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The water level in an open well tapping a confined formation is influenced by natural forces including the solid Earth tide (SET) and atmospheric pressure variation (APV). The spectral method is used to derive an analytical solution for well response to both the random and the periodic components of the combined SET and APV (CSA) forcings. Previously posed models for the individual SET and APV forcings are subsets of this more general model. An inverse theory and an algorithm are developed in order to provide improved results when using such models to estimate the hydraulic parameters associated with a given formation. A complex vector estimation criterion is used in developing a nonlinear, Gauss-Marquardt estimation algorithm. When compared to previous methods of fitting modulus and phase, the complex vector estimation methodology has less bias and variance, and is more robust. An examination of the response surface of the estimation criterion reveals that storativity (S) is relatively non-unique, and thus is not considered in the context of the parameter estimation problem. However, since there is little correlation between transmissivity (T) and S estimators, a good estimate for T is still possible independent of having knowledge of S. An estimate of T is possible only if the data contain sufficient information so that the analysis occurs within an identifiability window, which is defined with respect to the dimensionless transmissivity of the system. The CSA estimation methodology is compared to individual SET and APV schemes. The CSA scheme gives the greatest probability that sufficient information is contained in a data record so that T is identifiable. The results of applications to synthetic data indicate that the OEA scheme gives a T estimate with the most precision, and also that it requires collecting fewer observations.

More efficient methods are needed for the in-situ evaluation of mass transfer parameters which describe the movement of solutes through aquifer material. The objective of this study was to develop a method for estimating diffusion rate and capacity coefficients using a single-well, "push-pull" tracer test. The method consists of the pulse-type injection of a test solution into the saturated zone of an aquifer through the screen of an existing monitoring well. This is followed by a resting (diffusion) period, after which the test solution is extracted from the same well. During the extraction phase a concentration breakthrough curve is obtained. The method uses numerical simulations of the extraction phase breakthrough curve to estimate mass transfer parameters. The methodology was evaluated using a series of laboratory-scale experiments which were performed in a Physical Aquifer Model (PAM). The sediment pack contained in the PAM was modified to create an immobile region governed by diffusive processes. Results from four laboratory-scale experiments are inconclusive in determining the ability of the method to determine mass transfer parameters. Experimental difficulties contributed a significant source of error during the method evaluation. The resting period between the injection and extraction phase was to allow diffusion into the initially solute-free immobile region. Evidence suggests solute was introduced into the immobile region by advective processes during the injection phase of the experiments. Additional experimental work is required to evaluate the methodology. This may include either laboratory or field-scale evaluation of the test method. / Graduation date: 1999

Responses of biological indicators of soil quality to winter cover cropping were measured on soil samples collected from 6 commercial growers' fields and two experiment research stations in the Willamette Valley of Oregon. The research stations were the North Willamette Research and Extension Center (Aurora, OR), and the Oregon State University Vegetable Farm (Corvallis, OR). The research stations and five on-farm sites compared winter cover crops or winter fallow in rotation with a summer vegetable crop. In one on-farm site, minimum tillage or conventional till following winter cover crops was compared. The objectives of this study were to: 1) monitor changes in soil biological properties under field managed with cover crops; 2) test potential of buried cotton strip as indicator of soil biological activity and as a soil quality index; and 3) assess the degree of correlation between tensile strength and cotton strip weight loss. The major findings were: 1) microbial biomass carbon and ��-glucosidase activity were the most sensitive to cover crop management; 2) cotton strip decomposition was correlated to soil biological properties but was not very sensitive to management changes; and 3) that measuring weight loss was nearly as effective as tensile strength in assessing cotton strip decomposition in soils. / Graduation date: 1999

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Thesis (M.S.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains ix, 64 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 63-64).

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