The impact of physical heterogeneity and connectivity on LNAPL entrapment and dissolution

Silliman这项工作研究了LNAPL在地下水位边界区域的迁移行为。定义为部分饱和条纹或PSF(Berkowitz等人，2003)，界定地下水位的区域包括经典的毛细条纹(CF)和地下水位以下存在多个相(空气、水和/或LNAPL)的区域。这项工作建立在我们实验室内关于空气进入障碍的先前工作(例如，Silliman等人，2002；Dunn和Silliman等人，2003；Dunn等人，2003)以及关于LNAPL行为的实质性文献(例如，Nambi和Power，2000；Illangasekare.等人，1995a，b；Schroth等人，1998；Walser等人，1999；Van Dijke和Van Der Zee，1997)的基础上。本研究特别感兴趣的是非均质结构与地下水位波动条件下LNAPL的分布/溶解的相互作用。这项工作是基于对纯相和溶解相LNAPL在两区多孔介质(粗砂和细砂)中的分布的二维模拟和数值实验相结合的基础上的。在此范围内，将使用视觉和TDR技术来监测LNAPL饱和度。溶解相LNAPL组分的质量将在多孔介质的流出处进行监测。数值试验将在模拟的随机和尺度多孔介质和T2VOC上进行，T2VOC是劳伦斯伯克利国家实验室开发的TOUGH2[未饱和地下水和热量传输，版本II]的扩展。这些实验将基于产生一系列粗砂和细砂的随机分布的实现(基于平稳的随机渗透率分布和结构化的渗透率分布)，随后模拟在原始地下水位上方具有显著LNAPL相的波动地下水位。实验室实验将被用来验证数值模型预测的LNAPL行为，以及提供LNAPL行为的可视化。数值模型将被用来解决中心假设：细砂基质中粗砂透镜的连通度(在提案中定义)将影响被困在PSF中的LNAPL的量。具体地说，随着粗砂区连通性的增加(粗砂和细砂的相对体积相同)，包裹的LNAPL体积将减少。粗砂透镜体在细砂基质中的连通度的增加将导致困在PSF中的LNAPL的总体溶解速度降低。在智力方面，这项工作促进了对LNAPL在PSF中分布和溶解控制的理解。从理论上讲，这对物理结构对地下水位附近输运特征的影响提供了更多的洞察。从应用的角度来看，这项工作的扩展为修复LNAPL污染系统的创新手段提供了希望。就更广泛的影响而言，这项工作将为一名博士和一名硕士学生提供培训，并为地表水水文学和修复方面的本科生和研究生课程做出贡献。此外，这项工作将有助于进一步发展与西非(贝宁)同事的研究合作。

0408895SillimanThis work examines the transport behavior of LNAPLs in the region bounding thewater table. Defined as the Partially Saturated Fringe, or PSF (Berkowitz et al., 2003),the region bounding the water table includes the classic Capillary Fringe (CF) and theregion below the water table in which multiple phases (air, water, and/or LNAPL) arepresent. This work builds on prior work within our laboratory on Air Entry Barriers (e.g.,Silliman et al., 2002; Dunn and Silliman, 2003; Dunn et al., 2003) as well as thesubstantial literature on LNAPL behavior (e.g., Nambi and Powers, 2000; Illangasekareet al., 1995a,b; Schroth et al., 1998; Walser et al., 1999; Van Dijke and Van Der Zee,1997). Of particular interest for the present study is the interaction of the structure ofheterogeneity and the distribution / dissolution of LNAPLs under conditions of afluctuating water table. The work is based on a combination of two-dimensionallaboratory and numerical experiments on the distribution of pure- and dissolved-phaseLNAPL in a two-zone porous medium (coarse sand and fine sand). Within thelaboratory, visual and TDR techniques will be used to monitor LNAPL saturation. Massof dissolved-phase LNAPL constituents will be monitored at the outflow from the porousmedia. Numerical experiments will be performed on simulated random and scaledporous media and T2VOC, an extension of TOUGH2 [Transport Of UnsaturatedGroundwater and Heat, version II], developed at Lawrence Berkeley NationalLaboratory. These experiments will be based on generating a series of realizations ofrandom distributions of the coarse and fine sands (based on both stationary randompermeability distributions and structured permeability distributions), followed bysimulation of a fluctuating water table with significant LNAPL phase above the originalwater table. The laboratory experiments will be utilized to verify LNAPL behavior aspredicted by the numerical model, as well as to provide visualization of LNAPLbehavior. The numerical model will be utilized to address the central hypotheses:The degree of connectivity (defined within the proposal) of coarse sand lenseswithin a fine sand matrix will influence the amount of LNAPL entrapped withinthe PSF. Specifically, as the connectivity of the coarse regions increases (with thesame relative volume of coarse and fine sands), the volume of entrapped LNAPLwill decrease. An increase in the degree of connectivity of coarse sand lenses within a fine sandmatrix will result in a reduced overall rate of dissolution of LNAPL entrappedwithin the PSF.In terms of intellectual merit, this work advances the understanding of controls ofLNAPL distribution and dissolution in the PSF. From a theoretical standpoint, thisprovides greater insight into the impact of physical structure on transport characteristicsnear the water table. From an applied standpoint, extension of this work holds promisefor innovative means of remediation of LNAPL contaminated systems.In terms of broader impact, this work will provide training for one Ph.D. and oneMasters student, as well as contributing to undergraduate and graduate courses ingroundwater hydrology and remediation. In addition, this work will aid in furtherdevelopment of research collaborations with colleagues in western Africa (Benin).