Abstract: | Abstract Abstract Recently, substantial progress has been made in detection and observation of non-aqueous phase liquids (NAPLs) in the subsurface using different experimental techniques. However, there is still a lack of appropriate direct methods to measure the saturation of NAPL (θNAPL). This paper provides a guide for estimating θNAPL and water content (θ w ) in unsaturated and saturated sand based on direct measurements of soil dielectric constant (Ka ) and electrical conductivity (σ a ) using time domain reflectometry (TDR). The results show that the previously used dielectric mixing model fails to predict θNAPL in the case of a four-phase system. A new methodology is suggested and exemplified by showing that the measured Ka gives accurate estimation of θNAPL for a three-phase system while in a four-phase system, both θ a and Ka need to be measured. The results show that using the suggested methodology, accurate predictions of θ w (R 2 = 0.9998) and θNAPL lower than 0.20 m3 m-3 (average R 2 = 0.9756) are possible. |