REP01431

• Permit No: C1980007
• IBM Index Class Name: Report
• Doc Date: 5/5/1995
• Doc Name: 1994 ANNUAL HYDROLOGY REPORT
• Annual Report Year: 1994
• Permit Index Doc Type: HYDROLOGY REPORT
• Media Type: D
• Archive: No

•

2.0 HYDROLOGIC DATA INTERPRETATION AND
IMPACT ASSESSMENT FOR THE PERMIT
AND ADJACENT AREAS
This section focuses on three areas. First, it
analyzes the hydrologic data gathered during
WY 1994. Second, it assesses impacts of
mining on the quality and quantity of water
in surface streams, springs, groundwater
aquifers, mine inflows, and mine discharges
during WY 1994. Lastly, it estimates po-
tential impacts of mining on these waters
during WY 1995.
Data from the Colorado Agricultural
Experimental Station and College of
Engineering, Colorado State University
indicates that WY 1994 precipitation was
85 % of the 1961 to 1990 average.
Precipitation levels can affect surface water
and spring flow rate. It also has the
potential to influence mine water inflows in
areas of low overburden cover (i.e.,
Sylvester Gulch.).
2.1 ASSESSMENT OF MINE
WATER
The underground mining methods in use at
the West Elk Mine can affect groundwater
in essentially two ways. First, development
mining in areas where groundwater is pres-
ent in or near the coal seam can cause local-
ized movement of this water into the mine
workings. To date, groundwater movements
of this type have occurred in areas of low
cover which are highly fractured (near
outcrops and near stream channels) and
where sandstone channels bearing isolated
water immediately overlie the coal seam.
Secondly, retreat mining can cause subsi-
dence and the fracturing of overlying
groundwater formations. Again, water
usually moves into the mine workings. At
the West Elk Mine, the permeability of the
"F" and "B" seams and strata of the Mesa
R 1.210/ l0A/OS /05/95 (8:04am)
18
Verde Foundation overlying the "F" seam
and located between the "F" and "B" seams
is very low, and the areal extent and
quantity of water stored in these units are
small.
During WY 1994, the mine workings locat-
ed near the outcrop, the main portal area,
and along Sylvester Gulch behaved similarly
to previous years, relative to inflows. In-
flows occurred primarily from the roof in
areas of low overburden and near the "F"
seam outcrop. The seasonal pattern of mine
inflows observed at the main portal area and
along Sylvester Gulch indicates that the
colluvium, coal, and bedrock are unconfined
and recharge locally. The area along
Sylvester Gulch contains many naturally
occurring fractures. Water moves down
slope through the colluvium and fracture
zones and discharges as springs and seeps.
Water inflows appear to be controlled by the
amount of precipitation (mostly snowmelt),
depth of overburden, and location and extent
of fracture zones, and not by the extent of
the underground workings.
Mine water inflows for other areas of the
mine are related to site specific geologic and
topographic features as well as water-bear-
ing formations. Inflows of 35-50 gpm were
pumped from the Lone Pine area for
approximately three weeks. Mining activity
is dewatering the coal seam and local areas
of roof and floor fractures during mining.
Once initial dewatering is complete, there
appears to be no sustained flows. There
appears to be no correlation with seasons or
precipitation events. Water levels in
monitoring wells appear to be unaffected by