Measuring nonaqueous phase liquid saturation in soil using time domain reflectometry

[1] Transport of nonaqueous phase liquids (NAPLs) in soils is becoming an increasingly serious threat to the environment. Detection and observation of these substances are thus an increasingly important issue. During recent years, studies have used the apparent dielectric constant (K-a) measured by time domain reflectometry (TDR) for determining the saturation of NAPLs (theta(NAPL)) in soils (m(3) m(-3)). K-a has been related to theta(NAPL) using dielectric mixing models. In this approach for the unsaturated zone, the water content theta(w) should be known beforehand (by assumptions or measured using other techniques). Here, unlike previous research, detailed laboratory experiments were conducted to investigate the relationship between the TDR measured K-a and bulk electrical conductivity sigma(a) and theta(NAPL). Calibration was made in homogeneous sand using three different NAPLs. It was shown that the mixing model used previously led to errors up to 0.05 m(3) m(-3) in saturated sand. Moreover, in unsaturated sand, measurements of Ka only cannot be used for estimation of theta(NAPL) even if theta(w) is known. Instead, TDR's capability of determining both K-a and sigma(a) was utilized to estimate theta(w) and theta(NAPL). The approach presented in this study can be used for simultaneous observation of theta(w) and theta(NAPL) during NAPL transport experiments in both unsaturated and saturated sandy soils. Thus it is potentially helpful when developing new NAPL transport models.