Longevity of acid discharges from underground mines located above the regional water table.

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.