The fate of haloacetic acids and trihalomethanes in an aquifer storage andrecovery program, Las Vegas, Nevada

The fate of disinfection byproducts during aquifer storage and recovery (AS R) is evaluated for aquifers in southern Nevada, Rapid declines of haloacet ic acid (HAA) concentrations during ASR, with associated little change in C l concentration, indicate that HAAs decline primarily by in situ microbial oxidation, Dilution is only a minor contributor to HAA concentration declin es during ASR. Trihalomethane (THM) concentrations generally increased duri ng storage of artificial recharge (AR) water and then declined during recov ery. The decline of THM concentrations during recovery was primarily from d ilution of current season AR water with residual AR water remaining in the aquifer from previous ASR seasons and native ground water. In more recent A SR seasons, for wells with the longest history of ASR, brominated THMs decl ined during storage and recovery by processes in addition to dilution. Thes e conclusions about THMs are indicated by THM/Cl values and supported by a comparison of measured and model predicted THM concentrations, Geochemical mixing models were constructed using major-ion chemistry of the three end-m ember waters to calculate predicted THM concentrations. The decline in brom inated THM concentrations in addition to that from dilution may result from biotransformation processes.