Evaluation of groundwater flow and contaminant transport at the Wells G&H Superfund Site, Woburn, Massachusetts, from 1960 to 1986 and estimation of TCE and PCE concentrations delivered to Woburn residences

Contamination of municipal wells G and H was discovered in 1979 and was 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 is simulated using MT3D-HMOC code to determine the possible contamination history of the wells with TCE and PCE. 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. The 26-year transient groundwater flow model incorporates realistic pumping schedules and variable recharge rates.; 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. At least five local sources contributed TCE, PCE, and other contaminants to the groundwater system. The precise contaminant release times and source concentrations are not known for the sites. Historic aerial photographs, EPA documents, trial documents, and personal accounts of site investigators were used to estimate source locations and source release times. Water quality samples were used to estimate source concentrations.; Eleven plausible scenarios, comprising 66 simulations, are used to test hypotheses of source concentrations, source release times, and contaminant retardation factors. Based on the results, it is likely that TCE contamination reached well G between 1966 and 1968. The estimated range of TCE plus PCE concentrations at well G from 1964 to 1979 is from 10's to 100's of ppb.; The concentrations of TCE and PCE in wells G and H predicted by the contaminant transport model are multiplied by the fraction of wells G and H water predicted by a water distribution model to estimate the range of concentrations that were likely delivered to the residents in Woburn. Results show that exposure to TCE plus PCE varied greatly, depending on the date and location in Woburn. These results can be used by public health scientists to explore further the possible causes of the Woburn childhood leukemia cluster.