PERMFILE52447

• Permit No: C1982056
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: Exhibit 45 Fish Creek AVF/Stream Study Hydrologic Analysis
• Media Type: D
• Archive: No

Augwrt 1991 Cj~y.,a TLC • AnJytB of SwGddenn Effects on H~drologl ~ 7R
• The extent of the three zone of increased permeability depends on the thickness of the mined
strata and the lithologic composition of the overlying rock units In the Foidel Creek Mine ua
the mined Wadge coal seam overburden consists of 75% weak, elastic chiles, siltstones, and
laystones, and 25% strong, brittle sandstone and coals. Based on an extracted coal thicknes
of approzimately 8.5 to 9.5 feet and the high percentage of elutic shale in the Wadge coal seam
overburden, the following thicknesse for Zones 1, 2, and 3 were estimated for the study acct:
Zone 1 - 3.5 t 30 - 33 feet
Zone 2 - 10.0 t 80 - 95 feet
Zone 3 - 40.0 c 340 - 380 feet
The geologial composition and eaten[ of the five zone of potential impacts on rurfaa and
groundwater hydrology due to longwall mining ue shown on Figure 3. This cross-settion is
perpendicular to Panel b in the acct of Fish Creek. Review of this figure indicates thu only
water-bearing sandstone in the overburden immediately overlying the Wadge and Lennoz coal
seams ue within the zone of increased permeability due co subsidence.
The volume of actual water inflow into the Foidel Creek Mine confirms the extent of the zone
of inaeued permeability. Calculation of groundwater inflow into the Foidel Creek Mine, based
on the urumption that sandstone between the Wadge coal seam and upper Lennoz coal seam
(nluding the Lennoz Sandstone) are drained, indiata that inflow should amount to
approzimately lit gpm. This calculation used the 'Large Well' method of calculation of
groundwater inflow into horizontal workings (Mazimov, ed., 1975). This alculated inflow is
. conservative given meuured average mine inflows of about 90 gpm. It does, however, indicate
that the eaten[ of subsidence relazed groundwater effects will be consistent with projections
developed using the same alculation methods. In evaluating projected rubsidena related
groundwater impacts, it is important to recognize [hat if Zone 3 (Figure 4) eztended to the
Twentymile Sandstone, looted approzimately 600 feet above the Wadge coal seam, actual mine
inflows would be substantially higher.
Two monitoring wells (006.87-1 and 006-88-2) were installedw [he overburden immediately
above the Wadge coal seam. Both wells were completed within Zone 1 where severe suing due
to subsidence would be ezpeaed.
During groundwater monitoring activitiu in May 1989, an obstntction wu noted in Well 006-
87-1 indicating collapse or shearing of the using which preluded funhu monitoring activities
This failure ocwrred approzimuely three months prior to initiation of longwall mining in the
acct. Bued on the location of the obstruction, failure of Well 006.87-1 is believed to be due to
naturally otturring sheu resulting from swelling of the shah u the contact betwew the
Twentymile Sandstone and the underlying marine shales
Well 006.88-2, located itttmediately above the longwall eztrution acct, wu disrupted following
initiation of lognwill mining consistent with projected subsidence effects.
Bued on the above discussion, potential impacts of longwall mining in Panels 5 and b on the
Fish Creek illuviil aquifer will be limited to Zone 4, u shown on Figure 3. This zone of
horizontal eztension could develop above the limiu of the longwill panels and within an angle
• of draw of approzimately 17 degrees Impacts on groundwater within this zone could oaur if
rurfidil sacks develop. Due to the fine grained rltancter of the alluvial sediments, however,
the potential for development of rutfidil cracks is limited. Several stadia of longwill mining
~,"'„q ~ A t~ Inc. • P.O. Bar 77I01I • Suonbou Springy, Colordo YW77 •/303)87%260