USING HEAT TO DETERMINE GROUNDWATER VELOCITIES NEAR A RIVERBANK FILTRATION PRODUCTION WELL

Quantification of water travel time and infiltration velocities between rivers and nearby production wells is of interest because of the strong influence these parameters have on the extracted water quality. In this study, infiltration velocities during riverbank filtration were assessed by combining in situ temperature measurements and numerical modeling of groundwater flow and heat transport. Water temperature time series were obtained at 17 locations in the riverbed infiltration area beneath the Saint John River (New Brunswick, Canada). Temperatures within the underlying aquifer, to depths as great as 15 m, varied seasonally in response to the river temperature variations. Numerical simulations of subsurface heat transport were conducted for a three-dimensional region in the vicinity of a production well and the riverbed area. Using independent input parameters, with the exception of the hydraulic conductivity anisotropy ratio, the simulation results for temperature were found to be in good agreement with the field data for most locations (mean RMS of 3.4 ^oC). As expected, the simulated velocities varied with distance from the production well, with resultant velocities increasing to greater than 1 m/d close to the well intake. The simulated velocities at all locations were much more influenced by the transient pumping rate of the well than by the seasonally variable stage of the river.