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
N2O emissions from a nitrogen-enriched river
Nitrous oxide (N2O) emissions from the South Platte River in Colorado were measured using closed chambers in the fall, winter, and summer of 1994- 1995. The South Platte River was enriched in inorganic N (9-800 ??M) derived from municipal wastewater effluent and groundwater return flows from irrigated agricultural fields. River water was as much as 2500% supersaturated with N2O, and median N2O emi
Authors
P. B. McMahon, K. F. Dennehy
Denitrification in marine shales in northeastern Colorado
Parts of the South Platte River alluvial aquifer in northeastern Colorado are underlain by the Pierre Shale, a marine deposit of Late Cretaceous age that is <1000 m thick. Ground water in the aquifer is contaminated with NO3‐, and the shale contains abundant potential electron donors for denitrification in the forms of organic carbon and sulfide minerals. Nested piezometers were sampled, pore wate
Authors
Peter B. McMahon, J.K. Böhlke, Breton W. Bruce
Shallow ground-water quality of selected land-use/aquifer settings in the South Platte River basin, Colorado and Nebraska, 1993-95
No abstract available.
Authors
B. W. Bruce, P. B. McMahon
In-situ bioremediation of nitrate-contaminated ground water — A pilot test, Julesburg, Colorado, 1996–97
No abstract available.
Authors
P. B. McMahon, K. F. Dennehy, B. W. Bruce
Nitrous oxide fluxes from a claypan soil overlying nitrate-enriched glacial drift
The closed chamber method was used to assess nitrous oxide (N2O) fluxes from corn (Zea mays, L.) fields during the 1995 growing season. The study area was characterized by a claypan soil overlying a nitrate (NO31-)-enriched glacial-drift aquifer. Denitrification produced N2O fluxes of 0.2-6.9 g ha-1 hr-1 early in the growing season. Fluxes increased with increasing soil temperature, soil water pot
Authors
M.L. Pomes, D.H. Wilkison, P. B. McMahon
Water quality in the South Platte River basin, Colorado, Nebraska, and Wyoming, 1992-95
No abstract available.
Authors
Kevin F. Dennehy, David W. Litke, Cathy M. Tate, Sharon L. Qi, Peter B. McMahon, Breton W. Bruce, Robert A. Kimbrough, Janet S. Heiny
Effect of nitrate, organic carbon, and temperature on potential denitrification rates in nitrate-rich riverbed sediments
A study conducted in 1994 as part of the US Geological Survey's National Water-Quality Assessment Program, South Platte River Basin investigation, examined the effect of certain environmental factors on potential denitrification rates in nitrate-rich riverbed sediments. The acetylene block technique was used to measure nitrous oxide (N2O) production rates in laboratory incubations of riverbed sedi
Authors
K.S. Pfenning, P. B. McMahon
Distribution of terminal electron-accepting processes in an aquifer having multiple contaminant sources
Concentrations of electron acceptors, electron donors, and H2 in groundwater were measured to determine the distribution of terminal electron-accepting processes (TEAPs) in an alluvial aquifer having multiple contaminant sources. Upgradient contaminant sources included two separate hydrocarbon point sources, one of which contained the fuel oxygenate methyl tertbutyl ether (MTBE). Infiltrating rive
Authors
P. B. McMahon, B. W. Bruce
Shallow ground-water quality beneath a major urban center: Denver, Colorado, USA
A survey of the chemical quality of ground water in the unconsolidated alluvial aquifer beneath a major urban center (Denver, Colorado, USA) was performed in 1993 with the objective of characterizing the quality of shallow ground-water in the urban area and relating water quality to land use. Thirty randomly selected alluvial wells were each sampled once for a broad range of dissolved constituents
Authors
B. W. Bruce, P. B. McMahon
Denitrification and mixing in a stream-aquifer system: Effects on nitrate loading to surface water
Ground water in terrace deposits of the South Platte River alluvial aquifer near Greeley, Colorado, USA, had a median nitrate concentration of 1857 μmol l−1. Median nitrate concentrations in ground water from adjacent floodplain deposits (468 μmol l−1) and riverbed sediments (461 μmol l−1), both of which are downgradient from the terrace deposits, were lower than the median concentration in the te
Authors
P. B. McMahon, J.K. Böhlke
Hydrologic and geochemical effects on oxygen uptake in bottom sediments of an effluent-dominated river
More than 95% of the water in the South Platte River downstream from the largest wastewater treatment plant serving the metropolitan Denver, Colorado, area consists of treated effluent during some periods of low flow. Fluctuations in effluent-discharge rates caused daily changes in river stage that promoted exchange of water between the river and bottom sediments. Groundwater discharge measurement
Authors
P. B. McMahon, J.A. Tindall, J.A. Collins, K.J. Lull, J.R. Nuttle
Water-quality assessment of the South Platte River basin, Colorado, Nebraska, and Wyoming: Analysis of available nutrient, suspended-sediment, and pesticide data, water years 1980-92
Nutrient, suspended-sediment, and pesticide data from surface- and ground-water sites in the South Platte River Basin for water years 1980-92 were compiled, screened, and interpreted. This activity is part of the U.S. Geological Survey's National Water Quality Assessment (NAWQA) program. The analysis of existing water-quality data provides a perspective on recent water-quality conditions in the So
Authors
K. F. Dennehy, D. W. Litke, P. B. McMahon, J. S. Heiny, C. M. Tate
Science and Products
Filter Total Items: 14
No Result Found
Filter Total Items: 116
N2O emissions from a nitrogen-enriched river
Nitrous oxide (N2O) emissions from the South Platte River in Colorado were measured using closed chambers in the fall, winter, and summer of 1994- 1995. The South Platte River was enriched in inorganic N (9-800 ??M) derived from municipal wastewater effluent and groundwater return flows from irrigated agricultural fields. River water was as much as 2500% supersaturated with N2O, and median N2O emi
Authors
P. B. McMahon, K. F. Dennehy
Denitrification in marine shales in northeastern Colorado
Parts of the South Platte River alluvial aquifer in northeastern Colorado are underlain by the Pierre Shale, a marine deposit of Late Cretaceous age that is <1000 m thick. Ground water in the aquifer is contaminated with NO3‐, and the shale contains abundant potential electron donors for denitrification in the forms of organic carbon and sulfide minerals. Nested piezometers were sampled, pore wate
Authors
Peter B. McMahon, J.K. Böhlke, Breton W. Bruce
Shallow ground-water quality of selected land-use/aquifer settings in the South Platte River basin, Colorado and Nebraska, 1993-95
No abstract available.
Authors
B. W. Bruce, P. B. McMahon
In-situ bioremediation of nitrate-contaminated ground water — A pilot test, Julesburg, Colorado, 1996–97
No abstract available.
Authors
P. B. McMahon, K. F. Dennehy, B. W. Bruce
Nitrous oxide fluxes from a claypan soil overlying nitrate-enriched glacial drift
The closed chamber method was used to assess nitrous oxide (N2O) fluxes from corn (Zea mays, L.) fields during the 1995 growing season. The study area was characterized by a claypan soil overlying a nitrate (NO31-)-enriched glacial-drift aquifer. Denitrification produced N2O fluxes of 0.2-6.9 g ha-1 hr-1 early in the growing season. Fluxes increased with increasing soil temperature, soil water pot
Authors
M.L. Pomes, D.H. Wilkison, P. B. McMahon
Water quality in the South Platte River basin, Colorado, Nebraska, and Wyoming, 1992-95
No abstract available.
Authors
Kevin F. Dennehy, David W. Litke, Cathy M. Tate, Sharon L. Qi, Peter B. McMahon, Breton W. Bruce, Robert A. Kimbrough, Janet S. Heiny
Effect of nitrate, organic carbon, and temperature on potential denitrification rates in nitrate-rich riverbed sediments
A study conducted in 1994 as part of the US Geological Survey's National Water-Quality Assessment Program, South Platte River Basin investigation, examined the effect of certain environmental factors on potential denitrification rates in nitrate-rich riverbed sediments. The acetylene block technique was used to measure nitrous oxide (N2O) production rates in laboratory incubations of riverbed sedi
Authors
K.S. Pfenning, P. B. McMahon
Distribution of terminal electron-accepting processes in an aquifer having multiple contaminant sources
Concentrations of electron acceptors, electron donors, and H2 in groundwater were measured to determine the distribution of terminal electron-accepting processes (TEAPs) in an alluvial aquifer having multiple contaminant sources. Upgradient contaminant sources included two separate hydrocarbon point sources, one of which contained the fuel oxygenate methyl tertbutyl ether (MTBE). Infiltrating rive
Authors
P. B. McMahon, B. W. Bruce
Shallow ground-water quality beneath a major urban center: Denver, Colorado, USA
A survey of the chemical quality of ground water in the unconsolidated alluvial aquifer beneath a major urban center (Denver, Colorado, USA) was performed in 1993 with the objective of characterizing the quality of shallow ground-water in the urban area and relating water quality to land use. Thirty randomly selected alluvial wells were each sampled once for a broad range of dissolved constituents
Authors
B. W. Bruce, P. B. McMahon
Denitrification and mixing in a stream-aquifer system: Effects on nitrate loading to surface water
Ground water in terrace deposits of the South Platte River alluvial aquifer near Greeley, Colorado, USA, had a median nitrate concentration of 1857 μmol l−1. Median nitrate concentrations in ground water from adjacent floodplain deposits (468 μmol l−1) and riverbed sediments (461 μmol l−1), both of which are downgradient from the terrace deposits, were lower than the median concentration in the te
Authors
P. B. McMahon, J.K. Böhlke
Hydrologic and geochemical effects on oxygen uptake in bottom sediments of an effluent-dominated river
More than 95% of the water in the South Platte River downstream from the largest wastewater treatment plant serving the metropolitan Denver, Colorado, area consists of treated effluent during some periods of low flow. Fluctuations in effluent-discharge rates caused daily changes in river stage that promoted exchange of water between the river and bottom sediments. Groundwater discharge measurement
Authors
P. B. McMahon, J.A. Tindall, J.A. Collins, K.J. Lull, J.R. Nuttle
Water-quality assessment of the South Platte River basin, Colorado, Nebraska, and Wyoming: Analysis of available nutrient, suspended-sediment, and pesticide data, water years 1980-92
Nutrient, suspended-sediment, and pesticide data from surface- and ground-water sites in the South Platte River Basin for water years 1980-92 were compiled, screened, and interpreted. This activity is part of the U.S. Geological Survey's National Water Quality Assessment (NAWQA) program. The analysis of existing water-quality data provides a perspective on recent water-quality conditions in the So
Authors
K. F. Dennehy, D. W. Litke, P. B. McMahon, J. S. Heiny, C. M. Tate