GROUNDWATER - SURFACE-WATER EXCHANGE IN AN ACID MINE DRAINAGE SETTING

The abandoned Green Valley Coal Mine, located NW of Terre Haute, IN, has been contributing to the poor water quality of the adjacent West Little Sugar Creek for over half a century. Most notably, the creek has low pH values and high iron concentrations as a result of runoff from the former mine despite reclamation efforts by the Indiana Department of Natural Resources. The goal of this project is to determine the relative contributions of groundwater and surface water to West Little Sugar Creek and the controls on the variability of flow from these sources. Groundwater was investigated through the installation of mini-piezometers to various depths at transects upstream and downstream of the points of confluence of surface channels from the site. The mini-piezometers were built based on the design of Baxter (2003, Am. Fish. Soc. v132). Water levels were monitored during varying weather conditions to see how the groundwater flow differed between periods of heavy rain and periods of little to no precipitation. Water samples were collected from these wells and then analyzed using atomic adsorption and ion chromatography.

The pH of water upstream of the site was commonly 8.2, and the pH of water of a surface spring was as low as 3.2. The pH of the stream generally decreased downstream heterogeneously. The pH of the water in the piezometers varied on the order of several pH units, but was generally less than the adjacent stream water. Elevated levels of iron and aluminum were found in the wells. When groundwater discharges into an oxygenating environment, these metals form various hydroxide complexes. Consequently, the majority of the streambed located along the coalmine site is encrusted with a thick layer of orange to red ferricrete. During periods of heavy precipitation, groundwater flow was significant compared to periods of little to no precipitation. Differences in hydraulic head were recognized in downstream wells, which confirmed that groundwater and surface water exchange was occurring. We believe that during periods of increased groundwater flow, contaminant levels in the stream increase causing further degradation in the water quality. This contamination has a negative effect on the nearby environment and community.