Publications

[1] Geophysical imaging has traditionally provided qualitative information about geologic structure; however, there is increasing interest in using petrophysical models to convert tomograms to quantitative estimates of hydrogeologic, mechanical, or geochemical parameters of interest (e.g., permeability, porosity, water content, and salinity). Unfortunately, petrophysical estimation based...

Our results show that subsurface crude-oil degradation rates at a long-term research site were strongly influenced by small-scale variations in hydrologic conditions. The site is a shallow glacial outwash aquifer located near Bemidji in northern Minnesota that became contaminated when oil spilled from a broken pipeline in August 1979. In the study area, separate-phase oil forms a...

Because surface water can be a source of undesirable water quality in a drinking water well, an understanding of the amount of surface water and its travel time to the well is needed to assess a well's vulnerability. Stable isotope ratios of oxygen in river water at the City of La Crosse, Wisconsin, show peak-to-peak seasonal variation greater than 4‰ in 2001 and 2002. This seasonal...

Microbial reductive dechlorination of [1,2-14C]trichloroethene to [14C]cis-dichloroethene and [14C]vinyl chloride was observed at 4°C in anoxic microcosms prepared with cold temperature-adapted aquifer and river sediments from Alaska. Microbial anaerobic oxidation of [1,2-14C]cis-dichloroethene and [1,2-14C]vinyl chloride to 14CO2 also was observed under these conditions.

The variability (1990–2002) of potential evapotranspiration estimates (ETo) and related meteorological variables from a set of stations from the California Irrigation Management System (CIMIS) is studied. Data from the National Climatic Data Center (NCDC) and from the Department of Energy from 1950 to 2001 were used to validate the results. The objective is to determine the...

The objective of this study was to test the effectiveness of a nitrate-rich nutrient solution and hydrogen peroxide (H2O2) to enhance in-situ microbial remediation of toluene in the unsaturated zone. Three sand-filled plots were tested in three phases (each phase lasting approximately 2 weeks). During the control phase, toluene was applied uniformly via sprinkler irrigation. Passive...

Soil moisture data collected using an automated data logging system were used to estimate ground water recharge at a crude oil spill research site near Bemidji, Minnesota. Three different soil moisture probes were tested in the laboratory as well as the field conditions of limited power supply and extreme weather typical of northern Minnesota: a self‐contained reflectometer probe, and...

Amphibians occupy a range of habitats throughout the world, but species richness is greatest in regions with moist, warm climates. We modeled the statistical relations of anuran and urodele species richness with mean annual climate for the conterminous United States, and compared the strength of these relations at national and regional levels. Model variables were calculated for county...

Water, bed sediment, and biota were sampled in streams from Butte to below Missoula as part of a program, conducted in cooperation with the U.S. Environmental Protection Agency, to characterize aquatic resources in the upper Clark Fork basin of western Montana. Sampling sites were located on the Clark Fork, five major tributaries, and three smaller tributaries. Water-quality samples were...

The highly variable timing of streamflow in snowmelt-dominated basins across western North America is an important consequence, and indicator, of climate fluctuations. Changes in the timing of snowmelt-derived streamflow from 1948 to 2002 were investigated in a network of 302 western North America gauges by examining the center of mass for flow, spring pulse onset dates, and seasonal...

Kharaka has been a research hydrogeochemist with the U.S. Geological Survey since1975. His current research covers the fields of water-rock-gas interactions, CO2 sequestration, contamination from agricultural drainage and petroleum produced water, and fluid-fault interactions. Kharaka has authored more than 100 scientific papers and book chapters and has delivered about 200 presentations...

Diurnal cycles of streamflow in snow‐fed rivers can be used to infer the average time a water parcel spends in transit from the top of the snowpack to a stream gauge in the river channel. This travel time, which is measured as the difference between the hour of peak snowmelt in the afternoon and the hour of maximum discharge each day, ranges from a few hours to almost a full day later...