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Co‐occurrence of 1,4‐dioxane with trichloroethylene in chlorinated solvent groundwater plumes at US Air Force installations: Fact or fiction

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Increasing regulatory attention to 1,4‐dioxane has prompted the United States Air Force (USAF) to evaluate potential environmental liabilities, primarily associated with legacy contamination, at an enterprise scale. Although accurately quantifying environmental liability is operationally difficult given limited historic environmental monitoring data, 1,4‐dioxane is a known constituent (i.e., stabilizer) of chlorinated solvents, in particular 1,1,1‐trichloroethane (TCA). Evidence regarding the co‐occurrence of 1,4‐dioxane and trichloroethylene (TCE), however, has been heavily debated. In fact, the prevailing opinion is that 1,4‐dioxane was not a constituent of past TCE formulations and, therefore, these two contaminants would not likely co‐occur in the same groundwater plume. Because historic handling, storage, and disposal practices of chlorinated solvents have resulted in widespread groundwater contamination at USAF installations, significant potential exists for unidentified1,4‐dioxane contamination. Therefore, the objective of this investigation is to determine the extent to which 1,4‐dioxane co‐occurs with TCE compared to TCA, and if these chemicals are co‐contaminants, whether or not there is significant correlation using available monitoring data. To accomplish these objectives, the USAF Environmental Restoration Program Information Management System (ERPIMS) was queried for all relevant records for groundwater monitoring wells (GMWs) with 1,4‐dioxane, TCA, and TCE, on which both categorical and quantitative analyses were performed. Overall, ERPIMS contained 5,788 GMWs from 49 installations with records for 1,4‐dioxane, TCE, and TCA analytes. 1,4‐Dioxane was observed in 17.4% of the GMWs with detections for TCE and/or TCA, which accounted for 93.7% of all 1,4‐dioxane detections, verifying that 1,4‐dioxane is seldom found independent of chlorinated solvent contamination. Surprisingly, 64.4% of all 1,4‐dioxane detections were associated with TCE independently. Given the extensive dataset, these results conclusively demonstrate for the first time that 1,4‐dioxane is a relatively common groundwater co‐contaminant with TCE. Trend analysis demonstrated a positive log‐linear relationship where median 1,4‐dioxane levels increased between ∼6% and ∼20% of the increase in TCE levels. In conclusion, this data mining exercise suggests that 1,4‐dioxane has a probability of co‐occurrence of ∼17% with either TCE and/or TCA. Given the challenges imposed by remediation of 1,4‐dioxane and the pending promulgation of a federal regulatory standard, environmental project managers should utilize the information presented in this paper for prioritization of future characterization efforts to respond to the emerging issue. Importantly, site investigations should consider 1,4‐dioxane a potential co‐contaminant of TCE in groundwater plumes. Integr Environ Assess Manag © 2012 SETAC

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