The purpose of this thesis is to show, using computer simulation of flow systems in a variety of hypothetical slopes, how different geological environments affect the groundwater flow regime, which in turn is fundamental to the stability of a slope. Galerkin's method is used to derive a finite element program to model two dimensional, saturated, steady state flow through anisotropic and heterogeneous rigid porous media. An understanding of the regional geology is required in order to understand the regional flow system. The following points are illustrated. a. In anisotropic media, the most adverse groundwater condition for slope stability occurs when the major axis of conductivity lies down the dip of the slope. b. Depending on their characteristics, faults, contacts and dykes can be either detrimental or favourable in their effect on the flow system. Careful field investigation is required to establish that effect. c. Deep weathering commonly causes a confining zone of low conductivity, a situation very detrimental to stability. d. Stress relief fractures on valley walls can adversely influence the effect of groundwater on stability. e. A regional aquifer can cause high pore pressure development beneath a valley. f. Fluctuations in the regional groundwater system can cause instability in Pleistocene terraces. g. The presence of an underlying less conductive zone or unit can have an adverse effect on the flow system. Conductivity contrasts of less than two orders of magnitude can cause pore pressure development critical to stability. Three other points are demonstrated which have direct application to slope stability analysis and control. 1. The pressure head distribution on rock wedges can be nonlinear rather than the commonly assumed linear distribution. 2. The introduction of a reservoir at the toe of a slope can influence the groundwater regime well above the reservoir surface; even a low reservoir can cause, the change required to cause instability. 3. Piezometric measurements and drainage systems must penetrate through any less conductive unit that might be acting as a slide plane. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Master of Science

Groundwater accounts for approximately 99% of the available freshwater on Earth, and is an important resource for irrigation, potable water, and domestic use in the United States. However, the overuse of groundwater has led to aquifer depletion in several basins across the USA, resulting in storage reduction, contamination, salt water intrusion, and depletion of surface waters. To properly manage groundwater for the future, there is a need for well-informed Groundwater Management Plans (GWMPs) in order to prevent further depletion and erosion of the resource. Previous studies have focused on groundwater management relative to groundwater laws, regulations, and institutional arrangements. This study analyzed GWMPs to better understand how allowable yields are set, how interconnected groundwater conditions are addressed, and how groundwater systems are managed when information on the system is lacking through planning. The findings of this study delineate how groundwater management goals are set across the United States and provides recommendations to inform future GWMPs.

Releases of nonaqueous phase liquids (NAPLs) to groundwater systems are a serious and widespread problem throughout the United States. Research was conducted to determine if numerical groundwater flow and transport models could evaluate the effectiveness of alternative remedial strategies to reduce dissolved hydrocarbon contamination in aquifers, and therefore serve as tools to aid environmental managers in the remedial decision making process. A fuel distribution terminal in the Eastern United States was selected as the test site. A release of diesel and jet fuels from the terminal loading rack area contaminated the unconfined aquifer beneath the terminal and migrated off-site, impacting commercial and residential areas. In the analyses, groundwater flow and transport models were calibrated to site data. The calibrated models were applied to simulate four remedial options: (1) natural attenuation, (2) groundwater extraction, (3) groundwater flushing, and (4) microbial fences. Results of the predictive simulations indicated that the groundwater flushing remedial option provided the greatest reduction of benzene and TEX mass from the NAPL source as well as the lowest concentrations of benzene and TEX in the aquifer. The calibrated numerical models were able to predict the effectiveness of various remedial options and provide a basis for comparison. The modeling in conjunction with other factors, such as cost, were utilized to facilitate the decision making process. / Master of Science

A suite of tools to reduce the computational effort in groundwater modeling validation and testing has been developed. The work herein explores reduction of computational effort via smart adaptivemeshing, optimization techniques, which require fewer model calls, and the development of surrogate models. Adaptive meshing reduces the computational domain by allowing for mesh refinement in areas of interest determined dynamically by the model through error indicators instead of requiring a priori knowledge or a posteriori determination and rebuilding of the computational domain. As the areas of interest change with the physics, the refinement is removed to lower computational time by using unrefinement. The computational time for dynamic mesh adaption versus uniform refinement is orders of magnitudes smaller. Further reduction in computational time may be required especially when using parameter estimation techniques that require on the order of 2n computations, where n is the number of parameters being estimated. A demonstration of the usefulness of parameter estimation techniques is given, followed by a discussion of methods to further reduce computational time. It may also be necessary to look at reduced physics-type methods to further reduce computational time for the physics-based model. Surrogate models, such as proper orthogonal decomposition (POD), greatly reduce the computational time while maintaining the most important aspects of the physics being solved. The idea here is to run the full model, create the PODs basis, then use this basis to run parameter estimation. Once a better fit has been determined, the full model is run again to capture the full-physics results. The technique is repeated as necessary to capture the “best” parameters to numerically represent the observed behavior.

No description available.

Domestic water wells in Eastern Ontario were identified in potentially vulnerable fractured and karst bedrock aquifers using geologic and geochemical data. A novel methodology is presented that evaluates ¹³⁷Cs and ²¹⁰Pbₑₓ as local indicators of groundwater vulnerability. The method is designed to determine the vulnerability of a specific well. Suspended sediment samples and well-bottom sediment samples were collected from both potentially vulnerable and non-vulnerable wells. Surface soil samples were also collected from West Rural Ottawa and the Township of Alfred & Plantagenet in Ontario, Canada. Gamma spectroscopy was used to analyze the samples and quantify the presence of the radionuclides in cps and cps/g. The spectral data indicate no significant difference in the activities of ²¹⁰Pbₑₓ among samples, but a significant difference in the activities of ¹³⁷Cs was observed between surface soil samples and well-bottom sediment samples collected from vulnerable wells. The data suggest that ²¹⁰Pbₑₓ does not act as a good indicator of vulnerable aquifers because of its geogenic origin. The anthropogenic origin of ¹³⁷Cs precludes this issue, and while ¹³⁷Cs was detected in measurable quantities at the surface, its use as an indicator of vulnerable aquifers is limited by hydrologic and geologic controls that prevent infiltration in vulnerable terrains.

Wetland systems have been widely studied and found to have enhanced capacity to transform meaningful amounts of nitrate (NO3-N) from shallow subsurface water before the improved-quality water is delivered to lake, river, and groundwater systems. Wetland are characterized by the abundant presence of electron donors and acceptors (i.e., organic carbon & NO3-N, respectively) as well as anoxic and reducing conditions which are crucial for supporting denitrification processes and the reduction of excessive nitrate levels in the environment. When favorable conditions within the wetland systems are not present, denitrification is often limited to the biofilm-protected bacteria hosted on the sediment surfaces. However, there is still a need to determine if floodplain wetlands are being utilized to their maximum potential in excess nitrate removal.

Delta Store #3033 in Indianola, MS is suspected of having had a release of petroleum, which may have contaminated the underlying soil and shallow groundwater. Exploratory boring/monitoring wells were drilled on-site noting all soil formations and groundwater encountered. The soil facies encountered show a fining upward sequence, representative of a fluvial depositional environment. Soil contamination is mostly confined to the surficial soil; however, evaluation of lab data, boring logs, and cross sections suggests it is likely the contamination migrated through the surficial confining layer into the underlying strata. The hydraulic conductivity of 1.2 x 10-5 cm/sec, surficial geology consisting mostly of low and some high plasticity clays (CL and CH), a hydraulic gradient of 0.01 to 0.02 ft/ft, and the presence of an overlying concrete pavement suggests that any recent release of hydrocarbons should be confined to the immediate vicinity under the site.

No description available.