Determination Of Light Non - Aqueous Liquid In Saturated Soil By Time Domain Reflectometry

Time Domain Reflectometry(TDR) is a detection technology using propagation time of electromagnetic waves in the medium to determine the properties of the medium, which has been widely used in many fields such as industry and agriculture. TDR technique on determination of light non-aqueous phase liquids(LNAPLs) content in soil has an advantage of rapid, accurate,continuous in-situ, nonradiat, and minimal soil disturbing. Recently, research on TDR monitoring non-aqueous phase liquids is relatively weak. Especially, the studies on the effect of the electrical characteristics and the determination of LNAPLs content in contaminated soil are rarely. In this study, we investigated the relationships among the light non-aqueous phase liquids(colza oil and motor oil) content, soil(sand and loam) dielectric properties, and electrical conductivity. Furtherly, we estimated the LNAPLs content in saturate soil by fitting a parameter α in the dielectric mixing model(CDM). Evaluation results indicated that that there were no significant changes on soil dielectric constant with the volume oil content varied from 0 to 0.05 m3m-3 in the saturated sandy soil. Then, soil dielectric constant linearly decreased with the LNAPLs content increased. There was no effects of soil bulk density and the LNAPLs types on dielectric constant.There was a linear negative correlation between the LNAPLs content and soil electrical conductivity with R2 = 0.96. Soil bulk density did not influence electrical conductivity for the same saturation. The dielectric mixed model(α=0.5) overestimated the LNAPLs content in saturated sandy soil, with the average root mean square error of 0.038 cm3cm-3. The accuracy of dielectric mixed model was improved 23.2%-30.4% after adjusting the parameter α to0.52. All of this results demonstrated that time domain reflectometry was reliable to monitor the LNAPLs content in soils.