EXPOSURE-ASSESSMENT EVALUATION

To understand the exposures that occurred because of the contamination of water supplies at Camp Lejeune, it is important to characterize the contamination—including its location, magnitude, duration, and variability—and the individual water-use patterns and other water-related behavior of the population that was exposed. The first component involves identifying the contaminants of concern, their sources, and their estimated concentrations in any particular water-supply system over time. The second component is to characterize how members of the population may have been exposed to the contaminated water supply at home, at work, and in other settings through water consumption, dermal contact, and inhalation of volatile compounds during showering, bathing, dishwashing, and other activities. Such factors are important determinants of exposure and are likely to vary widely in the population.

Water-Supply Contamination

The Tarawa Terrace and Hadnot Point water-supply systems began operating in 1952 and 1943, respectively. From a conceptual standpoint, their operations were similar. Water-supply wells collected groundwater and pumped it to a water-treatment plant. The wells were “cycled,” meaning that only a subset of wells pumped water to the treatment plant at any given time. A few wells on both systems were contaminated. When those wells were operating, they delivered contaminated water to the treatment plant, where it was mixed with water from other wells and processed before being distributed on the base. Over the years, wells were added and some were taken temporarily offline or were closed for various reasons. Thus, concentrations of contaminants to which people were exposed varied substantially on a short-term and long-term basis.

The residential areas served by the two water systems were primarily enlisted family housing and barracks for unmarried service personnel. Thus, many of the exposed were young families and people of reproductive age. The population was also transient, with some people living on the base for a few months for training or for a few years for longer assignments.

Tarawa Terrace

The committee reviewed the available data on the exposures that occurred at Camp Lejeune. For Tarawa Terrace, the Agency for Toxic Substances and Disease Registry (ATSDR) performed a historical reconstruction of contamination scenarios and used its model to estimate the concentrations of chemical contaminants that occurred during different periods. ATSDR’s historical reconstruction involved investigation into operations of the off-base dry cleaner, on-base operations, operation of water-supply wells and water-treatment plants, water-monitoring data, groundwater flow, and other data relevant to providing a chronology of events related to the contamination. The primary contaminant identified as present at Tarawa Terrace is PCE. PCE is typically degraded by natural processes in the soil and groundwater to TCE, trans-1,2-dichloroethylene (1,2-DCE), and vinyl chloride. Groundwater models were used to reconstruct the migration of PCE from the dry cleaners to the water-supply wells serving Tarawa Terrace, and then mixing models were used to predict monthly concentrations of PCE and its degradation products in finished water (groundwater that was treated at a water-treatment plant for delivery to residences) from 1957 to 1985. Because the models were based on several simplifying assumptions and were calibrated by using a small number of water-quality measurements taken during a narrow window (1980-1985) of the total contamination period, considerable uncertainty is associated with the predictions. Some of the uncertainty was characterized when ATSDR performed statistical analyses to calculate the probability that its exposure estimates were reasonable. To gain some perspective on its estimates, ATSDR compared its monthly estimates with the U.S. Environmental Protection Agency (EPA) maximum contaminant level (MCL) for PCE in drinking water of 5 μg/L that was established in 1985. The model estimated that starting in No-



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