The relationship between air-water relative permeabilities was investigated in a series of laboratory experiments using repacked Berino loamy fine sand and 30 mesh medium sand samples. The relative permeability curves demonstrated the classic characteristics reported for two phase immiscible flow. Factors affecting non-Darcian behavior in the air permeability were further studied for the Berino sand. Among these factors were slip flow effects and inertial effects and their relationship to liquid saturation. The magnitude of the observed slip was small and did not appear to be a function of saturation. However, the magnitude of the slip was dependent on the air pressure gradient for samples at intermediate saturations. Inertial effects became more apparent at relatively smaller pressure gradients and air fluxes as water saturation increased. The results indicate that, although these non-Darcian effects are small, they should be considered when interpreting air permeability measurements in unconsolidated materials.

The fate and transport of a conservative and two bacteriophage tracers during Soil Aquifer Treatment (SAT) has been examined. A 12 foot x 12 foot mini-basin containing seven stainless steel suction samplers ranging in depth from 1 to 20 feet below land surface was constructed in an existing recharge basin. Bromide ion and MS-2 and PRD-1 virus tracers were introduced into the mini-basin during recharge of secondary effluent during three of nine flooding cycles in order to aid in interpreting transport processes and to determine the presence of preferred-flow channels. High infiltration rates and discontinuous impeding layers resulted in 150 feet of horizontal transport. Preferential-flow channels were observed in both the vertical and horizontal directions. Less removal of bacteriophage MS-2 (hydrophilic, 28 nm dia) was observed at all depths compared to PRD-1 (hydrophobic, 62 nm dia). Results suggest that the fate of the virus transport in sandy alluvium is determined by the size and hydrophobicity of the viral particles, the quality of the percolating fluid, and composition of the soils.

This study examines future water management options for the Upper San Pedro Basin. It is an effort to better understand the water related social values present within the basin and how they might be used to formulate sound water resource policy. To this end, techniques based upon decision analysis were employed to elicit and analyze the judgements of a sample of basin residents regarding water management. Relevant social values for the management of water were identified and then the Multi-Attribute Tradeoff System (MATS) program was utilized to rank available water management policy options. No option was found upon which all groups agreed, but directions can be provided for the development of future policies.

Ground-water exploitation in the Upper San Pedro Basin has produced the formation of a cone of depression around the Sierra Vista-Fort Huachuca area. A portion of the mountain front recharge that otherwise would reach the San Pedro River is being intercepted by pumping, and portions of baseflow are being captured by pumping. The purpose of this study is to construct a simulation model capable of simulating the ground-water system as well as the ground-water-surface water interactions. The flow simulation was done by a three-dimensional, finite-difference ground-water flow model (MODFLOW) that incorporates a new stream-aquifer interaction package. Steady state simulations were performed to represent mean annual conditions. Transient simulations cover a 48 year period, starting in 1940 and ending in 1988. A sensitivity analysis of the steady state model was also performed.

A hydrogeological study was performed on the cross-boundary valley between Organ Pipe Cactus National Monument, Arizona and the Rio Sonoyta Valley, west of Sonoyta, Mexico. The study was carried out to evaluate present hydrologic conditions in the valley and to assess the impact of irrigation ground-water withdrawals in Sonora on water resources in the Monument and in particular the spring system in the Quitobaquito Hills. Through evaluation of available hydrogeologic data, three main aquifers were identified in the north half of the valley. These are the alluvial basin fill and fan system of La Abra Plain, the fractured crystalline rock system of the pediments of the Quitobaquito Hills, and the fluvial aquifer associated with the active channel of the Rio Sonoyta. A detailed evaluation of the location, discharge, and radioisotope composition of the springs in the Quitobaquito Hills was made to characterize the ground-water flow system supplying the springs and to evaluate the possible effects of irrigation withdrawals in Sonora on their discharge. (Abstract shortened by UMI.)

Six intermediate-scale experiments were performed to determine the effects of melt rate, melt-freeze cycles, and initial chemical distribution on the timing and magnitude of the ionic pulse from a physically homogeneous snowpack. The greatest ionic concentration in the initial snowmelt resulted when long melt-freeze cycles were applied to a chemically homogeneous snowpack. Low melt rates resulted in faster initial ion removal than did high melt rates. Chemical species applied in a layer at mid pack were removed slower than species applied as a layer on the top. Sulfate and NO₃⁻ were consistently removed in preference to Cl⁻. Three ice-sphere experiments showed that the preferential release of SO₄⁻ and NO₃⁻ over Cl⁻ is influenced by microscale effects. In each case, SO₄⁻ and NO₃⁻ were rejected from the ice-crystal lattice to a greater extent than was Cl⁻, facilitating their early removal at the onset of melt.

Sources of high nitrate concentrations in ground water from the western part of the Salt River Valley in central Arizona historically have not been well identified. This thesis presents chemical and isotopic data for surface and ground water collected in the study area during 1990. These data are used to characterize general ground-water chemistry in the study area and to evaluate the applicability of 87 and delta11B data to identify different types of nitrate sources. Ground water from northern and southern regions in the study area are differentiated by major ion compositions, metal concentrations, pH, and 3 and 87 data. 87 data identify ground-water flowpaths in the study area. delta11 and delta7Li values are useful for the identification of sewage treatment outflow. delta7Li data may also identify leachates from manure. Effects from a halite deposit on ground water are also distinctive.

This thesis concerns a groundwater modeling study south of Tucson, Arizona where 10,000 acre-feet of Central Arizona Project water may be annually recharged. South and west of the site are the Santa Cruz River and the Tohono O'odham Indian Nation. Well fields to the immediate east, west and south supply water to the City of Tucson and to farming and copper mining corporations. Operation of the corporate well fields has lead to a water table depression just west of the site. The purpose of the model is to understand of the most probable groundwater flow regime in light of aquifer recharging and groundwater mining. The model serves to compare groundwater conditions with previous investigations. Lack of data precluded the construction of a model capable of producing reliable predictive results. Hydrogeologic data gathered provide a foundation for future modeling studies. Insufficient data serve as indicators of present groundwater monitoring deficiencies.

Water-unsaturated column experiments using benzene and p-xylene were performed with a desert soil sample (fc = 0.001) to simulate the removal of volatile organic compounds (VOC) by soil-vapor extraction. Higher flow rates of air were found to facilitate quicker VOC removal but lower flow rates were more efficient. Initial concentrations had no effect on the rate of VOC removal. Sorption of both compounds by the solid phase at 18 and 10 percent wetness was similar to that reported for saturated systems. At these moisture contents, Kp the for benzene averaged 0.03 cm 3/g and that for p-xylene averaged 0.61 cm 3/g. At the driest soil condition, higher than predicted sorption of benzene (Kp = 0.12 cm3/g) is attributed to VOC sorption on dry mineral sites. Mechanisms that limited transport of both compounds are assumed to be intra-aggregate aqueous diffusion and desorption. (Abstract shortened with permission of author.)

Two optimization algorithms and two objective functions were applied to determine erosion parameters for a physically-based, event-oriented model designed to simulate the processes of sedimentation for small watersheds. Three different flow-induced erosion equations were also tested with the four optimization procedures to examine the predictive capabilities of the equations. Synthetic error-free data as well as data contaminated with correlated and random error provided the means for determining the effectiveness of the four optimization procedures studied. After selecting the most effective optimization procedure and flow-induced erosion equation, the model was tested using sediment data from rainfall simulator plots and a small experimental watershed. The results from the rainfall simulator studies indicated that a structural problem may exist within the model. The agreement between simulated and observed responses for the watershed events studied indicated that the model was capable of describing sedimentation processes when they occurred on a larger scale.