Chemicals Of Potential Concern in Underground Tanks
Chemicals of potential concern (COPCs) were originally identified through the Industrial Hygiene Chemical Vapor Technical Basis, initiated in 2004 and revised in 2006 as part of a broader effort to strengthen the Tank Farms Industrial Hygiene program. Under that original framework, chemicals detected in tank farm sources at or above 10 percent of the applicable occupational exposure limit (OEL) were evaluated for inclusion on the COPC List to support hazard communication, sampling, monitoring, training, and worker protection.
As the Tank Vapor program matured and the body of technical, toxicological, characterization, and exposure assessment information grew, the terminology and classification approach were refined. In addition to introducing Tank Vapor Chemicals of Concern (COCs) as a separate classification, the program also refined the definition of the Tank Vapor COPC from its earlier use in the original framework. The current definitions for Tank Vapor COPCs and COCs are provided below.
Tank Vapor COPC. Tank Vapor chemical, highest result or based on statistical examination, found in any tank headspace or anywhere in the Tank Farm at a concentration greater than or equal to 10%, but less than 50%, of their OEL.
Tank Vapor COC. Tank Vapor chemical, highest result or based on statistical examination, found in tank headspaces at a concentration greater than or equal to 50% of their OEL, making it reasonably likely they could occur outside the tank headspace, and pose a potential exposure hazard in the work area.
The COPC List remains the program list of tank vapor chemicals that have been identified as a COPC or COC in any Tank Farm. Farm-specific designation as a Tank Vapor COC or COPC is provided on each Farm’s Tank Vapor Information Sheet (TVIS). (Note: AY and AZ-Farms are listed together on a single TVIS as they share a common ventilation exhauster, 702-AZ.)
The original COPC list was developed by evaluating tank vapor chemicals against applicable occupational exposure limits (OELs). The primary OELs used were the more protective of the OSHA Permissible Exposure Limit (PEL) and the ACGIH Threshold Limit Value (TLV). Established PELs or TLVs were available for only 131 of the chemicals evaluated at the time. When neither existed for a chemical, the Technical Basis considered other established U.S. occupational exposure guidance values, specifically NIOSH RELs and AIHA WEELs, as equivalent for evaluation purposes. Chemicals without suitable established values were further evaluated using screening values.
- OSHA PEL: Occupational Safety and Health Administration Permissible Exposure Limits
- ACGIH TLV: American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV)®
- AIHA WEEL: American Industrial Hygiene Association (AIHA) Workplace Environmental Exposure Level (WEEL)
- NIOSH REL: National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limit (REL)
Screening Values
Chemicals that did not have any of the above established OELs or other U.S. occupational exposure guidance values 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), later termed Hanford Tank Farm OELs (HTFOELs) 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 the original comprehensive review documented in the Industrial Hygiene Chemical Vapor Technical Basis, 48 chemicals were placed on the COPC list. Since that review, the list has been periodically updated as additional characterization data, technical evaluations, and toxicological information have become available. Those updates have included revisions to individual listings and the addition of compounds identified through continued evaluation.
The current COPC list contains 61 chemicals.
Historical Assessments of the COPC List and Exposure Limits:
COPC/Exposure Limits
In response to the Tank Vapor Assessment Team Recommendation Dose Recommendation #2 (DR2), Pacific Northwest National Laboratory (PNNL) performed assessments to both review the COPC list and evaluate the HTFOELs associated with those chemicals.
These efforts addressed the recommendation to ensure the COPC list remained current and to better document the basis for updates over time. The resulting reports included PNNL-25880, Hanford Tank Vapors COPCs Update, which evaluated the COPC list and its updates, and PNNL-25790, State of Knowledge Assessment: COPC/Exposure Limits, which examined whether sufficiently new technical information existed to support re-evaluation of current COPC HTFOELs.
Additional PNNL reports on COPCs can be found at this link.