Flushing is one of the most common and important remediation technologies to deal with the contaminated aquifers. However, the present solutions used to calculate contaminant flushing are sometimes too complicated to apply in engineering practice for quick screening purposes. This thesis uses the finite-element COMSOL Multiphysics as a platform to obtain a new solution to describe the flushing process on the homogeneous aquifers, which has been verified to be reliable. This thesis will investigate two kinds of heterogeneity in which: 1) the flow direction is parallel to; or 2) perpendicular to the two-zone interface. To analyze how the transport properties of the zones of these with contrasting hydraulic properties will impact on the contaminant transport during the flushing process, one or more parameter values were changed, while the other parameter values were kept constant. Then the predicted breakthrough curves (BTCs) were compared with each other. Through the analysis of a series of hypothetical scenarios, the results of this thesis are summarized as follows: 1) For the case when the flow direction is perpendicular to the interface of two different heterogeneous zones, the order of heterogeneous aquifers in series will not affect the flushing results, and the properties (dispersivity, porosity, and retardation factor) of heterogeneity in series can be homogenized with the arithmetic mean. Furthermore, when the averaged dispersivity increases along the flowpath from the up-gradient to the down-gradient zones, the BTC will decline slower. When the averaged porosity or retardation factor is increasing, it takes less time to flush out the same amount of contaminants, but does not affect the decline rate of the BTC; 2) For the case when the flow direction is parallel with the interface of two different heterogeneous zones, a greater difference of porosities of two zones will lead to a greater mass flux between two zones; a greater difference of transverse dispersivities will lead to a greater mass flux between the two zones; and the difference of thickness of two zones will not affect the results. This research is expected to fill the gap of flushing model on homogeneous and heterogeneous aquifers.
ETD Chair
Zhan, Hongbin Holder of Endowed Dudley J. Hughes '51 Chair in Geology and Geophysics
