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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 52 (2002), Pages 365-375

An Evaluation of Hydrogeologic Parameters on Natural Attenuation of Explosives

Harrelson, Danny W., Zakikhani, Mansour, and Pennington, Judy C.

ABSTRACT

The Louisiana Army Ammunition Plant (LAAP) is a 14,974-acre government-owned property that was placed on the EPA National Priorities List in 1989 due to contamination caused by past disposal of explosives-laden wastewater in 16 unlined surface impoundments located in an area designated as Area P. The near surface geology at LAAP consists of Pleistocene, terraced fluvial deposits (basal gravels fining upward to clays) unconformably overlying Eocene, nonmarine, massive sands, silty sands, silty clays, and occasional lignitic beds. These Pleistocene sediments occur as fining-upward sequences of materials that were deposited as fluvial terraces associated with the ancestral Red River of the South. Maximum thickness of these deposits is about 60 feet, but local variations are present. Immediately underlying the terrace deposits is an effectively impermeable boundary, the Cane River Formation (Eocene in age). This unit consists of consolidated claystones and is not an aquifer in this area. Data from the late 1980s indicated that the explosives contaminants from the Area P lagoons had entered the two terrace aquifers below the site. Groundwater plumes containing RDX, TNT, and 1,3,5-trinitrobenzene (TNB, a photodecomposition product of TNT) had been detected. Concentrations in the upper terrace aquifer were lower in 1994 than in 1990, suggesting an improvement in the groundwater quality since the removal of the lagoons. The groundwater contaminant plumes had not advanced very far laterally, suggesting very slow transport and the potential for attenuation.


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