Publications

The impact on ground water quality from increasing fertilizer application rates over the past 40 years is evaluated within a glacial aquifer system beneath a thick unsaturated zone. Ground water ages within the aquifer could not be accurately determined from the measured distribution of 3H and as a result, chlorofluorocarbon (CFC) and 3H/3He dating techniques were applied. Beneath a 25 m...

The Little River, an ephemeral stream that drains a watershed of approximately 88 km2 in northern Florida, disappears into a series of sinkholes along the Cody Scarp and flows directly into the carbonate Upper Floridan aquifer, the source of water supply in northern Florida. The changes in the geochemistry of ground water caused by a major recharge pulse from the sinking stream were...

The partition behavior was determined for three polycyclic aromatic hydrocarbons (PAHs), i.e., naphthalene, phenanthrene, and pyrene, from water to a range of soil and sediment samples. The measured partition coefficients of the individual PAHs between soil/sediment organic matter (SOM) and water (i.e., K(oc) values) are relatively invariant either for the 'clean' (uncontaminated) soils...

We extend the finite-volume Eulerian-Lagrangian localized adjoint method (FVELLAM) for solution of the advection-dispersion equation to two dimensions. The method can conserve mass globally and is not limited by restrictions on the size of the grid Peclet or Courant number. Therefore, it is well suited for solution of advection-dominated ground-water solute transport problems. In test...

The contribution of hydroxylated atrazine degradation products (HADPs) to the total atrazine load (i.e., atrazine plus stable metabolites) in streams needs to be determined in order to fully assess the impact of atrazine contamination on stream ecosystems and human health. The objectives of this study were (1) to determine the contribution of HADPs to the total atrazine load in streams...

The relative importance of advection and dispersion for both solute and vapor transport can be determined from type curves or concentration, flux, or cumulative flux. The dimensionless form of the type curves provides a means to directly evaluate the importance of mass transport by advection relative to that of mass transport by diffusion and dispersion. Type curves based on an...

Wetlands cannot exist without water, but wetland hydrology is difficult to characterize. As a result, compensatory wetland mitigation often only assumes the proper hydrology has been created. In this study, water sources and mass transfer processes in a natural and constructed wetland complex were investigated using isotopes of water and strontium. Water isotope profiles in the saturated...

Metal concentrations of the soluble fraction of the cytoplasm (cytosol) and the whole body were determined in the caddisfly Hydropsyche spp. (Trichoptera). Metal accumulation in the cytosol and the whole body were compared in samples collected along 380 kms of a contamination gradient in the Clark Fork river in four consecutive years (1992–1995), and from a contaminated tributary (Flint...

A theoretical analysis is presented that compares the response characteristics of the constant head and the constant flowrate (flow pump) laboratory techniques for quantifying the hydraulic properties of geologic materials having permeabilities less than 10-10 m/s. Rigorous analytical solutions that describe the transient distributions of hydraulic gradient within a specimen are...

The in situ measurement of water flow and chemical transport through clay pan soils is crucial to understanding potential water contamination from agricultural sources. It is important due to the large areal extent of these soils in agricultural regions of the midwestern United States and because of preferential flow paths caused by desiccation cracks, worms burrowing, and root...

Bacterial oxidation of14CH2Br2 and14CH3Br was measured in freshwater, estuarine, seawater, and hypersaline-alkaline samples. In general, bacteria from the various sites oxidized similar amounts of14CH2Br2 and comparatively less 14CH3Br. Bacterial oxidation of14CH3Br was rapid in freshwater samples compared to bacterial oxidation of 14CH3Br in more saline waters. Freshwater was also the...

Saturated hydraulic conductivity of aquifer sediments at a crude-oil spill research site near Bemidji, Minnesota were examined using pneumatically-induced head-difference tests and packer/vacuum system tests. Results from slug tests on 58 wells show that hydraulic conductivity varies both horizontally and vertically in the range from about 10-7 to 10-4 meters per second (m/s), with a...