Quantification of the Factors Influencing the Performance of Hydraulic Barriers in Western Pennsylvania Underground Coal Mines

Present regulations prohibit surface-water-impairing discharges from abandoned underground coal mines. However, some recently abandoned mines in western Pennsylvania have experienced unplanned, high-flow discharges. The Surface Mining Control & Reclamation Act of 1977 requires underground coal mines with acid-forming potential to mine down-dip, establishing a protective barrier capable of containing the resultant mine pool. The primary factors responsible for the performance of ‘down-dip’ hydraulic barriers are complex and influence the design process.\ud This investigation characterizes down-dip coal barriers and produces a set of general guidelines or recommendations applicable to ‘down-dip’ barrier design. To identify factors influencing barrier performance, several detailed case studies are examined.\ud Case studies of the Solar 7 & 10, Little Toby, Dora 6, Grove 1, and Penn View mines were investigated. The research included detailed analysis and select modeling of hydraulic coal barriers constituting both successful and unsuccessful performances in western Pennsylvania underground coal mines. The analysis shows that the following factors impact the performance of hydraulic coal barriers:\ud • Primary Factors\ud o Geology,\ud o Extraction ratio,\ud o Hydraulic conductivity, and\ud o Overburden thickness\ud \ud • Secondary Factors\ud \ud o Hydraulic gradient\ud o Barrier thickness\ud \ud These factors were quantified to provide guidelines to safely engineer a barrier given a set of conditions. Ultimately, this analysis will aid industry, responsible for designing these structures, and regulatory agencies, responsible for approving these designs, to utilize observations from this analysis to reduce the potential for high-flow discharges from abandoned coal mines.\u