Resolution of the mixed waste issue for EDTA-based steam generator chemical cleaning waste solutions

The valence state of chromium in an EDTA-based iron oxide removal solvent waste was determined under various storage conditions. The solvent is used to remove deposits from the secondary sides of nuclear power plant steam generators and was developed under the sponsorship of the Electric Power Research Institute and the Steam Generator Owners Group. Chromium is typically present in such waste at a level greater than 5 ppm, thus creating the possibility that the waste could be subject to regulatory control as a hazardous waste under RCRA. Additionally, the waste typically contains trace levels of radioactivity, and could potentially be classified as mixed waste. In the past, interim processing has been used to reduce the chromium concentration in the waste to allow storage for greater than 90 days without the waste being subject to regulatory control. Extended storage prior to final processing and disposal is routinely required. However, the results reported herein clearly show that any chromium in the waste is exclusively trivalent and will remain so indefinitely under any credible storage scenario. Thus, the waste qualifies for the trivalent chromium exclusion provided under RCRA. Further, the results show that the valence state of chromium in the waste cannot be changed without extraordinary effort.