The objective of this study was to use an applied tracer to study lateral ground water flow paths in the top ~0.5 m of clay settling areas (CSA) in order to gain better understanding of hydrologic connectivity of CSAs to the surrounding hydrologic systems. The study site was located on the non-operational Mosaic Fort Mead Mine property in Fort Meade, Polk County, Florida. This lateral tracer test study is a follow up from a vertical tracer test study performed at the same site location in 2007. The CSA is generally composed of a well developed, clay rich, subangular-blocky surface layer ~0-1.0m, which exhibits abundant desiccation cracks plus other macropores underlain by a massive, saturated, clay-rich sublayer from ~1.0-2.5 m. A bromide tracer was applied into an injected trench. All 60L of the applied tracer flowed out of the down gradient face of the trench quickly, over an eleven minute period. The Bromide tracer was rapidly transported laterally and was detected as far as 16 m from the starting point just 24 hours after application, as well as in the inundated north pond adjacent to the study area. Bromide concentration distribution was not uniform over the study area during any time period, with an initial disorganized bromide pulse followed by secondary pulse concentrated on the north side of the sampling area. This spatial-temporal distribution of bromide indicates preferential flow through desiccation cracks or other macropores. Bromide concentrations in the north pond increased over time while pond stage fluctuated due to this shallow lateral macropore dominated flow in and out. Although it is most likely true that flow paths from the CSA to the adjacent hydrologic landscape during the wet season is dominated by rapid shallow lateral flow through macropores, specific flow paths, macropore length, diameter and distribution and fluxes still remain unquantified. Therefore, how the hydrology of CSAs affects the adjacent hydrologic landscape still remain unquantified.

The objective of this study was to use applied and naturally-occurring geochemical tracers to study the hydrology of clay settling areas (CSAs) and the hydrological connectivity between CSAs and surrounding hydrological landscapes. The study site is located on the Fort Meade Mine in Polk County, Florida. The surface of the CSA is covered in desiccation cracks which swell and shrink in response to wetting and drying. Bromide was used as an applied tracer to study hydrological processes in the upper part of the CSA. Bromide infiltrated rapidly and perched on an uncracked massive sublayer. Bromide concentrations attenuated in the upper part of the profile without being translated vertically down through the lower part of the profile suggesting that bromide was lost to lateral rather than to vertical downward transport. Infiltration and lateral flow were rapid suggesting that preferential flow through desiccation cracks and other macropores likely dominates flow in the upper part of the profile. Naturally-occurring dissolved constituents and stable isotopes of hydrogen and oxygen were used as naturally-occurring tracers to study the hydrological connectivity between the CSA and the surrounding hydrological landscape. The relative contributions of source waters were determined using a two-end, mass-balance mixing model with sodium as a conservative natural tracer. On average, water samples downgradient from the CSA were ~80% rainfall/ambient water and ~20% CSA water. Discharge from the CSA to the surrounding surface water bodies and surficial aquifer occurs laterally over, through, and/or under the berms and/or vertically through the thick uncracked massive sublayer. However, the precise flowpaths from the CSA to the surrounding hydrological landscape are unclear and the fluxes remain unquantified, so the effects of CSAs on the hydrology of the surrounding and underlying hydrological landscape also remain unquantified.

<p>Owing to the lack of knowledge pertaining to the fate and transport of microorganisms in fractured aquifers, the research presented in this thesis was designed to improve the mechanistic understanding of particulate transport in fractures by conducting tracer experiments in natural and epoxy replica fractures. This research demonstrated that particulate retention within fractures is heavily dependent on the equivalent mass balance aperture, followed by the coefficient of variation of the aperture field, and then by the flow conditions. It was also shown that the fracture aperture field alone, not the flow rate or the matrix properties, determines the number of fracture volume flushes required to achieve a 2-3 log decrease in effluent concentration. Moreover, a statistical model was developed that identifies the most important factors affecting particulate retention as the ratio of the ionic strength of solution to the charge of the collector, the ratio of the particle to collector charges, and the Peclet number. The model is able to reasonably predict particulate retention. Finally, tracer experiments conducted in a natural fracture and an epoxy replica of that fracture isolated the effects of matrix properties on attachment, and hence, retention. The transparent nature of the replica fracture was exploited to capture images of <em>E. coli</em> RS2-GFP transport. These images reveal preferential transport within the fracture, and also show that the preferential pathway broadens slightly under increasing flow conditions. This broadening is likely due to higher fluid pressures associated with larger specific discharges. In the groundwater field, there is so little fracture-specific information available that coupling the understanding of a critical environmental setting (fractures) with high-quality particulate tracer experiments and associated modeling represents a significant contribution to the body of science.</p> / Doctor of Philosophy (PhD)