Laboratory study on the dielectric properties of contaminated soil using CPT deployed probe

Abstract

Over the past decade, direct-push geotechnical sensors or penetration probes have earned widespread acceptance in the geoenvironmental fields of study as a more viable and cost-effective solution for the assessment of soil and groundwater contamination. Of these, resistance cone penetrometer (RCPT) devices equipped with electrical sensors have been successful in qualitatively locating contaminated areas. While the RCPT method has proved to be successful for delineating inorganic contaminants in the saturated zone, its applicability in the vadose zone and soils contaminated by hydrocarbon compounds have been doubtful. The objective of this research is therefore focused on verifying the applicability of capacitance measurements on an existing RCPT module to provide information on the moisture content and presence of various kinds of contaminants. Laboratory experiments were performed on carefully prepared soil layers to investigate the sensitivity of the measured capacitance on the soil moisture content and different types of contaminants. Results confirmed that the measured capacitance of soils reflected the volumetric amount of water present in both un-contaminated and contaminated soils. In addition, capacitance measurement showed potentials for applicability in detecting plumes of non-aqueous phase contaminants above the groundwater table. Consequently, recommendations were made on the basis to which capacitance measurements can support interpretations of the electrical resistivity data.