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

/unt 1992 Cypnn TCC • Analysis o~Subsidrnct Efferu on Hydrology • S
Similaz observations were made during several studies of longwall mine subsidence impacts on
hydrology in Ohio and West Virginia completed by Hydro-Geo Consultants, Inc. (1988 and
1991). Typically, in wells installed within Zones 2 and 3, water levels declined during
undermining and returned to levels somewhat lower than pre-mining. The slight decline of the
water table after longwall mining wu attributed by these studies to limited increases in the
permeability of the water-bearing strata u measured prior to, and aher mining.
A study of subsidence effects due to longwall mining on hydrology in Marshal County, West
Virginia wu published by the U.S. Geological Survey (Schultz, 1988). In this study, ten
observation wells underlain by longwall panels were monitored prior to, and after mining.
Testing of three wells for transmissivity prior to, and aker mining, resulted in the finding that
transmissivity increued substantially after mining in two out of the three wells. The study also
concluded [hat changes in water levels prior to and after mining a:seeded ten feet in only two
of [he ten monitored wells.
Those cases where water levels decrease subsequent to undermining typically reflect increued
permeability of the water-bearing strata. The decrease of water level in most wells is
compensated for by increased well yields. Therefore, the slight deaeue of water levels aher
mining in some wells does not materially effect post-mining water availability.
An extensive study of ground water inflows for longwall panels and changes in hydraulic
conductivities induced by longwall mining wu conducted by researchers at the University of
Nottingham, England, (Singh, 1986; Singh, Hibberd and Fawcett, 1986; and Whittaker, Singh
and Neate, 1979). Their conclusions may be summarized u follows:
The main zone of appreciable change of in-situ permeability wu found to lie
be[ween the face of longwall operation and 40 meters (131.2 feet) behind the face
• Appreciable in-situ permeability changes were observed to occur up to 40 meters
(131.2 feet) above the extraction zone
• Changes in ground water flow properties of the effected strata were found to be
of stepped chazaaeristia. This wu thought to be due to opening and closing of
fractures and bed separations.
Studying effects of longwall mining at the Kushiro Mine in Japan, Nakajima (1976) found that
immediately subsequent to mining, the ratio of vaant space to vertical height in the caved roof
wu about 30%. Data gathered from boreholes in the gob two years after mining, indicated that
this ratio had dropped to an average of 6.2%. This indicates that signifiant reconso]idationhctd
taken place and that permeability wu greatly reduced over the two year period.
Conclusions from the referenced studies of subsidence related hydrologic impacts for longwall
coal mining operations can be summarized u follows:
Longwall induced subsidence create a zone of increased permeability above the
minedout area and within a IS to 25 degree angle of draw
• • Cracking and opening of fissures at the ground surface can occur within the zone
of tensile and compressive strain. However, the depth of such subsidence
fractures is limited
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