Projects by Discipline / Water Resources Engineering

TCE Contamination, Redlands, California

The city of Redlands California obtains approximately one half of its water supply from wells. In 1980, tricholorethylene (TCE) was detected in several of these wells. In 1997, the perchlorate anion was also detected in several wells. In 1996, the first of a series of lawsuits was filed in California State Court alleging that the source of these contaminants was a manufacturing facility located up-gradient from the most seriously contaminated wells. One of these lawsuits claimed that plaintiffs were harmed by exposure to toxic chemicals that were improperly disposed of at the manufacturing site and found their way into groundwater that was subsequently extracted through the City's wells and delivered to water customers, including the plaintiffs.

The plaintiffs' burden of proof requires them to reconstruct, over a roughly thirty-year period, the historical conditions in the water distribution system of the City of Redlands along with their exposures to, and resulting intakes of, TCE and perchlorate. Hydrosphere was retained to reconstruct the historical conditions in the Redlands water distribution system and to calculate probabilistic estimates of human intakes of the contaminants.

The Redlands water distribution system currently consists of two water treatment plants, more than 30 wells, 17 reservoirs, 39 pump stations, and more than 350 miles of pipe organized into seven primary pressure zones. To reconstruct the historical conditions in the system, a set of hydraulic and water quality models of the system were constructed. These models represented the evolution of the system physical plant and operating rules from the late 1950's through the 1990's. Distributed water demand estimates were made at parcel-level detail based on land use data, supplemented by historical aerial photography. Diurnal water use characteristics and water demand intensities were established for primary classes of land use. Day-to-day water use data were reconstructed from production records. These models were run over extended periods (generally one year) using a modified version of EPANET 2. To facilitate data management and a subsequent Monte Carlo analysis, response matrices were developed based on the EPANET model runs. Altogether, more than 200 model runs were made. Approximately half of these were sensitivity analyses. From these sensitivity analyses a distribution of uncertainty attributable to the water distribution model was estimated.

Estimates of human intake of TCE and perchlorate were made using a Monte Carlo simulation. Hydrosphere worked closely with medical experts in exposure analysis and epidemiology to implement exposure models in a Monte Carlo framework. The results of this analysis were probabilistic estimates of human intake of contaminants by individual plaintiffs.