Abstract
All aquifers are heterogeneous to a certain degree. The spatial distribution of hydraulic conductivity K(x, y, z), or aquifer heterogeneity, significantly influences the groundwater flow movement and associated solute transport. Of particular importance in designing an in-situ remediation plan is a knowledge of low-K layers because they are less accessible to remedial agents and form a bottleneck in remediation. The characterization of aquifer heterogeneity is essential to the solution of many practical and scientific groundwater problems. This article reviews the field technique using the multilevel slug test (MLST), which determines a series of K estimates at depths of interest in a well by making use of a double-packer system. The K(z) obtained manifests the vertical variation of hydraulic conductivity in the vicinity of the test well, and the combination of K(z) from different wells gives rise to a three-dimensional description of K(x, y, z). The MLST response is rather sensitive to hydraulic conductivity variation; e.g., it is oscillatory for highly permeable conditions (K > 5×10^(-4) m s^(-1)) and a nonoscillatory for K < 5×10^(-4) m s^(-1). In this article we discuss the instrumentation of the double-packer system, the implementation of the depth-specific slug test, the data analysis methods for a spectrum of response characteristics usually observed in the field, and field applications of the MLST.
Highlights
All aquifers are heterogeneous to a certain degree as they are composed of geological materials of different hydraulic conductivities
Butler and Zhan (2004) found that aquifer storage in highly permeable aquifers can be neglected for α < 130. These criteria of neglecting aquifer storage are commonly satisfied in the field, and the quasi-steady state approach is reasonable for modeling the multilevel slug test (MLST) responses
The characterization of aquifer heterogeneity is essential to the solutions of many practical and scientific groundwater problems
Summary
All aquifers are heterogeneous to a certain degree as they are composed of geological materials of different hydraulic conductivities. The spatial variability of hydraulic conductivity in an aquifer, K(x, y, z), is usually referred to as aquifer heterogeneity, which significantly influences groundwater flow behavior as well as the underlying solute transport. It is well recognized that the low-K layers in a contaminated aquifer are bottlenecks to many in-situ remediation measures. This is because they are able to store massive contaminants through molecular diffusion in the contamination stage that. It is well recognized that the heavy breakthrough tails normally observed in either laboratory or field tracer tests are largely controlled by back diffusion, and the influence of the low-K layers is a dominant factor underlying the non-Fickian transport phenomena (Haggerty and Gorelick 1995; Schumer et al 2003; Zhang et al 2008, 2009; Bianchi et al 2011; and references given therein). How to characterize aquifer heterogeneity has been a major concern in hydrogeology and contaminant hydrogeology
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