Sorption of Military Explosive Contaminants on Bentonite Drilling Muds

摘要

Concern over the environmental fate of explosives has brought about the development of sensitive analytical methods for measuring them in groundwater. In turn this concern has been extended to validating the sampling procedures for groundwater. This report addresses the potential effects of residual drilling muds on the analysis for explosive contaminants (TNT, DNT, RDX, and HMX) in monitoring wells. The approach was to determine sorption isotherms for each contaminant. Sorption appeared to be independent of solids concentration. Linear isotherms were obtained for RDX and HMX over a range of analytic concentrations; therefore, a single constant can be used to estimate the amount sorbed when the solution concentration is known. Isotherms for TNT and DNT were not linear, however. Scatchard analysis suggested that the isotherms for these analytes could be resolved into two predominant components: a linear component above a certain sorbed quantity and a Langmuir-type component below this quantity. The experimental data were fitted by regression analysis using the appropriate model. The equations developed can be used to predict the sorbed fraction (analytical bias) for any combination of solids and analyte concentration. The amounts of bentonite found in some existing wells do not appear to be sufficient to cause significant bias in analyses for these explosive contaminants.