Hydraulic conditions at the source zone and their impact on plume behavior

A laboratory sandbox model (105 × 60 × 15 cm) was filled with different types of sediments to arrange different hydraulic conditions at the tracer’s injection zone. Tracer-input functions were monitored at the injection location and tracer breakthrough curves (BTCs) were measured at a downgradient detection plane. Numerical transport simulations analogous to the sandbox experiments were conducted in a numerical model parameterized with the properties of the sediments used in the sandbox. The results of the study demonstrate that the hydraulic conditions at the source zone have a major influence on plume development. Tracer injection into high-permeability zones causes early arrival, and enhanced transverse and reduced longitudinal spreading. Tracer injection into low-permeability zones causes late arrival, and reduced transverse and enhanced longitudinal spreading. It was further found that using simplified tracer-input functions in the analysis of BTCs can lead to biased transport parameters. The results suggest that transport parameter estimation based on tracer experiments can benefit from monitoring of the tracer-input function and subsequent consideration of the measured tracer-input function in the analysis of BTCs.