Publications

To determine whether NO3− concentration pulses in surface water in early spring snowmelt discharge are due to atmospheric NO3−, we analyzed stream δ15N-NO3− and δ18O-NO3− values between February and June of 2001 and 2002 and compared them to those of throughfall, bulk precipitation, snow, and groundwater. Stream total Al, DOC and Si concentrations were used to indicate preferential water...

Groundwater under the direct influence of surface water (GWUDISW) is of concern in communities where growing public demand on groundwater resources has resulted in increased withdrawals and hydraulic stress near surface water bodies. Under these conditions, contaminants such as methyl-tert butyl ether (MTBE) and biological materials have been detected in domestic wells. Other...

The U.S. Geological Survey (USGS) in cooperation with the East Dakota Water Development District conducted a reconnaissance study to determine the occurrence of organic wastewater compounds (OWCs) in wastewater effluent and the Big Sioux River at or near the cities of Watertown, Volga, and Brookings in the upper Big Sioux River Basin during August 2003 through June 2004. For each city...

During 1902 to 1906 as a soil physicist at the USDA Bureau of Soils (BOS), Edgar Buckingham originated the concepts of matric potential, soil–water retention curves, specific water capacity, and unsaturated hydraulic conductivity (K) as a distinct property of a soil. He applied a formula equivalent to Darcy's law (though without specific mention of Darcy's work) to unsaturated flow. He...

Three-dimensional modeling of groundwater flow and solute transport in the Pearl Harbor aquifer, southern Oahu, Hawaii, shows that the readjustment of the freshwater–saltwater transition zone takes a long time following changes in pumping, irrigation, or recharge in the aquifer system. It takes about 50 years for the transition zone to move 90% of the distance to its new steady position...

Natural unsaturated-zone gas profiles at the U.S. Geological Survey's Amargosa Desert Research Site, near Beatty, Nevada, reveal the presence of two physically and isotopically distinct CO2 sources, one shallow and one deep. The shallow source derives from seasonally variable autotrophic and heterotrophic respiration in the root zone. Scanning electron micrograph results indicate that at...

Soil denitrification is an ecologically important nitrogen removal mechanism that releases to the atmosphere the greenhouse gas N2O, an intermediate product from the reduction of NO3- to N 2. In this study we evaluate the relationship between soil carbon and denitrification potential in watersheds with bedrock acting as a nonpoint source of nitrogen, testing the hypothesis that nitrate...

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...

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...

[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...

Freshwater research and management efforts could be greatly enhanced by a better understanding of the relationship between landscape-scale factors and water quality indicators. This is particularly true in urban areas, where land transformation impacts stream systems at a variety of scales. Despite advances in landscape quantification methods, several studies attempting to elucidate the

A multiple well aquifer test to determine anisotropic transmissivity was conducted on a coal-bed in the Powder River Basin, southeastern Montana, as part of a multidisciplinary investigation to determine hydrologic conditions of coal-beds in the area. For the test, three wells were drilled equidistant from and at different angles to a production well tapping the Flowers–Goodale coal seam...