The focus of this study was on recharge mechanisms and recharge estimation within the Table Mountain Group area. The study evaluated recharge processes and recharge estimation methods in the Table Mountain Group aquifer systems.

Arsenic is a prevalent contaminant at a large fraction of US Superfund sites. Therefore, establishing techniques for accelerating As remediation could benefit many contaminated sites. Remediation of As contaminated groundwater by conventional methods, i.e. pump and treat (P&T), can be impeded by slow desorption of As from Fe and Al (hydr)oxides in aquifer solids. Through experimentation at different physical scales (grain, bench, and field scale), the potential for chemical additions to increase As release from sediments and possibly accelerate P&T remediation is examined. The work described here focuses on As contamination and remediation at the Vineland Chemical Co. Superfund site in southern NJ. The site is extensively contaminated with As resulting from decades of poor chemical storage and disposal practices by the Vineland Chemical Co., which manufactured As-based biocides from 1949-1994. Despite significant intervention, including groundwater remediation by P&T and treatment of solids via soil washing, sufficient site clean up could require many decades with current technologies. Chemical amendments that either compete with As for sorption sites or dissolve Fe and Al (hydr)oxides can increase As mobility and potentially improve P&T remediation efficiency. Simple extrapolations from bench scale column experiments based on pore volumes suggest that treatment with 10 mM oxalic acid could lower the time necessary for clean up at the Vineland site from 600 years (with current techniques involving just groundwater) to potentially on the order of 4 years. Small scale (<1 mm2) X-ray fluorescence maps from columns performed within the synchrotron beamline showed As release during oxalic acid treatment that was consistent with the bulk column materials and suggested that microscale processes can be predictive of the larger system. Finally, during a 3-month pilot study at the Vineland site, oxalic acid was injected into a section of the aquifer via an injection manifold system that was designed and built for the experiment. Groundwater samples indicate that introduction of oxalic acid led to increased As release at a sampling well and pump and treat recovery well in the study area. Addition of oxalic acid shows promise for accelerating treatment of a highly contaminated site.

Many small communities depend on groundwater sources for drinking water and they often use septic tanks for their sewer system needs. However, nitrates and other pollutants from septic systems can percolate to the aquifers and deteriorate quality of the groundwater, threatening the public health. This study has developed a groundwater model using Visual MODFLOW for an aquifer that is used as a water supply source for the cities of Beaumont and Cherry Valley, California. Septic systems are the suspected major source of nitrate contamination of the aquifer. The model has been developed to clarify the extent of interactions between nitrate pollutants, infiltration and percolation from a recently established series of artificial recharge ponds, groundwater recharge from natural sources, and pumping activities to meet local water uses. The primary objective of this study is to evaluate alternative hydraulic solutions that would limit the movement of the contaminants and minimize the risk of affecting the pumping wells. The study attempts to identify the best way to recharge the aquifer and influence movement of the nitrates so that polluted waters may have lower nitrate concentrations in the future, rather than allowed to encroach on critical production wells or led away from production wells to become a problem for future generations or neighboring areas. The data needed to build the model, including geological logs, precipitation, evapotranspiration, well locations, pumping schedules, water levels, and nitrate concentrations have been obtained from the Beaumont Cherry Valley Water District. The model has been calibrated to simulate the observed groundwater levels and the extent of pollution corresponding to the historical pumping rates, recharge rates and climate. The calibrated model has been used to evaluate alternative hydraulic solutions that would either localize the nitrate pollution thus limiting the impact on public welfare, or remove the nitrate pollution for potential treatment and remediation on the surface. The study results show that increased pumping of production wells or strategic placement of additional artificial recharge may reduce the concentrations of nitrate in the Beaumont Basin.

This thesis investigates nutrient contribution to six hyper-eutrophic lakes located within close proximity of each other on the Swan Coastal Plain and 20 kilometres south of the Perth Central Business District, Western Australia. The lakes are located within a mixed land use setting and are under the management of a number of state and local government departments and organisations. These are a number of other lakes on the Swan Coastal Plain for which the majority are less than 3 metres in depth and considered as an expression of the groundwater as their base is below the regional groundwater table throughout most of the year. The limited amount of water quality data available for these six lakes and the surface water and groundwater flowing into them has restricted a thorough understanding of the processes influencing the water quality of the lakes. Various private and public companies and organisations have undertaken studies on some of the individual wetlands and there is a wide difference in scientific opinion as to the major source of the nutrients to those wetlands. These previous studies failed to consider regional surface water and groundwater effects on the nutrient fluxes and they predominantly only investigated single wetland systems. This study attempts for the first time to investigate the regional contribution of nutrients to this system of wetlands existing on the Swan Coastal plain. As such, it also includes new research on the nutrient contribution to some of the remaining wetlands. The research findings indicate that the lake sediments represent a considerable store of nutrients (nitrogen and phosphorus). These sediments in turn control the nutrient status of the lake's water column. Surface water is found to contribute on an event-basis load of nutrients to the lakes whilst the groundwater surprisingly appears to contribute a comparatively low input of nutrients but governs the water depth. Analysis of the regional groundwater shows efficient denitrifying abilities as a result of denitrifying bacteria and the transport is localised. Management recommendations for the remediation of the social and environmental value of the lakes include treatment of the lake’s sediments via chemical bonding or atmospheric oxidation; utilising the regional groundwater’s denitrifying abilities to ‘treat’ the surface water via infiltration basins; and investigating the merits of managed or artificial aquifer recharge (MAR).

Thesis (M.S. in environmental Science)--Washington State University, December 2007. / Includes bibliographical references (p. 27).

Thesis (M.S.)--University of Delaware, 2006. / Principal faculty advisor: William J. Ullman, College of Marine and Earth Studies. Includes bibliographical references.

The thesis contains two studies: First is the water budget analysis using the groundwater modeling and next is the groundwater modeling using the MCMC scheme. The case study for the water budget analysis was the Norman Landfill site in Oklahoma with a quite complex hydrology. This site contains a wetland that controls the groundwater-surface water interaction. This study reports a simulation study for better understanding of the local water balance at the landfill site using MODFLOW-2000. Inputs to the model are based on local climate, soil, geology, vegetation and seasonal hydrological dynamics of the system to determine the groundwater-surface water interaction, water balance components in various hydrologic reservoirs, and the complexity and seasonality of local/regional hydrological processes. The model involved a transient two- dimensional hydrogeological simulation of the multi-layered aquifer. In the second part of the thesis, a Markov Chain Monte Carlo (MCMC) method were developed to estimate the hydraulic conductivity field conditioned on the measurements of hydraulic conductivity and hydraulic head for saturated flow in randomly heterogeneous porous media. The groundwater modeling approach was found to be efficient in identifying the dominant hydrological processes at the Norman Landfill site including evapotranspiration, recharge, and regional groundwater flow and groundwater-surface water interaction. The MCMC scheme also proved to be a robust tool for the inverse groundwater modeling but its strength depends on the precision of the prior covariance matrix.

Near-surface sediments play an important role in governing the movement of water and contaminants from the land surface through the vadose zone to groundwater. Generally, low permeability surficial soils restrict water flow through the vadose zone and form a natural protective barrier to migration of surface applied contaminants. These types of fine-grained soils commonly contain macropores, such as fractures, animal burrows, and root holes, that have been identified as preferential flow pathways in the subsurface. Accordingly, macropores have the potential to influence groundwater recharge rates and compromise the protective capacity of surficial soils, particularly where the overburden is thin and aquifers are close to the surface. Partially saturated flow and transport in these environments is inherently complex and not well understood. The objective of this thesis was to examine preferential flow processes and the associated movement of contaminants in macroporous, low permeability soils. This was accomplished by conducting numerical and field experiments to investigate and describe the dynamics of macropore flow during episodic infiltration through the vadose zone and evaluate the corresponding influence of macropores on vertical water flow and contaminant transport. Numerical simulations were conducted to identify the important physical factors controlling flow and transport behaviour in partially saturated, fractured soils. A three-dimensional discrete fracture model, HydroGeoSphere, was used to simulate infiltration into homogeneous soil blocks containing a single vertical rough-walled fracture. Relatively large rainfall events with return periods ranging from 5 to 100 years were used, since they are more likely to generate significant preferential flow. Initial results showed that flow system dynamics were considerably more sensitive to matrix properties, namely permeability and antecedent moisture content, than fracture properties. Capillary forces, combined with the larger water storage capacity in the soil matrix, resulted in significant fracture-matrix interaction which effectively limited preferential flow down the fracture. It is also believed that fracture-matrix interaction reduced the influence of fracture roughness and other related small-scale fracture properties. The results imply that aperture variability within individual fractures may be neglected when modeling water flow through unsaturated soils. Nevertheless, fracture flow was still an important process since the fracture carried the majority of the water flow and virtually all of the mass of a surface applied tracer to depth in the soil profile. Model runs designed to assess transport variability under a variety of different physical settings, including a wider range of soil types, were also completed. Vertical contaminant fluxes were examined at several depths in the soil profile. The results showed that the presence of macropores (in the form of fractures) was more important than matrix permeability in controlling the rate of contaminant migration through soils. The depth of contaminant migration was strongly dependent on the antecedent moisture content and the presence of vertically connected fractures. Soil moisture content played a pivotal role in determining the onset and extent of preferential flow, with initially wet soils much more prone to macropore flow and deep contaminant migration. Simulations showed that surface applied tracers were able to reach the base of 2 m thick fractured soil profiles under wetter soil conditions (i.e., shallow water table). Likewise, long-duration, low-intensity rainfall events that caused the soil to wet up more resulted in proportionately more contaminant flux at depth. Fractured soils were particularly susceptible to rapid colloid movement with particle travel times to depths of 2 m on the order of minutes. The main implication is that the vulnerability of shallow groundwater is related more to vertical macropore continuity and moisture conditions in the soil profile, rather than traditional factors such as soil thickness and permeability. Macropore flow and transport processes under field conditions were investigated using small-scale infiltration experiments at sites in Elora and Walkerton, Ontario. A series of equal-volume infiltration experiments were conducted at both sites using a tension infiltrometer (TI) to control the (negative) infiltration pressures and hence the potential for macropore flow. A simulated rainfall experiment was also conducted on a small plot at Walkerton for comparison with the TI tests. Brilliant Blue FCF dye and fluorescent microsphere tracers were applied in all tests as surrogates for dissolved and colloidal contaminant species, respectively. Upon completion of infiltration, excavations were completed to examine and photograph the dye-stained flow patterns, map soil and macropore features, and collect soil samples for analysis of microspheres. Cylindrical macropores, in the form of earthworm burrows, were the most prevalent macropore type at both sites. In the TI tests, there was a clear relationship between the vertical extent of infiltration and the maximum pressure head applied to the TI disc. Larger infiltration pressures resulted in increased infiltration rates, more spatial and temporal variability in soil water content, and increased depths of dye penetration, all of which were attributed to preferential flow along macropores. Preferential flow was limited to tests with applied pressure heads greater than -3 cm. Under the largest applied pressures (greater than -1.0 cm), dye staining was observed between 0.7 and 1.0 m depth, which is near the seasonal maximum water table depth at both field sites. The tension infiltrometer was also used to infiltrate dye along an exposed vertical soil face, thereby providing a rare opportunity to directly observe transient macropore flow processes. The resulting vertical flow velocities within the macropores were on the order of tens of meters per day, illustrating the potential for rapid subsurface flow in macropores, even under partially saturated conditions. The results suggest that significant flow occurred in partially saturated macropores and this was supported by simple calculations using recent liquid configuration models for describing flow in idealized macropores. On all excavated sections, microspheres were preferentially retained (relative to the dye) in the top five centimeters of the soil profile. Below this zone, dye patterns correlated well with the presence of microspheres in the soil samples. There was evidence for increased retention of microspheres at lower water contents as well as a slightly greater extent of transport for smaller microspheres. In general, the microsphere and dye distributions were clearly dictated by vadose zone flow processes. As in the numerical experiments, water storage in the soil matrix and related macropore-matrix interaction were important factors. Mass transfer of water through the macropore walls promoted flow initiation in the macropores near surface. Deeper in the soil, water drawn away from the macropores into the matrix significantly retarded the downward movement of water along the macropores. Imbibition of dye from the macropores into the matrix was repeatedly observed on excavated soil sections and during the transient dye test. Microspheres were also transported laterally into the soil matrix indicating that conceptual models for colloid transport in the vadose zone need to account for this mass transfer process. Overall, the tension infiltrometer performed extremely well as a tool for controlling macropore flow under field conditions and, together with the dye and microsphere tracers, provided unique and valuable insights into small-scale flow and transport behavior. The field experiments raise concerns about the vulnerability of shallow groundwater in regions with thin, macroporous soils. Only a fraction of the visible macropores contributed to flow and transport at depths greater than 40 cm. However, with dye and microsphere transport observed to more than 1.0 m depth, rapid macropore flow velocities, and the sheer number of macropores present, there was clearly potential for significant flow and transport to depth via macropores. Under the right conditions, it is reasonable to speculate that macropores may represent a significant pathway for migration of surface applied contaminants to groundwater over the course of a single rainfall event.

<p>This study focuses on the development of a Direct Aqueous Injection Gas Chromatographic method with Flame Ionization Detection (DAI-GC/FID) for the analysis of MTBE and TBA. The analytical method was then applied in a site specific study where MTBE contamination was evident. The method achieved detection limits of 1 ppm for MTBE and 0.1 ppm for TBA. The method showed good precision, accuracy and selectivity. The method was selected primarily for its ability to simultaneously analyze MTBE and TBA. The result of the site specific study showed the persistence of high concentrations of MTBE and TBA at the source of contamination, whilst concentrations at the adjacent primary school dropped to below detection limits as a result of rapid natural attenuation. It was found that an overall decrease in MTBE concentrations was met with an increase in TBA concentrations / which is a direct indication of MTBE degradation. Despite the fact that problematic MTBE concentrations persist at the source of contamination, limited evidence of the persistence of MTBE contamination was identified at the adjacent primary school. As such, MTBE health risks from existing pathways were found to be irrelevant for receptors at the adjacent school.</p>

Near-surface sediments play an important role in governing the movement of water and contaminants from the land surface through the vadose zone to groundwater. Generally, low permeability surficial soils restrict water flow through the vadose zone and form a natural protective barrier to migration of surface applied contaminants. These types of fine-grained soils commonly contain macropores, such as fractures, animal burrows, and root holes, that have been identified as preferential flow pathways in the subsurface. Accordingly, macropores have the potential to influence groundwater recharge rates and compromise the protective capacity of surficial soils, particularly where the overburden is thin and aquifers are close to the surface. Partially saturated flow and transport in these environments is inherently complex and not well understood. The objective of this thesis was to examine preferential flow processes and the associated movement of contaminants in macroporous, low permeability soils. This was accomplished by conducting numerical and field experiments to investigate and describe the dynamics of macropore flow during episodic infiltration through the vadose zone and evaluate the corresponding influence of macropores on vertical water flow and contaminant transport. Numerical simulations were conducted to identify the important physical factors controlling flow and transport behaviour in partially saturated, fractured soils. A three-dimensional discrete fracture model, HydroGeoSphere, was used to simulate infiltration into homogeneous soil blocks containing a single vertical rough-walled fracture. Relatively large rainfall events with return periods ranging from 5 to 100 years were used, since they are more likely to generate significant preferential flow. Initial results showed that flow system dynamics were considerably more sensitive to matrix properties, namely permeability and antecedent moisture content, than fracture properties. Capillary forces, combined with the larger water storage capacity in the soil matrix, resulted in significant fracture-matrix interaction which effectively limited preferential flow down the fracture. It is also believed that fracture-matrix interaction reduced the influence of fracture roughness and other related small-scale fracture properties. The results imply that aperture variability within individual fractures may be neglected when modeling water flow through unsaturated soils. Nevertheless, fracture flow was still an important process since the fracture carried the majority of the water flow and virtually all of the mass of a surface applied tracer to depth in the soil profile. Model runs designed to assess transport variability under a variety of different physical settings, including a wider range of soil types, were also completed. Vertical contaminant fluxes were examined at several depths in the soil profile. The results showed that the presence of macropores (in the form of fractures) was more important than matrix permeability in controlling the rate of contaminant migration through soils. The depth of contaminant migration was strongly dependent on the antecedent moisture content and the presence of vertically connected fractures. Soil moisture content played a pivotal role in determining the onset and extent of preferential flow, with initially wet soils much more prone to macropore flow and deep contaminant migration. Simulations showed that surface applied tracers were able to reach the base of 2 m thick fractured soil profiles under wetter soil conditions (i.e., shallow water table). Likewise, long-duration, low-intensity rainfall events that caused the soil to wet up more resulted in proportionately more contaminant flux at depth. Fractured soils were particularly susceptible to rapid colloid movement with particle travel times to depths of 2 m on the order of minutes. The main implication is that the vulnerability of shallow groundwater is related more to vertical macropore continuity and moisture conditions in the soil profile, rather than traditional factors such as soil thickness and permeability. Macropore flow and transport processes under field conditions were investigated using small-scale infiltration experiments at sites in Elora and Walkerton, Ontario. A series of equal-volume infiltration experiments were conducted at both sites using a tension infiltrometer (TI) to control the (negative) infiltration pressures and hence the potential for macropore flow. A simulated rainfall experiment was also conducted on a small plot at Walkerton for comparison with the TI tests. Brilliant Blue FCF dye and fluorescent microsphere tracers were applied in all tests as surrogates for dissolved and colloidal contaminant species, respectively. Upon completion of infiltration, excavations were completed to examine and photograph the dye-stained flow patterns, map soil and macropore features, and collect soil samples for analysis of microspheres. Cylindrical macropores, in the form of earthworm burrows, were the most prevalent macropore type at both sites. In the TI tests, there was a clear relationship between the vertical extent of infiltration and the maximum pressure head applied to the TI disc. Larger infiltration pressures resulted in increased infiltration rates, more spatial and temporal variability in soil water content, and increased depths of dye penetration, all of which were attributed to preferential flow along macropores. Preferential flow was limited to tests with applied pressure heads greater than -3 cm. Under the largest applied pressures (greater than -1.0 cm), dye staining was observed between 0.7 and 1.0 m depth, which is near the seasonal maximum water table depth at both field sites. The tension infiltrometer was also used to infiltrate dye along an exposed vertical soil face, thereby providing a rare opportunity to directly observe transient macropore flow processes. The resulting vertical flow velocities within the macropores were on the order of tens of meters per day, illustrating the potential for rapid subsurface flow in macropores, even under partially saturated conditions. The results suggest that significant flow occurred in partially saturated macropores and this was supported by simple calculations using recent liquid configuration models for describing flow in idealized macropores. On all excavated sections, microspheres were preferentially retained (relative to the dye) in the top five centimeters of the soil profile. Below this zone, dye patterns correlated well with the presence of microspheres in the soil samples. There was evidence for increased retention of microspheres at lower water contents as well as a slightly greater extent of transport for smaller microspheres. In general, the microsphere and dye distributions were clearly dictated by vadose zone flow processes. As in the numerical experiments, water storage in the soil matrix and related macropore-matrix interaction were important factors. Mass transfer of water through the macropore walls promoted flow initiation in the macropores near surface. Deeper in the soil, water drawn away from the macropores into the matrix significantly retarded the downward movement of water along the macropores. Imbibition of dye from the macropores into the matrix was repeatedly observed on excavated soil sections and during the transient dye test. Microspheres were also transported laterally into the soil matrix indicating that conceptual models for colloid transport in the vadose zone need to account for this mass transfer process. Overall, the tension infiltrometer performed extremely well as a tool for controlling macropore flow under field conditions and, together with the dye and microsphere tracers, provided unique and valuable insights into small-scale flow and transport behavior. The field experiments raise concerns about the vulnerability of shallow groundwater in regions with thin, macroporous soils. Only a fraction of the visible macropores contributed to flow and transport at depths greater than 40 cm. However, with dye and microsphere transport observed to more than 1.0 m depth, rapid macropore flow velocities, and the sheer number of macropores present, there was clearly potential for significant flow and transport to depth via macropores. Under the right conditions, it is reasonable to speculate that macropores may represent a significant pathway for migration of surface applied contaminants to groundwater over the course of a single rainfall event.