Effects of pore-scale dispersion, degree of heterogeneity, sampling size, and source volume on the concentration moments of conservative solutes in heterogeneous formations
Effects of pore-scale dispersion, degree of heterogeneity, sampling size, and source volume on the concentration moments of conservative solutes in heterogeneous formations
复制标题
孔隙尺度分散度、非均质性程度、采样大小和源体积对非均质地层中保守溶质的浓缩矩的影响
DOI：
10.1016/j.advwatres.2007.08.009
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发表时间：
2008
影响因子：
4.7
通讯作者：
A. Bellin
中科院分区：
文献类型：
--
作者：
D. Tonina;A. Bellin
孔隙尺度弥散（PSD），含水层的非均质性，采样体积，和源的大小影响溶质浓度的保守示踪剂在非均质多孔地层中传输。在这项工作中，我们开发了一套新的分析解决方案的浓度合奏平均值，方差和变异系数（CV），考虑所有这些因素的影响。我们发展了这些模型，作为[Fiori A，Dagan G。含水层输运中的浓度波动：严格一阶解及其应用。J Contam Hydrol 2000;45（1-2）：139-163]。我们的一阶解决方案比较以及与数值模拟的小和中等的地层非均质性和从小到大的采样和源体积。然而，对于高度非均质地层，它们的性能恶化。随后，我们使用我们的模型来研究采样器大小，源体积和PSD之间的相互作用。我们的分析显示了这些因素之间复杂而重要的相互作用。此外，我们表明，这些因素的相对重要性也是一个函数的羽年龄，含水层的异质性，和相对于平均羽重心的测量位置。我们发现，浓度矩主要是由采样体积与孔尺度分散发挥较小的作用，在短时间内和小源体积。但当源体积大于采样体积时，其影响不可忽略。不同的行为发生了很长一段时间，这可能与旧的污染，或小注射体积。在这些情况下，PSD导致显著稀释，这反映在浓度统计中。此外，在中心的平均羽流，高浓度是最有可能发生的，我们发现，采样量和PSD的衰减机制的浓度合奏平均值和变异系数，除了在非常大的源和采样器的大小，其中的变异系数随采样器的大小和PSD的增加。地层的不均匀性导致更快的整体平均浓度的减少和更大的不确定性在中心的平均羽。因此，我们的研究结果强调了在进行风险评估时考虑地层非均质性、暴露量、PSD、源大小和测量位置的综合影响的重要性。
Pore-scale dispersion (PSD), aquifer heterogeneity, sampling volume, and source size influence solute concentrations of conservative tracers transported in heterogeneous porous formations. In this work, we developed a new set of analytical solutions for the concentration ensemble mean, variance, and coefficient of variation (CV), which consider the effects of all these factors. We developed these models as generalizations of the first-order solutions in the log-conductivity variance of point concentration proposed by [Fiori A, Dagan G. Concentration fluctuations in aquifer transport: a rigorous first-order solution and applications. J Contam Hydrol 2000;45(1–2):139–163]. Our first-order solutions compare well with numerical simulations for small and moderate formation heterogeneity and from small to large sampling and source volumes. However, their performance deteriorates for highly heterogeneous formations. Successively, we used our models to study the interplay among sampler size, source volume, and PSD. Our analysis shows a complex and important interaction among these factors. Additionally, we show that the relative importance of these factors is also a function of plume age, of aquifer heterogeneity, and of the measurement location with respect to the mean plume center of gravity. We found that the concentration moments are chiefly controlled by the sampling volume with pore-scale dispersion playing a minor role at short times and for small source volumes. However, the effect of the source volume cannot be neglected when it is larger than the sampling volume. A different behavior occurs for long periods, which may be relevant for old contaminations, or for small injection volumes. In these cases, PSD causes a significant dilution, which is reflected in the concentration statistics. Additionally, at the center of the mean plume, where high concentrations are most likely to occur, we found that sampling volume and PSD are attenuating mechanisms for both concentration ensemble mean and coefficient of variation, except at very large source and sampler sizes, where the coefficient of variation increases with sampler size and PSD. Formation heterogeneity causes a faster reduction of the ensemble mean concentrations and a larger uncertainty at the center of the mean plume. Therefore, our results highlight the importance of considering the combined effect of formation heterogeneity, exposure volume, PSD, source size, and measurement location in performing risk assessment.