The cut-off wall is an effective countermeasure to prevent contaminant transport from a contaminated site. However, the aquitard beneath the cut-off wall may serve as a preferential path, leading to an earlier breakthrough of contaminants in the cut-off wall system. In this study, we present a 2-D analytical model for characterizing the contaminant transport in the cut-off wall and aquitard system. The Green function method and discretization method are used to investigate contaminant migration in a semi-infinite domain. We show that the one-dimensional cut-off wall model may be insufficient to predict contaminant transport when the aquitard hydraulic conductivity (k2) exceeds 5 × 10-10 m/s. The contaminant mass outflow from the aquitard for the case with k2 = 2 × 10-9 m/s may account for 53 % of the total contaminant mass outflow. Increasing k2 from 5 × 10-10 m/s to 5 × 10-9 m/s leads to a 2.9-fold increase of cumulative mass outflow. An approximate fitting formula is proposed to calculate the required minimum thickness of cut-off wall under different type of aquitards. The thicker cut-off wall is required to ensure the cumulative mass outflow will not exceed the allowable value when k2 is relatively high (e.g., 1 × 10-9 m/s).

中文翻译：

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截留壁和滞水层系统中二维污染物迁移的分析模型


截流墙是防止污染物从受污染场地输送的有效对策。然而，截留壁下方的滞水层可能作为优先路径，导致污染物更早地突破截留壁系统。在本研究中，我们提出了一个二维分析模型，用于表征截留壁和滞水层系统中的污染物传输。Green 函数法和离散化方法用于研究半无限域中的污染物迁移。我们表明，当滞水层水力传导率 （k2） 超过 5 × 10-10 m/s 时，一维截留壁模型可能不足以预测污染物的迁移。在 k2 = 2 × 10-9 m/s 的情况下，从滞水层流出的污染物质量可能占总污染物质量流出量的 53%。将 k2 从 5 × 10-10 m/s 增加到 5 × 10-9 m/s，导致累积质量流出增加 2.9 倍。提出了一个近似拟合公式来计算不同类型滞水层下所需的最小截流壁厚度。当 k2 相对较高时（例如，1 × 10-9 m/s），需要更厚的截止壁来确保累积质量流出不会超过允许值。