Publications

The distribution and fate of chlorinated pesticides, biomarkers, and polycyclic aromatic hydrocarbons (PAHs) in surficial sediments along a contamination gradient in the Lauritzen Canal and Richmond Harbor in San Francisco Bay was investigated. Compounds were identified and quantified using gas chromatography-ion trap mass spectrometry. Biomarkers and PAHs were derived primarily from weathered pet

Field and laboratory experiments indicate that a number of factors associated with filtration other than just pore size (e.g., diameter, manufacturer, volume of sample processed, amount of suspended sediment in the sample) can produce significant variations in the “dissolved” concentrations of such elements as Fe, Al, Cu, Zn, Pb, Co, and Ni. The bulk of these variations result from the inclusion/e

The simulation-optimization approach is used to identify ground-water pumping strategies for control of the shallow water table in the western San Joaquin Valley, California, where shallow ground water threatens continued agricultural productivity. The approach combines the use of ground-water flow simulation with optimization techniques to build on and refine pumping strategies identified in prev

Groundwater age dating through the combination of transient tracer methods (chlorofluorocarbons (CFCs) and tritium/helium 3 (3H/3He)) and groundwater flow path analysis is useful for investigating groundwater travel times, flow patterns, and recharge rates, as demonstrated by this study of the homogeneous shallow, unconfined Kirkwood-Cohansey aquifer system in the southern New Jersey coastal plain

The effect of 4 different 0.45 μm pore size filter membrane systems on the ‘dissolved’ concentration of 28 elements in 5 natural water samples of varying matrix is reported. In 3 of the 5 waters, consistently higher concentrations of most elements (minor and trace) are obtained using Nucleopore 47 mm filter and the cellulose acetate/nitrate 47 mm filter than those measured using the 142 mm cellulo

Mass spectrometry and tandem mass spectrometry, coupled by a thermospray interface to a high-performance liguid chromatography system and equipped with a photodiode array detector, were used to determine the presence of nitroaromatic explosives and their degradation products in USA unsaturated-zone water samples. Using this approach, the lower limits of quantitation for explosives determined by ma

The almost universally accepted operational definition for dissolved constituents is based on processingThe almost universally accepted operational definition for dissolved constituents is based on processing whole-water samples through a 0.45-μm membrane filter. Results from field and laboratory experiments indicate that a number of factors associated with filtration, other than just pore size (e

Oxygen isotope and total inorganic carbon values of cored sediments from the Owens Lake basin, California, indicate that Owens Lake overflowed most of the time between 52,500 and 12,509 carbon-14 (14C) years before present (B.P.). Owens Lake desiccated during or after Heinrich event H1 and was hydrologically closed during Heinrich event H2. The magnetic susceptibility and organic carbon content of

The potential for hydrophobic organochlorine contaminants to be sequestered in submersed aquatic vegetation was evaluated by determining the concentrations of cis- and trans-chlordane, dieldrin, and polychlorinated biphenyls (PCBs) in feral aquatic macrophytes (Hydrilla verticillata (L.f.) Royle) collected from the tidal Potomac River. Similarities in mean dry-weight concentrations of the identifi

The mechanisms that resuspend bottom sediments in Hillsborough Bay, a shallow, microtidal, subtropical estuary in West-central Florida, were determined by analysing hydrodynamic and suspended-solids concentration data collected during several instrument deployments made in 1990 and 1991. Large vessels in a dredged ship channel can generate forced solitary long waves that cause large water velociti

A nonnormal and heteroscedastic Tobit model is used to determine the primary factors that affect nitrate concentrations in near-surface aquifers, using data from the U.S. Geological Survey collected in 1991. Both normality and homoscedasticity of errors are rejected, justifying the use of a nonnormal and heteroscedastic model. The following factors are found to have significant impacts on nitrate

Pesticides in stormwater runoff, within the Sacramento River Basin, California, were assessed during a storm that occurred in January 1994. Two organophosphate insecticides (diazinon and methidathion), two carbamate pesticides (molinate and carbofuran), and one triazine herbicide (simazine) were detected. Organophosphate pesticide concentrations increased with the rising stage of the hydrographs;