Publications

Recharge rates of nitrate (NO3−) to groundwater beneath agricultural land commonly are greater than discharge rates of NO3− in nearby streams, but local controls of NO3−distribution in the subsurface generally are poorly known. Groundwater dating (CFC, 3H) was combined with chemical (ions and gases) and stable isotope (N, S, and C) analyses to resolve the effects of land use changes...

A two-dimensional numerical solute transport model was developed for simulating an enhanced in situ denitrification experiment performed in a nitrate-contaminated aquifer on Cape Cod, Massachusetts. In this experiment, formate (HCOO-) was injected for a period of 26 days into the carbon-limited aquifer to stimulate denitrification. Calibration of the vertical-profile site model was...

Geochemical data were collected to investigate the effects of topography and focused recharge on the transport of agricultural chemicals to groundwater through sandy soils. The research was done at a topographically high (upland) site and a depressional (lowland) site within a corn field. Agricultural chemicals that move readily with water were most directly affected by focused recharge...

Adsorption, complexation, and dissolution reactions strongly influenced the transport of metal ions complexed with ethylenediaminetetraacetic acid (EDTA) in a predominantly quartz-sand aquifer during two tracer tests conducted under mildly reducing conditions at pH 5.8 to 6.1. In tracer test M89, EDTA complexes of zinc (Zn) and nickel (Ni), along with excess free EDTA, were injected such...

The binding of Hg(II) to dissolved organic matter (DOM; hydrophobic acids isolated from the Florida Everglades by XAD-8 resin) was measured at a wide range of Hg-to-DOM concentration ratios using an equilibrium dialysis ligand exchange method. Conditional distribution coefficients (KDOM‘) determined by this method were strongly affected by the Hg/DOM concentration ratio. At Hg/DOM ratios...

The n-alkylated cyclohexanes (CHs) are a homologous series of hydrocarbon compounds that are commonly present in crude oil and refinery products such as diesel fuel. These compounds exhibit specific distribution patterns for different fuel types, providing useful fingerprints for characterizing petroleum products, especially after degradation of n-alkanes has occurred. However, there are...

Watersheds in mineralized zones may contain many mines, each of which can contribute to acidity and the metal load of a stream. In this study the authors delineate hydrogeologic characteristics determining the transport of metals from the watershed to the stream in the watershed of Cement Creek, Colorado. Combining the injection of a chemical tracer, to determine a discharge, with...

Ground water chemistry data collected over a six‐year period show that the distribution of contaminants and redox processes in a shallow petroleum hydrocarbon‐contaminated aquifer has changed rapidly over time. Shortly after a gasoline release occurred in 1990, high concentrations of benzene were present near the contaminant source area. In this contaminated zone, dissolved oxygen in...

Methyl tert-butyl ether (MTBE), the widely used gasoline oxygenate, has been identified as a common ground water contaminant, and BTEX compounds (benzene, toluene, ethylbenzene, and xylenes) have long been associated with gasoline spills. Because not all instances of ground water contamination by MTBE and BTEX can be attributed to spills or leaking storage tanks, other potential sources...

A novel, sensitive, linker-assisted enzyme-linked immunosorbent assay (L'ELISA) was compared to on-line solidphase extraction (SPE) with high-performance liquid chromatography/mass spectrometry (HPLC/MS) for the analysis of glyphosate in surface water and groundwater samples. The L'ELISA used succinic anhydride to derivatize glyphosate, which mimics the epitotic attachment of glyphosate...

Arsenite [As(III)]-enriched anoxic bottom water from Mono Lake, California, produced arsenate [As(V)] during incubation with either nitrate or nitrite. No such oxidation occurred in killed controls or in live samples incubated without added nitrate or nitrite. A small amount of biological As(III) oxidation was observed in samples amended with Fe(III) chelated with nitrolotriacetic acid...

A method is described that allows precise determination of 234U/238U activity ratios (UAR) in most natural waters using commonly available inductively coupled plasma/mass spectrometry (ICP/MS) instrumentation and accessories. The precision achieved by this technique (±0.5% RSD, 1 sigma) is intermediate between thermal ionization mass spectrometry (±0.25% RSD, 1 sigma) and alpha particle