ABSTRACT
Site characterization studies have been performed for a 36-Ha facility in Muscle Shoals, Alabama, which is approximately 6 km upgradient of a 150,000 m3/day domestic spring. Overburden at the site consists of > 15 m of clayey residuum underlain by karstic Tuscumbia Limestone. Hydraulic tests at the site included pumping tests, borehole flowmeter surveys, and slug tests in both the residuum and bedrock. Additional field work included dye tracing, photo lineament surveys, cone penetrometer tests, and permeameter tests on selected cores in the overburden. Results of dye tracing on and around the site indicate groundwater velocities of up to 350 and > 4,400 m/day, respectively. Well tests and flowmeter logs show that an important stratigraphic influence on groundwater transport is a 1 to 2 m thick weathered zone at the overburden/bedrock contact. This zone, designated as the epikarst zone, consists of residual chert fragments with some silty clay matrix. Lineament analysis and karst geomorphic features indicate that groundwater movement within the lower bedrock is controlled by a joint system with a rectilinear orientation. An elongate basin mapped from well logs using the Chattanooga Shale as a marker is correlated with major lineament trends and is oriented in the direction of the 150,000 m3/day spring. A conceptual model for the bedrock aquifer at the site includes two distinct flow regimes. The upper layer [epikarst zone] consists of 1 to 2 m of highly interconnected solution features with local transmissivities as high as 46 m2/day. The lower zone consists of a >15 m bedrock interval with local transmissivities being highly variable, and primarily controlled by the interconnectivity of discrete solution-widened fractures.
