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Three-dimensional numerical modeling of the influence of faults on groundwater flow at Yucca Mountain, Nevada.

机译：内华达州尤卡山断层对地下水流量影响的三维数值模拟。

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Numerical simulations of groundwater flow at Yucca Mountain, Nevada are used to investigate how the faulted hydrogeologic structure influences groundwater flow from a proposed high-level nuclear waste repository. Simulations are performed using a 3-D model that has a unique grid block discretization to accurately represent the faulted geologic units, which have variable thicknesses and orientations. Irregular grid blocks enable explicit representation of these features. Each hydrogeologic layer is discretized into a single layer of irregular and dipping grid blocks, and faults are discretized such that they are laterally continuous and displacement varies along strike. In addition, the presence of altered fault zones is explicitly modeled, as appropriate. The model has 23 layers and 11 faults, and approximately 57,000 grid blocks and 200,000 grid block connections. In the past, field measurement of upward vertical head gradients and high water table temperatures near faults were interpreted as indicators of upwelling from a deep carbonate aquifer. Simulations show, however, that these features can be readily explained by the geometry of hydrogeologic layers, the variability of layer permeabilities and thermal conductivities, and by the presence of permeable fault zones or faults with displacement only. In addition, a moderate water table gradient can result from fault displacement or a laterally continuous low permeability fault zone, but not from a high permeability fault zone, as others postulated earlier. Large-scale macrodispersion results from the vertical and lateral diversion of flow near the contact of high and low permeability layers at faults, and from upward flow within high permeability fault zones. Conversely, large-scale channeling can occur due to groundwater flow into areas with minimal fault displacement. Contaminants originating at the water table can flow in a direction significantly different than that of the water table gradient, and isolated zones of contaminants will occur at the water table downgradient. This behavior is not predicted by traditional models of contaminant transport. In addition, the influence of a particular type of fault cannot be generalized; depending on the location where contaminants enter the saturated zone, faults may either enhance or inhibit vertical dispersion.
机译：内华达州尤卡山地下水流动的数值模拟用于研究断层水文地质结构如何影响拟建的高级核废料库中的地下水流动。使用具有独特网格块离散化功能的3-D模型进行仿真，以准确表示具有可变厚度和方向的断层地质单元。不规则的网格块使这些功能的显式表示。每个水文地质层被离散为不规则且浸入的网格块的单层，并且断层也被离散化，使得它们在横向上是连续的，位移沿走向变化。另外，适当地显式地模拟了改变的断层带的存在。该模型具有23层和11个断层，以及大约57,000个网格块和200,000个网格块连接。过去，垂直测量水头梯度和断层附近地下水位高的现场测量被解释为深层碳酸盐岩含水层上涌的指示。然而，模拟表明，这些特征可以很容易地通过水文地质层的几何形状，层渗透率和热导率的变化以及存在渗透性断层带或仅具有位移的断层来解释。另外，断层位移或横向连续的低渗透性断层带可能会引起中等地下水位梯度，但高渗透性断层带不会引起地下水位梯度，正如其他先前假设的那样。大规模宏观分散是由于断层处高低渗透率层接触附近的垂直和横向分流，以及高渗透率断层带内的向上流动所致。相反，由于地下水流入断层位移最小的区域，因此可能发生大规模的窜流。源自地下水位的污染物的流动方向可能与地下水位梯度的流动方向大不相同，并且污染物的孤立区域将在地下水位下降时出现。传统的污染物传输模型无法预测这种行为。另外，不能归纳出特定类型故障的影响。根据污染物进入饱和区的位置，断层可能会增强或抑制垂直扩散。

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