Surface geophysical investigation of the areal and vertical extent of metallic waste at the former Tyson Valley Powder Farm near Eureka, Missouri, Spring 2004

The former Tyson Valley Powder Farm near Eureka, Missouri, was used primarily as a storage facility for the production of small arms ammunition during 1941?47 and 1951?61. A secondary use of the site was for munitions testing and disposal. Surface exposures of small arms waste, characterized by brass shell casings and fragments, as well as other miscellaneous scrap metal are remnants of disposal practices that took place during U.S. Army operation and can be found throughout the site. Little historical information exists describing disposal practices, and more debris is believed to be buried in the subsurface. The U.S. Army Corps of Engineers has identified several areas of concern throughout the former Tyson Valley Powder Farm. A surface-geophysical investigation was performed by the U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers, to evaluate the areal and vertical extent of metallic debris in the subsurface within three of these areas of concern. Electromagnetic and magnetic methods were used to locate anomalies indicating relatively large concentrations of buried metallic debris within the selected areas of concern. Maps were created identifying twelve anomalous zones in the three areas of concern, and three of these zones were selected for further investigation. The extent and depth of the anomalies within these zones were explored using two-dimensional direct-current resistivity methods. Resistivity and time-domain induced polarization data were compared to the anomalous locations of the electromagnetic and magnetic surveys. The geophysical methods selected for this study were useful in determining the areal and vertical extent of metallic waste within the former Tyson Valley Powder Farm. However, electromagnetic and magnetic methods were not able to differentiate magnetic scrap metal from non-magnetic metallic small arms waste, most likely due to the small size and scattered distribution of the small arms waste, in addition to the mixing of both types of debris in the subsurface. Electromagnetic and magnetic data showed some zones of concentrated anomalies, while there was a general scattering of small anomalies throughout the site. Inverted resistivity sections, as well as induced polarization sections, showed the debris to have a maximum depth of approximately 1 to 2 meters below the surface.