The objective of this study is to evaluate the effects of pedogenesis on the properties of soils and geosynthetics in landfill final covers and the mechanisms that control pedogenic changes. This objective will be met by conducting physical experiments while exhuming large-scale test sections simulating final covers that were constructed in 1999-2000 for the Alternative Cover Assessment Program (ACAP). Field hydraulic conductivity tests will be conducted on each test section to identify the magnitude and variability in saturated hydraulic conductivity, and dye and salt tracer tests will be conducted to assess preferential flow. Data from these tests will be analyzed with a variably saturated flow and transport model that accounts for coupling between the matrix and preferential flow paths, and using data collected regarding state variables (matric suction, water content, temperature, etc.). Large block samples will be removed from each test section at various locations and depths and tested to evaluate how the hydraulic properties vary spatially and with scale. Geomorphic mapping will be conducted to provide quantitative information on soil structure that can be used to interpret the magnitude and scale-dependence of changes in hydraulic properties. Vegetation surveys will be conducted to evaluate transitions in species distribution, rooting depth and density, and other characteristics affecting transpiration, and to assess whether transitions are coupled to pedogenesis. The results will be used to identify physical, hydrological, and biological mechanisms that affect cover performance and to provide insight into how covers change over time. The lessons learned will be used to improve cover design and construction and for assessments of long-term performance. The findings will also apply to other hydrologic problems (e.g., natural recharge, urban watershed hydrology, infiltration and runoff in engineered landscapes). Additional broader impacts will be obtained by enhanced student learning via inter-disciplinary and inter-institutional collaboration, development of a hydrology module for a middle school environmental science curriculum, and by recruiting diversity students to the project.
