Shellfish beds in the Chesapeake Bay region are being contaminated with fecal coliform bacteria which can cause the beds to be closed to harvesting. The cause of the bacteria contamination is basically unknown but has been hypothesized to be coming from non-point sources of pollution. The suggested source of the bacteria is on-site waste disposal systems (OSWDS) including septic tanks. Septic tank effluent (STE) may be transported through the soil and contaminate the groundwater. Submarine groundwater discharge (SGWD) may then be providing a conduit into the estuary for the bacteria. Data of OSWDS locations was not available, thus the groundwater transport mechanism was the focus of the study. A comprehensive analysis was performed on fecal coliform concentration measurements taken from 1981 through 1992 in the Chesapeake Bay region. In all, over 191,000 bacteria concentration measurements in the main database were considered. An analysis of various hydrological factors was made to determine how much these factors affected the bacteria most probable number (MPN) concentration levels. Subsets of the data consisting of heavy rain events, low tide and high tide were analyzed which had geometric mean bacteria MPN concentrations of 16.1 fecal coliforms (FC) / 100 mL, 9.4 FC / 100 mL, and 6.9 FC / 100 mL respectively compared to an overall geometric mean of 7.8 FC / 100 mL. Of the factors analyzed, rain events and tidal elevation had the most affect on bacteria MPN levels. Other factors analyzed were secchi depth, salinity, season, and water temperature. Additional data was available for Virginia's Eastern Shore including soil permeability, hydraulic gradient and land use which allowed for a more detailed analysis of samples taken in this area. A multiple regression correlation on bacteria MPN measurements with water quality data of the Eastern Shore yielded an R* value of 22.2% which does not statistically link groundwater transport and high bacteria counts. Many factors, which were calculated using a geographic information system (GIS), were examined, including near shore soil permeability, season, and surface area of water within a 400 meter radius, to determine their contribution to high area of water within a 400 meter radius, to determine their contribution to high bacteria concentration measurements. The factors used in the multiple regression were near shore soil permeability, near shore soil Darcy velocity, near shore soil hydraulic gradient, proximity to shoreline, proximity to wastewater treatment plant, rain in the last two days prior to sample collection, runoff event occurrence, salinity, season, urban land use, agricultural land use, pasture land use, surface area of water in a 400 meter radius, tide elevation, and water temperature. Of these factors, distance upstream, rain, tide and season were determined to have the highest effect on geometric mean bacteria concentrations. Groundwater transport could not be statistically linked to high bacteria MPN counts. Thus OSWDS can not be linked as the source of the contamination. Further research on a more local basis is necessary to examine the relationship between OSWDS usage and bacteria MPN levels. A GIS proved to be a very important tool for examining the effects of the different data sets. / Master of Science

Patterns of fossil diagenesis caused by groundwater leaching provide insight into how shells are altered. This study analyzes fossils in unconsolidated terrigenous sediments from the Virginia Coastal Plain, unlike previous studies conducted mostly in carbonate terranes. The vertical and lateral distribution of diagenetic states was mapped in an outcrop (63 m by 2.1 m) of the Yorktown Formation. A paleostream channel located at one end was incised during the Pleistocene and filled with sediments of the Shirley Formation. The Tabb Formation unconformably overlies the outcrop. Acidic groundwater caused the observed patterns of fossil and sediment diagenesis. These patterns include zones of fossil alteration, diagenetic stratification of the sediment, and fossil diagenesis on a microstructural level. Groundwater movement, controlled by the presence of the paleochannel, caused diagenetic alteration or complete dissolution of the fossils, and possibly caused precipitation of fine-grained iron oxyhydroxides. All carbonate material in the vicinity of the paleochannel is completely dissolved away, although iron oxyhydroxide coatings of fossils remain. Away from the paleochannel Crepidula fornicata (gastropod; aragonite), Ostrea sp. (bivalve; calcite), Balanus sp. (barnacle; calcite), and bryozoans (calcite) are found in parallel zones of alteration that dip toward the paleochannel and cut across horizontal sedimentologic and fossiliferous layers. Groundwater also leached the Yorktown sediments. This alteration caused a diagenetic stratification of the sediment, with unaltered greenish-gray silty fine sand along the base of the outcrop, overlain by leached yellowish-brown silty fine sand and areas of concentrated iron oxyhydroxides. The preservation of both aragonitic and calcitic shells was affected by groundwater movement. Original aragonitic shell material is found as chalky, uncrystallized specimens or neomorphosed shells, or is completely dissolved with only molds or ghosts remaining. Neomorphosed specimens typically consist of calcite-replaced shell material with pockets of original aragonite, and sparry calcite filling empty shell cavities. Original calcitic shell material is either chalky or unaltered. Chalky shells range from relatively hard to soft and pasty. Crepidula shells of intermediate chalkiness tend to separate into thin flakes, caused by dissolution along growth surfaces. Chalkiness of pasty shells is caused by dissolution of shell material (without recrystallization) and not simply loss of organic matrix. SEM photos of Crepidula reveal the more porous and leached appearance of chalky shells in contrast with hard; unaltered shells. The presence of chalky aragonitic and calcitic shells indicates that chalky textures are, to some degree, independent of mineralogy and microstructure. / M.S.