ANALYSIS OF THE 1998 WATER-DISTRIBUTION SYSTEM
SERVING THE DOVER TOWNSHIP AREA, NEW JERSEY:
Field Data Collection Activities and
Water Distribution System Modeling
ATSDR and NJDHSS have initiated an exposure assessment for use in an epidemiologic study of childhood leukemia and brain and CNS cancers that occurred in the period 1979 through 1996 in Dover Township, New Jersey. Because groundwater contamination has been documented historically in public- and private-supply wells in the Dover Township area, human exposure through this pathway is possible. The Dover Township area has been primarily served by public water supply that relies solely on groundwater; therefore, ATSDR has developed a protocol for using a water-distribution model, (e.g., EPANET) as a tool to assist the exposure assessment component of the epidemiologic investigation. This report has presented the following aspects of the overall exposure assessment effort: (1) data gathered during field tests conducted in March and August 1998, (2) the development, calibration, and testing of the water-distribution system model for 1998 conditions, (3) a water-quality simulation of a naturally occurring conservative element, barium, to further test the reliability of the model calibration, and (4) the simulation of the proportionate contribution of water from points of entry (i.e., well fields) to various locations throughout the distribution system for 1998 conditions.
The present-day (1998) water-distribution system has 23 municipal wells distributed at eight points of entry (wells or well fields). In 1997, it serviced a population of 92,160. Preliminary simulations using an equivalent network representation of the water-distribution system (pipe diameters ranging from 6 in. to 16 in.) indicated higher-than-expected pressures-exceeding 125 psi in the southernmost areas of Dover Township, in the borough of South Toms River, and in Berkeley Township. Measured data were not available to either confirm or negate these initial simulation results. Therefore, system operation and pressure data were gathered during 48-hour tests in March and August 1998. Data were gathered simultaneously at 25 hydrants using continuous- pressure-recording data loggers with one-minute sampling rates. Data for storage tank water-levels, system demand, and pump and well cycling status were also obtained. Results of the tests indicated that system-wide pressures ranged from a low of about 40 psi to a maximum of slightly more than 100 psi.
For this investigation, the water-distribution system is being modeled as a network consisting of 16,071 pipe segments (or links) ranging in diameter from 2 in. to 16 in., six ground-level and three elevated storage tanks, and 17 high service or booster pumps. The model network also consists of 14,987 junctions or nodes. The model has been calibrated against winter-demand conditions for March 1998 and further tested against data gathered in August 1998 under peak-demand conditions. The reliability of the calibrated mode was judged in terms of the frequency of the absolute pressure difference (absolute value of difference between measured and simulated hourly pressure data). For the March 1998 simulation, 90% or more of the simulated hourly values for all hydrant locations resulted in an absolute pressure difference of approximately 5 psi or less. For the August 1998 simulation, 90% or more of the simulated hourly for all hydrant locations resulted in an absolute pressure difference of approximately 7.5 psi or less. These results are within the calibration limits established by ATSDR investigators at the outset of modeling activities and are within the general calibration guidelines suggested by Cesario and Davis (1984) and Walski (1984). Comparison of: (1) measured and simulated pressures for the 25 hydrants (Appendices I and J), (2) measured and simulated hydraulic head at ground-level and elevated storage tanks (Appendices K and L), (3) measured and simulated booster pump flows (Appendices M and N), and (4) measured and simulated groundwater well flows (Appendices O and P) support the assertion that the model presented herein is calibrated and an acceptable and reliable representation of water-distribution system conditions existing during 1998.
As further evidence of the reliability of the calibrated model, a simulation of the transport of a naturally occurring conservative element, barium, was conducted and compared with data gathered at 21 schools and 6 points of entry to the water-distribution system for March and April 1996. Measured concentrations of barium ranged from 13 µg/L to 51 µg/L. Comparison of measured and simulated barium concentrations at the 21 school locations indicates a difference ranging from 0.2 µg/L to 12.4 µg/L, which results in a mean relative difference of 13.6% with a range of 0.6% to 25.6%. Additional analyses comparing measured and simulated concentrations of barium show 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 correlation between measured concentrations and simulated values. Therefore, this water-quality simulation is further evidence that the model is reasonably calibrated and an acceptable representation of the present-day water-distribution system characteristics.
To demonstrate the concept of "proportionate contribution" of water, the trace analysis option available within EPANET was used in conjunction with characterization of the present-day (1998) water-distribution system. For each point of entry to the water-distribution system (well or well fields) operating during March and August 1998, a trace analysis was conducted. These analyses provide an estimate of the percentage of water that any location of interest receives from the 8 points of entry to the distribution system. The results are presented in a series of 10 maps, a graph, and a table showing the percentage of water contributed by specific wells and storage tanks to locations in the Dover Township area for 1998 conditions. Based on residence histories, the trace-simulation results will be used in an epidemiologic investigation to estimate exposure of participants to specific water sources by determining the percentage of water they may have received from each of the points of entry to the distribution system serving the Dover Township area.
The authors acknowledge their colleagues at ATSDR for providing assistance and advice with all aspects of this investigation: Robert C. Williams, Juan J. Reyes, Richard E. Gillig, Gregory V. Ulirsch, Sven E. Rodenbeck, Thomas A. Mignone, Brian Von Gunten, Allan S. Susten, Ann Walker, Kathy Skipper, Kevin A. Ryan, and Patrick Brady. The following organizations and their staff provided suggestions, assistance, and personnel in developing the protocol and conducting the field investigations described above: NJDHSS, New Jersey Department of Environmental Protection, UWTR, and the Multimedia Environmental Simulations Laboratory at the Georgia Institute of Technology. The authors would like to specifically acknowledge Jerald A. Fagliano of the NJDHSS for suggestions and advice on the epidemiologic aspects of this investigation, Michael J. McLinden, formerly with the NJDHSS, for assistance with selecting and visually confirming the locations of the test hydrants, and Lewis Rossman of the U.S. Environmental Protection Agency, National Risk Management Laboratory, for assistance with and requested modifications to the EPANET water-distribution system model. The authors also acknowledge Steven G. Buchberger and Richard H. Johnston for providing additional technical review of this report.
Use of trade names and commercial sources is for identification only and does not imply endorsement by the Agency for Toxic Substances and Disease Registry or the U.S. Department of Health and Human Services.
Availability of Model Input Data Files
Readers wishing to obtain model input data files for the March or August 1998 simulations described herein, should contact the senior author of the report at the following address:
Morris L. Maslia, P.E.
Agency for Toxic Substances and Disease Registry
1600 Clifton Road, Mail Stop E-32
Atlanta, Georgia 30333
Telephone: (404) 639-0674
Facsimile: (404) 639-0656
Email: mfm4@cdc.gov
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1. The reader should refer to the section on "Water-Distribution System Model Development" for detailed description of the hydraulic and water-quality simulators used in the EPANET model.
2. The database supplied by UWTR was used by the water utility as input for a proprietary water-distribution model, Piccolo (SAFEGE Consulting Engineers 1994). ATSDR conducted simulations on the equivalent hydraulic network using both the Piccolo and EPANET models. Comparison showed results (pressures, tank levels, and flows) were nearly the same for both models.
3. Information relating to the use of GPS equipment including post analysis and differential correction of data is provided in an ATSDR report by Maslia et al. (1997)
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