Tetrachloroethylene (PCE) Exposure Reconstruction for an Epidemiologic Study: The Effect of Historical Supply-Well Schedule Variation on Arrival Time

Health scientists and epidemiologists rely on groundwater-flow and fate-and-transport models to reconstruct historical exposures to groundwater contaminants when conducting environmental health studies. One of the key factors in determining human exposure to contaminants is reliable estimates of historical contaminants arrival times at water-supply wells and at the associated water distribution system (WDS), including the water treatment plant (WTP). One uncertain variable that may affect the arrival time is the scheduling, or on/off cycling, of water-supply wells feeding the WDS. Uncertainty related to pump scheduling and thus the arrival time can significantly impact the related epidemiologic study. In this paper, a procedure is described that combines groundwater simulation models and an optimization method to evaluate the change in the Maximum Contaminant Level (MCL, 5 ppb for tetrachloroethylene (PCE)) arrival time at the WTP. The procedure was applied to an epidemiologic study currently being conducted at U.S. Marine Corps Base Camp Lejeune, North Carolina.