Peter B McMahon
Peter is a Research Hydrologist with the USGS Colorado Water Science Center in Lakewood, CO.
Pete McMahon’s current research interests include understanding the effects of hydrocarbon production activities on groundwater quality and identifying natural and human processes that create regional- and national-scale patterns in the chemistry of groundwater. He uses geochemical, isotope, noble-gas, and groundwater-age tracers to understand the origin and fate of chemicals of concern in groundwater.
Education and Certifications
Ph.D., 1990, Geology, University of South Carolina at Columbia
M.A., 1984, Geology, University of Texas at Austin
B.S., 1981, Geology, University of Missouri at Columbia
Science and Products
Filter Total Items: 14
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Filter Total Items: 116
Nitrate transport and transformation processes in unsaturated porous media
A series of experiments was conducted on two contrasting agricultural soils to observe the influence of soil texture, preferential flow, and plants on nitrate transport and denitrification under unsaturated conditions. Calcium nitrate fertilizer was applied to the surface of four large undisturbed soil cores (30 cm diameter by 40 cm height). Two of the cores were a structured clay obtained from ce
Authors
James A. Tindall, Robin L. Petrusak, Peter B. McMahon
Deducing the distribution of terminal electron-accepting processes in hydrologically diverse groundwater systems
The distribution of microbially mediated terminal electron-accepting processes (TEAPs( was investigated in four hydrologically diverse groundwater systems by considering patterns of electron acceptor (nitrate, sulfate) consumption, intermediate product (hydrogen (H2)) concentrations, and final product (ferrous iron, sulfide, and methane) production. In each hydrologic system a determination of pre
Authors
Francis H. Chapelle, Peter B. McMahon, Neil M. Dubrovsky, Roger F. Fujii, Edward T. Oaksford, Don A. Vroblesky
Some bacteria are beneficial!
Most people would agree that bacteria usually spell trouble where the quality of drinking water is con cerned. However, recent studies conducted by the U.S. Geological Survey (USGS) under the National Water-Quality Assessment (NAWQA) program have shown that some bacteria can improve the quality of water.
Authors
Peter B. McMahon
Effects of carbon and nitrate on denitrification in bottom sediments of an effluent-dominated river
Nitrogen and carbon limitation of denitrification in the bed sediments of an effluent-dominated stream were investigated by quantifying the effects of nitrate and glucose additions on the rate of sediment N2O production. Bed sediment samples were collected from a 30-km stretch of the South Platte River where up to 95% of the base flow discharge consists of effluent from a water treatment plant in
Authors
P. M. Bradley, P. B. McMahon, F. H. Chapelle
Quantity and quality of ground-water discharge to the South Platte River, Denver to Fort Lupton, Colorado, August 1992 through July 1993
Water-quality studies conducted by the Metro Wastewater Reclamation District have indicated that during low flow in segments of the South Platte River between Denver and Fort Lupton, concentrations of dissolved oxygen are less than minimum concen- trations set by the State of Colorado. Low dissolved-oxygen concentrations are observed in two reaches of the river-they are about 3.3 to 6.4 miles and
Authors
P. B. McMahon, K.J. Lull, K. F. Dennehy, J.A. Collins
Effect of ground-water/surface-water interactions on nitrate concentrations in discharge from the South Platte River alluvial aquifer, Colorado
Concentrations of dissolved nitrate in recharge-area water from a 200-km2 segment of the South Platte River alluvial aquifer near Greeley, Colorado, range from less than 0.1 to 58 mg/l as nitrogen, and the median concentration is 26 mg/l as nitrogen. Hydraulic-head data indicate that this nitrate-enriched ground water move toward the South Platte River. However, the median concentration of nitrate
Authors
P. B. McMahon, J.K. Böhlke
Effect of atrazine on potential denitrification in aquifer sediments
Agriculturaf use of fertilizers and herbicides has often resulted in nitrate and atrazine contamination of the shallow aquifers that underlay cultivated fields. In several cases, the concentrations of atrazine and nitrate dissolved in ground water are positively correlated (Spalding ef al., 1979; Chen and Druliner, 1987; Spalding et al., 1989). Because simultaneous application of nitrate fertilize
Authors
P. M. Bradley, F. H. Chapelle, M.L. Jagucki, P. B. McMahon
Role of microbial processes in linking sandstone diagenesis with organic-rich clays
Numerous chemical reactions within clay sequences have been proposed to produce dissolved material for diagenesis of deeply-buried sands. However, reactions responsible for solubilizing inorganic and organic constituents in clays at intermediate depths, and their importance to sandstone diagenesis, have not been evaluated. Results from this study show that the processes of microbial organic-acid p
Authors
P. B. McMahon, F. H. Chapelle, W. F. Falls, P. M. Bradley
Atrazine mineralization potential of alluvial-aquifer sediments under aerobic conditions
No abstract available.
Authors
P. B. McMahon, F. H. Chapelle, M.L. Jagucki
Geochemistry of dissolved inorganic carbon in a Coastal Plain aquifer. 2. Modeling carbon sources, sinks, and δ13C evolution
Stable isotope data for dissolved inorganic carbon (DIC), carbonate shell material and cements, and microbial CO2 were combined with organic and inorganic chemical data from aquifer and confining-bed pore waters to construct geochemical reaction models along a flowpath in the Black Creek aquifer of South Carolina. Carbon-isotope fractionation between DIC and precipitating cements was treated as a
Authors
Peter B. McMahon, Francis H. Chapelle
Geochemistry of dissolved inorganic carbon in a Coastal Plain aquifer. 1. Sulfate from confining beds as an oxidant in microbial CO2 production
A primary source of dissolved inorganic carbon (DIC) in the Black Creek aquifer of South Carolina is carbon dioxide produced by microbially mediated oxidation of sedimentary organic matter. Groundwater chemistry data indicate, however, that the available mass of inorganic electron acceptors (oxygen, Fe(III), and sulfate) and observed methane production is inadequate to account for observed CO2prod
Authors
F. H. Chapelle, P. B. McMahon
Microbial production of organic acids in aquitard sediments and its role in aquifer geochemistry
MICROBIAL activity in aquifers plays an important part in the chemical evolution of ground water1-5. The most important terminal electron-accepting microbial processes in deeply buried anaerobic aquifers are iron reduction, sulphate reduction and methanogenesis5-8, each of which requires simple organic compounds or hydrogen (H2) as electron donors. Until now, the source of these compounds was unkn
Authors
P. B. McMahon, F. H. Chapelle
Science and Products
Filter Total Items: 14
No Result Found
Filter Total Items: 116
Nitrate transport and transformation processes in unsaturated porous media
A series of experiments was conducted on two contrasting agricultural soils to observe the influence of soil texture, preferential flow, and plants on nitrate transport and denitrification under unsaturated conditions. Calcium nitrate fertilizer was applied to the surface of four large undisturbed soil cores (30 cm diameter by 40 cm height). Two of the cores were a structured clay obtained from ce
Authors
James A. Tindall, Robin L. Petrusak, Peter B. McMahon
Deducing the distribution of terminal electron-accepting processes in hydrologically diverse groundwater systems
The distribution of microbially mediated terminal electron-accepting processes (TEAPs( was investigated in four hydrologically diverse groundwater systems by considering patterns of electron acceptor (nitrate, sulfate) consumption, intermediate product (hydrogen (H2)) concentrations, and final product (ferrous iron, sulfide, and methane) production. In each hydrologic system a determination of pre
Authors
Francis H. Chapelle, Peter B. McMahon, Neil M. Dubrovsky, Roger F. Fujii, Edward T. Oaksford, Don A. Vroblesky
Some bacteria are beneficial!
Most people would agree that bacteria usually spell trouble where the quality of drinking water is con cerned. However, recent studies conducted by the U.S. Geological Survey (USGS) under the National Water-Quality Assessment (NAWQA) program have shown that some bacteria can improve the quality of water.
Authors
Peter B. McMahon
Effects of carbon and nitrate on denitrification in bottom sediments of an effluent-dominated river
Nitrogen and carbon limitation of denitrification in the bed sediments of an effluent-dominated stream were investigated by quantifying the effects of nitrate and glucose additions on the rate of sediment N2O production. Bed sediment samples were collected from a 30-km stretch of the South Platte River where up to 95% of the base flow discharge consists of effluent from a water treatment plant in
Authors
P. M. Bradley, P. B. McMahon, F. H. Chapelle
Quantity and quality of ground-water discharge to the South Platte River, Denver to Fort Lupton, Colorado, August 1992 through July 1993
Water-quality studies conducted by the Metro Wastewater Reclamation District have indicated that during low flow in segments of the South Platte River between Denver and Fort Lupton, concentrations of dissolved oxygen are less than minimum concen- trations set by the State of Colorado. Low dissolved-oxygen concentrations are observed in two reaches of the river-they are about 3.3 to 6.4 miles and
Authors
P. B. McMahon, K.J. Lull, K. F. Dennehy, J.A. Collins
Effect of ground-water/surface-water interactions on nitrate concentrations in discharge from the South Platte River alluvial aquifer, Colorado
Concentrations of dissolved nitrate in recharge-area water from a 200-km2 segment of the South Platte River alluvial aquifer near Greeley, Colorado, range from less than 0.1 to 58 mg/l as nitrogen, and the median concentration is 26 mg/l as nitrogen. Hydraulic-head data indicate that this nitrate-enriched ground water move toward the South Platte River. However, the median concentration of nitrate
Authors
P. B. McMahon, J.K. Böhlke
Effect of atrazine on potential denitrification in aquifer sediments
Agriculturaf use of fertilizers and herbicides has often resulted in nitrate and atrazine contamination of the shallow aquifers that underlay cultivated fields. In several cases, the concentrations of atrazine and nitrate dissolved in ground water are positively correlated (Spalding ef al., 1979; Chen and Druliner, 1987; Spalding et al., 1989). Because simultaneous application of nitrate fertilize
Authors
P. M. Bradley, F. H. Chapelle, M.L. Jagucki, P. B. McMahon
Role of microbial processes in linking sandstone diagenesis with organic-rich clays
Numerous chemical reactions within clay sequences have been proposed to produce dissolved material for diagenesis of deeply-buried sands. However, reactions responsible for solubilizing inorganic and organic constituents in clays at intermediate depths, and their importance to sandstone diagenesis, have not been evaluated. Results from this study show that the processes of microbial organic-acid p
Authors
P. B. McMahon, F. H. Chapelle, W. F. Falls, P. M. Bradley
Atrazine mineralization potential of alluvial-aquifer sediments under aerobic conditions
No abstract available.
Authors
P. B. McMahon, F. H. Chapelle, M.L. Jagucki
Geochemistry of dissolved inorganic carbon in a Coastal Plain aquifer. 2. Modeling carbon sources, sinks, and δ13C evolution
Stable isotope data for dissolved inorganic carbon (DIC), carbonate shell material and cements, and microbial CO2 were combined with organic and inorganic chemical data from aquifer and confining-bed pore waters to construct geochemical reaction models along a flowpath in the Black Creek aquifer of South Carolina. Carbon-isotope fractionation between DIC and precipitating cements was treated as a
Authors
Peter B. McMahon, Francis H. Chapelle
Geochemistry of dissolved inorganic carbon in a Coastal Plain aquifer. 1. Sulfate from confining beds as an oxidant in microbial CO2 production
A primary source of dissolved inorganic carbon (DIC) in the Black Creek aquifer of South Carolina is carbon dioxide produced by microbially mediated oxidation of sedimentary organic matter. Groundwater chemistry data indicate, however, that the available mass of inorganic electron acceptors (oxygen, Fe(III), and sulfate) and observed methane production is inadequate to account for observed CO2prod
Authors
F. H. Chapelle, P. B. McMahon
Microbial production of organic acids in aquitard sediments and its role in aquifer geochemistry
MICROBIAL activity in aquifers plays an important part in the chemical evolution of ground water1-5. The most important terminal electron-accepting microbial processes in deeply buried anaerobic aquifers are iron reduction, sulphate reduction and methanogenesis5-8, each of which requires simple organic compounds or hydrogen (H2) as electron donors. Until now, the source of these compounds was unkn
Authors
P. B. McMahon, F. H. Chapelle