Electromagnetic Mapping (Em Map) Of Perched Water To Improve Remedial Activities At Hill Air Force Base

This report contains a description of how a proprietary geophysical technique was used to assist<br>groundwater investigations, in and around Operable Unit 1, OU1, located on the eastern side of Hill Air<br>Force Base, (HAFB), Utah. The primary objective was to define the sources of a groundwater plume<br>contaminated with Light Non Aqueous Phase Liquids, LNAPLs, which originated within OU1. An<br>additional objective was to locate subsurface channels for the plume that extended into off-base areas.<br>Although investigations have defined 7 individual groundwater bearing zones, most of these<br>investigations focused on the near-surface water, i.e., about 20 ft below the surface, groundwater<br>flowing horizontally on top of the clays of the Alpine Formation and within the sands and gravels of the<br>Provo Formation.<br>Results of the geophysical surveys defined water channels feeding seeps along the east and north<br>sides of two landfills within OU1. An additional survey defined sources for groundwater recharge.<br>Channels contributing to the off-Base groundwater were mapped in a separate survey. The technique<br>also proved useful in determining groundwater sources for off-Base landslides. A final survey was able<br>to confirm that water in the lower water-bearing zones of the Alpine Formation was not connected to the<br>near-surface groundwater plume.<br>The paper defines how this proprietary geophysical technique, based on U. S. Patent #5,825,188,<br>is a cost-effective means of defining groundwater flows. When coupled with the other investigative<br>tools used at OU1, including monitoring well/piezometer installations, Cone Penetrometer Tests (CPT),<br>and soil borings, the technique improves the overall understanding of groundwater flows at the site and<br>provides for a higher degree of confidence in the siting of other investigative tools. Examples are<br>provided showing where a groundwater channel feeding a seep, missed in a large drilling/CPT program,<br>was identified. In addition, the technique also provided essential data for the design of a groundwater<br>interception trench to connect contaminated groundwater and LNAPLs.