GENERAL41258

• Permit No: C1981034
• IBM Index Class Name: General Documents
• Doc Date: 6/14/1993
• Doc Name: PROPOSED DECISION & FINDINGS OF COMPLIANCE FOR RN2
• Permit Index Doc Type: FINDINGS
• Media Type: D
• Archive: No

not be in direct contact with the unconsolidated
glacial/alluvial material. The applicant has determined
that significant vertical permeabilities do not exist in
the strata near the mine (see pages 20-35 of Volume 8).
Therefore, vertical infiltration of leachate from the
refuse pile into underlying aquifers should not be a
significant problem.
No predictions of specific quality are available;
however, experience at backfilled areas in northwestern
Colorado suggest that a rough estimate of volume can be
calculated from an acreage analysis. Given 21 acres of
disturbance at Red Canyon, peak spoils discharge could
reach 30 gallons per minute following snowmelt. This
value probably overestimates the discharge, given the
lower precipitation regime near Cedaredge.
b. Surface Water Effects and Mitigation
Three probable impacts to the surface water regime have been
identified by the applicant. During the active mining phase,
mine dewatering may have lessened the volume of water dis-
charging to the streams from the alluvium and could poten-
tially have caused a gradient reversal. The discharge of
mine inflow water would change the location of groundwater
discharge to the surface water system and result in a
degradation of water quality. Following sealing of the mine,
and the reestablishment of the coal aquifer, discharge of the
mine water to the glacial-alluvial aquifer could result in a
diminution of water quality of the adjacent streams.
Some depletion of the stream/alluvial aquifer system could
occur through the coal seams themselves which subcrop beneath
the Williams Creek and Ward Creek valleys. Groundwater
movement in the permit area discharges to the stream/alluvial
aquifer system. Mining will dewater adjacent portions of the
coal seam aquifer and will intercept some of the groundwater
currently discharging to the stream/alluvial aquifer system.
In addition, the presence of the underground workings beneath
the valley could reverse the pre-existing groundwater flow
direction between the valley and the mine workings, and water
from the stream/alluvial aquifer system could enter the mine
workings through the coal seams. This reversal of ground
water flow direction would occur only in areas where the coal
seams are fractured.
The applicant has provided a prediction of inflow to the mine
for the D and E coal seams on a yearly basis. The maximum
predicted inflow, 78.67 gpm (0.17 cfsl in 1983, provides an
estimate of worst-case streamflow depletion. One-third of
the measurable mine inflows in the E seam mine were found in
the area below ward Creek. Little inflow was observed below
Williams Creek. The effect will be temporary, since once the
workings become flooded, discharge will once again be to the
surficial aquifer via the subcrop.
Since some of the ground water inflow comes from other
sources, such as depletion of ground water storage, the
actual stream flow depletion would probably be less than
predicted. Actual inflow in Mine No. 1 (E-Seam) never
exceeded 25 gpm. The applicant's modeling estimates that two
years after ground water removal begins, the total volume of
water intercepted by the mine would be taken directly £rom
the stream. The addendum reports that the minimum streamflow
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