Dense non-aqueous phase liquids (DNAPLs) such as trichloroethene (TCE) and perchloroethene (PCE) present long-term challenges in terms of quantification in the subsurface at many DOE facilities. Over the past year we have continued investigating a potentially lower cost method for quantifying DNAPLs in the subsurface using naturally occurring, in situ dissolved radon as a partitioning tracer. Radon can be used as a partitioning tracer in both static (i.e., no flow) and dynamic methodologies (Semprini et al., 1993; Semprini et al., 1998; Semprini et al., 2000). The static radon method involves obtaining radon samples from DNAPL-contaminated and non-contaminated portions of the aquifer and using the change in radon concentrations to locate and quantify DNAPL saturation in the aquifer. The dynamic radon method incorporates single-well injectionwithdrawal (i.e., push-pull) tests to estimate radon retardation and DNAPL saturation. These methods have the potential to provide a robust method for DNAPL saturation quantification while decreasing the costs associated with these activities.