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|Title:||Phenomenological investigations of the Jefferson Proving Ground UXO technology demonstrations|
|Authors:||Environmental Laboratory (U.S.)|
U.S. Army Environmental Center.
Butler, Dwain K.
Llopis, José L.
Simms, Janet E.
|Keywords:||Environmental and geologic backgrounds|
Unexploded ordnance (UXO)
Jefferson Proving Ground, Indiana
|Publisher:||Geotechnical Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Technical report (U.S. Army Engineer Waterways Experiment Station) ; GL-99-7.|
Abstract: Environmental conditions and geophysical properties and their spatial and temporal variability for the Jefferson Proving Ground (JPG) UXO test sites are examined. The four JPG phases are discussed, and geophysical anomaly signatures are calculated for Phases II and III baseline ordnance items. Rainfall and its resulting effect on soil water content are the dominant environmental parameters. The near-surface soil electrical conductivity varies significantly between wet site conditions and dry site conditions. Implications of wet-versus-dry site conditions for detection of buried ordnance are significant for ground penetrating radar (GPR) and somewhat less significant for the electromagnetic (EM) induction methods. The presence of a clay layer as shallow as 0.3 m and 1.5 to 5 m thick can cause significant difficulties for GPR detection of ordnance items buried within the layer for any site condition (wet or dry). Above the clay layer, the material is predominantly very fine-grained quartz, with only small amounts of clay minerals, which refutes prior claims that high-clay content soils limited the depth of investigation of GPR at the JPG sites. Significant spatial variation in near-surface magnetic susceptibility are discussed, with magnetic susceptibility of materials in the upper 0.5 m of the site varying by an order of magnitude over horizontal distances of 2 to 3 m. The susceptibility variations produce "geologic" magnetic anomalies that significantly interfere with detection of the magnetic anomalies of buried ordnance. Magnetic background areas of the 40-acre site vary from "quiet" (< 5 nT) to noisy (~ 20 nT). Predicted total magnetic field anomalies for the Phases II and III baseline ordnance items indicate the minimum peak positive anomaly magnitude for Phase III is 18 nT, while some Phase II baseline ordnance targets have anomaly values < 10 nT. For magnetically quiet areas of the site, only some of the Phase II baseline ordnance targets are problematically detectable. For magnetically noisy areas of the site, however, a small number of Phase III ordnance targets and a significant number of Phase II targets become problematically detectable. Similarly, EM61 time domain electromagnetic (TDEM) maps indicate considerable areas exist where background noise levels are < 2 mV, although some areas have noise levels -5- 10 mV. While only a small number of Phase III ordnance targets are problematically detectable with a TDEM system, a significantly larger number of Phase II targets could be problematically detectable, depending on the burial location at the site. The results indicate the need to evaluate the results of UXO detection surveys based on site-specific criteria. Selection of appropriate geophysical survey methods should be guided by a priori assessment of environmental parameter variations, topography, accessibility, geology and soil type variations, and geophysical parameter variations. Geophysical signature modeling for expected ordnance types and depths should be conducted, with site-specific signal-to-noise considerations.
|Rights:||Approved for public release; distribution is unlimited.|
|Appears in Collections:||Technical Report|
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