Capture zone delineation is a simple analytical tool that has been employed in many aspects of hydrological sciences throughout recent history. While using capture zone remediation techniques, the dilution of the source contaminant is closely examined and monitored. The dilution factor is the ratio of the contaminant concentration in the pumped water over the contaminant source concentration (assumed to be constant) in a pump-and-treat setup. It is important because it provides critical information about the fluid dynamics within the aquifer, and shows how much the source has been diluted within the aquifer. The objective of this thesis is to investigate how changing the source geometry and orientation impacts the dilution factor. The scenario includes an arbitrary line-source length and orientation, fully vertically penetrating well in a homogeneous, horizontally isotropic, confined aquifer. The experiment is set under steady-state conditions. Two analytical models are performed, the first dealing with three subcases consisting of constant source concentrations (cases 1-3), and the second dealing with three subcases cases involving time-dependent source concentrations (cases 4-6). The integrals associated with cases 4- 6 are solved in MATLAB using Gaussian quadrature and Gaussian Kronrod integration methods and demonstrate how each of these source types impacts the dilution factor calculation. After analyzing the results for the first analytical model, the overall conclusion is that the distance between the pumping well and the source is the dominant variable for increasing or decreasing the dilution factor. The source angle and source length also have an impact on the dilution factor. As these values decrease, so do the dilution factor values. The MATLAB model shows differing trends for both of the integration methods (Gaussian quadrature and Gaussian Kronrod) and the source types influence the dilution factor. The finite source decreases rapidly as the last of the source reaches the well, and then slowly flattens out until there is no longer a concentration in the system. The radioactive source and the Gaussian type source decrease with increasing time measurements. The models can be retrofitted for other source types and different variables to fit differing scenarios. Overall, the results will help with planning for future remediation projects, and these models allow for an initial screening test to be done before more robust, time intensive and expensive models can be put into place.
ETD Chair
Zhan, Hongbin Holder of Endowed Dudley J. Hughes '51 Chair in Geology and Geophysics
