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The Agency for Toxic Substances and Disease Registry (ATSDR), an agency of the United States Department of Health and Human Services, under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA, also known as Superfund) is required to evaluate the public health threat of hazardous waste sites using environmental characterization data, community health concerns, and health outcome data. In the spring of 1996, ATSDR and the New Jersey Department of Health and Senior Services (NJDHSS) initiated an investigation to address health concerns of the Dover Township, Ocean County, New Jersey, community. In particular, community members expressed the concern that exposure to environmental contaminants from the area’s hazardous waste sites, including two National Priorities List (NPL) or Superfund sites (Figure 1, Plate 14) was related to the elevated incidence of childhood leukemia and brain and central nervous system cancers.
In 1997, NJDHSS and ATSDR began designing a case-control epidemiologic study of childhood cancers that occurred in Dover Township (Berry and Haltmeier 1997). In a case-control study, a population is delineated and cases of diseases arising in that population over a specified time period are identified. The exposure experiences of the case group are compared to the exposure experiences of a sample group of non-diseased persons in the population from which the cases arose. The exposure experiences that are more common among the diseased cases may be considered possible risk factors for the disease (Rothman and Greenland 1998).
The study is exploring multiple possible risk factors, including environmental exposures. ATSDR and NJDHSS have determined that completed human exposure pathways to groundwater contaminants have occurred in the past through private and municipal water supplies in some parts of the Dover Township area community (ATSDR 2001a,b,c,d). Therefore, one of the environmental factors being evaluated is the past exposure to certain previously contaminated drinking-water sources.
To assist with the drinking-water exposure assessment component of the epidemiologic study, ATSDR developed a water-distribution model using the EPANET 2 software (Rossman 2000) to reconstruct historical patterns of water-supply distribution for the period January 1962 through December 1996. The key steps of this historical reconstruction analysis and the location in this report where these key steps are discussed are shown in flow-chart format in figure 2. Owing to the lack of pertinent historical information, particularly the availability of spatially and temporally distributed hydraulic and contaminant-specific data, the water-distribution model was first calibrated to accurately represent present-day (1998) Dover Township area water-distribution system characteristics. Data utilized for this initial calibration were gathered during March and August 1998. The reliability of the calibrated model was tested by using the model to simulate the transport of barium through the water-distribution system. Barium is a naturally occurring, dissolved, conservative element. Simulated barium concentrations were compared to measured concentrations at 21 schools and 6 points of entry to the water-distribution system determined in March and April 1996. Comparison of measured and simulated barium concentrations at the 21 school locations showed a mean relative difference of 13.6%, with the range of differences being 0.6% to 25.6%. Additionally, comparison of the measured and simulated barium concentrations showed a geometric bias of 0.93, indicating a slight under prediction by the model (1.00 indicates perfect agreement), and a correlation coefficient of 0.81, indicating a high agreement between measured concentrations and simulated values. A complete description of the field-data collection activities, model calibration, and reliability test results were described previously in an ATSDR report and technical article (Maslia et al. 2000a,b).
In the second step of the historical reconstruction analysis, and the subject of this report, distribution-system networks were derived from diverse data sources for the historical period of January 1962 through December 1996 (Figure 2). Given the paucity of historical contaminant- specific concentration data during most of the period relevant to the epidemiologic study, ATSDR and NJDHSS decided that modeling efforts should concentrate on estimating the percentage of water that a study subject might have received from each point of entry (well or well fields) to the water-distribution system (Plate 2). Percentage contributions would be determined at monthly intervals during the historical period. This approach uses the concept of "proportionate contribution" described in Maslia et al. (2000a, p. 4) wherein at any given point in the distribution system, water may be derived from one or more sources in differing proportions. The percentage or proportionate contribution of water to locations in the distribution system from points of entry then becomes a surrogate for exposure pathways and exposure intervals. This approach allows epidemiologists to more accurately assess the association between the occurrence of childhood cancers and exposure to each of the sources of potable water entering the distribution system, including those known to have been historically contaminated. A literature review of epidemiologic investigations relating water-supply contamination with health effects is provided in Maslia et al. (2000a, p. 3).
The configuration of the water-distribution system serving the Dover Township area (number of pipelines, wells, storage tanks, and high-service and booster pumps) during the historical period has changed each year (Table 1). For example, the 1962 water-distribution system served nearly 4,300 customers from a population of about 17,200 persons5 (Board of Public Utilities, State of New Jersey 1962) and was characterized for modeling by (Plate 3):
By contrast, in 1996—the last year of the historical reconstruction period—the water-distribution system served nearly 44,000 customers from a population of about 89,300 persons (Board of Public Utilities, State of New Jersey 1996) and was characterized for modeling by (Plate 37):
A summary of the configuration of the water-distribution system serving the Dover Township area during the historical period is provided in Table 1. Some of the data listed in Table 1 are presented and discussed elsewhere in this report in greater detail. For example, the number of pipeline segments and total pipeline miles are presented in Appendix A, and the number of groundwater wells, number of well fields, and the rated capacity of the groundwater wells are presented in Appendix B.
Because this report is considered a companion document to the analysis of the 1998 water-distribution system serving the Dover Township area—previously described by Maslia et al. (2000a)—certain topics such as water-distribution system model development and data input requirements and terminology used by EPANET 2 will not be described or provided herein. Rather, these topics are thoroughly described and discussed in the earlier publication and the reader shouldrefer to that report for details. The focus of the current report includes the following five aspects of the historical reconstruction analysis: (1) data sources and requirements, (2) methods of analysis, (3) simulation strategies, (4) selected simulation results, and (5) the use of sensitivity analysis to address issues of uncertainty and variability of historical system operations.
Because of the scientific complexity and length of this report, some readers may prefer a summary of the analyses presented herein. Accordingly, a "Summary of Findings" report (ATSDR 2001f) has been prepared and released by ATSDR. The summary report provides a simpler and less technical description of the historical reconstruction analysis. Because of the brevity of the "Summary of Findings" report, presentation of some topics, illustrations, and tables may have been modified slightly in comparison to those contained in this comprehensive report. However, all information and conclusions provided in the "Summary of Findings" report are based solely on data and analyses contained herein. The "Summary of Findings" report is also available over the Internet at the ATSDR web site at URL: www.atsdr.cdc.gov.
