Field Research Opportunities at the Old Rifle UMTRA Site

Current NABIR research activities at the Old Rifle UMTRA Site are focused on accelerating microbially mediated reduction of U(VI) to U(IV) by adding an electron donor such as acetate. As described in the Summary of Results from Field Research section, this process has been demonstrated on Shiprock, Gunnison, and Rifle sediment samples under laboratory conditions. Push-pull tests have been completed at the Old Rifle Site and key site-specific rate data used to design and implement a field-scale experiment involving long-term (3 months) addition of acetate. The acetate injection is now complete. Significant removal of U(VI) from solution was observed and data and samples obtained during acetate addition are being analyzed. Over the next several months, the system will be monitored to estimate re-mobilization rates of bio-reduced U(IV). The injection gallery and observation wells installed during the initial experiment may be available for future experiments provided necessary UMTRA, regulatory, landowner, and stakeholder approvals are obtained.

In addition, U(VI)-contaminated groundwater and alluvial sediment samples from the Old Rifle Site can be made available for research purposes. Figure 2 shows the monitoring wells available for sampling.

Typically, the wells encounter groundwater at about 3 to 5 meters depth with a screened interval of approximately 1.5 m (5.0 feet) in length. The wells typically are completed in sand and gravel of the alluvium and tag the underlying bedrock (Wasatch Formation). Wells completed in the Wasatch Formation are also available, but these typically are free of U contamination. Figure 3 shows the current status of the U plume and overall groundwater chemistry is summarized in Table 1.

Figure 3. Uranium Distribution in Alluvial Aquifer-Old Rifle, May 1998 (From http://www.doegjpo.com/gwwp/rfl/sowp/rfl_old/u42501.pdf)

Additional information on site characteristics is available at http://www.doegjpo.com/umtra_gw/umtra_3.htm#3.2.8 (summary level information for both the Old and New Rifle Sites) and http://www.doegjpo.com/gwwp/rfl/sowp/rfl_old/u42501.pdf (detailed information for the Old Rifle Site).