Development of a vadose zone advanced monitoring system: Tools to assess groundwater vulnerability

Abstract

Performing repeat pore‐fluid sampling over long time‐scales can provide valuable information on unsaturated zone contaminants and their potential flux to ground water. This information can be used to manage groundwater remedies and identify contaminants that need to be sequestered in the vadose zone to minimize flux to ground water. Pore‐water samples are commonly used to obtain contaminant concentrations within the vadose zone, but existing methods are limited as they only provide a single sample at one location and time. The vadose zone advanced monitoring system (VZAMS) has been designed to integrate multiple technologies into a single down‐borehole system that allows for sampling of pore fluids (liquid and gas) to provide information about contamination and hydraulic conditions at multiple depths (∼0.3‐m intervals) within a cased borehole. Testing has been completed at the laboratory scale to verify the sampling elements of VZAMS, including geochemical testing for representative contaminants known to exist at the Hanford Site, located in southeastern Washington State. Physical tests focused on the ability of the sampler to draw fluid under unsaturated conditions. Initial geochemical testing showed that the stainless steel material used with the porous cuff may affect the sampled concentrations of redox‐sensitive contaminants under very dry conditions. Additional laboratory testing demonstrated that the VZAMS components are able to collect representative samples for substances of interest under expected field conditions. In this paper, the design and functionality of a novel instrument are demonstrated in support of subsequent testing in the field.

Interpretation of large‐scale, long‐term electrical geophysical monitoring guided by a process simulation

“…One way to understand contaminant flux is by conducting a geochemical and microbial analysis of cores, but this analysis is limited because the data are restricted to a single point source location and a snapshot in time. Recent sensor development aimed at in situ sampling of pore water and/or soil gases shows promise (Linneman et al., 2022), but these data are confined to borehole locations. There is a need to acquire spatially dense information to advance the understanding of contaminant flux in the vadose zone, for which a limited number of borehole samples are not representative of the whole subsurface environment.…”