Book excerpt: The overall goal of the project is to explore the use of an innovative in-situ method (partitioning tracer tests) for detection and quantification of dense nonaqueous phase liquids (DNAPLs) in subsurface systems. DNAPLs occur in the subsurface at numerous contaminated sites and can act as long-term sources of groundwater contamination. Both effective risk assessment and remediation of DNAPL-contaminated sites is limited by current site characterization techniques. A major limitation of the current methods is that they provide data at discrete points, such that the probability of sampling a zone of localized DNAPL is quite small. The results of this research will lead to an improved method for characterizing DNAPL-contaminated sites and will enhance our understanding of the distribution of immiscible liquids in the subsurface. The use of this method will help reduce the uncertainty associated with risk assessments and remediation planning.