THE EFFECTS OF PRECIPITATION ON THE GEOCHEMISTRY OF ACID MINE DRAINAGE IN THE MAHANOY CREEK WATERSHED IN EAST-CENTRAL PENNSYLVANIA

Acid mine drainage (AMD), classified as the second largest threat to the environment by the United Nations, occurs as a direct consequence of flooding in abandoned coal mines. In the Mahanoy Creek Watershed (MCW) in east-central PA, there has been an ongoing problem of AMD for several decades, since multiple anthracite coal mines in the Western Middle Field were abandoned. This problem is further aggravated by an underground coal mine fire in Centralia that has been burning over forty years.

Water samples were collected along Mahanoy Creek and AMD sites throughout the MCW in 2010 and 2011. The samples were divided into four groups: (i) reference streams, (ii) tributaries, (iii) mine drainage sites and (iv) Mahanoy Creek. These samples were analyzed using ion chromatography to obtain concentrations of the major ions (sodium, potassium, magnesium, calcium, chloride, and sulfates). The concentrations of bicarbonate ions were calculated using AQUACHEM.

Based on these values, several trends were observed. The chemical signatures of the reference stream and tributaries remained relatively constant, thus validating the results in general. The major ions indicate that there is active weathering of silicate-rich rocks that may be exacerbated by AMD. The data indicate that there are high levels of sulfate in both sampling years, which possibly reflects the high content of AMD in the water. Interestingly, the samples from the mine drainage have relative higher amounts of bicarbonate ions in 2010 whereas they have elevated sulfate in 2011. The differences in the overall major ion ratios may have resulted from the higher than usual precipitation in 2011. The precipitation recharging the ground most likely caused the underground mine pools to overflow and released an increased amount of AMD, resulting in raised concentrations in the main waterways. Further results of this study and more detailed analysis will be presented at the conference.