B. Mack² and J. Skousen

Abstract

           Several measurements of acidity concentrations from 40 abandoned, above-drainage underground mines (34 Upper Freeport and 6 Pittsburgh coal seam) over 38 years were plotted against a range of acidity decay curves.  The objective of this study was to determine the average amount of acidity lost over time and the rate at which this loss occurs.  Ideal acidity decay curves of 2, 5, and 10% were used for this comparison.  Acidity values of the 34 mines that had mined the Upper Freeport coal seam were split into four different groups by the acidity concentration of the mine from the first sampling point.  An exponential trend line was drawn through the data to determine how well the groups matched the ideal decay curves.  Both the Pittsburgh and the Upper Freeport mines most closely matched the 5% decay curve.  Acidity values from the T&T #2 mine, which was closed 12 years ago, were also plotted against decay curves.   T&T most closely matched the 10% decay curve during its first 12 years after closure.  This is likely due to the relatively short time since mine closure of T&T compared to a longer period of 50-70 years since mine closure for the 40 sites.

Additional Key Words:  acid mine drainage, prediction, mine closure