Assess the risk posed by the hazardous characteristics of the waste. A primary purpose of the risk assessment is to determine which hazardous constituent of the multihazardous waste presents the greatest risk. This knowledge can help identify source reduction and treatment possibilities to reduce the risk of the waste. An assessment that determines that a waste constituent does not present a significant risk may provide an opportunity for regulatory flexibility. For example, the USNRC or state authority may allow a licensee to manage a chemical–radioactive waste as a chemical waste without regard to radioactivity when the radioactive constituent concentration is less than what the USNRC specifies for an unrestricted area.

Minimize the hazardous constituents in the waste. Consider applying the waste minimization methods specific to each hazardous constituent of the waste. This strategy could result in reducing or eliminating one hazardous constituent from the waste stream and managing the waste as a single-hazard waste. For example, the substitution of nonignitable liquid scintillation fluid (LSF) for toluene-based LSF reduces a chemical–radioactive waste to a radioactive waste.

Determine options for managing the multihazardous waste. Waste management options include recycling, laboratory methods, management at institutional waste facilities, and treatment and disposal at commercial sites. Options can vary considerably between laboratories depending upon institutional capabilities and state and local laws. It may be appropriate to manage the waste in order of risk priority, from high to low risk. Options must be compatible with all hazards, and combinations of waste management methods may be limited by their order of application. Reject any combination or sequence of methods that may create an unreasonable risk to waste handlers or the environment, or that might increase the overall risk. If an option has a clear advantage in efficiency and safety, it should have highest priority. For example, if safe facilities are available on-site, hold short-half-life radioactive waste for decay before managing it as a chemical or biological waste. The EPA Final Rule on the storage, treatment, transportation, and disposal of low-level mixed waste will allow holding the waste for longer than 90 days.

Select a single management option when possible. Some waste management methods are appropriate for more than one waste hazard. Some multihazardous waste can be disposed of safely in the sanitary sewer when allowed by the local POTW.

8.C.1 Chemical–Radioactive (Mixed) Waste

LLMW is the most common form of multihazardous waste generated in laboratories and the most problematic for waste management. “Mixed waste” is the regulatory term for multihazardous waste that exhibits both chemical and radioactive hazards (40 CFR § 266.210). Mixed wastes are defined by EPA as “wastes that contain a chemical hazardous waste component regulated under Subtitle C of RCRA and a radioactive component consisting of source, special nuclear, or byproduct material regulated under the Atomic Energy Act of 1946 (AEA)” (EPA, 1986). The complex challenge of managing waste controlled by two federal agencies was reduced by the EPA Final Rule on the storage, treatment, transportation, and disposal of low-level mixed waste of 2001 (40 CFR Part 266, Subpart N). The rule conditionally exempts the hazardous waste constituents of LLMW from RCRA during storage and treatment. This change provides more opportunities for treatment of the chemical constituents in LLMW, enabling disposal as a single hazard constituent LLRW. State regulations may continue to inhibit laboratory and on-site minimization, storage, and treatment of mixed waste. The rule applies only to LLMW that meets the specified conditions and is generated under a single USNRC license or USNRC Agreement State license. The rule also exempts LLMW and hazardous naturally occurring or accelerator-produced radioactive materials (NARM) waste from RCRA manifest, transportation, and disposal requirements that adhere to the specified conditions. Under this conditional exemption, the waste remains subject to manifest, transport, and disposal requirements under the USNRC (or USNRC Agreement State) regulations for LLW or eligible NARM. This flexibility allows on-site storage of LLMW for periods longer than 90 days. The management opportunity to treat the hazardous waste constituents of LLMW on-site can reduce the dependence on services provided by commercial treatment and disposal facilities.

Examples of laboratory mixed waste include

   used flammable (e.g., toluene) liquid scintillation cocktails,

   phenol–chloroform mixtures from extraction of nucleic acids from radiolabeled cell components,

   aqueous solutions containing radioactive material and chloroform that occur in solutions generated by the neutralization of radioactive trichloroacetic acid solutions,

   certain gel electrophoresis waste (e.g., methanol or acetic acid containing radionuclides), and

   lead contaminated with radioactive materials.

Mixed waste produced at university, clinical, and medical research laboratories is typically a mixture of a LLRW and chemical hazardous waste. Mixed waste from nuclear and energy research laboratories can



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