USING TIME DOMAIN REFLECTOMETRY FOR NON-AQUEOUS PHASE LIQUID SATURATION MEASUREMENTS

During recent years, studies have used the apparent dielectric constant (K_a) measured by time domain reflectometry (TDR) for determining the concentration of non-aqueous phase liquids (q_NAPL) in soils. The K_a has been related to q_NAPL using dielectric mixing models. In the unsaturated zone, the water content (q_w) had to be known (by assumptions or measured using other techniques) to utilize these models. In the present study, unlike previous research, detailed laboratory experiments were conducted to investigate the relationship between TDR measurements and q_NAPL. Calibration was made in homogeneous sand using three different NAPLs. It was shown that the previously used mixing model led to errors up to 0.05 m³ m^-3 for saturated soils. In unsaturated soil, it was shown that measurements of only K_a can not be used for estimation of q_NAPL even if q_w is known. Instead, the TDRs capability of determining both K_a and bulk electrical conductivity (s_a) was utilized to estimate q_w and q_NAPL. The approach presented in this study can be used for simultaneous observation of q_w and q_NAPL during NAPL transport experiments in both unsaturated and saturated soils. Thus, it is a potential tool for develop and test new NAPL transport models.

 

Magnus Persson
Department of Water Resources Engineering
Lund University
Sweden.