Hydraulic Tomography: Continuity and Discontinuity of High-K and Low-K Zones

<p> Hydraulic tomography is an emerging &filig;eld and modeling method that provides a continuous hydraulic conductivity ( <em> K </em> ) distribution for an investigated region. Characterization approaches that rely on interpolation between one-dimensional (1D) pro&filig;les have limited ability to accurately identify high- <em> K </em> channels, juxtapositions of lenses with high <em> K </em> contrast, and breaches in layers or channels between such pro&filig;les. However, locating these features is especially important for groundwater &fllig;ow and transport modeling, and for design and operation of in situ remediation in complex hydrogeologic environments. We use transient hydraulic tomography to estimate 3D <em> K </em> in a volume of 15-m diameter by 20-m saturated thickness in a highly heterogeneous uncon&filig;ned alluvial (clay to sand-and-gravel) aquifer with a <em> K </em> range of approximately seven orders of magnitude at an active industrial site in Assemini, Sardinia, Italy. A modi&filig;ed Levenberg-Marquardt algorithm was used for geostatistical inversion to deal with the nonlinear nature of the highly heterogeneous system. The imaging results are validated with pumping tests not used in the tomographic inversion. These tests were conducted from three of &filig;ve clusters of continuous multichannel tubing (CMTs) installed for observation in the tomographic testing. Locations of high- <em> K </em> continuity and discontinuity, juxtaposition of very high- <em> K </em> and very low- <em> K </em> lenses, and low- <em> K </em> &lsquo;&lsquo;plugs&rsquo;&rsquo; are evident in regions of the investigated volume where they likely would not have been identi&filig;ed with interpolation from 1D pro&filig;les at the positions of the pumping well and &filig;ve CMT clusters. Quality assessment methods identi&filig;ed a suspect high- <em> K </em> feature between the tested volume and a lateral boundary of the model.</p>