Danny W. Harrelson

Monitored Natural Attenuation of Explosives

Explosives are subject to several attenuation processes that potentially reduce concentrations in groundwater over time. Some of these processes are well defined, while others are poorly understood. The objective of the project was to optimize data collection and processing procedures for evaluation and implementation of monitored natural attenuation of explosives. After conducting experiments to optimize data quality, a protocol was established for quarterly monitoring of thirty wells over a 2-year period at a former waste disposal site. Microbial biomarkers and stable isotopes of nitrogen and carbon were explored as additional approaches to tracking attenuation processes. The project included a cone penetrometry sampling event to characterize site lithology and to obtain sample material for biomarker studies. A three-dimensional groundwater model was applied to conceptualize and predict future behavior of the contaminant plume. The groundwater monitoring data demonstrated declining concentrations of explosives over the 2 years. Biomarker data showed the potential for microbial degradation and provided an estimate of the degradation rate. Measuring stable isotopic fractions of nitrogen in TNT was a promising method of monitoring TNT attenuation. Overall, results of the demonstration suggest that monitored natural attenuation is a viable option that should be among the options considered for remediation of explosives-contaminated sites.

The Great Red River Raft and its Sedimentological Implications

The Red River Raft was a series of log jams believed to have developed over 2,000 years ago when the Mississippi River avulsed and captured the Red River to the South. Navigation of the Red River and the Red River Raft presented major challenges during the settlement of the Red River Valley. This Raft extended approximately 150 miles along the river from Natchitoches, Louisiana to the Louisiana-Arkansas State line. Several theories on how this raft developed include catastrophic flooding, climatic change, and prehistoric human activities. The presence and eventual clearing of the Raft influenced the geomorphic evolution of the Red River and the Atchafalaya basin as well as changed the geomorphic character of the Red River with considerable physical and historical consequences. Numerous attempts were made to clear parts or even the full extent of the Raft beginning in the 1830s. After years of struggle, the Raft was eventually cleared by AD 1873. In AD 1968, the Red River Waterway navigation effort was authorized providing for a 9 ft., navigation channel from its confluence with the Atchafalaya near Simmsport to Shreveport, Louisiana. The Red River Navigation project consisting of a series of five locks and dams was completed in AD 1994. This chapter will review and describe the historic and current geomorphic evolution of the Red River attributable to the completion of the Red River Navigation Project and the removal of the Raft.