Groundwater remediation and no-further action decision making at petroleum underground storage tank (UST) sites has largely been based on an understanding of plume length, plume stability, and attenuation rates for key hydrocarbon constituents. Regulatory guidance to support and guide such decisions is based in part on plume studies involving individual hydrocarbon constituents, namely benzene and methyl tert-butyl ether (MTBE). Questions remain regarding whether current guidance is applicable to chemical mixtures such as gasoline range organics (GRO), diesel range organics (DRO), and oxygen containing organic compounds (OCOCs) resulting from hydrocarbon biodegradation. To help address this concern, data from California's GeoTracker database were used to estimate maximum plume lengths, plume stability, and attenuation rates of DRO (which can be used as an analytical surrogate for OCOCs) and GRO relative to benzene and MTBE. The distributions of maximum plume lengths were similar for the four constituents with medians ranging from 27 to 32 m. The fraction of monitoring wells with a decreasing concentration trend ranged from 19% for DRO to 40% for MTBE, while fewer than 7% of the wells had an increasing concentration trend for any of the constituents. Median attenuation rates ranged from 0.10% day⁻¹ for DRO to 0.17% day⁻¹ for MTBE. The results suggest attenuation based risk management is appropriate for DRO and GRO plumes at most petroleum UST sites.

中文翻译：

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DRO、GRO、苯和 MTBE 的比较烟羽研究：对风险管理的影响

石油地下储罐 (UST) 场地的地下水修复和无进一步行动决策主要基于对关键碳氢化合物成分的羽流长度、羽流稳定性和衰减率的了解。支持和指导此类决定的监管指南部分基于涉及单个碳氢化合物成分的烟羽研究，即苯和甲基叔丁基醚 (MTBE)。目前的指南是否适用于汽油有机物 (GRO)、柴油有机物 (DRO) 和由碳氢化合物生物降解产生的含氧有机化合物 (OCOC) 等化学混合物仍存在问题。为了帮助解决这个问题，加州 GeoTracker 数据库的数据被用来估计最大羽流长度、羽流稳定性、DRO（可用作 OCOC 的分析替代品）和 GRO 相对于苯和 MTBE 的衰减率。四种成分的最大羽流长度分布相似，中值范围为 27 至 32 m。浓度呈下降趋势的监测井比例从 DRO 的 19% 到 MTBE 的 40%，而任何成分的浓度呈上升趋势的井不到 7%。中值衰减率范围为 0.10% 天 而不到 7% 的井中任何一种成分的浓度都有增加的趋势。中值衰减率范围为 0.10% 天 而不到 7% 的井中任何一种成分的浓度都有增加的趋势。中值衰减率范围为 0.10% 天^-1为 DRO 至 0.17% 天^-1为 MTBE。结果表明，基于衰减的风险管理适用于大多数石油 UST 站点的 DRO 和 GRO 羽流。