Gwo Jin-Ping, Jardine Philip M, Sanford William E
University of Maryland, Baltimore County, Department of Civil and Environmental Engineering, 1000 Hilltop Circle, Baltimore, MD 21250, USA.
J Contam Hydrol. 2005 Mar;77(1-2):91-118. doi: 10.1016/j.jconhyd.2004.12.002.
Multiple factors may affect the scale-up of laboratory multi-tracer injection into structured porous media to the field. Under transient flow conditions and with multiscale heterogeneities in the field, previous attempts to scale-up laboratory experiments have not answered definitely the questions about the governing mechanisms and the spatial extent of the influence of small-scale mass transfer processes such as matrix diffusion. The objective of this research is to investigate the effects of multiscale heterogeneity, mechanistic and site model conceptualization, and source term density effect on elucidating and interpreting tracer movement in the field. Tracer release and monitoring information previously obtained in a field campaign of multiple, conservative tracer injection under natural hydraulic gradients at a low-level waste disposal site in eastern Tennessee, United States, is used for the research. A suite of two-pore-domain, or fracture-matrix, groundwater flow and transport models are calibrated and used to conduct model parameter and prediction uncertainty analyses. These efforts are facilitated by a novel nested Latin-hypercube sampling technique. Our results verify, at field scale, a multiple-pore-domain, multiscale mechanistic conceptual model that was used previously to interpret only laboratory observations. The results also suggest that, integrated over the entire field site, mass flux rates attributable to small-scale mass transfer are comparable to that of field-scale solute transport. The uncertainty analyses show that fracture spacing is the most important model parameter and model prediction uncertainty is relatively higher at the interface between the preferred flow path and its parent bedrock. The comparisons of site conceptual models indicate that the effect of matrix diffusion may be confined to the immediate neighborhood of the preferential flow path. Finally, because the relatively large amount of tracer needed for field studies, it is likely that source term density effect may exaggerate or obscure the effect of matrix diffusion on the movement of tracers from the preferred flow path into the bedrock.
多种因素可能会影响从实验室向实地扩大结构化多孔介质中多示踪剂注入规模的过程。在瞬态流动条件下以及实地存在多尺度非均质性的情况下，以往扩大实验室实验规模的尝试并未明确回答有关控制机制以及诸如基质扩散等小尺度传质过程影响的空间范围等问题。本研究的目的是调查多尺度非均质性、机理和场地模型概念化以及源项密度效应在阐明和解释实地示踪剂运移方面的影响。本研究使用了先前在美国田纳西州东部一个低放废物处置场在自然水力梯度下进行的多次保守示踪剂注入实地活动中获得的示踪剂释放和监测信息。校准了一套双孔隙域或裂隙 - 基质地下水流动与运移模型，并用于进行模型参数和预测不确定性分析。一种新颖的嵌套拉丁超立方抽样技术推动了这些工作。我们的结果在实地尺度上验证了一个先前仅用于解释实验室观测结果的多孔隙域、多尺度机理概念模型。结果还表明，在整个实地场地范围内，归因于小尺度传质的质量通量率与实地尺度溶质运移的质量通量率相当。不确定性分析表明，裂隙间距是最重要的模型参数，并且在优先流动路径与其母岩基岩的界面处模型预测不确定性相对较高。场地概念模型的比较表明，基质扩散的影响可能局限于优先流动路径的紧邻区域。最后，由于实地研究需要相对大量的示踪剂，源项密度效应可能会夸大或掩盖基质扩散对示踪剂从优先流动路径进入基岩运移的影响。
