Open AccessEstimating Nonaqueous‐Phase Liquid Content in Variably Saturated Soils Using Time Domain Reflectometry
Author(s) -
Comegna Alessandro,
Coppola Antonio,
Dragonetti Giovanna,
Sommella Angelo
Publication year - 2016
Publication title -
vadose zone journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.036
H-Index - 81
ISSN - 1539-1663
DOI - 10.2136/vzj2015.11.0145
Subject(s) - reflectometry , loam , soil water , soil science , water content , time domain , silt , dielectric , soil test , environmental science , materials science , geology , geotechnical engineering , paleontology , optoelectronics , computer science , computer vision
Core Ideas A TDR waveform interpretation method for NAPL content in soils was developed. Correlations between the dielectric response and the NAPL content were determined. The α dielectric mixing model for predicting NAPL presence in soils was expanded. This methodology can be used to obtain predictions of volumetric NAPL content. In recent years, several studies have been conducted in the detection and observation of nonaqueous‐phase liquids (NAPLs) in contaminated soils. Successful remediation of an NAPL‐contaminated site requires appropriate characterization of both the plume extent and the soil volumetric NAPL content (θ NAPL ). Noninvasive geophysical techniques, such as time domain reflectometry (TDR), may be used to discriminate between θ NAPL and soil volumetric water content (θ w ). Accordingly, the main aim of this work was to develop a TDR waveform interpretation method based on soil dielectric permittivity measurement and observation of the change in the reflected TDR signal amplitude at relatively long times from the waveform source. We demonstrated that the asymptotic value of the reflection signal coefficient can be univocally related with θ NAPL in an unsaturated soil. In the procedure adopted, a new formulation of a dielectric mixing model was also derived, introducing a fourth phase that takes the NAPL presence into account. Multiple samples of sandy, silt loam, and loamy soils, at predetermined different θ w and θ NAPL , were tested, each test consisting in emitting a TDR signal to the soil sample and receiving and analyzing the reflected electromagnetic wave. An empirical dielectric mixing model was calibrated and implemented to estimate the θ NAPL . Equipment calibration, measurement accuracy, and error sources, related both to the experimental procedure setup and to the sample preparation conditions, are discussed. The results show that the suggested methodology can be used to obtain predictions of volumetric NAPL content (θ NAPL ) with acceptable accuracy ( R 2 = 0.95).