Vadose zone flow model parameterisation using cross-borehole radar and resistivity imaging

Cross-borehole geoelectrical imaging, in particular electrical resistivity tomography (ERT) and transmission radar tomography, can provide high-resolution images of hydrogeological structures and, in some cases, detailed assessment of dynamic processes in the subsurface environment. Through appropriate petrophysical relationships, these tools offer data suitable for parameterising and constraining models of groundwater flow. This is demonstrated using cross-borehole radar and resistivity measurements collected during a controlled vadose zone tracer test, performed at a field site in the UK Sherwood Sandstone. Both methods show clearly the vertical migration of the tracer over a 200 h monitoring period. By comparing first and second spatial moments of changes in moisture content predicted from a numerical simulation of vadose zone flow with equivalent statistics from two- and three-dimensional ERT and cross-borehole radar profiles the effective hydraulic conductivity is estimated to be approximately 0.4 m/d. Such a value is comparable to field estimates from borehole hydraulic tests carried out in the saturated zone at the field site and provides valuable information that may be utilised to parameterise pollutant transport models of the site.