A characterization program has been developed at Hanford to image past leaks in and around the underground storage tank facilities. The program is based on electrical resistivity, a geophysical technique that maps the distribution of electrical properties of the subsurface. The method was shown to be immediately successful in open areas devoid of underground metallic infrastructure, due to the large contrast in material properties between the highly saline waste and the dry sandy host environment. The results in these areas, confirmed by a limited number of boreholes, demonstrate a tendency for the lateral extent of the underground waste plume to remain within the approximate footprint of the disposal facility. In infrastructure-rich areas, such as tank farms, the conventional application of electrical resistivity using small point-source surface electrodes initially presented a challenge for the resistivity method. The method was then adapted to directly use the buried infrastructure, specifically the steel-cased wells that surround the tanks, as "long" electrodes for both transmission of electrical current and measurements of voltage. Overcoming the drawbacks of the long electrode method has been the focus of our work over the past 7 years. The drawbacks include low vertical resolution and limited lateral coverage. The lateral coverage issue has been improved by supplementing the long electrodes with surface electrodes in areas devoid of infrastructure. The vertical resolution has been increased by developing borehole electrode arrays that can fit within the small-diameter drive casing of a direct push rig. The evolution of the program has led to some exceptional advances in the application of geophysical methods, including logistical deployment of the technology in hazardous areas, development of parallel processing resistivity inversion algorithms, and adapting the processing tools to accommodate electrodes of all shapes and locations. The program is accompanied by a full set of quality assurance procedures that cover the layout of sensors, measurement strategies, and software enhancements while insuring the integrity of stored data. The data have been shown to be useful in identifying previously unknown contaminant sources and defining the footprint of precipitation recharge barriers to retard the movement of existing contamination.

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Yellowstone National Park hosts over 10,000 thermal features (e.g. geysers, fumaroles, mud pots, and hot springs), yet little is known about the circulation depth of meteoric water feeding these features, the pathways that guide deep, hot fluids to the surface, or the separation depth of the steam that sources vapor-dominated systems. Previous near-surface geophysical studies have been effective in imaging shallow hydrothermal pathways in some areas of the park, but these methods are difficult to conduct over the large areas needed to characterize entire hydrothermal systems. Transient electromagnetic (TEM) soundings and 2D direct current (DC) resistivity profiles show that hydrothermal fluids at active sites have a higher electrical conductivity than the surrounding hydrothermally inactive areas. For that reason, airborne TEM should be an effective method to characterize large areas and identify hydrothermally active and inactive zones using electrical conductivity.Here we present preliminary results from an airborne transient electromagnetic (TEM) and magnetic survey acquired jointly by the U.S. Geological Survey (USGS) and the University of Wyoming (UW) in November 2016. At the time of this writing, the survey is planned to cover 2600 line-km of data at two scales: regional surveys with lines spaced 450 apart and two smaller, high-resolution surveys with line spacing of 150 m. The regional survey will cover northern Yellowstone Lake, the Norris-Mammoth corridor, and the Upper Geyser basin. The high-resolution surveys focus on the Upper Geyser Basin (including Old Faithful) and the Norris Geyser Basin. Data will be acquired with the SkyTEM 312, with a magnetic moment of 0.5 M A-m2. We will present preliminary inversions using the Aarhus Workbench software, with particular focus on the depths of vapor phase separation and the connectivity of pathways of meteoric water recharge. AbstractThe source of adequate groundwater resources to support community and industry (pastoral and mining) in the arid APY Lands of northern South Australia has been the subject of considerable concern since the establishment of cattle stations and community centres in the early 1900's. Although small, locally confined fractured rock aquifer systems have been defined, finding large sustainable sedimentary alluvial aquifers has been problematic despite numerous drilling campaigns over 60+ years. Challenges to their identification include a complex, apparently compartmentalised sedimentary (regolith) cover sequence, highly varying alluvial aquifer thicknesses, and the paucity of spatial information. The low sporadic rainfall/recharge and high average annual evaporation results in a highly variable groundwater quality adding to the complexity of resource determination.The role of geophysical data in addressing these shortcomings has been the subject of more recent investigation. Local scale exploration airborne EM data sets have highlighted the spatial complexity of the alluvial aquifers in the region. Airborne magnetic data, also acquired...

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