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A vacuum permeability test utilizing high hydraulic gradients has been devised for compacted clay of low permeability. The test induces easily measurable flow rates in virtually impervious soils by placing a vacuum at the drainage end of the sample and an elevation head at the inflow end. The apparatus used in the test could easily be constructed with materials commonly available in laboratories for routine soil tests. The sample can either be compacted in the permeameter (a glass cylinder) or can be seated in sand and sealed with an asphalt bond. The anticipated difficulties, capillary effects, undetected leakage, and permeability reduction by entrapped air, do not introduce appreciable error as shown by the linearity of flow velocity-hydraulic gradient curves and the general agreement of test results with those obtained from a falling bead, non-vacuum test. Relative coefficients of permeability can be obtained within a few days after the start of the test. It is concluded that this rapid, inexpensive method gives adequate values of coefficient of permeability for most experimental work on compacted clays. / M.S.

The design, performance, and analysis of a soil vapor extraction system to identify zones most conductive to air transport and quantify kair in sequential soil layers is presented. A multi-level extraction well, with alternating solid and screened sections, was utilized to characterize multi-layered media. The field site, located in the Carolina Slate Belt within the physiographic region known as the Piedmont, is comprised of alternating layers of different soil types of varying kair, including thin bands of clay, silt, and sand. The pneumatic test consisted of one multi-level extraction well and four multi-level pressure monitoring wells. Screen locations were based on previous site characterization. Vapors were extracted at one screen while pressure, temperature, and volumetric flow rate were monitored using a computer data acquisition system. Data was analyzed by both steady-state and transient solution techniques using pressure drawdown versus time data collected at various locations. Results from vapor extraction tests indicate that the multi-level approach is advantageous when dealing with heterogenous media, since the most permeable layer was identified. Transient and steady-state solutions indicate that a k_air= 2.0 X 10⁻⁷ cm² is representative of the located permeable layer within the subsurface. Vacuum system, formation, and extraction well characteristics are evaluated to determine pressure as a function of volumetric flow rate. / Master of Science

Call number: LD2668 .T4 1984 S22 / Master of Science

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

Subsurface fluids may travel along paths having a minimum permeabilility greater than the effective permeability of the rock. This may have an important impact on contaminant migration. A stochastic approach related to percolation theory is advanced to address the question of what is the probability that a high permeability path extends across a given volume of the subsurface. The answer is sought numerically through subdividing the volume of interest into a three-dimensional grid of elements and assigning a random permeability to each element. Four permeability processes are considered: 1) Stationary with independence between grid elements; 2) Stationary and autocorrelated; 3) Nonstationary due to conditioning on measured values; and 4) Random rock volume included in grid. The results utilizing data from fractured granites suggest that in large grids, at least one path having a minimum permeability in excess of the "effective" rock permeability will cross the grid. Inclusion of autocorrelation causes an increase in the expected value of the minimum permeability of such a path. It also results in a significantly increased variance of this permeability. Conditioning on field permeabilities reduces the variance of this value over that obtained by unconditional, correlated simulation, but still produces a variance greater than that obtained when independence was assumed. When conditioning is performed, the mean of the minimum permeabilities along these paths is dependent on the principal axis of the path. Finally, including a random rock volume by allowing the length of the grid to be random increases the variance of the minimum permeability.

Groundwater contamination on irrigated land is of concern in this nation and around the world. In order to reduce the potential of groundwater contamination by agricultural practices such as irrigation, fertilizer and pesticide application, vadose-zone monitoring and sampling are needed. The main objective of this study was to evaluate impacts of current irrigation treatments and soil structures on the migration of pollutants to groundwater. Passive CAPillary wick pan Samplers (PCAPS) and suction cups were installed in two cracking clays and one sandy soil under the pear tree root zone. PCAPS and suction cups were used to collect nitrate-nitrogen and tracer samples. Tracers were applied to track the spatial and temporal patterns of compounds that mimic nitrate-nitrogen and pesticide movement. The observed magnitude of water leaching over 3 months differed between irrigation methods and soil structures and decreased in this order: flooding over 3 months in clay soil (22.8 cm) > micro-sprinkler in clay soil (16.1 cm) > over-head sprinkler in sandy soil (4.1 cm). Leaching patterns were varied spatially; soil structures, irrigation methods, preferential flow, and high water table may have been responsible for the spatial variation of leaching. Mass recovery of all three tracers, including bromide, blue dye, and rhodamine had the same decreasing order: flooding in clay soil > micro-sprinkler in clay soil > over-head sprinkler in sandy soil. Average blue dye and rhodamine concentrations had the following order: flooding in clay soil > micro-sprinkler in clay > over-head sprinkler in sandy soil. Since blue dye and rhodamine have similar properties to some moderately adsorbed pesticides, we may infer that the risk of pesticide movement in three sites should also decrease in this order. Presumably pesticide movement in clay soil would have been more pronounced for flooding than sprinkler irrigation. On the annual/seasonal basis, the total mass of nitrate-nitrogen leaching differed between irrigation methods and soil structures and decreased in the following order: over-head sprinkler in sandy soil > flooding in clay soil > micro-sprinkler in clay soil. The annual average nitrate-nitrogen concentration observed under over-head sprinkler in sandy soil was 15 mg/l over the maximum allowed concentration level (10 mg/l) by the EPA while seasonal nitrate-nitrogen concentration was low in clay soil under current irrigation practices. Strong evidence suggested the occurrence of preferential flow in this study. Preferential flow may contribute to high water leachate, nitrate and pesticide migration. High correlation coefficients between paired PCAPS indicated that PCAPS have similar responses to water and solute leaching. Several improvements in PCAPS are needed to obtain representative samples under severe flooding conditions. Limited data suggested that ultra-low rate irrigation devices could reduce the water leaching and the potential of pollutant migration to the groundwater because ultra-low rate application devices minimize the soil macropore flow. / Graduation date: 1995

Prevention of groundwater contamination by agricultural chemicals requires an understanding of the complex processes that control pesticide movement below the soil surface. Through this understanding it is possible to try to predict which areas may be most vulnerable to contamination. The many models that have been developed to characterize pesticide movement vary widely in their conceptual approach and degree of complexity. A soil properties model was developed in this thesis to determine the relative overall pesticide movement potential in Oregon agricultural soils. Its focus is ease of use in both acquisition of input values and running of the model. The model is based on soil properties important in controlling pesticide movement. It is a rating system model that uses scoring of factors and matrices to weigh the soil values. It is organized into two processes: leaching and sorption. The leaching potential is based on soil permeability and drainage class. The sorption potential is based on organic matter content and texture of the soil surface horizon(s). The interaction of these two processes results in the overall pesticide movement potential. / Graduation date: 1991

The Woodlands, Texas, is a 27,000-acre new town created with Ian McHarg's ecohydrological planning approach. The Woodlands is the best example of ecologically based new town planning in the United States during the 1970s. The Woodlands survived storms in excess of one-hundred-year levels in 1979 and 1994 with little property damage, while Houston, 31 miles away, was severely flooded in both events. For the past three decades, very few studies have been conducted to assess the effectiveness of McHarg's planning approach. The objective of this study is three fold: (1) To document McHarg's ecohydrological planning concepts, implementation and unveil the barriers to continue his approach; (2) To compare flood mitigation effectiveness of different drainage systems used in The Woodlands development; and (3) To simulate "what if" land-use scenarios using different planning approaches. Original development information is collected from published monographs, journal articles, newspapers and designers' collections. Geographic Information System (GIS) parcel data are obtained from Montgomery County Appraisal District. Streamflow data are acquired from the USGS website. Weather data are downloaded from the NOAA website. Land use and land cover data are collected from various national datasets. Two GIS hydrologic models--the Soil and Water Assessment Tool (SWAT) and the Kinematic Runoff and Erosion model (KINEROS)--are used for watershed simulation. The statistic analysis tool SPSS is used for correlation analysis. Results show that McHarg's planning approach was followed in the early phases of development (1974-1996) but was largely abandoned in the later phases when its ownership was changed in 1997. McHarg's approach ceased to be implemented because of the low public acceptance of ecohydrological planning strategies and the conflicts between short-term investment return and long-term environmental stewardship. In addition, comparative study shows that the early phases of development responded to rainfall similarly to its pre-development forest conditions. However, the later phases generated runoff volumes three times greater than the early phases. Therefore, McHarg's ecohydrological planning approach demonstrates flood mitigation effectiveness that is superior to the conventional approach. Finally, using soil permeability to coordinate development density and land use presents a viable solution for mitigating environmental impacts from a stormwater perspective.

Dispersivity data compiled over many lengths show that values at typical interwell distances are about two to four factors of ten larger than those measured on cores. Such large dispersivities may represent large mixing zones in the reservoir or they may be a result of convective spreading driven by permeability heterogeneity. This dissertation uses the idea of flow reversal (echo tests) to distinguish between convective spreading and dispersive mixing. Spreading is reversible, mixing is not. A zero or small value of echo dispersivity (estimated after flow reversal) implies little or no mixing and convection dominated transport. An echo dispersivity value equal to the transmission value (estimated after forward flow) would imply well mixed transport. A particle tracking code is developed to simulate echo tests for tracer transport in single phase, incompressible flow through three-dimensional, heterogeneous permeable media. Echo dispersivities are estimated for typical heterogeneity realizations and compared with corresponding transmission values at the field scale. The most important observation is that echo dispersivities are significantly larger than core scale values. They also lie on the overall trend of measured dispersivities and corroborate the large echo dispersivities previously inferred from single well tracer test data. This implies that significant mixing occurs in field scale transport. Echo dispersivities increase with permeability heterogeneity (variance and autocorrelation lengths). This is the effect of local (point or pore scale) mixing in the transverse direction, integrated over long and tortuous flow paths. Transport in typical reservoir formations, with significant autocorrelation in permeabilities, is most likely to be in a pre-asymptotic regime and cannot be described by a unique dispersivity value. This is because the Fickian model for dispersion fails to capture the mixing zone growth correctly in this regime. These results highlight the need to develop representative models for dispersion and improve upscaling methodologies. / text