Browsing by Subject "Groundwater--Pollution--Mathematical models"
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Item Designing and analyzing test programs with censored data for civil engineering applications(2004) Finley, Cynthia; Gilbert, Robert B.The objective of this research was to develop a method for incorporating censored data into the design and analysis of test programs. In engineering applications, it is common to encounter censored data. The exact value of a censored data point is not known, only that it is above or below some specified threshold value. Existing methods for analyzing censored data are limited and usually involve assumptions about the data, such as normally-distributed or statistically independent data. This research extends the First-Order Second-Moment (FOSM) Bayesian method (Gilbert 1999) to data sets that include censored data and have any type of distribution. This method is used for test program design and data analysis, allowing the Bayesian approach to be applied to practical engineering problems with large data sets and correlated data. The extension for censored data was validated through numerical experiments. The method developed for analysis of censored data with a non-normal distribution was applied to a real site with contaminated groundwater. The concentration measurements from the site, which were taken both before and after remediation, were calibrated with a groundwater model. The calibration resulted in reasonable estimates for the model parameters describing the physical characteristics of the site. The calibration also successfully fit the non-normal distribution of the measurements. The method was proven useful in considering all the complexities of the site: concentrations measured above and below the detection limit, the effects of remediation on the concentrations, measurements at many different times and locations, and correlations between concentrations that represent the heterogeneities at the site and the random errors in measurements. The method was also used to predict future contaminant concentrations at the site, which is helpful in making decisions regarding monitoring and remediation.Item Modeling the effects of aerosols on groundwater systems(1989-12) Brown, Theresa Jean; Sharp, John Malcolm, Jr., 1944-Just as children eventually learn that covering their eyes does not make them invisible, we as adults have realized that just because harmful substances are "out-of-site" it does not necessarily mean they are gone for good. As we expanded our ability to think abstractly we began to consider how our actions affect our future and the lives of future generations. For example, we established procedures for the handling and disposal of high level radioactive waste and other hazardous materials because of the threat such materials pose to the environment. To date, however, the effect of atmospheric pollutants on groundwater supplies has been virtually ignored. Atmospheric pollution sources include, but are not limited to, smoke stack emissions, releases from power plants, weapons testing and manufacturing, fires, explosions, and deflation from tailings, spills and playas. This study evaluates the potential for groundwater to be contaminated by a point-source atmospheric emission. Pollutant concentrations in groundwater are estimated using a Gaussian model of atmospheric transport, a transfer function model for transport through the unsaturated zone, and a two-dimensional groundwater flow model based on Darcy's law to simulate transport in the saturated groundwater system. A sensitivity analysis of the composite atmospheric-groundwater transport model suggests that the most important factors influencing the susceptibility of a groundwater system to contamination by an aerosol source are: the concentration of the source, the amount of recharge, the depth to the water-table, and the velocity distribution in the unsaturated zone. This study indicates a significant potential for pollution of groundwater systems by aerosols. Shallow aquifers are especially vulnerable; however, deeper aquifers where rapid travel times through the unsaturated zone exist are also susceptible to aerosol contamination.