Publications

The Sacramento-San Joaquin River Delta of California once was a great tidal freshwater marsh blanketed by peat and peaty alluvium. Beginning in the late 1800s, levees were built along the stream channels, and the land thus protected from flooding was drained, cleared, and planted. Although the Delta is now an exceptionally rich agricultural area (over a $500 million crop value in 1993)...

Calcite grew continuously for 500,000 years on the submerged walls of an open fault plane (Devils Hole) in southern Nevada, U.S.A. at rates of 0.3 to 1.3 mm/ka, but ceased growing approximately 60,000 years ago, even though the fault plane remained open and was continuously submerged. The maximum initial in-situ growth rate on pre-weighed crystals of Iceland spar placed in Devils Hole...

We employed a three-dimensional finite difference gas diffusion model to simulate the performance of chambers used to measure surface-atmosphere tace gas exchange. We found that systematic errors often result from conventional chamber design and deployment protocols, as well as key assumptions behind the estimation of trace gas exchange rates from observed concentration data...

The potential for the biological conversion of long-chain saturated hydrocarbons to methane under anaerobic conditions has been demonstrated by using an enrichment culture of bacteria to degrade pure-phase hexadecane. The formation of methane in hydrocarbon-rich subsurface zones could be explained if a similar conversion of long-chain alkanes to methane were to take place in subsurface

Silica-coated titania (TiO2) and zirconia (ZrO2) colloids were synthesized in two sizes to provide easily traced mineral colloids for subsurface transport experiments. Electrophoretic mobility measurements showed that coating with silica imparted surface properties similar to pure silica to the titania and zirconia colloids. Measurements of steady electrophoretic mobility and size (by...

This special issue is devoted to recent and ongoing research relating to the fate and transport of agricultural chemicals in the Mississippi River Basin by the US Geological Survey Toxic Substances Hydrology (Toxics) Program. The Mississippi River Basin drains approximately 3 200 000 km2 representing 41% of the United States. This is the largest river in the United States and the third...

Analyses of water samples collected from the Mississippi River at Baton Rouge, Louisiana, during 1991–1997 indicate that hundreds of metric tons of herbicides and herbicide metabolites are being discharged annually to the Gulf of Mexico. Atrazine, metolachlor, and the ethane-sulfonic acid metabolite of alachlor (alachlor ESA) were the most frequently detected herbicides and, in general...

In Part 1 of this study, the general solution to the transient-pulse test (Hsieh et al. 1981) was extended to evaluate quantitatively the transient variations in hydraulic head and the corresponding distributions of hydraulic gradient within a test specimen. In addition, the conditions and the validity of using the expression proposed by Brace et al. (1968) to compute the low...

Geobacter become dominant members of the microbial community when Fe(III)-reducing conditions develop as the result of organic contamination, or when Fe(III) reduction is artificially stimulated. These results suggest that further understanding of the ecophysiology of Geobacter species would aid in better prediction of the natural attenuation of organic contaminants under anaerobic...

Solute transport in streams and rivers is governed by a suite of hydrologic and geochemical processes. Knowledge of these processes is needed when assessing the fate of contaminants that are released into surface waters. The study of solute fate and transport often is aided by solute transport models that mathematically describe the underlying processes. This fact sheet describes a model...

Engineered stimulation of Fe(III) has been proposed as a strategy to enhance the immobilization of radioactive and toxic metals in metal-contaminated subsurface environments. Therefore, laboratory and field studies were conducted to determine which microbial populations would respond to stimulation of Fe(III) reduction in the sediments of sandy aquifers. In laboratory studies, the...

A pore network simulation model was developed to investigate the fundamental physics of nonequilibrium nonaqueous phase liquid (NAPL) dissolution. The network model is a lattice of cubic chambers and rectangular tubes that represent pore bodies and pore throats, respectively. Experimental data obtained by Powers [1992] were used to develop and validate the model. To ensure the network...