POSSIBLE SEWAGE BUFFERING OF ACID MINE DISCHARGE IN MAHANOY CREEK WATERSHED, EAST-CENTRAL PENNSYLVANIA

The Mahanoy Creek Basin, a tributary of the Lower Susquehanna River, is located in east-central Pennsylvania. The Western Middle anthracite coalfield underlies 27% of its watershed area. The long-term anthracite mining in the region has degraded the watershed through acid mine drainage, resulting from water interacting with the surface mine waste or flowing through the abandoned underground mines. Some coalmines are hydrologically interconnected, and the water flows to the surface by either tunnel outlets or surface seeps.

In July 2010, field parameters were measured, and samples collected at locations along Mahanoy Creek, its tributaries, and several acid mine discharge sites. Three tributaries are considered reference streams for this study. The reference tributaries’ pH and temperatures range from 5.49 to 6.75 and from 17.5 to 23.0°C, respectively. Along Mahanoy Creek, the pH varies from 5.14 to 8.07, and the temperature ranges from 13.3 to 19.8°C. The mine drainage from the Centralia Mine Tunnel is acidic (pH 3.77-3.80; temp: 17.5-20.8°C) while the East Potts Mine Seep is near neutral (pH 6.94; temp: 15.2°C).

With 34 known sources of acid mine drainage into Mahanoy Creek, the pH of the main stem is higher than expected (pH 5.14-8.07). The pH could reflect the interaction of Mahanoy Creek with the direct discharges of raw sewage and leaky sewage disposal systems throughout the watershed. Another possibility is that groundwater and water-rock interactions may be buffering the acid mine drainage in Mahoney Creek, as indicated by the East Potts Mine Seep.

The preliminary data indicate that the reference streams have very low levels of the major ions and are suitable to serve as background. The acid mine drainage samples have concentrations that are several times higher than background. As Mahanoy Creek flows westerly, a rapid rise of ions begins after Gilberton. At one-third of the sites, fluoride levels illustrate that there is some influence of sewage on the stream. As sodium and chloride (in meq/L) do not balance, the excess sodium may indicate that sewage is either directly discharged or leaked into Mahanoy Creek. Through the contribution of calcium and magnesium, sewage may be buffering the acid mine drainage from the regional abandoned mines and increasing the overall pH of Mahanoy Creek.