Does longwall mining have a detrimental effect on shallow ground water sources?

Longwall mining typically affects the entire overburden rock mass from the unit immediately above the coalbed being mined to the ground surface. It is natural to assume that any water-bearing zones contained within this interval may be influenced to some degree. In some cases, a complete loss of water may be experienced and in others an increase in the hydrologic properties may occur. To address this apparent dichotomy, the US Bureau of Mines is conducting a comprehensive program of subsidence research in select mining areas of the United States. One such site was located in Vinton County, Ohio where two contiguous longwall panels were designated as a study area. The two longwall panels measured approximately 900 ft wide and 9,000 ft long. The thickness of the extracted coal was about 55 inches. The longwall panels were separated by five entries or approximately 350 ft. Overburden thickness in the study area varied from 200 to 350 ft. To evaluate the effects of mining, seven, 8 5/8-inch diameter observation wells were drilled at critical positions above the longwall panels. Water level fluctuations, surface subsidence and hydrologic properties were measured as mining progressed through the study area. Results of this study show mining of both longwall panels did not interrupt the hydrologic regime. This paper provides a detailed case study delineating the timing and effects of mining on local shallow ground water sources