Modernizing Deep Groundwater Testing: Rapid Stacked-Dynamic Profiling with Long Screened Test Wells

The tracer flowmeter and depth-dependent sampler (TFDDS) has been used to characterize flow and chemistry in hundreds of public supply wells. The TFDDS surveys address production and water quality compliance issues for utilities facing mounting treatment costs. Surveyed wells often show a stratified distribution for constituents of concern that were underestimated and poorly discretized using conventional zone testing in the pilot hole. Elevated concentrations of metals, semimetals, and radionuclides typically occurring at or near lithologic boundaries between fine- and coarse-grained sediments are missed since the primary focus of the zone test is to estimate the yield of the permeable sediments that are centered within a coarse unit. To minimize the risk of constructing new wells that fail to produce compliant drinking water relative to regulatory standards, we propose a new approach that vertically stacks flow and mass balance chemistry profiling of long screened test wells (LSTWs) under pumping conditions prior to installing the more costly public supply well. This approach integrates the TFDDS with a spectrum of drilling methods to rapidly provide hydraulic and chemistry data. A detailed distribution of anthropogenic and geogenic constituents within the saturated zones is produced, characterizing both permeable sediments and contaminant-laden boundaries between finer- and coarser-grained deposits. Applying this high-resolution data to well design leads to informed predictions on whether the new well will be compliant. Two case studies are presented, one for public supply well design and the other for managed aquifer recharge.