Following a remedial investigation, the U.S. Army has developed the Proposed Remedy for the Section 36 Lime Basins Dense Non-Aqueous Phase Liquid (DNAPL). The discovery of DNAPL in August 2009 triggered the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) process and performance of a Remedial Investigation/Feasibility Study. The recommended remedial alternative, which is consistent with EPA guidance and with which the Colorado Department of Public Health and Environment and Tri-County Health Department concurred, is detailed in a fact sheet now available for public
review.
The Proposed Remedy for the Section 36 Lime Basins DNAPL does not alter the overall hazardous waste management remedy selected for the On-Post Record of Decision (ROD) for the areas within the Rocky Mountain Arsenal boundaries.
The former Lime Basins, in use from 1942 to 1957, were designed to receive various aqueous wastes and remove arsenic from South Plants wastewater. In August 2009, field monitoring of the Section 36 Lime Basins dewatering wells indicated the presence of DNAPL composed primarily of compounds used during the historic chemical manufacturing processes conducted in the South Plants. (DNAPL is a liquid that is denser than water and that will not dissolve in groundwater.)
In 2010, a remedial investigation was conducted to assess the nature and extent of DNAPL in the Lime Basins area. Following an analysis using CERCLA evaluation criteria, a remedy was proposed that removes DNAPL to the extent practicable; verifies continued source containment through monitoring of water levels within and outside a slurry wall; and monitors potential DNAPL movement through trending of DNAPL related compounds in groundwater. The proposed remedy meets the requirements for the presumptive remedy developed by EPA based on the evaluation and cleanup of similar contaminants at other sites. This fact sheet is available at the RMA Joint Administrative Record and Document Facility, 5650 Havana St., Building 129, Commerce City, CO 80022; 303-289-0983; open M – F 12 – 4 p.m. or by appointment.
Questions and comments should be directed to: Ms. Peggy Machamer, RVPRO, RMA, 5650 Havana St., Building 129, Commerce City, CO 80022; 303-289-0300; Fax: 303-289-0582; E-mail: pao@rma.army.mil.
