FORENSIC CHEMICAL TRANSPORT MODEL OF TCE AND PCE AT THE WELLS G&H SITE IN WOBURN, MASSACHUSETTS

Contamination of municipal wells G and H was discovered in 1979 and has been statistically linked by epidemiological studies to leukemia cases that occurred in Woburn, Massachusetts in the late 1960’s through the early 1980’s. Historical contamination of the buried valley aquifer at the 133 hectare Wells G&H Superfund site in is simulated using MT3D HMOC code to determine the possible contamination history of wells G and H with TCE and PCE. Although the wells operated from 1964 to 1979, the transport model spans the period 1960 to 1985 so that the simulated concentrations can be compared to water quality measurements from 1979 through 1985. A MODFLOW groundwater flow model calibrated using measured heads, measured streamflow gains and losses, and tritium/helium-3 groundwater ages was used to compute flow velocities. During the 26-year time period, at least five local sources contributed organic solvents, pesticides, heavy metals, and other contaminants to the groundwater system. Because the uncontrolled dumping of industrial waste occurred up to 30 years prior to site investigations, the precise source release times, source concentrations, and quantity of contaminants is not known for the sites. Historic aerial photographs, EPA documents, pre-trial depositions, and personal communications of scientists who worked first-hand on the Wells G&H site were used to estimate source locations and source release times. Soil and water quality samples were used to estimate source concentrations. Seven plausible scenarios are simulated that represent a range of source concentrations, source release times, and contaminant retardation factors. Based on the results, it is likely that TCE contamination reached pumping well G as early as 1966 and as late as 1968, well before the discovery of contamination in 1979. The estimated range of TCE plus PCE concentrations at well G over the 26-year simulation period is from 10’s to 100’s of parts per billion.