Applying the HPT-GWS System for Evaluation of Managed Recharge in Unconsolidated Aquifers
During field work, subtle variations in the EC log across the coarse-grained aquifer were observed where the corrected HPT pressure log was flat. A strong relation also was observed between groundwater specific conductance and bulk formation EC in the coarse-grained aquifer facies. Modeling of field data found that the DP EC logs follow Archie’s Law in the aquifer facies even at the relatively low dissolved ion concentrations observed. Negative EC anomalies were observed where fresh water recharge was occurring below local storm water retention basins. Conversely, positive EC anomalies were observed where brine from the underlying shale bedrock was impacting the water at the base of the aquifer. These results demonstrate that the HPT-GWS can be used to define formation hydrostratigraphy at the centimeter-scale and sample for contaminants at multiple depths (profiling) in unconsolidated, permeable formations. The system also could be used to effectively assess seawater/brine impact and evaluate sites for placement of aquifer recharge basins or wells. Additionaly, the logs and profile samples may be useful in assessing the changes in groundwater geochemistry and extent of artificial recharge in unconsolidated aquifers.