forming Trout Creek Sandstone member
of the Isles Formation. Four Lower coal beds in the Williams Fork Formation,
which can be mined only by underground methods, are described in the Northwest
Colorado Environmental Statement, Site-Specific Analysis.
Bedrock ground water at Colowyo occurs as isolated, perched aquifers in the
interbedded and lenticular sandstones and coals. Base flow in the two perennial
streams in the general area is mainly ground water discharge from the
alluvial aquifers in the stream valleys, Stratigraphically, the Trout Creek
Sandstone is the first major, regional aquifer in the area. It is approximately
800 feet beneath the Lowest coal seam to be mined. The principal recharge
for the aquifer is to the south of the permit area in the headwaters of
Taylor and Good Spring Creeks. There is no continuous, regional ground water
system on the permit area above the flood plain of Good Spring Creek. Infor-
mation contained in the permit application and the Northwest Colorado EIS
indicates that, in test holes drilled by W.R. Grace and Company, and the USGS,
no saturation was encountered in any of the beds that are to be mined.