MODELING THE IMPACT OF BODY-CONTACT RECREATION ON PATHOGEN CONCENTRATIONS IN A SOURCE DRINKING-WATER RESERVOIR

A modeling study was conducted to evaluate the impact of body-contact recreation (e.g., water skiing, jet skiing, swimming) on pathogen conc entrations in a source drinking water reservoir under construction in eastern Riverside County in Southern California. A hybridized Monte Ca rlo-finite segment model was used to pl edict pathogen concentrations in the reservoir resulting from pathogen inputs associated with shed f ecal material and accidental fecal releases (AFRs). Monte Carlo techni ques were incorporated into the finite segment model to define charact eristics about individual recreators which affect pathogen loading to the reservoir (e.g., infection, pathogen shedding rate, location). Res ults of simulations are provided in the form of cumulative distributio n and probability density functions derived from uncertainty analyses. The model predicted considerable spatial and temporal variability in pathogen concentrations within the reservoir, with elevated levels of Cryptosporidium rotavirus, and poliovirus in the epilimnion during per iods of high recreational use. Predicted Giardia concentrations were l ower than the other pathogens. Hypolimnetic concentrations of all path ogens were generally 1-3 orders of magnitude lower than the overlying epilimnetic concentrations. Model results also suggest that field samp ling will underestimate the mean, range and variance of pathogen conce ntrations in the reservoir. The model was further modified to include a particle tracking scheme to allow for transport of aggregated fecal material. Results from simulations using this approach demonstrate a p otential for high pathogen loads due to body-contact recreation period ically reaching treatment plants. (C) 1998 Elsevier Science Ltd. All r ights reserved.