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: 112
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
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
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
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
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
Regional patterns in the isotopic composition of natural and anthropogenic nitrate in groundwater, High Plains, U.S.A.
Mobilization of natural nitrate (NO3-) deposits in the subsoil by irrigation water in arid and semiarid regions has the potential to produce large groundwater NO3- concentrations. The use of isotopes to distinguish between natural and anthropogenic NO3- sources in these settings could be complicated by the wide range in δ15N values of natural NO3-. An ∼10 000 year record of paleorecharge from the
Authors
P. B. McMahon, J.K. Böhlke
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
Use of isotopes, age-dating, and numerical simulation to evaluate source histories and transport of NO3- to public supply wells in principal aquifers of the United States
No abstract available.
Authors
P. B. McMahon, John K. Böhlke, C. Brown, K. Burow, C. A. Crandall, Matthew K. Landon
Vertical gradients in water chemistry and age in the southern High Plains Aquifer, Texas, 2002
The southern High Plains aquifer is the primary source of water used for domestic, industrial, and irrigation purposes in parts of New Mexico and Texas. Despite the aquifer's importance to the overall economy of the southern High Plains, fundamental ground-water characteristics, such as vertical gradients in water chemistry and age, remain poorly defined. As part of the U.S. Geological Survey's Na
Authors
P. B. McMahon, J.K. Böhlke, T.M. Lehman
Geochemistry, radiocarbon ages, and paleorecharge conditions along a transect in the central High Plains aquifer, southwestern Kansas, USA
Water samples from short-screen monitoring wells installed along a 90-km transect in southwestern Kansas were analyzed for major ions, trace elements, isotopes (H, B, C, N, O, S, Sr), and dissolved gases (He, Ne, N2, Ar, O2, CH4) to evaluate the geochemistry, radiocarbon ages, and paleorecharge conditions in the unconfined central High Plains aquifer. The primary reactions controlling water chemis
Authors
P. B. McMahon, J.K. Böhlke, S. C. Christenson
Science and Products
Filter Total Items: 14
No Result Found
Filter Total Items: 112
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
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
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
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
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
Regional patterns in the isotopic composition of natural and anthropogenic nitrate in groundwater, High Plains, U.S.A.
Mobilization of natural nitrate (NO3-) deposits in the subsoil by irrigation water in arid and semiarid regions has the potential to produce large groundwater NO3- concentrations. The use of isotopes to distinguish between natural and anthropogenic NO3- sources in these settings could be complicated by the wide range in δ15N values of natural NO3-. An ∼10 000 year record of paleorecharge from the
Authors
P. B. McMahon, J.K. Böhlke
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
Use of isotopes, age-dating, and numerical simulation to evaluate source histories and transport of NO3- to public supply wells in principal aquifers of the United States
No abstract available.
Authors
P. B. McMahon, John K. Böhlke, C. Brown, K. Burow, C. A. Crandall, Matthew K. Landon
Vertical gradients in water chemistry and age in the southern High Plains Aquifer, Texas, 2002
The southern High Plains aquifer is the primary source of water used for domestic, industrial, and irrigation purposes in parts of New Mexico and Texas. Despite the aquifer's importance to the overall economy of the southern High Plains, fundamental ground-water characteristics, such as vertical gradients in water chemistry and age, remain poorly defined. As part of the U.S. Geological Survey's Na
Authors
P. B. McMahon, J.K. Böhlke, T.M. Lehman
Geochemistry, radiocarbon ages, and paleorecharge conditions along a transect in the central High Plains aquifer, southwestern Kansas, USA
Water samples from short-screen monitoring wells installed along a 90-km transect in southwestern Kansas were analyzed for major ions, trace elements, isotopes (H, B, C, N, O, S, Sr), and dissolved gases (He, Ne, N2, Ar, O2, CH4) to evaluate the geochemistry, radiocarbon ages, and paleorecharge conditions in the unconfined central High Plains aquifer. The primary reactions controlling water chemis
Authors
P. B. McMahon, J.K. Böhlke, S. C. Christenson