A CASE STUDY OF URANIUM MOBILITY IN GROUNDWATER AT THE DUPONT CHAMBERS WORKS SITE

摘要

To determine whether uranium mobility via groundwater is a concern at a Manhattan Engineering District (MED) project uranium-processing site, a three step investigative approach was utilized. First, existing data and data sources were analyzed. Second, the site was screened using a Geoprobe? to locate potential problem areas. Finally, a focused investigation is underway using monitoring wells located in suspect areas. This study charts the investigative approach taken to determine if MED-related contamination is present at the DuPont Chambers Works Site in Deepwater, New Jersey. Specific tasks of the investigation will focus on the nature and extent of the contaminants in soil and groundwater and the potential for mobility from site soils to groundwater. The rationale and methodologies for the investigation of soil and groundwater are presented in the following sections of this paper. In the course of these investigations, soil mineralogies were identified using X-ray diffraction (XRD) analysis. Bulk soil chemistry was determined using Scanning Electron Microscopy (SEM). To determine how strongly other potentially mobile uranium phases are bound to site soils, sequential extraction desorption experiments were performed on soil samples from areas with elevated levels of soil uranium concentrations. Each sample was subjected to progressively stronger extractants designed to dissolve particular chemical phases, and the resultant liquids were analyzed for uranium. This test was a good proxy for field conditions at the Chambers Works site due to the presence of various chemical plumes and a wide range of groundwater Eh and pH. XRD analysis of two samples showed the presence of low solubility/mobility uranium oxides including pitchblend and uraninite. However, in addition to immobile phases, six of the seven samples analyzed by sequential extraction showed that thirty to seventy-five percent of the uranium bearing phases present may be mobilized under dilute to weakly acidic groundwater conditions. One sample showed forty percent of uranium present may be mobilized by rainwater. These findings suggest that uranium mineralogy at the site does not exclude the presence of uranium plumes, although only localized plumes have been found.