Tm. Johnson et al., Groundwater "fast paths" in the Snake River Plain aquifer: Radiogenic isotope ratios as natural groundwater tracers, GEOLOGY, 28(10), 2000, pp. 871-874
Preferential flow paths are expected in many groundwater systems and must b
e located because they can greatly affect contaminant transport. The fundam
ental characteristics of radiogenic isotope ratios in chemically evolving w
aters make them highly effective as preferential now path indicators. These
ratios tend to be more easily interpreted than solute-concentration data b
ecause their response to,vater-rock interaction is less complex. We demonst
rate this approach with ground,vater Sr-87/Sr-86 ratios in the Snake River
Plain aquifer within and near the Idaho National Engineering and Environmen
tal Laboratory. These data reveal slow-flow zones as lower Sr-87/Sr-86 area
s created by prolonged interaction with the host basalts and a relatively f
ast flowing zone as a high Sr-87/Sr-86 area.