Analysis of three oxygenated solvents (acetone, THF and 1,4-dioxane) in groundwater was conducted by dynamic thermal stripping followed by thermal desorption into a GC-MSD with monitoring of selected ions. This method has a significantly better practical quantitation limit than the current EPA method (13 vs. 150 μg/L for 1,4-dioxane). Using this method a plume of groundwater contaminated with 1,4-dioxane emanating from a former solvent disposal site was mapped. More than 10 years after disposal, concentrations of 1,4-dioxane greater than 3 mg/L were measured at points more than 300 m from the site.