Oklahoma Geological Survey, Mewbourne College of Earth and Energy, The University of Oklahoma, Norman, OK 73019, USA; Earth and Ecosystem Science Program, Central Michigan University, Mount Pleasant, MI 48859, USA.
Department of Earth and Atmospheric Sciences, Central Michigan University, 314 Brooks Hall, Mount Pleasant, MI 48859, USA; Institute for Great Lakes Research, Central Michigan University, Mount Pleasant, MI 48859, USA.
Sci Total Environ. 2022 Jun 1;823:153634. doi: 10.1016/j.scitotenv.2022.153634. Epub 2022 Feb 8.
1,4-Dioxane released at the Gelman Site in Washtenaw County, Michigan, produced a series of contaminant plumes migrating up to 3 km through a heterogenous glacial aquifer system. An analysis of 1,4-dioxane concentrations in the Eastern Area of the Gelman Site between 2011 and 2017 documented a mass balance deficit of 2200 kg in excess of 2100 kg of 1,4-dioxane removed via remediation. Five mechanisms were evaluated to account for the mass deficiency: sorption, matrix diffusion, biodegradation, surface discharge, and bypass of the existing monitoring well network. The mass of 1,4-dioxane sorbed to aquifer and aquitard materials and the mass of 1,4-dioxane diffused into low permeability zones were estimated. However, decreasing aqueous concentrations across most of the contaminated area between 2011 and 2017 are expected to induce desorption and back diffusion during this period. Surface water discharge to a storm drain in the downgradient portion of the site was analyzed using concentration measurements and stream gage data. Results suggest that 1,4-dioxane mass entering the drain during the period between 2011 and 2017 was insufficient to account for the mass deficiency. Although available geochemical measurements indicate predominantly anaerobic aquifer conditions at the Gelman Site, biodegradation of 1,4-dioxane was estimated using first order decay rate constants from other sites where conditions may be more favorable. Results suggest that biodegradation could explain some but not all of the missing mass. Bypass of the downgradient monitoring well network is the most parsimonious explanation for the 1,4-dioxane mass deficit. This conclusion is supported by documented flow path complexity through the aquifer system and the sparse density of monitoring wells in the downgradient Eastern Area. These findings underscore the importance of characterizing aquifer heterogeneity when modeling and remediating persistent groundwater contaminants such as 1,4-dioxane.
密歇根州 Washtenaw 县 Gelman 场地释放的 1,4-二恶烷通过非均质地层潜水系统向上迁移了 3 公里，形成了一系列污染物羽流。2011 年至 2017 年期间，对 Gelman 场地东部地区的 1,4-二恶烷浓度进行分析，发现 2100 公斤通过修复去除的 1,4-二恶烷，存在 2200 公斤的质量平衡亏缺。评估了 5 种机制来解释质量亏缺：吸附、基质扩散、生物降解、地表排放和绕过现有的监测井网络。估算了含水层和隔水层材料吸附的 1,4-二恶烷质量和扩散到低渗透带的 1,4-二恶烷质量。然而，在 2011 年至 2017 年期间，大多数受污染区域的水溶液浓度降低，预计在此期间会引起解吸和反向扩散。使用浓度测量和河流流量数据分析了场地下游的雨水渠的地表水排放。结果表明，2011 年至 2017 年期间，进入排水渠的 1,4-二恶烷质量不足以解释质量亏缺。尽管可用的地球化学测量表明 Gelman 场地的含水层条件主要为厌氧条件，但使用其他条件可能更有利的地点的一级衰减速率常数估算了 1,4-二恶烷的生物降解。结果表明，生物降解可以解释部分但不是全部的缺失质量。下游监测井网络的旁路是 1,4-二恶烷质量亏缺的最合理解释。这一结论得到了通过含水层系统的记录的流径复杂性和下游东部地区监测井的稀疏密度的支持。这些发现强调了在模拟和修复 1,4-二恶烷等持久性地下水污染物时，描述含水层非均质性的重要性。
