Browsing by Author "Johnson, Jeffrey A."

Now showing 1 - 3 of 3
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    Aquifer Characterization in the Blue Ridge Physiographic Province
    Seaton, William (Virginia Tech, 2002-01-25)
    Existing models of the hydrogeology in the Blue Ridge Province in the eastern United States generally assume a simplified two-layered system consisting of shallow unconsolidated and relatively homogeneous and porous regolith with a water-table aquifer that slowly supplies water downward to the underlying variably fractured crystalline bedrock. In these models, interconnected fractures in the crystalline bedrock act as conduits for predominantly downward vertical and limited horizontal flow. Fracture density is depthà limited and correlated with proximity to topographic lineaments. Current models consider the porous regolith as the primary water storage reservoir for the entire aquifer system. In this research, detailed hydrogeologic studies in the Blue Ridge Province in Floyd County, Virginia reveal a substantially different framework for groundwater flow. Recent acquisition of two-dimensional surface resistivity profiles collected using a variety of array techniques combined with borehole geophysical logs revealed new insights into this geologically complex province. Dipole-dipole arrays were particularly important in gathering high resolution resistivity profiles that document horizontal and vertical resistivity variation reflecting changes in subsurface geology and anomalous low resistivity areas in crystalline bedrock associated with fault zones. The shallow regolith contains unsaturated areas and also localized sand and clay prone facies with water table and confined aquifer conditions residing locally. Hydraulic heads between the shallow aquifer and the deeper fractured bedrock aquifer can vary by 20 m vertically. Within the crystalline bedrock are anomalous lower resistivity intervals associated with ancient fault shear zones. Brecciated rock adjacent to the shear zones, and the shear zones themselves, can be hydraulically conductive and serve as pathways for groundwater movement. Aquifer testing of the regolith-bedrock fracture system occurred over a 6-day period and produced rapid and relatively uniform drawdowns in surrounding wells completed in the fractured bedrock aquifers. The shallow aquifers experienced minimal drawdowns from the aquifer test indicating low vertical hydraulic conductivity and limited communication between the shallow and deeper bedrock aquifers. Water chemistry and chlorofluorocarbon (CFC) age dating analyses indicated significant differences between water samples from the shallow and deep aquifers. A new conceptual model for Blue Ridge aquifers is proposed based on these research findings.
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    Assessing Various Technologies to Remediate a Hydrocarbon Contaminated Aquifer
    Parcher, Mary Ann (Virginia Tech, 1999-01-13)
    Releases of nonaqueous phase liquids (NAPLs) to groundwater systems are a serious and widespread problem throughout the United States. Research was conducted to determine if numerical groundwater flow and transport models could evaluate the effectiveness of alternative remedial strategies to reduce dissolved hydrocarbon contamination in aquifers, and therefore serve as tools to aid environmental managers in the remedial decision making process. A fuel distribution terminal in the Eastern United States was selected as the test site. A release of diesel and jet fuels from the terminal loading rack area contaminated the unconfined aquifer beneath the terminal and migrated off-site, impacting commercial and residential areas. In the analyses, groundwater flow and transport models were calibrated to site data. The calibrated models were applied to simulate four remedial options: (1) natural attenuation, (2) groundwater extraction, (3) groundwater flushing, and (4) microbial fences. Results of the predictive simulations indicated that the groundwater flushing remedial option provided the greatest reduction of benzene and TEX mass from the NAPL source as well as the lowest concentrations of benzene and TEX in the aquifer. The calibrated numerical models were able to predict the effectiveness of various remedial options and provide a basis for comparison. The modeling in conjunction with other factors, such as cost, were utilized to facilitate the decision making process.
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    Effects of a mentor program on the academic success and self concept of selected black males in the junior high school
    Jones, Barbara Archer (Virginia Tech, 1994-05-05)
    Lack of academic success among Black male students has become a focus of educational debate. Concerned educators have led the search for effective models of intervention and prevention. Current literature indicates that positive interaction with adult male mentors in the educational. setting might foster academic success among Black male students. This study investigated the effects of a mentor program on the academic success and self concept of selected Black males in the junior high school. A mentor program was implemented in an Alexandria, Virginia junior high school. Based upon teacher and administrator referral, 50 students who might benefit from participation in a mentor program were identified. Twenty-five students were randomly assigned to the treatment group and participated in the full mentor program. The control group of 25 students was monitored. Eleven city agency and school staff members served as mentors to the experimental group.