Acidity of water from abandoned underground mines decreases over time, and the rate of decrease can help formulate remediation approaches and treatment system designs. Th e objective of this study was to determine an overall acidity decay rate for above-drainage underground mines in northern West Virginia from a large data set of mines that were closed 50 to 70 yr ago. Water quality data were obtained from 30 Upper Freeport and 7 Pittsburgh coal seam mines in 1968, 1980, 2000, and 2006, and acidity decay curves were calculated. Th e mean decay constant, k, for Upper Freeport mines was 2.73 × 10 −2 yr −1 , with a 95% confi dence interval of ± 0.0052, whereas the k value for Pittsburgh mines was not signifi cantly diff erent at 4.26 × 10 −2 yr −1 ± 0.017. Acidity from the T&T mine, which was closed 12 yr ago, showed a k value of 11.25 × 10 −2 yr −1 . Th is higher decay rate was likely due to initial fl ushing of accumulated metal salts on reaction surfaces in the mine, rapid changes in mine hydrology after closure, and treatment. Although each site showed a specifi c decay rate (varying from 0.04 × 10 −2 yr −1 to 13.1 × 10), the decay constants of 2.7 × 10 −2 yr −1 to 4.3 × 10 −2 yr −1 are useful for predicting water quality trends and overall improvements across a wide spectrum of abandoned underground mines. We found fi rst-order decay models improve long-term prediction of acidity declines from above-drainage mines compared with linear or percent annual decrease models. Th ese predictions can help to select water treatment plans and evaluate costs for these treatments over time.

Steel slag is a highly alkaline substance that is a byproduct of the steelmaking process. This substance has been used in many different applications, including the remediation of mine drainage. However, some research has shown that large concentrations of possibly toxic metals may leach from the steel slag matrix when it is used in this capacity.

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Abstract:The duration of acid mine drainage (AMD) flowing out of underground mines is important in watershed restoration and abandoned mine land reclamation projects. Past studies report that AMD flows from underground mines for hundreds of years with little change, while others find that poor drainage quality only lasts 20 to 40 years. In northern West Virginia, 20 above-drainage underground mines with AMD discharges were located and sampled during 1968, 1980, 2000, and 2005. Water flow, pH, acidity, Fe, Al, and sulfate were measured at all sampling times. From earlier work, 33 out of 44 sites (77%) were found to improve in drainage quality between 1968 and 2000. The results of the 2005 water sampling period confirmed these earlier findings. Out of 20 sites in the present study, only nine sites gave sufficient flow for water samples to be taken again in 2005. Of these nine discharges sampled in 2005, two showed a 22% and 32% increase of acidity, while the other seven sites (78%) decreased in acidity between 64 to 93%. Further sampling will quantify acidity changes of the original 44 above-drainage underground mine sites and more water samples will be collected during all four seasons of the year, which will represent both wet and dry periods. In this way, quantification of the effects of flow on underground mine chemistry may be evaluated.