A soil non-aqueous phase liquid (NAPL) flushing laboratory experiment based on measuring the dielectric properties of soil–organic mixtures via time domain reflectometry (TDR)

Abstract

Abstract. The term non-aqueous phase liquid (NAPL) refers to a group of organic compounds with scarce solubility in water. They are the products of various human activities and may be accidentally introduced into the soil system. Given their toxicity level and high mobility, NAPLs constitute a serious geo-environmental problem. Contaminant distribution in the soil and groundwater contains fundamental information for the remediation of polluted soil sites. The present research explored the possible employment of time domain reflectometry (TDR) to estimate pollutant removal in a silt-loam soil that was primarily contaminated with a corn oil as a light NAPL and then flushed with different washing solutions. Known mixtures of soil and NAPL were prepared in the laboratory to achieve soil specimens with varying pollution levels. The prepared soil samples were repacked into plastic cylinders and then placed in testing cells. Washing solutions were then injected upward into the contaminated sample, and both the quantity of remediated NAPL and the bulk dielectric permittivity of the soil sample were determined. The above data were also used to calibrate and validate a dielectric model (the α mixing model) which permits the volumetric NAPL content (θNAPL; m3 m−3) within the contaminated sample to be determined and quantified during the different decontamination stages. Our results demonstrate that during a decontamination process, the TDR device is NAPL-sensitive: the dielectric permittivity of the medium increases as the NAPL volume decreases. Moreover, decontamination progression can be monitored using a simple (one-parameter) mixing model.

Vadose Zone Monitoring as a Key to Groundwater Protection

“…As such, infiltration events that result in a significant change in the vadose zone water content or salinity may be detected and visualized in a 3D representation of the water and salinity distribution in the subsurface (Hayley et al, 2009;Brindt et al, 2019). Although the potential for real-time monitoring of contamination processes with geophysical tools is promising (Wang et al, 2015;Comegna et al, 2019), the current state-of-the-art is not efficient enough to identify the transport of pollutants in concentrations that do not significantly alter the medium's electrical conductivity or dielectric properties.…”

Time domain reflectometry (TDR) for dielectric characterization of olive mill wastewater (OMW) contaminated soils

“…Detection of contaminants in multiphase soil systems by means of geophysical methods is problematic even if the pollutant is homogeneously distributed within the soil matrix (Redman and De Ryck, 1994;Persson and Berndtsson, 2002;Haridy et al, 2004;Moroizumi and Sasaki, 2006;Francisca and Montoro, 2012, amongst others). The TDR technique has the potential to reveal the presence of a contaminant in soils (see Comegna et al, 2013a;Comegna et al, 2016, Comegna et al, 2017Comegna et al, 2019). However, as the TDR waveform only returns "aggregate"…”

Integrated use of chemical and geophysical monitoring to study the diesel oil biodegradation in microcosms with different operative conditions

“…The measured parameters are sensitive to the contaminant chemistry and the processes generated by bacteria during the biodegradation activity [24]. Electromagnetic monitoring of contaminated soil focused on the use of ground penetrating radar (GPR) in the assessment of hydrocarbon contaminations [25] and time domain reflectometry (TDR) to monitor the dielectric properties of soil-organic mixtures [26]. In this context, we focused on the detection of biodegradation related processes in contaminated soil by using an open-ended coaxial probe, because of its ability to provide a wide range of information about the dielectric properties of a material at different frequencies.…”