Report of Investigations--KGS

Abstract

Use of water in abandoned underground coal mines for municipal, industrial, agricultural, or domestic water supplies is dependent upon the water quantity and quality. For either of these factors, the requirements of the user will play a role in what water quantity or quality is acceptable. This report provides analysis of field-derived water-quality and -quantity characteristics for six abandoned underground coal mines in the Eastern Kentucky Coal Field. In addition, some ancillary data from State regulatory agencies were used to help characterize water quality coming from the mines.

This study demonstrates that water quality in abandoned deep mines can be quite variable. Water-quality characteristics vary from mine to mine because of the position of the mine within the groundwater flow system, the mineralogy of the coal seam and the enclosing bedrock, and the time elapsed since the mine was flooded. Total dissolved solids values ranged from 194 to 2,016 µS/cm. Based on TDS, coal mines in the Manchester and Upper Elkhorn No. 3 coals produced the poorest water quality. In the study area, these seams were mined below the elevation of local drainage. The increase in TDS is a result of increased mineralization of groundwater caused by relatively slow movement and increased age of the water in the distal ends of the groundwater fl ow system. Another water-quality factor to consider in below-drainage mines is the length of time since mine closure. The time since closure and subsequent flooding of the mine is important because the reduction of acid-generating salts depends on the amount of time available for flushing. For these reasons, water quality should be analyzed for each potential water source, even within a given mine. Water-quality monitoring must include sampling and analysis during water-withdrawal testing to identify any changes in quality associated with induced mobility of otherwise slow-moving to stagnant water within a mine.

Water quantity from abandoned deep mines varies greatly, depending on many variables that control flooded volume of and recharge rate to the mine. Major variables controlling groundwater discharge from a mine are the surface area overlying the mine, the position of the mine within the local and regional groundwater systems, and the structural geology of the site, which determines how groundwater drains from the mine. Recharge rates ranged from 120,000 to 1,230,000 gal/day; however, some deep mines showed net losses in storage because of lack of recharge during drought periods.

This study demonstrates that water quality and quantity in abandoned deep mines are suitable for water supplies. Both quantity and quality are variable between mines, however. Variations can be attributed to geologic controls, physical setting, the age of the mine, and the rate of flushing. Therefore, water quality and quantity must be analyzed for each potential mine source, and must be analyzed throughout the time of water withdrawal.

Publication Date

2006

Series

Series XII

Report Number

Report of Investigations 12

Digital Object Identifier (DOI)

https://doi.org/10.13023/kgs.ri12.12

Funding Information

Partial funding for this study was provided by the Kentucky Infrastructure Authority.

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