Abstract
The single-well push-pull tracer test is a convenient and cost-effective tool to estimate hydrogeological properties of a subsurface aquifer system. However, it has a limitation that test results can be affected by various experimental designs. In this study, a series of laboratory-scale push-pull tracer tests were conducted under various conditions controlling input tracer density, pumping rate, drift time, and hydraulic gradient. Based on the laboratory test results, numerical simulations were performed to evaluate the effects of density-induced plume sinking and pumping rate on the proper estimation of groundwater background linear velocity. Laboratory tests and numerical simulations indicated that the actual linear velocity was underestimated for the higher concentration of the input tracer because solute travel distance and direction during drift time were dominantly affected by the plume density. During the pulling phase, reasonable pumping rates were needed to extract the majority of injected tracer mass to obtain a genuine center of mass time (tcom). This study presents a graph showing reasonable pumping rates for different combinations of plume density and background groundwater velocity. The results indicate that careful consideration must be given to the design and interpretation of push-pull tracer tests.
Highlights
One of the commonly utilized methods to estimate aquifer hydrogeologic properties is a tracer test, in which nonreactive or reactive tracers are injected into a borehole to generate a breakthrough curve of the injected tracer transporting through the aquifer medium [1,2,3]
Several case studies were simulated to verify the impact of concentration breakthrough curves was minimized
It is known that many factors affect the result of a push-pull tracer test, density effect and pumping rate have rarely been considered as important influential factors in estimating linear groundwater velocity
Summary
One of the commonly utilized methods to estimate aquifer hydrogeologic properties is a tracer test, in which nonreactive or reactive tracers are injected into a borehole to generate a breakthrough curve of the injected tracer transporting through the aquifer medium [1,2,3]. Based on the analysis of the obtained breakthrough curves from the tracer test, information about the aquifer geometry, solute transport dynamics, microbial processes, and reactive movement of the tracer can be evaluated [4,5,6,7]. The first step is the injection phase (so-called “push”). In this step, a prepared solution is injected into the aquifer at an injection well. The second step is the drift phase, where the injected solution moves along with the ambient groundwater flow
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