Rapid transport of viruses in a floodplain aquifer

An unconfined floodplain aquifer near Missoula, MT, was instrumented with 89 monitoring wells and 20 four-port multilevel samplers. Bromide, bacteriophages MS2, PRD1 and X174 and the attenuated enterovirus, polio virus (type-1 CHAT strain), were seeded into the aquifer as slug injections. Bromide transport rates ranged between 22–29 m/d. Input concentrations of the tracers and the placement of monitoring wells limited detection of bromide and polio virus to 19.4 m and the detection of three bacteriophage to 40.5 m downgradient from the injection point. After 7.5 m of transport, the calculated relative attenuations [Harvey R. W and Garabedian S. P. (1991) Env. Sci. Tech. 25, 178–185] for MS2, PRD-1, X174 and attenuated polio virus were 49, 71, 65 and 99%, respectively. During the 72-h experiment, die-off was negligible (less than 1%) and attachment of virus to sediment surfaces resulted in the overall differences in bromide and virus behavior. Although relative attenuations at downgradient monitoring wells indicated that the virus tracers were attaching to aquifer material along the flowpath, virus peaks arrived at observation wells at rates similar to the bromide peak. The high collision efficiency of the attenuated polio virus resulted in breakthrough curve truncation. Natural attenuation of slug input virus over a “typical” source–supply set-back distance of 30.5 m would most likely not reduce virus concentrations to proposed acceptable risk levels in this or a similar cold-water high-velocity groundwater system.