Soil and ground water samples on- and off-site implicated a solvent recycling facility as the source of chlorinated solvents on and downgradient of the facility in soil and ground water.  Release timing, specifically whether any releases occurred before 1990, was a key factor in determining liability for site remediation.  The primary solvents released at the facility were believed to be PCE, TCE, and 1,1,1-TCA.  Four methods were used to assess the likely timing of releases.  The site operational history, focusing on materials handling and spill control procedures, was evaluated.  Second, locations at which contamination was found were evaluated in the context of the site development and grading history.  Third, transport rates in the vadose and saturated zones were evaluated to determine the likely time required for chlorinated solvents to move from the source locations to the locations at which they were found in samples from monitoring wells and surface water.  Fourth, a sequential degradation model incorporating both biotic and abiotic degradation pathways was used to estimate the amount of time chlorinated solvents in ground water had been undergoing degradation.  Degradation rates were estimated from a combination of site and literature data.  The abiotic degradation rate of 1,1,1-TCA to 1,1-DCE was based on rates reported in the literature, and other degradation rates were constrained by a rates reported in the literature taken in context of the site geochemical conditions.  The model was calibrated by varying degradation rates, within appropriate constraints, until the variation in the estimated time of degradation for compounds reported in each well was minimized.  These four methods each supported the hypothesis that there were significant chlorinated solvent releases prior to 1990.