Mechanism of unconventional radial dispersion of radiotracer in confined aquifers
The mechanism of migration of radiotracer in confined aquifers is particularly important when it is used to evaluate the sensitivity of confined aquifers to pollution and reconstruct the history of pollutant vechange.In this study,a new mobile-immobile model was used to establish a radial dispersion mathemati-cal model considering the mixing effect to study the unconventional radial dispersion mechanism of radio-tracer in confined aquifers.Analytical solution was derived using the Laplace transform,and the Stehfest method was used to facilitate the numerical inverse Laplace transform.To test the assumptions used in the mathematical model,a numerical simulation was executed by the finite element method developed by the COMSOL Multiphysics.The results are as follows:①A larger mixing effect can result in a smaller concen-tration of radiotracer in the wellbore;②The greater the decay constant of the radiotracer,the slower the migration of the radiotracer in the aquifer;③The unconventional radial dispersion in an aquifer can be neg-lected when the mass transfer coefficient is less than 0.001 a-1.Otherwise,the greater the mass transfer coefficient,the lower the concentration of the radiotracer in the aquifer.
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