The U.S. Army Corps of Engineers (USACE) has accomplished a great deal at the St. Louis Airport Site (SLAPS) since the October 1997 transition of the program. FUSRAP's primary goal for SLAPS is to restrict the release of contaminated materials and minimize their potential impact on human health, wildlife and the environment. To accomplish this goal, USACE invited the public to participate in setting the interim cleanup standards for the site.
In 1997, an Engineering Evaluation/Cost Analysis (EE/CA) developed by DOE proposed the removal of radioactive contaminated materials immediately adjacent to Coldwater Creek (CWC) at the West End of SLAPS next to the gabion wall (constructed of rock-filled wire baskets) and shipped to a licensed, out-of-state disposal facility. This action would minimize the potential for migration of contaminated material to CWC under current and anticipated site conditions as excavation of the site proceeded. Contaminated materials would be removed in accordance with DOE Order 5400.5, which specifies that the guideline for radionuclide concentrations for radium and thorium in soil is 5 picocuries per gram (pCi/g) above background in the top 15 centimeters (6 inches) of soil and 15 pCi/g above background in any subsequent 15-centimeter layer (below top 6 inches). The guideline concentration for uranium-238 (U-238) would be 50 pCi/g (surface and subsurface soils). In October 1997, the execution of FUSRAP was transferred from DOE to USACE under the Energy and Water Development Appropriations Act. Initially, USACE continued the removal of material under the authority of the DOE EE/CA document. Completion of this removal action resulted in the disposal of 5,100 cubic yards of contaminated material, which were subsequently shipped by rail in covered gondola cars to an out-of-state, licensed disposal facility.
Additionally, in 1997, USACE conducted baseline groundwater characterization studies for SLAPS. These studies involved the installation of groundwater monitoring wells, measurement of groundwater levels, and radiological and chemical analysis of groundwater samples.
In March 1998, USACE prepared an EE/CA proposing measures to stabilize SLAPS and the adjacent Ballfields until a comprehensive cleanup could be achieved. Essentially, the EE/CA called for the excavation of material exceeding radium-226 (Ra-226) and thorium-230 (Th-230) at 5 pCi/g above background in the top 6 inches of soil (surface) averaged over a 100 square-meter area; Ra-226 and Th-230 at 15 pCi/g above background below the top 6 inches of soil (subsurface) averaged over a 100 square-meter area; and U-238 at 50 pCi/g above background in the surface and subsurface of the soil with off-site disposal in a licensed facility. The goal of the 1998 EE/CA was to give USACE the authority to address the contaminated materials in these properties and prevent off-site migration. The second objective of the EE/CA was to restore these properties to beneficial use.
Under the authority of the 1998 EE/CA, USACE installed infrastructure to facilitate the future remediation of the site and took action to control surface water and off-site migration of contamination. A 1,200-foot rail spur was constructed to allow for rapid shipment of contaminated material via rail. A sedimentation basin was also constructed on the west end of the site (near Coldwater Creek).
Once the infrastructure was in place and surface-water run-off was under control, USACE began excavating and shipping material from the site. Initial efforts began at the upstream end of the site (i.e. often referred to as the “East End”) and in the upstream segments of the drainage ditches along McDonnell Boulevard. The next priority was removal of an area referred to as the “Radium Pits,” which was believed to be the on-site location of the highest levels of contamination based on historical use. Excavation/remediation under the authority of the EE/CA continued until 2005, when a Record of Decision was completed.
The Record of Decision (ROD) presented the Final Remedy for the site (as opposed to the EE/CA, which presented an interim action). The ROD – which addressed not only the St. Louis Airport Site, but the Latty Avenue Site and the SLAPS Vicinity Properties Site as well – was the result of USACE investigations and CERCLA planning activities that had been occurring concurrent with the EE/CA removal action at SLAPS. USACE developed cleanup alternatives and presented them to the public for review in the Feasibility Study (FS) and Proposed Plan (PP) in May 2003. Comments on the documents were accepted through July 14, 2003. The public’s input was considered, and a final ROD (Record of Decision for the North St. Louis County Sites, dated Sept. 2, 2005) was issued. The final remedy consisted of excavation to achieve remediation goals:
- top 6-inch layer averaged over any 100 square-meter area: 5 pCi/g Ra-226/14 pCi/g Th-230/50 pCi/g U-238 above background;
- subsurface soil (below the top 6 inches) averaged over any 100 square-meter area and averaged over a 6-inch thick layer of soil: 15 pCi/g Ra-226/15 pCi/g Th-230/50 pCi/g U-238 above background;
- Sediment below the mean water gradient will be removed if radionuclide concentrations averaged over any 100 square-meter area:: 15 pCi/g Ra-226/43 pCi/g Th-230/150 pCi/g of U-238 above background.
- All accessible contaminated soils/material will be disposed of off-site at a properly permitted facility.
The remainder of SLAPS was remediated in accordance with the ROD. More than 600,000 cubic yards of radiologically contaminated material was removed from the SLAPS over a nine-year period. A formal closing ceremony took place May 30, 2007.
A final Post Remedial Action Report/Final Status Survey Evaluation for the site was completed in May 2009.
Current activities include site monitoring and maintenance of the rail spur, which is still used to ship material excavated from the various SLAPS Vicinity Properties, or SLAPS VPs. Upon completion of remediation of the SLAPS Vicinity Properties, the rail spur will also be removed, and the site (and associated files) will be turned over to the Department of Energy's Office of Legacy Management for long-term management.
Because of the extended time period for remediation, Five-Year Reviews have occurred in accordance with CERCLA and the National Contingency Plan (NCP). Five-year reviews are conducted to ensure that human health and the environment are being protected by the response action being implemented. A team – led by USACE and including representatives from the EPA and Missouri Department of Natural Resources – documents conditions at each site and the surrounding area. In addition, members of the community are contacted for their views about the cleanup process to date. Five-Year Review Reports have been issued in 2004 and 2010.