Low level radioactive waste pile closure: An innovative approach

For 17 years, a specialty alloy manufacturing facility produced ferrocolumbium alloys utilizing feedstock ores that contained small quantities of natural uranium and natural thorium. The byproducts of this process, slag and baghouse filter dust, were accumulated on company property or used as sub-base for roads and paved areas. The processing partitioned the radioactive species to the slag while the baghouse dust remained relatively free of radionuclides. The dust, however, contained high concentrations of heavy metals including barium, nickel, lead and especially chromium. As part of the overall cleanup of the 130-acre facility, in accordance with US Nuclear Regulatory Commission regulations, it was necessary to decommission an eight-acre slag pile. This paper discusses an innovative approach to this closure developed by ENSR engineers. Baghouse dust, chemically stabilized by the Chemfix reg-sign process into a clay-like product was placed as a final impermeable layer over the pile along with natural clay. Other criteria for closure design included: no intrusion into the adjacent wetland, reduction in gradient of the existing steep slopes of the pile sides for stability and use of the pile during closure as a repository for radioactively contaminated soils. Implementation of this closure plan showed the Chemfix reg-sign process successfully reduced the EP Toxicity levels in the baghouse dust to well below hazardous levels and achieved an average bulk permeability of 1 x 10-6 cm/sec for the hardened stabilized dust. Radiation levels on the pile were reduced to background levels. Currently, documentation of the program is undergoing final review before the closure is completed. 5 figs., 2 tabs