GENERAL32987

• Permit No: C1981044
• IBM Index Class Name: General Documents
• Doc Date: 3/2/1984
• Doc Name: Revised Proposed Decision & Findings of Compliance
• Permit Index Doc Type: Findings
• Media Type: D
• Archive: No

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Water levels in the underlying regional rock aquifers, the Trout Creek
sandstone (Eagle No. 5 Mine) and the Twentymile sandstone (Eagle No.9 Mine),
show no signs of depletion. The Trout Creek sandstone is separated from the
Eagle No. 5 Mine in the "F" seam by 320 to 360 feet of shales, siltstones,
sandy shales, thin sandstones and coals. Ground water levels in the Trout
Creek sandstone show no evidence of dewatering into overlying mine workings.
Also, inflows through the Eagle No. 5 Mine's floor strata (underlying strata)
are very minor. The Trout Creek sandstone remains confined, as evident in the
continued artesian pressures sustained in the companies water supply well
completed in this aquifer.
Empire Energy Corporation has predicted no impact to the quantity of ground
water in the Twentymile sandstone through dewatering into mine workings. The
over and underlying strata have sufficient thicknesses and low permeabilities
to prevent the dewatering of the Twentymile sandstone aquifer into either the
underlying Eagle No. 5 Mine or the overlying Eagle No. 9 Mine. The
hydrograph, Figure III-17d of the permit application, for this aquifer shows
no water level declines, thus this aquifer is not being impacted by either the
Eagle No. 5 Mine or the Eagle No. 9 Mine.
Dewatering of the White sandstones may impact discharges to Yampa River/Big
Bottom stream/alluvial system and may cause dewatering of stream/alluvial
system. The applicant has addressed the interrelationship between the three
White Sandstones and the Yampa River/Big Bottom stream/alluvial system. The
applicant has made a worst-case projection of the current stream depletions
from the Yampa River by the Eagle No. 9 Mine. These projections were made
using an equation developed by McWhorter (1981). The depletion of stream flow
from the Yampa River was calculated to be 35 gpm from a combined "P" seam and
White Sandstone subcrop areas which are 1,737 feet in length and are 2,000
feet from the mine workings (page III-77a, revised 10/24/83). The stream
flows depletions through the "P" coal seam and the 3 White Sandstones are
expected to increase as the mine workings move closer to the subcrop areas and
beneath the Yampa River.
Mining in the Eagle No. 9 Mine could cause declines in alluvial ground water
levels in the Big Bottom alluvium. Dewatering the Big Bottom alluvium may
occur through the "P" coal seam, the White sandstones, and overlying
discontinuous, lenticular and interbedded sandstones of the Williams Fork
Formation. Communication between the ground water in the alluvium and the
Eagle No. 9 Mine workings may be enhanced by faults and subsidence induced
fractures. The dewatering of the alluvial body may impact flood and
subirrigation on the Big Bottom alluvial valley floor. The declines in
alluvial ground water levels could result from; 1) dewatering through faults
and fractures to the mine workings; 2) dewatering through subcrops of the "P"
coal seam and the affected over and underlying water-bearing strata; and 3)
reducing the quantity of ground water naturally discharging to the alluvium at
subcrops of rock aquifers by diversion of this discharge water into the mine
workings; and 4) dewatering through subsidence induced fractures.