The objective of this study was to characterize the behavior of a groundwater contaminant (trichloroethene) plume after implementation of a source-containment operation at a site in Arizona. The plume resides in a quasi three-layer system comprising a sand/gravel unit bounded on the top and bottom by relatively thick silty clayey layers. The system was monitored for 60 months beginning at start-up in 2007 to measure the change in contaminant concentrations within the plume, the change in plume area, the mass of contaminant removed, and the integrated contaminant mass discharge. Concentrations of trichloroethene in groundwater pumped from the plume extraction wells have declined significantly over the course of operation, as have concentrations for groundwater sampled from 40 monitoring wells located within the plume. The total contaminant mass discharge associated with operation of the plume extraction wells peaked at 0.23 kg/d, decreased significantly within one year, and thereafter began an asymptotic decline to a current value of approximately 0.03 kg/d. Despite an 87% reduction in contaminant mass and a comparable 87% reduction in contaminant mass discharge for the plume, the spatial area encompassed by the plume has decreased by only approximately 50%. This is much less than would be anticipated based on ideal flushing and mass-removal behavior. Simulations produced with a simplified 3-D numerical model matched reasonably well to the measured data. The results of the study suggest that permeability heterogeneity, back diffusion, hydraulic factors associated with the specific well field system, and residual discharge from the source zone are all contributing to the observed persistence of the plume, as well as the asymptotic behavior currently observed for mass removal and for the reduction in contaminant mass discharge.

中文翻译：

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在氯溶剂污染现场，水力源封闭之后，地下水污染物羽流的持久性。

这项研究的目的是表征在亚利桑那州的某处实施源头遏制操作后，地下水污染物（三氯乙烯）羽流的行为。羽流位于准三层系统中，该系统包括由相对较厚的粉质黏土层在顶部和底部界定的沙子/砾石单元。自2007年启动以来，对系统进行了60个月的监测，以测量烟羽中污染物浓度的变化，烟羽面积的变化，去除的污染物的质量以及综合的污染物排放量。从羽状抽气井抽出的地下水中的三氯乙烯浓度在运行过程中已显着下降，从羽状抽气井中的40个监测井中抽取的地下水浓度也有明显下降。与羽状抽气井运营相关的总污染物排放量峰值为0.23 kg / d，在一年内显着下降，此后开始逐渐下降至当前值约0.03 kg / d。尽管羽流的污染物质量降低了87％，污染物排放的污染物质量降低了87％，但羽流所包围的空间面积仅减少了约50％。这远少于根据理想冲洗和去除质量行为所预期的结果。使用简化的3D数值模型进行的仿真与测量数据相当吻合。研究结果表明，与特定井场系统相关的渗透率非均质性，向后扩散，水力因素，