Report of Investigations--KGS

Abstract

An investigation of the hydrologic effects of longwall coal mining is in progress in the Eastern Kentucky Coal Field. The study area is located in a first-order watershed in southern Leslie County over Shamrock Coal Company's Beech Fork Mine (Edd Fork Basin on the Helton 7.5-minute quadrangle). Longwall panels approximately 700 feet wide are separated by three-entry gateways 200 feet wide. The mine is operating in the Fire Clay coal (Hazard No. 4); overburden thickness ranges from 300 to 1,000 feet. Mining in the watershed began in late summer 1993. Undermining of the instrumented panel (panel 7) is anticipated for summer 1994. This report documents pre-mining hydrogeologic conditions.

Three sites over panel 7 (ridge-top, valley-side, and valley-bottom settings) were selected for intensive monitoring. An NX core hole was drilled at each site to provide stratigraphic control for well installation, to evaluate fractures, to conduct pressure-injection tests, and to provide a borehole for installation of time domain reflectometry cables. A rain gage and flume were installed in the basin in summer 1992. Twenty-four monitoring wells, completed in July 1992, provide water-level and water-quality data on individual stratigraphic zones represented by the three well locations.

Interpretation of pre-mining conditions was used to develop a conceptual model of ground-water flow in the study basin. Three ground-water zones were identified on the basis of hydraulic properties. The shallow-fracture zone, a highly conductive region parallel to the ground surface, extends to a depth of 60 to 70 feet. The elevation-head zone includes the ridge interior, mostly above drainage, where total head consists of elevation head only. The pressure head zone, largely below drainage, is the region where total head is the sum of elevation head and pressure head. Two fresh-water geochemical facies are also present. Shallow ground water is a calcium-magnesium-bicarbonatesulfate type, whereas ground water in the deeper regional system is sodium-bicarbonate type.

Anticipated effects from longwall mining include a decrease in water levels in the pressure-head zone. Temporary decreases are expected in the shallow-fracture zone as newly created void spaces subsequently fill. The elevation-head zone should not be greatly affected because it is predicted to be in the aquiclude zone.

Publication Date

1995

Series

Series XI

Report Number

Report of Investigations 9

Digital Object Identifier (DOI)

https://doi.org/10.13023/kgs.ri09.11

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