EFFECT OF GROUNDWATER PUMPING SCHEDULE VARIATION ON ARRIVAL OF TETRACHLOROETHYLENE (PCE)
AT WATER-SUPPLY WELLS AND THE WATER TREATMENT PLANT
J. Wang and M. M. Aral
Multimedia Environmental Simulations Laboratory
School of Civil and Environmental Engineering
Georgia Institute of Technology
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 compounds that contaminated the drinking water at the U.S. Marine Corps Base Camp Lejeune, North Carolina, were associated with specific birth defects and childhood cancers that are observed at the site. The study includes the births that occurred to women who were pregnant while they resided in the family housing at the base during the period 1968 – 1985. There is no exposure data and very limited site-specific contamination data are available to support the epidemiological study. As a result, ATSDR is using modeling techniques to estimate the historical and present-day contamination conditions in the groundwater and the water treatment plant at Camp Lejeune, North Carolina. Owing to the complexity of the historical reconstruction process, a number of reports are being prepared to provide a comprehensive description of information and data used in historical reconstruction and present-day analyses at Tarawa Terrace and vicinity. To complement these studies, this report describes the effect of groundwater pumping schedule variations on the arrival times of Tetrachloroethylene (PCE) at water-supply wells and the water treatment plant (WTP). During the historical reconstruction study, as described in various ATSDR reports accompanying this report, the groundwater flow and fate-and-transport of contaminants in the Tarawa Terrace area of the Camp Lejeune base and its vicinity have been simulated to evaluate the contaminant concentration in the WTP. Due to the uncertainty residing in the reconstructed input data used in these simulations, uncertainty may be present in the simulated contaminant concentrations in the water-supply wells and the WTP, hence the times for contaminant concentrations to reach the maximum contaminant level (MCL) at these locations. A major cause and contributor to this uncertainty is the pumping schedules used in the ATSDR model, therefore, in this study the focus is on the uncertainty associated with the pumping schedules. The study included the development of a simulation and optimization (S/O) procedure identified as PSOpS (Pumping Schedule Optimization System), which combines simulation models and optimization techniques to optimize the pumping schedules for maximum or minimum contaminant concentrations in the WTP. Based on the optimized pumping schedules, variations of PCE concentration and the maximum contaminant level (MCL, 5 ppb for PCE) arrival time at water-supply wells and the WTP are evaluated. The results of this study indicate that the variation of pumping schedules may cause significant changes in the contaminant concentration levels and MCL arrival time at the WTP.
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