Porous aquifer materials are often characterized by layered heterogeneities that influence groundwater flow and present complexities in contaminant transport modeling. Such flow variations also have the potential to impact the dissolution flux from dense nonaqueous phase liquid (DNAPL) pools. This study examined how these heterogeneous flow conditions affected the dissolution of a tetrachloroethene (PCE) pool in a two-dimensional intermediate-scale flow cell containing coarse sand. A steady-state mass-balance approach was used to calculate the PCE dissolution rate at three different flow rates. As expected, aqueous PCE concentrations increased along the length of the PCE pool and higher flow rates decreased the aqueous PCE concentration in the effluent. Nonreactive tracer studies at two flow rates confirmed the presence of a vertical flow gradient, with the most rapid velocity located at the bottom of the tank. These results suggest that flow focusing occurred near the DNAPL pool. Effluent PCE concentrations and pool dissolution flux rates were compared to model predictions assuming local equilibrium (LE) conditions at the DNAPL pool/aqueous phase interface and a uniform distribution of flow. The LE model did not describe the data well, even over a wide range of PCE solubility and macroscopic transverse dispersivity values. Model predictions assuming nonequilibrium mass-transfer-limited conditions and accounting for vertical flow gradients, however, resulted in a better fit to the data. These results have important implications for evaluating DNAPL pool dissolution in the field where subsurface heterogeneities are likely to be present.

中文翻译：

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非生物四氯乙烯稠密非水相液池溶解在非均相流动环境中的质量通量分析

多孔含水层材料通常具有层状异质性，这些异质性会影响地下水流动并在污染物传输建模中呈现复杂性。这种流动变化也有可能影响致密非水相液体 (DNAPL) 池的溶解通量。本研究检查了这些非均质流动条件如何影响四氯乙烯 (PCE) 池在含有粗砂的二维中等规模流动池中的溶解。使用稳态质量平衡方法计算三种不同流速下的 PCE 溶解速率。正如预期的那样，水性 PCE 浓度沿 PCE 池的长度增加，较高的流速降低了流出物中的水性 PCE 浓度。两种流速下的非反应性示踪剂研究证实了垂直流动梯度的存在，以最快的速度位于罐底。这些结果表明流动聚焦发生在 DNAPL 池附近。假设 DNAPL 池/水相界面处的局部平衡 (LE) 条件和流量均匀分布，将流出物 PCE 浓度和池溶解通量率与模型预测进行比较。LE 模型没有很好地描述数据，即使在广泛的 PCE 溶解度和宏观横向分散值范围内也是如此。然而，假设非平衡传质限制条件和考虑垂直流动梯度的模型预测结果更好地拟合数据。这些结果对于评估可能存在地下异质性的领域中的 DNAPL 池溶解具有重要意义。