Three-Dimensional Modeling of Contaminants Transport in Subsurface Environment: From the Land Surface Through the Unsaturated Zone and Fully Saturated Aquifers

9317009在过去的十年里，田野非均质性在地下水污染问题上的重要性已经得到了广泛的认识。已经进行了许多实地和理论研究，以加强我们对其影响的了解，并提高我们对污染物在实地迁移的预测能力。条件模拟被普遍认为是最符合逻辑的方法，可以改善我们对现场污染物迁移的预测。然而，许多研究都采用了简化和不切实际的情景，如一维或二维稳态流动。从来没有进行过污染物通过非饱和区多维移动到地下水位并通过含水层传播的研究。限制因素之一是多维数值模拟所需的计算难度和巨大的CPU时间。在非饱和区流动和输运的情况下，由于控制流动方程的非线性，这一问题最为严重。随机条件模拟更加强大。研究人员最近开发的一种方法将模拟二维非饱和非均质土壤中溶质运移的CPU时间减少了两到三个数量级。这一技术突破允许在非饱和条件下有条件地模拟非均质多孔介质中的溶质运移。这种方法的稳健性迫使我们在污染物从非均质非饱和包气带到完全饱和含水层的三维传输上进行尝试。这项研究的总体目标是开发一种计算上可行的算法来模拟变饱和条件下三维非均匀多孔介质中的污染物迁移，并研究我们提出的条件概念在设计采样程序方面的潜力，以改进我们对地下环境中污染物迁移的预测。换句话说，我们想评估预测污染物在地下环境中迁移所需的采样程度。

9317009 Yeh The importance of field heterogeneities in groundwater pollution problems has been widely recognized during the last decade. Many field and theoretical studies have been conducted to enhance our understanding of their impacts and to improve our predictive ability of contaminant migration in the field. Conditional simulation is generally accepted as the most logical approach that can improve our prediction of contaminant transport in the field. Many studies are, however, adopt simplified and unrealistic scenarios such as one or two-dimensional steady-state flow. Studies have never been conducted where contaminants move multi- dimensionally through the unsaturated zone to the water table and propagate through the aquifer. One of the limiting factors is computational difficulty and the enormous amount of CPU time required for multi-dimensional numerical simulation. This problem is most severe in the case of flow and transport in the unsaturated zone due to the nonlinearity of the governing flow equation. Stochastic conditional simulations are even more formidable. An approach recently developed by the investigator reduces the CPU time for simulating transport of solutes in two-dimensional unsaturated heterogeneous soils by two or three orders of magnitude. This technical breakthrough allows conditional simulation of solute transport in heterogeneous porous media under unsaturated conditions. The robustness of the approach compels us to try it on three-dimensional transport of contaminants from heterogeneous unsaturated vadose zones to fully saturated aquifers. The overall objectives of the study are to develop a computationally feasible algorithm for simulation of contaminant transport in three-dimensional heterogeneous porous media under variably saturated conditions and to investigate the potential of our proposed conditional concept for designing sampling procedures that improves our prediction of contaminant migration in subsurface envir onment. In other words, we would like to assess the degree of sampling is necessary to predict migration of contaminants in the subsurface environment.