REV106617

• Permit No: C1980007
• IBM Index Class Name: Revision
• Doc Name: FORMAT AND SUPPLEMENTAL INFORMATION
• Type & Sequence: RN1
• Media Type: D
• Archive: No

A revised projection of mine inflows and resulting surface water depletion
for the Life of mine is given in response [o question V. A. 9. below,
These projections are based on actual observations and data collected from
the mining operation and are therefore thought to be more reliable than
previous projections. The results of these revised calculations indicate a
life of mine operations may result in maximum projected depletion from the
Dry Fork of Minnesota Creek Basin of about 130 gpm from interception of
snowmelt runoff during the spring period and about 110 gpm from
interception of shallow groundwater, springs and streamflow associated with
the fracture zone of the creek valley. The latter depletion would be
applicable throughout the year and thus could be considered a perennial
inflow or depletion. The projections axe based on conservative assumptions
and represent maximum anticipated depletions. Actual depletions are
expected to be considerably less than these projections.
After 5 years of mining at the Mt Gunnison No. 1 Mine there will be no
anticipated depletion of water from the Minnesota Creek Basin. The results
of the analysis provided in new Table 2.8.S.J, "Projected Mine Inflows and
Stream Depletions Mt. Gunnison Mine #1," in response to question V. A. 9.
indicate that the first potential for depletion would occur in 1992. This
is consistent with mine inflow observations through 1985 which show no
aquifer inflows or cone of depression associated with mining under the high
overburden cover near the surface divide between the North Fork Gunnison
Rivet and Dry Fork Minnesota Creek.
(This answer is referred to in the answers to questions: V. B. 9; V. D. 1,
S, 8, 13, 29, and 30; 3/17/86 question #1.)
• 8. "High rates of inflow were noted in wells along the Dry Fork of Minne-
sota Creek and Lick Creek. The Creeks in the North Fork Valley are
known to be fault controlled. Since other mines in the North Fork
Valley have experienced increased inflows while mining under creeks the
wells may indicate zones of higher permeability. From data obtained
from these monitoring wells how much mine inflow can be expected when
these creeks are undermined? Additional wells properly installed along
Minnesota Creek will aid in this determination."
Creeks in the North Fork Valley are believed to be related to zones of
higher fracturing but not faulting. Ground water inflows in the Mt.
Gunnison Mine adjacent to Sylvester Gulch are interpreted as being a result
of the higher bedrock permeability associated with such fracture zones,
The existing mine inflow data were used in formulating a revised model for
projecting mine inflows for the life-of-mine case. The model assumes
higher vertical permeability in the vicinity of fracture-controlled creek
valleys. The basis and results of the model are described ir, more detail
in the answer to question V. A. 9 below.
The projected mine inflows and resulting surface and shallow ground water
depletions are mainly dependent on the value of average vertical
permeability assumed for the Barren Member. In stratified bedrock
formations the vertical movement of groundwater is primarily controlled by
the units having the lowest vertical permeability. Even when permeability
is fracture-controlled there is usually some lithologic influence on
fracture propagation and continuity. Consequently, the vertical
• permeability values that would be most appropriate for the estimation of
V-15