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
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Hydrogeology, Chemical Characteristics, and Transport Processes in the Zone of Contribution of a Public-Supply Well in York, Nebraska
In 2001, the U.S. Geological Survey, as part of the National Water Quality Assessment (NAWQA) Program, initiated a topical study of Transport of Anthropogenic and Natural Contaminants (TANC) to PSW (public-supply wells). Local-scale and regional-scale TANC study areas were delineated within selected NAWQA study units for intensive study of processes effecting transport of contaminants to PSWs. Thi
Authors
Matthew K. Landon, Brian R. Clark, Peter B. McMahon, Virginia L. McGuire, Michael J. Turco
Source and transport controls on the movement of nitrate to public supply wells in selected principal aquifers of the United States
In 2003–2005, systematic studies in four contrasting hydrogeologic settings were undertaken to improve understanding of source and transport controls on nitrate movement to public supply wells (PSW) in principal aquifers of the United States. Chemical, isotopic, and age tracer data show that agricultural fertilizers and urban septic leachate were the primary sources of large nitrate concentrations
Authors
P. B. McMahon, J.K. Böhlke, L. J. Kauffman, K.L. Kipp, M.K. Landon, C. A. Crandall, K.R. Burow, C. J. Brown
Potential for 4-n-nonylphenol biodegradation in stream sediments
The potential for in situ biodegradation of 4-nonylphenol (4-NP) was investigated in three hydrologically distinct streams impacted by wastewater treatment plants (WWTPs) in the United States. Microcosms were prepared with sediments from each site and amended with [U-ring-14C]4-n-nonylphenol (4-n-NP) as a model test substrate. Microcosms prepared with sediment collected upstream of the WWTP outfal
Authors
P. M. Bradley, L. B. Barber, D.W. Kolpin, P. B. McMahon, F. H. Chapelle
Redox processes and water quality of selected principal aquifer systems
Reduction/oxidation (redox) conditions in 15 principal aquifer (PA) systems of the United States, and their impact on several water quality issues, were assessed from a large data base collected by the National Water-Quality Assessment Program of the USGS. The logic of these assessments was based on the observed ecological succession of electron acceptors such as dissolved oxygen, nitrate, and sul
Authors
P. B. McMahon, F. H. Chapelle
Susceptibility to enhanced chemical migration from depression-focused preferential flow, High Plains aquifer
Aquifer susceptibility to contamination is controlled in part by the inherent hydrogeologic properties of the vadose zone, which includes preferential-flow pathways. The purpose of this study was to investigate the importance of seasonal ponding near leaky irrigation wells as a mechanism for depression-focused preferential flow and enhanced chemical migration through the vadose zone of the High Pl
Authors
Jason J. Gurdak, Michelle Ann Walvoord, Peter B. McMahon
Simulated response of water quality in public supply wells to land use change
Understanding how changes in land use affect water quality of public supply wells (PSW) is important because of the strong influence of land use on water quality, the rapid pace at which changes in land use are occurring in some parts of the world, and the large contribution of groundwater to the global water supply. In this study, groundwater flow models incorporating particle tracking and reacti
Authors
P. B. McMahon, K.R. Burow, L. J. Kauffman, S. M. Eberts, J.K. Böhlke, J.J. Gurdak
Water-Quality Assessment of the High Plains Aquifer, 1999-2004
Water quality of the High Plains aquifer was assessed for the period 1999-2004 as part of the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program. This effort represents the first systematic regional assessment of water quality in this nationally important aquifer. A stratified, nested group of studies was designed to assess linkages between the quality of water recharging t
Authors
Peter B. McMahon, Kevin F. Dennehy, Breton W. Bruce, Jason J. Gurdak, Sharon L. Qi
Vertical gradients in water chemistry and age in the Northern High Plains Aquifer, Nebraska, 2003
The northern High Plains aquifer is the primary source of water used for domestic, industrial, and irrigation purposes in parts of Colorado, Kansas, Nebraska, South Dakota, and Wyoming. Despite the aquifer’s importance to the regional economy, fundamental ground-water characteristics, such as vertical gradients in water chemistry and age, remain poorly defined. As part of the U.S. Geological Surve
Authors
P. B. McMahon, J.K. Böhlke, C. P. Carney
Climate variability controls on unsaturated water and chemical movement, High Plains aquifer, USA
Responses in the vadose zone and groundwater to interannual, interdecadal, and multidecadal climate variability have important implications for groundwater resource sustainability, yet they are poorly documented and not well understood in most aquifers of the USA. This investigation systematically examines the role of interannual to multidecadal climate variability on groundwater levels, deep infi
Authors
J.J. Gurdak, R. T. Hanson, P. B. McMahon, B. W. Bruce, J.E. McCray, G.D. Thyne, R.C. Reedy
Nitrous oxide fluxes from cultivated areas and rangeland: U.S. High Plains
Concentration profiles of N2O, a greenhouse gas, and the conservative trace gases SF6 and the chlorofluorocarbons CFC-11, CFC-12, CFC-113, and were measured periodically through thick vadose zones at nine sites in the U.S. High Plains. The CFC and SF6 measurements were used to calibrate a one-dimensional gas diffusion model, using the parameter identification program UCODE. The calibrated model wa
Authors
Edwin P. Weeks, Peter B. McMahon
Biotransformation of caffeine, cotinine, and nicotine in stream sediments: Implications for use as wastewater indicators
Microbially catalyzed cleavage of the imadazole ring of caffeine was observed in stream sediments collected upstream and downstream of municipal wastewater treatment plants (WWTP) in three geographically separate stream systems. Microbial demethylation of the N-methyl component of cotinine and its metabolic precursor, nicotine, also was observed in these sediments. These findings indicate that str
Authors
Paul M. Bradley, Larry B. Barber, Dana W. Kolpin, Peter B. McMahon, Francis H. Chapelle
Storage and transit time of chemicals in thick unsaturated zones under rangeland and irrigated cropland, High Plains, United States
In 2000-2002, three rangeland and six irrigated sites were instrumented to assess the storage and transit time of chemicals in thick (15 to 50 m) unsaturated zones (UZ) in the High Plains. These processes are likely to influence relations between land use and groundwater quality, yet they have not been documented systematically in the High Plains. Land use and climate were important controls on th
Authors
P. B. McMahon, K. F. Dennehy, B. W. Bruce, J.K. Böhlke, R. L. Michel, J.J. Gurdak, D.B. Hurlbut
Science and Products
Filter Total Items: 14
No Result Found
Filter Total Items: 116
Hydrogeology, Chemical Characteristics, and Transport Processes in the Zone of Contribution of a Public-Supply Well in York, Nebraska
In 2001, the U.S. Geological Survey, as part of the National Water Quality Assessment (NAWQA) Program, initiated a topical study of Transport of Anthropogenic and Natural Contaminants (TANC) to PSW (public-supply wells). Local-scale and regional-scale TANC study areas were delineated within selected NAWQA study units for intensive study of processes effecting transport of contaminants to PSWs. Thi
Authors
Matthew K. Landon, Brian R. Clark, Peter B. McMahon, Virginia L. McGuire, Michael J. Turco
Source and transport controls on the movement of nitrate to public supply wells in selected principal aquifers of the United States
In 2003–2005, systematic studies in four contrasting hydrogeologic settings were undertaken to improve understanding of source and transport controls on nitrate movement to public supply wells (PSW) in principal aquifers of the United States. Chemical, isotopic, and age tracer data show that agricultural fertilizers and urban septic leachate were the primary sources of large nitrate concentrations
Authors
P. B. McMahon, J.K. Böhlke, L. J. Kauffman, K.L. Kipp, M.K. Landon, C. A. Crandall, K.R. Burow, C. J. Brown
Potential for 4-n-nonylphenol biodegradation in stream sediments
The potential for in situ biodegradation of 4-nonylphenol (4-NP) was investigated in three hydrologically distinct streams impacted by wastewater treatment plants (WWTPs) in the United States. Microcosms were prepared with sediments from each site and amended with [U-ring-14C]4-n-nonylphenol (4-n-NP) as a model test substrate. Microcosms prepared with sediment collected upstream of the WWTP outfal
Authors
P. M. Bradley, L. B. Barber, D.W. Kolpin, P. B. McMahon, F. H. Chapelle
Redox processes and water quality of selected principal aquifer systems
Reduction/oxidation (redox) conditions in 15 principal aquifer (PA) systems of the United States, and their impact on several water quality issues, were assessed from a large data base collected by the National Water-Quality Assessment Program of the USGS. The logic of these assessments was based on the observed ecological succession of electron acceptors such as dissolved oxygen, nitrate, and sul
Authors
P. B. McMahon, F. H. Chapelle
Susceptibility to enhanced chemical migration from depression-focused preferential flow, High Plains aquifer
Aquifer susceptibility to contamination is controlled in part by the inherent hydrogeologic properties of the vadose zone, which includes preferential-flow pathways. The purpose of this study was to investigate the importance of seasonal ponding near leaky irrigation wells as a mechanism for depression-focused preferential flow and enhanced chemical migration through the vadose zone of the High Pl
Authors
Jason J. Gurdak, Michelle Ann Walvoord, Peter B. McMahon
Simulated response of water quality in public supply wells to land use change
Understanding how changes in land use affect water quality of public supply wells (PSW) is important because of the strong influence of land use on water quality, the rapid pace at which changes in land use are occurring in some parts of the world, and the large contribution of groundwater to the global water supply. In this study, groundwater flow models incorporating particle tracking and reacti
Authors
P. B. McMahon, K.R. Burow, L. J. Kauffman, S. M. Eberts, J.K. Böhlke, J.J. Gurdak
Water-Quality Assessment of the High Plains Aquifer, 1999-2004
Water quality of the High Plains aquifer was assessed for the period 1999-2004 as part of the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program. This effort represents the first systematic regional assessment of water quality in this nationally important aquifer. A stratified, nested group of studies was designed to assess linkages between the quality of water recharging t
Authors
Peter B. McMahon, Kevin F. Dennehy, Breton W. Bruce, Jason J. Gurdak, Sharon L. Qi
Vertical gradients in water chemistry and age in the Northern High Plains Aquifer, Nebraska, 2003
The northern High Plains aquifer is the primary source of water used for domestic, industrial, and irrigation purposes in parts of Colorado, Kansas, Nebraska, South Dakota, and Wyoming. Despite the aquifer’s importance to the regional economy, fundamental ground-water characteristics, such as vertical gradients in water chemistry and age, remain poorly defined. As part of the U.S. Geological Surve
Authors
P. B. McMahon, J.K. Böhlke, C. P. Carney
Climate variability controls on unsaturated water and chemical movement, High Plains aquifer, USA
Responses in the vadose zone and groundwater to interannual, interdecadal, and multidecadal climate variability have important implications for groundwater resource sustainability, yet they are poorly documented and not well understood in most aquifers of the USA. This investigation systematically examines the role of interannual to multidecadal climate variability on groundwater levels, deep infi
Authors
J.J. Gurdak, R. T. Hanson, P. B. McMahon, B. W. Bruce, J.E. McCray, G.D. Thyne, R.C. Reedy
Nitrous oxide fluxes from cultivated areas and rangeland: U.S. High Plains
Concentration profiles of N2O, a greenhouse gas, and the conservative trace gases SF6 and the chlorofluorocarbons CFC-11, CFC-12, CFC-113, and were measured periodically through thick vadose zones at nine sites in the U.S. High Plains. The CFC and SF6 measurements were used to calibrate a one-dimensional gas diffusion model, using the parameter identification program UCODE. The calibrated model wa
Authors
Edwin P. Weeks, Peter B. McMahon
Biotransformation of caffeine, cotinine, and nicotine in stream sediments: Implications for use as wastewater indicators
Microbially catalyzed cleavage of the imadazole ring of caffeine was observed in stream sediments collected upstream and downstream of municipal wastewater treatment plants (WWTP) in three geographically separate stream systems. Microbial demethylation of the N-methyl component of cotinine and its metabolic precursor, nicotine, also was observed in these sediments. These findings indicate that str
Authors
Paul M. Bradley, Larry B. Barber, Dana W. Kolpin, Peter B. McMahon, Francis H. Chapelle
Storage and transit time of chemicals in thick unsaturated zones under rangeland and irrigated cropland, High Plains, United States
In 2000-2002, three rangeland and six irrigated sites were instrumented to assess the storage and transit time of chemicals in thick (15 to 50 m) unsaturated zones (UZ) in the High Plains. These processes are likely to influence relations between land use and groundwater quality, yet they have not been documented systematically in the High Plains. Land use and climate were important controls on th
Authors
P. B. McMahon, K. F. Dennehy, B. W. Bruce, J.K. Böhlke, R. L. Michel, J.J. Gurdak, D.B. Hurlbut