GROUNDWATER FLOW AND CONTAMINANT TRANSPORT THROUGH ZONES OF ENHANCED SECONDARY PERMEABILITY IN TWO KARST DRAINAGE SYSTEMS, USA

The Mitchell Plain and the eastern edge of the Crawford Upland in Southern Indiana are characterized by karst drainage features such as sinkholes, springs, caves and sinking streams. The development of karst in two areas of this region and how it affects groundwater flow and contaminant transport have been studied extensively. The formation of zones of enhanced permeability are generally a function of the joint and fracture intensity, thickness of the bedding and the material overlying the carbonate rock. Lemon Lane Landfill research has focused on the delineation and description of a karst drainage contaminated with polychlorinated biphenyls (PCBs). Studies using storm hydrograph separation techniques (stable isotopes), dye tracing and shallow surface geophysics have been initiated to understand groundwater contaminant flow. The contaminant transport occurs along the top of the soil/bedrock interface moving laterally until it encounters large vertical joints connecting to a conduit which discharge at Illinois Central Spring. The epikarst features in this area are developed in the middle Mississippian St. Louis and Salem Limestone. The Ammunition Burning Ground, located at the headwaters of Little Sulfur Creek, is the location for the demolition and disposal of ordnance. The karst conduit is developed in the Upper Mississippian Beech Creek Limestone that discharges at Spring A approximately one mile down Little Sulfur Drainage. The spring is contaminated with by-products of ordinance disposal such as RDX and TNT. The Upper Mississippian Beech Creek Limestone is capped by the Big Clifty Sandstone in this area. Development of karst is controlled by fractures and joints in the sandstone. Karst development is enhanced along joint intersections and more localized in this area compared to the large lateral epikarst development at Lemon Lane Landfill. A comparison of the results from studies such as hydrograph separations using stable isotopes, chemistry and dye tracing show that groundwater flow in the two karst systems are similar. This study provides information important to understanding groundwater flow and contaminant transport in different karst aquifers.