Use of Direct Push Logging and Sampling to Characterize a Groundwater Recharge Plume

This presentation details field work to characterize groundwater in the area of a recharge basin located in an unconsolidated alluvial aquifer. Direct push logging techniques were used to differentiate recent groundwater recharge from background waters and to obtain samples for measurement of water quality indicator parameters to depths exceeding 90 feet. Logging and sampling at this site were performed using a groundwater profiling tool which gives simultaneous logs of soil electrical conductivity (EC) and hydraulic profiling tool (HPT) injection pressure as well as permitting multi-level groundwater sampling. The EC and HPT logs provided information about lithology and relative permeability to guide selection of sampling zones. Water quality parameters (specific conductance, pH, ORP, and DO) were monitored to stability as purging was conducted at each sample interval. This combined logging/sampling tool was used at several locations around the recharge basin to show the thickness of the groundwater recharge lens. Logs from this project clearly demonstrate the utilization of combined EC and HPT logs to identify the interface between recent recharge waters and background aquifer water, and between fresh aquifer water and intruding brines found at the base of the alluvium. The specific conductance data from the groundwater profile samples confirmed the HPT and EC log interpretation and provided additional data on water quality.