SGER: Forensic Analysis of a Final Cover Relying on a Clay Barrier

最终覆盖层依靠压实粘土屏障层作为渗透的主要障碍，在美国通常用于废物遏制和污染材料的隔离。覆盖层通常由一层450-900毫米厚的压实粘土层和一层150毫米至900毫米厚的侵蚀层组成。一般要求粘土的饱和水力导率小于10 - 7cm /s，对应于连续重力排水条件下的最大渗流速率为32mm /yr。美国已经建造了数千个这样的盖子。然而，越来越多的人担心，由于干燥和霜冻作用的破坏性影响，这些覆盖物不太可能长期发挥预期的作用。来自几个地点的现场数据表明，这些过程导致的渗透速率远高于预期（每年数百毫米），但尚未进行详细的调查，以表明高渗透速率确实与粘土屏障层的形态变化有关。在拟议的研究中，将对覆盖物进行法医调查，结果是一个独特而新颖的数据集，描述风化对覆盖物中粘土屏障的织物、水文特性和现场性能的影响。将进行一系列实地和实验室测试。现场渗透不同体积土壤的导电性试验将直接在屏障层上进行，并将大量未受干扰的屏障层样品回收用于实验室导电性测试。将用添加到用于水力导电性测试的渗透水中的染料来标记传导流体的途径。渗透后，将在覆盖层中挖掘样条，研究染色裂缝的孔径、长度和间距。在渗透实验室标本后，将进行类似的检查。这项研究具有经济、环境和社会影响。经济和环境影响将通过对超级基金项目中使用的最常见补救措施的有效性进行全面评估来实现。这项研究的结果可能表明，从长期来看，其他覆盖技术可能比依赖于压实粘土屏障的覆盖技术更具成本效益和环境保护性。社会影响将通过PI在本科和研究生学习中的多样化努力来实现。

Final covers that rely on a compacted clay barrier layer as the primary impediment to percolation are commonly used in the US for waste containment and isolation of contaminated materials. The cover generally consists of a layer of compacted clay 450-900 mm thick overlain by an erosion layer that is 150 mm to 900 mm thick. The saturated hydraulic conductivity of the clay generally is required to be less than 10 -7 cm/s, which corresponds to a maximum percolation rate of 32 mm/yr under conditions of continuous gravity drainage. Thousands of these covers have been constructed in the US. However, there is growing concern that these covers are unlikely to perform as intended over the long-term due to the destructive effects of desiccation and frost action. Field data from several sites suggest that these processes are resulting in percolation rates that are much higher than intended (hundreds of mm per yr), but detailed investigations have not yet been conducted to show that the high percolation rates are definitively tied to morphological changes in the clay barrier layer. In the proposed study, a forensic investigation of the cover will be conducted, the result being a unique and novel data set describing the effects of weathering on the fabric, hydrologic properties, and field performance of a clay barrier in a cover. A series of field and laboratory tests will be conducted. Field hydraulic conductivity tests that permeate different volumes of soil will be conducted directly on the barrier layer and large undisturbed samples of the barrier layer will be retrieved for laboratory hydraulic conductivity testing. The pathways conducting flow will be marked with dye added to the permeant water used for the hydraulic conductivity tests. After permeation, transects will be excavated in the cover to study the aperture, length, and spacing of the dye-stained cracks. A similar examination will be conducted after permeating the laboratory specimens.The study has economic, environmental, and societal impacts. Economic and environmental impacts will be realized by providing a thorough evaluation of the effectiveness of the most common remedy used in Superfund projects. The results of this study may show that other cover technologies are likely to be more cost effective and environmentally protective over the long-term than covers relying on a compacted clay barrier. Societal impacts will be realized through the diversity efforts of the PI in undergraduate and graduate studies.