Chemicals Of Potential Concern

in Underground Tanks

A chemical of potential concern (COPC) is a chemical found in tank waste vapors that may pose a hazard in the work environment. The COPCs for Hanford tank wastes were categorized in 2006 by evaluating the chemicals detected and hypothesized in the Hanford tank vapor space as a source for vapor hazards, as listed in the IH Technical Basis. The IH Technical basis details the approach to controlling against vapor-related hazards and references a series of Pacific Northwest National Laboratory technical documents. The current COPC list is shown here. The current list is revised as necessary utilizing any new detailed headspace characterization.

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Evaluated Data

Tank waste and headspace characterization data were evaluated to identify volatile chemicals that could be emitted into the worker breathing zones. Waste chemistry and limitations of the characterization methods (minimum detection limits and uncertainties) were examined to hypothesize what other potentially hazardous chemicals might be present. The reported and hypothesized chemicals were then individually evaluated against toxicological criteria (detailed in PNNL-14949, “Toxicological Assessment of Hanford Tank Headspace Chemicals of Potential Concern”) to place on the COPC list.

 
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Screening Values

Chemicals that did not have any of the above established limits were screened based upon comparison of the maximum average headspace concentration to a conservatively established screening value. Screening values were assigned to be 10% of a suitable OEL when an established OEL from a non-U.S. agency was available. Additional safety factors were included when a surrogate chemical was used to establish the screening value, when differences between the chemical and chosen surrogate chemical were deemed significant, when the surrogate chosen was based on a metabolite, and when the chemical itself was a possible carcinogen. Screening values could also be raised by a factor of 10 if they had documented low toxicity. The magnitude of the safety factors were based on judgment by the responsible toxicologist.

The screening values, developed by an expert group, were based on international information where available, available toxicological data, and other toxicological data on surrogates. PNNL – 15640, “Screening Values for Non-Carcinogenic Hanford Waste Tank Vapor Chemicals that Lack Established Occupational Exposure Limits,” describes the procedure used to develop screening values and lists all chemicals screened, their screening values, and the bases of each screening value. PNNL-15736, “Proposed OEL for Non-Carcinogenic Hanford Waste Tank Vapor Chemicals,” details the “acceptable operational exposure limits” (AOELs) where no established limits existed. Chemicals with maximum reported concentrations less than their screening values were considered to not pose significant risks to workers.

Based on the Review

Based upon this comprehensive review 48 chemicals were placed on the COPC list. Since that review was completed, there have been numerous substitutions and additions. The majority of the expansion is the addition of individual identified substituted furans being individually listed and the addition of N-Nitrosodiethylamine. Dimethyl mercury does not currently appear on the COPC list. Dimethyl mercury is still sampled as part of the environmental program and all samples to date have been less than the OEL. Consistent with our periodic COPC review, dimethyl mercury sample results will be analyzed for potential inclusion. Lastly, hydrocarbons were moved to the “general hazard” category. The current COPC list contains 59 chemicals.