A COUPLED, DIRECT-PUSH APPROACH TO RESOLVING PREFERENTIAL FLOW AND CHLORIDE DISTRIBUTION IN THE EQUUS BEDS AQUIFER

The Equus Beds alluvial aquifer is the primary agricultural, municipal, and commercial water resource for a growing population center in Kansas, and is threatened by historic brine contamination. Because demand on the aquifer is expected to double, a large-scale artificial recharge system that includes infiltration basins, injection wells, and bank storage wells is being piloted. We examined four, high-resolution, direct-push methods for their ability to independently and collectively characterize hydrostratigraphic features that complicate recharge system designs and predictions of contaminant migration. Direct-push Electrical Conductivity (EC) and Hydraulic Profiling Tool (HPT) logs were obtained at five locations across a Cl^- plume. Discrete-depth, groundwater sampling and slug tests were performed using a 1-ft screened groundwater sampler at 15 depths adjacent to the logs. EC logs corroborate a previously established three-layer model for the site, and new EC models reveal detailed information about lateral variations in layer thicknesses and textures. A range of sample Cl^- concentrations (<20 to >2000 mg/L) allow the influence of fluid conductivity on the EC logs to be determined, and the establishment of Cl^- distribution models that demonstrate vertical, chemical stratification and lateral gradients. High hydraulic conductivity zones suggested by the EC and Cl^- models are supported by HPT and slug test results. A strong correlation observed between HPT and EC profiles in low Cl^- conditions is less significant where Cl^- is greater than 200 mg/l. Predictions of variations in hydraulic conductivity are supported by slug test estimates for K. Our results demonstrate that characterization of fine-scale stratification and chemical heterogeneity, such as that observed in coarse sand aquifers like the Equus Beds aquifer, can benefit from a multi-faceted, direct-push approach.