Methodology to remediate a mixed-waste site

Both hazardous and radioactive species contaminate mixed waste. This creates circumstances where dual regulations, which were promulgated to govern the management of either hazardous or radioactive waste, apply. Throughout the Department of Energy (DOE) complex, the mixed-waste problem is significant because definitive treatment standards have not been established and limited disposal facilities are available. In addition to these constraints, treatment capability and capacity are limited. Therefore, DOE sites must store mixed waste for future disposal, despite the fact that sites may present a risk to the public and regulations governing hazardous waste require remediation by specific deadlines.

In response to the need for a comprehensive and consistent approach to the complex issue of mixed-waste management, a generalized methodology for remediation of a mixed waste site has been developed. The methodology is based on requirements set forth in the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and the Resource Conservation and Recovery Act (RCRA) and incorporates "lessons learned" from process design, remediation methodologies, and remediation projects. The methodology is applied to the treatment of 32,000 drums of mixed-waste sludge at the Oak Ridge K-25 Site.

Process technology options are developed and evaluated, first with regard to meeting system requirements and then with regard to CERCLA performance criteria. The following process technology options are investigated: (1) no action; (2) separation of hazardous and radioactive species; (3) dewatering; (4) drying; and (5) solidification/stabilization. The first two options were eliminated from detailed consideration because they did not meet the system requirements. A quantitative evaluation clearly showed that, based on system constraints and project objectives, either dewatering or drying the mixed-waste sludge was superior to the solidification/stabilization process option. The ultimate choice between the drying and the dewatering options will be made on the basis of a technical evaluation of the relative merits of proposals submitted by potential subcontractors.

The methodology is generally applicable to mixed-waste remediation projects and is comprehensive. An evaluation of regulations is presented that clarifies complex mixed waste requirements. The application of the methodology to the K-25 Site mixed-waste remediation project is the first comprehensive case study, identified by the author, that is based on CERCLA evaluation criteria and uses a quantitative assessment of alternatives with data from rough order-of-magnitude material balance and cost estimates. This thesis serves as a guide to engineers and scientists who are evaluating options and implementing a mixed-waste remediation project at a DOE site.