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A Low-Cost, In Situ Resistivity and Temperature Monitoring System
Citation:
Sherrod, L., W. Sauck, AND D. D. WERKEMA. A Low-Cost, In Situ Resistivity and Temperature Monitoring System. GROUNDWATER MONITORING AND REMEDIATION. National Ground Water Association, Westerville, OH, 0(0):1-27, (2012).
Impact/Purpose:
While long-term geophysical monitoring provides a useful tool for the interpretation of subsurface hydrological properties and processes, the cost is often prohibitive. Resistivity measurements have long been utilized in hydrology as a non-invasive measurement technique. Whether utilized for determining water table depth (Reed et al. 1983), or observing preferential flow paths (Narbutovskih et al. 1996; Stephens 1996; Hagrey and Michaelsen 1999; Yang and LaBrecque 2000) resistivity data are valuable for non-invasive investigations. Additionally, contaminant and remediation characterization and monitoring efforts have also been imaged with this versatile technique (Daily and Ramirez 1995; Aaltonen and Olofsson 2002). The biodegradation of petroleum hydrocarbons has been observed and monitored through long-term resistivity experiments (Atekwana et al., 2000; Sauck, 2000; Werkema, 2002; Werkema et al., 2004). Other long-term three dimensional studies have been developed to characterize subsurface water flow and aquifer characteristics (Pfiefer and Andersen 1995; Cassiani et al. 2006). Steps toward the conversion of resistivity measurements into hydrological values have shown good success (Binley et al. 2002a; Binley et al. 2002b; Vanderborght et al. 2005; Linde et al. 2006; Johnson et al. 2009). Tracer studies have been performed in conjunction with electrical resistivity tomography (ERT) to identify the center of mass and concentration within tracer plumes (Kemna et al. 2002; Singha and Gorelick 2005; Singha and Gorelick 2006a; Singha and Gorelick 2006b). More recently, such resistivity devices have been employed through large collaborative efforts to monitor salt-water intrusions near important freshwater well sources (Ogilvy et al. 2009). While there is movement within this field of study toward autonomous systems, most of these studies do not employ such a system dedicated to on-site data collection for extended periods of time mostly due to the expense. Budget restrictive projects which require vadose zone measurements of water content do not have access to autonomous systems and are therefore confined to the use of other methods, including time-consuming manual data collection techniques. This work presents a low-cost method to reliably obtain long-term subsurface resistivity and temperature measurements.
Description:
We present a low-cost, reliable method for long-term in situ autonomous monitoring of subsurface resistivity and temperature in a shallow, moderately heterogeneous subsurface. Probes, to be left in situ, were constructed at relatively low cost with close electrode spacing. Once installed, these were wired to the CR-1000 Campbell Scientific Inc. datalogger at the surface to electrically image infiltration fronts in the shallow subsurface. This system was constructed and installed in June 2005 to collect apparent resistivity and temperature data from ninety-six subsurface electrodes and fourteen thermistors through May of 2008. From these data, a temperature and resistivity relationship was determined. The high vertical resolution of the data coupled with surface precipitation measurements allowed unique observations of infiltration related to seasonal changes. Both the vertical resistivity instrument probes and the data logger system functioned well for the duration of the test period and demonstrated the capability of this low cost monitoring system.