Karst Pathway Delineation Using Combined Spatial And Geophysical Analysis At Camp Crowder, Missouri

Camp Crowder, a Missouri Army National Guard training facility located south of<br>Neosho, Missouri, is part of the Pool’s Prairie NPL site. DNAPL contamination found within the<br>soil and groundwater is suspected of migrating off-post through conduit and fracture systems that<br>have developed within the underlying karst bedrock. Dye tracer studies have confirmed<br>groundwater movement towards the contaminated wells, though the actual route of migration is<br>not known. The overburden is dominantly a cherty residuum, through which the surface water<br>and contaminants percolate into the underlying karst aquifer. An integrated approach using<br>photo-geologic analysis, airborne electromagnetic surveys, seismic profiling, and twodimensional<br>electrical resistivity imaging (2D-ERI) was conducted to map subsurface changes<br>associated with this complex karst system.<br>Surface based geophysical surveys were able to map the character of the overburden and<br>underlying bedrock. Seismic refraction data proved best in resolving the top of the competent<br>bedrock (below the weathering layer), whereas the resistivity data imaged the top of the<br>weathered horizon (transition from low-to-high resistivity) and coarser grained intervals within<br>the overburden. In many instances, lineaments interpreted from aerial photographs coincide with<br>disruptions observed in the ground-based geophysics. Interpretation of the surface geophysical<br>data suggests that a mantle of friable, heavily fractured, and/or weathered rock overlies the<br>competent bedrock and may act as a zone for contaminant storage, and for migration over short<br>distances.<br>Airborne multi-frequency electromagnetic mapping provided a regional view of the site.<br>Conductivity inversion of the data correlated well with the surface geophysical data and indicated<br>that the mantle of friable material extended farther than originally anticipated. This extension<br>brought potential contaminant pathways into contact with several additional lineaments. Derived<br>bedrock topography indicates that the contaminant source area is situated on a transition zone<br>between deep and shallow residuum, with paths and pools leading in several directions.