Estimating the Nonaqueous‐Phase Liquid Content in Saturated Sandy Soil Using Amplitude Domain Reflectometry

Abstract

Groundwater contamination by nonaqueous‐phase liquids (NAPLs) has become a serious environmental issue. Therefore, it is necessary to estimate the NAPL content (θNAPL) in saturated soil to detect and monitor the NAPL contamination in groundwater. The objective of this study was to investigate three estimation methods for the θNAPL in saturated sandy soil, namely, the noncalibration method (NCM), the permittivity regression method (PRM), and the best‐fit α method (BFαM). These methods utilize the permittivity (K) measured by amplitude domain reflectometry (ADR) and two dielectric mixing models: a theoretical Maxell–de Loor (MD) model and an empirical α model. The NCM applies the measured K to the models directly. The PRM applies the measured K to the models indirectly using the regression equation between the measured and estimated K The RMSEs of the NCM for the α model were 0.038 m3 m−3 for light NAPL (LNAPL) and 0.015 m3 m−3 for dense NAPL (DNAPL) when the constant α value was set at 0.5. The RMSEs of the MD model, however, were 0.090 m3 m−3 for LNAPL and 0.070 m3 m−3 for DNAPL. Using the PRM, the RMSEs of the MD model became much better than those of the NCM. The RMSEs for θNAPL estimated by the BFαM were 0.007 m3 m−3 for LNAPL and 0.018 m3 m−3 for DNAPL. These results demonstrate that θNAPL was estimated easily and with sufficient accuracy with the α model and the PRM.

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)

“…Surfactant-enhanced flushing was developed from the conventional pump-andtreat method. The success of this approach is related to the capacity of such chemical compounds to greatly enhance the aqueous solubility of oils (Pennell et al, 1994;Parnian and Ayatollahi, 2008).…”

“…There is high interfacial tension between NAPL and water molecules that makes water a non-efficient cleaning material in removing NAPL from the soil. Instead, surfactants and cosolvent agents can promote the enhanced removal of NAPL from the subsurface through mobilization and solubilization (Martel et al, 1998;Rinaldi and Francisca, 2006;Parnian and Ayatollahi, 2008).…”

Time domain reflectometry-measuring dielectric permittivity to detect soil non-acqeous phase liquids contamination-decontamination processes

“…Most studies have demonstrated estimation of NAPL essentially in saturated coarse-grained media (Redman and DeRyck, 1994;Chenaf and Amara, 2001;Persson and Berndtsson, 2002;Haridy et al, 2004;Mohamed and Said, 2005;Ajo-Franklin et al, 2006;Moroizumi and Sasaki, 2006;Francisca and Montoro, 2012). Little is known about the dielectric behaviour of contaminated fine-grained soils.…”

“…In particular, the time domain reflectometry (TDR) technique has been proposed as potentially exhibiting sufficient sensitivity and lateral and vertical resolution for characterization of saturation of NAPLs ( NAPL). This is because commonly encountered NAPLs have a dielectric permittivity of 2-10 versus 81 for water, 1 for air, and 4-5 for soil mineral grains (Ajo-Franklin et al, 2006).Most studies have demonstrated estimation of NAPL essentially in saturated coarse-grained media (Redman and DeRyck, 1994;Chenaf and Amara, 2001;Persson and Berndtsson, 2002;Haridy et al, 2004;Mohamed and Said, 2005;Ajo-Franklin et al, 2006;Moroizumi and Sasaki, 2006;Francisca and Montoro, 2012). Little is known about the dielectric behaviour of contaminated fine-grained soils.…”

Measuring the dielectric properties of soil–organic mixtures using coaxial impedance dielectric reflectometry

“…The presence of liquid organic contaminants in soils can be identified due to their different dielectric, physical and chemical properties with respect to pore water (Ajo-Franklin et al, 2006;Moroizumi and Sasaki, 2008;Son et al, 2009). Although previous studies showed that NAPL affects the complex permittivity of soils, little concern has been given to the effect of medium heterogeneities and the spatial variability of NAPL saturation on computed concentrations of contaminants.…”