Arrival time of Tetrachloroethylene (PCE) and its Degradation byproducts
at Water-Supply Wells and the Water Treatment Plant at Camp Lejeune Base
W. Jang and M. M. Aral
Multimedia Environmental Simulations Laboratory
School of Civil and Environmental Engineering
Georgia Institute of Technology
Abstract
The Agency for Toxic Substances and Disease Registry (ATSDR) is conducting an epidemiological study to evaluate whether exposures in-utero and during infancy (up to 1 year of age) to volatile organic compound contaminated drinking water at U.S. Marine Corps Base Camp Lejeune, North Carolina were associated with specific birth defects and childhood cancers. The study includes births occurring during the period 1968–1985 to women who were pregnant while they resided in family housing at the base. No exposure data and very limited site contamination data are available to support the epidemiological study. As a result, ATSDR is using modeling techniques to estimate the historical and present-day conditions in groundwater and water-distribution systems at the base. Owing to the complexity of the historical reconstruction process, a number of reports are being prepared that provide comprehensive descriptions of information and data used to conduct historical and present-day analyses at Tarawa Terrace and vicinity. This report describes the three-dimensional simulation of the fate, degradation, and advective dispersive transport of tetrachloroethylene (PCE) and associated degradation by-products, including trichloroethylene (TCE), trans-1,2-Dichloroethylene (1,2-tDCE), and vinyl chloride (VC), within the Castle Hayne aquifer system in the vicinity of Tarawa Terrace. Migration of PCE and three associated volatile organic compounds (VOCs) (TCE, 1,2-tDCE, and VC) from the vicinity of ABC One-Hour Cleaners to Tarawa Terrace water supply wells was simulated using the code TechFlowMP. This model uses the hydrogeologic data that is utilized in a calibrated groundwater flow model which was based on the code MODFLOW (Faye and Valenzuela, 2007). Simulated mass loading at the site occurred at a constant rate of 1200 grams per day using monthly stress periods representing the period January 1953 to December 1984. Mass loading occurred at the elevation of 0-4 meters at the approximate location of ABC One-Hour Cleaners. The duration of the simulation covers the period January 1951 to December 1994. Until 1984, the vast majority of simulated PCE supplied to the Tarawa Terrace water treatment plant (WTP) was contributed by well TT-26. When the calibration pumping schedules are used, which will be identified as the original pumping schedule in this report, TechFlowMP simulations indicate that the breakthrough of PCE at well TT-26, the nearest supply well to ABC One-Hour Cleaners, occurred during February 1957 at the contaminant concentration level of 5 micrograms per liter (mg/L). The contaminant breakthrough at the location of well TT-23 occurred during January 1978. However, according to ATSDR records, Well TT-23 was not operational until about August 1984. Simulated average and maximum PCE concentrations at well TT-26 were 336 and 775 mg/L, respectively. Concentrations of PCE in finished (delivered) water at the Tarawa Terrace WTP were computed using a material mass balance mixing model. The computed maximum and average PCE concentrations in delivered water from the Tarawa Terrace WTP were 158 and 57 mg/L, respectively, during the period February 1957 to February 1985, at which time well TT-26 was removed from service. During the same period, the average concentrations of TCE, 1,2-tDCE, and VC in well TT-26 were 14, 45, and 25 mg/L, respectively, and the concentrations in the WTR were 2, 8, and 4 mg/L, respectively.