Temperature measurements during Managed Aquifer Recharge for safeguarding subsurface travel times
Subsurface travel time from the area of recharge to the abstraction during Managed Aquifer Recharge (MAR) is a critical parameter to ensure sufficient attenuation for hygienic parameters and other undesired substances. This study investigates seasonal temperature fluctuations observed in recharge water and MAR wells as a proxy for cheap and reliable travel time control at a basin infiltration site in Berlin-Spandau (Germany). Based on a time series from seven years of manual measurements, temperature fluctuations observed in infiltration basins and abstraction wells were fitted to sinusoidal functions. Peak values represented as local maxima and local minima from the fitted curves were used for the approximation of travel times between infiltration basin and abstraction wells. Uncertainty was assessed by Monte Carlo simulation of fitted curves based on standard deviation (2s) from residuals. The calculated error propagation from 2s in infiltration basin and 2s in wells range from 7 to 19 days. This study indicates that travel time approximation based on biased manual measurements of temperature is associated with high uncertainty. Nevertheless, the water temperature method for estimating subsurface travel times shows encouraging results and if temperature can be accurately determined, this method can be readily applied at other sites with similar characteristics.