Multi-dimensional Water Flow and Solute Transport in Heterogeneous, Layered Soils

  • Author / Creator
    Song, Yanyan Sunny
  • Onsite, at-grade wastewater treatment systems have the task of the remediation of wastewater for people living in remote areas. The design of efficient onsite wastewater treatment systems is very important to environmental safety and human health. The efficiency of the wastewater treatment depends on the travel time and the contact length of the wastewater through the vadose zone. Therefore, understanding and accurately modeling the hydraulic process of the system is very important for designing the system and quantifying the environmental risks of the system. The hydraulic processes occurring in an onsite at-grade wastewater treatment system are similar to those of a layered field soil under a surface line source boundary condition. Water flow and solute transport under these conditions has been investigated in simplified, homogeneous soils, but field soils are more complex with spatially variable hydraulic properties and soil horizons/layers. The overall objective of the research is to increase our understanding of, and develop methods to predict, the infiltration of water and solutes into field soils for boundary conditions typical of surface at-grade (on-site) wastewater treatment systems with the use of a numerical hydrological model (HYDRUS). Specially, the influence on the spatial variability, horizonation (layering) and spatial correlation of soil hydraulic properties on flow and transport behavior under surface line sources was quantified. The influence of the spatial correlation of the hydraulic variability in each horizon and the cross-correlation across the horizon interface was introduced into soil hydrological models and investigated in two ways: 1) assuming Miller-similar media and simulating scaling factors continuously across the domain using a spatially correlated random field generator; different average values of the scaling factors were assigned to each horizon simulate the differences of the hydraulic properties in two horizons; and 2) using the spatial pattern of the laboratory-measured hydraulic properties of a non-Miller-similar layered field soil to generate a more realistic three-dimensional soil domain. Results indicate that in a Miller-similar media, the hydraulic response was sensitive to the variability of the hydraulic properties, and more sensitive to the variability close to the surface line source than at greater depths. The magnitude of the variance and spatial correlation of the soil hydraulic properties significantly influenced the vertical solute travel time directly underneath the surface line source. The difference between the maximum and minimum solute travel time (10 days) was expected to have significant influence on the remediation of the pathogenic bacteria and potentially, viruses. The simulated hydraulic outputs (average and variance of the water storage) were also found to be sensitive to the variation of the input hydraulic properties for the non-Miller-similar field soil. These results indicate that soil type and soil heterogeneity should be considered for risk-based designs of on-site at-grade wastewater disposal systems.

  • Subjects / Keywords
  • Graduation date
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
  • Language
  • Institution
    University of Alberta
  • Degree level
  • Department
    • Department of Renewable Resources
  • Specialization
    • Soil Science
  • Supervisor / co-supervisor and their department(s)
    • Dyck, Miles Department of Renewable Resources
  • Examining committee members and their departments
    • Leung, Juliana Department of Civil and Environmental Engineering
    • Kachanoski, Gary Department of Renewable Resources