Peter B McMahon (Former Employee)
Science and Products
Oxidation/Reduction (Redox)
The redox state of groundwater—whether the groundwater is oxic (oxidized) or anoxic (reduced)—has profound implications for groundwater quality. Knowing the redox conditions of groundwater can help determine whether it contains elevated levels of many contaminants, including arsenic, nitrate, and even some manmade contaminants.
Groundwater Quality in Principal Aquifers of the United States, 1991—2010
A new U.S. Geological Survey (USGS) report summarizes the major findings of national and regional assessments of groundwater quality in 40 Principal Aquifers in the United States. Knowledge of contaminant occurrence and the factors that control contaminant concentrations can ensure the availability and quality of this vital natural resource in the future.
Developing the next generation of USGS resource assessments
Resource assessments constitute a key part of the USGS mission, and represent a crucial contribution toward Department of the Interior (DOI) and broader Federal objectives. Current USGS energy and mineral assessment methods evaluate total technically recoverable resources (energy) or economically exploitable materials (minerals); the fiscal year 2010 budget for this work is $82M. To help
NAWQA High Plains Regional Groundwater Study
As part of the National Water Quality Assessment Program (NAWQA), the USGS has evaluated ground-water quality in the High Plains aquifer system. Beginning in 1999 and continuing for a period of 6 years, the High Plains Regional Groundwater Study intensively investigated the quality of groundwater resources within the study area. Water quality impairment coupled with water-level declines focus...
NAWQA South Platte River Basin Study
The South Platte River Basin study, conducted as part of the U.S. Geological Survey's National Water-Quality Assessment Program, combines information on water chemistry, physical characteristics, stream habitat, and aquatic life to provide science-based insights for current and emerging water issues in surface waters (streams, rivers, reservoirs) and groundwaters of the South Platte River Basin...
Filter Total Items: 14
Produced water chemistry data collected from the Poso Creek, Midway-Sunset, and Buena Vista Oil Fields, 2020-21, Kern County, California Produced water chemistry data collected from the Poso Creek, Midway-Sunset, and Buena Vista Oil Fields, 2020-21, Kern County, California
The U.S. Geological Survey (USGS) in cooperation with the California State Water Resources Control Board collected produced water and gas samples in the Midway-Sunset, Poso Creek, and Buena Vista Oil Fields in Kern County in 2020 and 2021. Sampled sites included oil wells; injectate from tanks, pipelines, and injection wells where produced water from many wells, after removal of oil, is...
Water Chemistry data for samples collected at groundwater sites in the Poso Creek Oil Field study area, February 2020-December 2021, Kern County, California Water Chemistry data for samples collected at groundwater sites in the Poso Creek Oil Field study area, February 2020-December 2021, Kern County, California
The California State Water Resources Control Board (State Water Board) initiated the Oil and Gas Regional Monitoring Program (RMP) to assess effects of oil and gas development on groundwater designated for any beneficial use. The U.S. Geological Survey (USGS) is the technical lead in conducting the RMP through the California Oil, Gas, and Groundwater (COGG) Program, working in...
Oil well annular cement and casing damage data in mature oil fields undergoing hydraulic fracturing, South Belridge and Lost Hills Oil Fields, California Oil well annular cement and casing damage data in mature oil fields undergoing hydraulic fracturing, South Belridge and Lost Hills Oil Fields, California
This data release contains oil well annular cement and casing damage data from parts of the South Belridge and Lost Hills Oil Fields in western Kern County, California. The study area coincides with where groundwater with less than 10,000 milligrams per liter total dissolved solids and outside an exempt aquifer are located overlying oil-producing zones in these fields. In the study areas
Groundwater elevation data and models in and around select California oil fields (ver. 3.0, September 2025) Groundwater elevation data and models in and around select California oil fields (ver. 3.0, September 2025)
This data release contains groundwater elevation data and the associated model/code used to create groundwater elevation surfaces in and around select oil fields in California. The data and model provided here are intended to supplement interpretative manuscripts. Specific study areas will be added as Child Items found in this data release. Groundwater elevations are usually collected...
Data for Distribution of Groundwater Age in Aquifers Used for Public Supply in the Continental United States, 2004 - 2017 (Version 1.1: June 2022) Data for Distribution of Groundwater Age in Aquifers Used for Public Supply in the Continental United States, 2004 - 2017 (Version 1.1: June 2022)
This data release documents seven tables that contain environmental tracer data and lumped parameter model (LPM) results that are used for assessing the distribution of groundwater age in 21 Principal Aquifers of the continental United States. Groundwater samples were collected from 1,279 sites and analyzed for environmental tracers: tritium, tritiogenic helium-3, sulfur hexafluoride...
Geochemical and Geospatial Data for Per- and Polyfluoroalkyl Substances (PFAS) in Groundwater Used As a Source of Drinking Water in the Eastern United States Geochemical and Geospatial Data for Per- and Polyfluoroalkyl Substances (PFAS) in Groundwater Used As a Source of Drinking Water in the Eastern United States
Concentrations of inorganic constituents, dissolved organic carbon (DOC), tritium, per- and polyfluoroalkyl substances (PFAS), volatile organic compounds (VOCs), and pharmaceuticals were measured in groundwater samples collected from 254 wells in 2019 and 2020. Concentrations of inorganic constituents, DOC, VOCs, and pharmaceuticals were measured at the U.S. Geological Survey (USGS)...
Filter Total Items: 118
Groundwater quality near the Placerita Oil Field, California, 2018 Groundwater quality near the Placerita Oil Field, California, 2018
Groundwater-quality data and potential fluid-migration pathways near the Placerita Oil Field in Los Angeles County, California, were examined by the U.S. Geological Survey to determine if oil-field fluids (water and gas from oil-producing and non-producing zones) have mixed with groundwater resources. Six of the 13 new groundwater samples collected for this study contained petroleum...
Authors
Jennifer Stanton, Matthew Landon, David Shimabukuro, Justin Kulongoski, Andrew G. Hunt, Peter McMahon, Isabelle Cozzarelli, Robert Anders, Theron Sowers
Assessing potential effects of oil and gas development activities on groundwater quality near and overlying the Elk Hills and North Coles Levee Oil Fields, San Joaquin Valley, California Assessing potential effects of oil and gas development activities on groundwater quality near and overlying the Elk Hills and North Coles Levee Oil Fields, San Joaquin Valley, California
Groundwater resources are utilized near areas of intensive oil and gas development in California’s San Joaquin Valley. In this study, we examined chemical and isotopic data to assess if thermogenic gas or saline water from oil producing formations have mixed with groundwater near the Elk Hills and North Coles Levee Oil Fields in the southwestern San Joaquin Valley. Major ion...
Authors
John Warden, Matthew Landon, Michael Stephens, Tracy Davis, Janice Gillespie, Peter McMahon, Justin Kulongoski, Andrew G. Hunt, David Shimabukuro, Riley Gannon, Lyndsay Ball
Land-use interactions, Oil-Field infrastructure, and natural processes control hydrocarbon and arsenic concentrations in groundwater, Poso Creek Oil Field, California, USA Land-use interactions, Oil-Field infrastructure, and natural processes control hydrocarbon and arsenic concentrations in groundwater, Poso Creek Oil Field, California, USA
Like many hydrocarbon production areas in the U.S., the Poso Creek Oil Field in California includes and is adjacent to other land uses (agricultural and other developed lands) that affect the hydrology and geochemistry of the aquifer overlying and adjacent to oil development. We hypothesize that the distributions of hydrocarbons and arsenic in groundwater in such areas will be controlled...
Authors
Peter McMahon, Matthew Landon, Michael Stephens, Kimberly Taylor, Michael Wright, Angela Hansen, Tamara Kraus, Isabelle Cozzarelli, David Shimabukuro, Theron A. Sowers, Justin Kulongoski, Andrew G. Hunt, Ruta Karolyte, Darren Hillegonds, Chris Ballentine
Spectral characterization of dissolved organic matter in groundwater to assess mixing with oil-field water near selected oil fields, southern California Spectral characterization of dissolved organic matter in groundwater to assess mixing with oil-field water near selected oil fields, southern California
Samples of oil-field water (oil wells, injectate, disposal ponds) and groundwater near selected oil and gas fields in southern California were analyzed for dissolved organic carbon (DOC) concentration and by optical spectroscopic techniques (i.e., absorbance and fluorescence) to assess whether these measurements can be used to distinguish between oil-field water (Oil Field), native...
Authors
Angela Hansen, Tamara Kraus, Matthew Landon, Peter McMahon
Fluid migration pathways to groundwater in mature oil fields: Exploring the roles of water injection/production and oil-well integrity in California, USA Fluid migration pathways to groundwater in mature oil fields: Exploring the roles of water injection/production and oil-well integrity in California, USA
Mature oil fields potentially contain multiple fluid migration pathways toward protected groundwater (total dissolved solids, TDS, in nonexempted aquifer 10 m of uncemented annulus that straddles oil-well casing damage and/or the base of groundwater with TDS
Authors
Peter McMahon, Matthew Landon, Michael Stephens, Kimberly Taylor, Janice Gillespie, Tracy Davis, David Shimabukuro
Multiple-well monitoring site within the Poso Creek Oil Field, Kern County, California Multiple-well monitoring site within the Poso Creek Oil Field, Kern County, California
Introduction The Poso Creek Oil Field is one of the many fields selected for regional groundwater mapping and monitoring by the California State Water Resources Control Board as part of the Oil and Gas Regional Monitoring Program (RMP; California State Water Resources Control Board, 2015, 2022b; U.S. Geological Survey, 2022a). The U.S. Geological Survey (USGS), in cooperation with the...
Authors
Rhett Everett, Peter McMahon, Michael Stephens, Janice Gillespie, Mackenzie Shepherd, Nicole Fenton
Science and Products
Oxidation/Reduction (Redox)
The redox state of groundwater—whether the groundwater is oxic (oxidized) or anoxic (reduced)—has profound implications for groundwater quality. Knowing the redox conditions of groundwater can help determine whether it contains elevated levels of many contaminants, including arsenic, nitrate, and even some manmade contaminants.
Groundwater Quality in Principal Aquifers of the United States, 1991—2010
A new U.S. Geological Survey (USGS) report summarizes the major findings of national and regional assessments of groundwater quality in 40 Principal Aquifers in the United States. Knowledge of contaminant occurrence and the factors that control contaminant concentrations can ensure the availability and quality of this vital natural resource in the future.
Developing the next generation of USGS resource assessments
Resource assessments constitute a key part of the USGS mission, and represent a crucial contribution toward Department of the Interior (DOI) and broader Federal objectives. Current USGS energy and mineral assessment methods evaluate total technically recoverable resources (energy) or economically exploitable materials (minerals); the fiscal year 2010 budget for this work is $82M. To help
NAWQA High Plains Regional Groundwater Study
As part of the National Water Quality Assessment Program (NAWQA), the USGS has evaluated ground-water quality in the High Plains aquifer system. Beginning in 1999 and continuing for a period of 6 years, the High Plains Regional Groundwater Study intensively investigated the quality of groundwater resources within the study area. Water quality impairment coupled with water-level declines focus...
NAWQA South Platte River Basin Study
The South Platte River Basin study, conducted as part of the U.S. Geological Survey's National Water-Quality Assessment Program, combines information on water chemistry, physical characteristics, stream habitat, and aquatic life to provide science-based insights for current and emerging water issues in surface waters (streams, rivers, reservoirs) and groundwaters of the South Platte River Basin...
Filter Total Items: 14
Produced water chemistry data collected from the Poso Creek, Midway-Sunset, and Buena Vista Oil Fields, 2020-21, Kern County, California Produced water chemistry data collected from the Poso Creek, Midway-Sunset, and Buena Vista Oil Fields, 2020-21, Kern County, California
The U.S. Geological Survey (USGS) in cooperation with the California State Water Resources Control Board collected produced water and gas samples in the Midway-Sunset, Poso Creek, and Buena Vista Oil Fields in Kern County in 2020 and 2021. Sampled sites included oil wells; injectate from tanks, pipelines, and injection wells where produced water from many wells, after removal of oil, is...
Water Chemistry data for samples collected at groundwater sites in the Poso Creek Oil Field study area, February 2020-December 2021, Kern County, California Water Chemistry data for samples collected at groundwater sites in the Poso Creek Oil Field study area, February 2020-December 2021, Kern County, California
The California State Water Resources Control Board (State Water Board) initiated the Oil and Gas Regional Monitoring Program (RMP) to assess effects of oil and gas development on groundwater designated for any beneficial use. The U.S. Geological Survey (USGS) is the technical lead in conducting the RMP through the California Oil, Gas, and Groundwater (COGG) Program, working in...
Oil well annular cement and casing damage data in mature oil fields undergoing hydraulic fracturing, South Belridge and Lost Hills Oil Fields, California Oil well annular cement and casing damage data in mature oil fields undergoing hydraulic fracturing, South Belridge and Lost Hills Oil Fields, California
This data release contains oil well annular cement and casing damage data from parts of the South Belridge and Lost Hills Oil Fields in western Kern County, California. The study area coincides with where groundwater with less than 10,000 milligrams per liter total dissolved solids and outside an exempt aquifer are located overlying oil-producing zones in these fields. In the study areas
Groundwater elevation data and models in and around select California oil fields (ver. 3.0, September 2025) Groundwater elevation data and models in and around select California oil fields (ver. 3.0, September 2025)
This data release contains groundwater elevation data and the associated model/code used to create groundwater elevation surfaces in and around select oil fields in California. The data and model provided here are intended to supplement interpretative manuscripts. Specific study areas will be added as Child Items found in this data release. Groundwater elevations are usually collected...
Data for Distribution of Groundwater Age in Aquifers Used for Public Supply in the Continental United States, 2004 - 2017 (Version 1.1: June 2022) Data for Distribution of Groundwater Age in Aquifers Used for Public Supply in the Continental United States, 2004 - 2017 (Version 1.1: June 2022)
This data release documents seven tables that contain environmental tracer data and lumped parameter model (LPM) results that are used for assessing the distribution of groundwater age in 21 Principal Aquifers of the continental United States. Groundwater samples were collected from 1,279 sites and analyzed for environmental tracers: tritium, tritiogenic helium-3, sulfur hexafluoride...
Geochemical and Geospatial Data for Per- and Polyfluoroalkyl Substances (PFAS) in Groundwater Used As a Source of Drinking Water in the Eastern United States Geochemical and Geospatial Data for Per- and Polyfluoroalkyl Substances (PFAS) in Groundwater Used As a Source of Drinking Water in the Eastern United States
Concentrations of inorganic constituents, dissolved organic carbon (DOC), tritium, per- and polyfluoroalkyl substances (PFAS), volatile organic compounds (VOCs), and pharmaceuticals were measured in groundwater samples collected from 254 wells in 2019 and 2020. Concentrations of inorganic constituents, DOC, VOCs, and pharmaceuticals were measured at the U.S. Geological Survey (USGS)...
Filter Total Items: 118
Groundwater quality near the Placerita Oil Field, California, 2018 Groundwater quality near the Placerita Oil Field, California, 2018
Groundwater-quality data and potential fluid-migration pathways near the Placerita Oil Field in Los Angeles County, California, were examined by the U.S. Geological Survey to determine if oil-field fluids (water and gas from oil-producing and non-producing zones) have mixed with groundwater resources. Six of the 13 new groundwater samples collected for this study contained petroleum...
Authors
Jennifer Stanton, Matthew Landon, David Shimabukuro, Justin Kulongoski, Andrew G. Hunt, Peter McMahon, Isabelle Cozzarelli, Robert Anders, Theron Sowers
Assessing potential effects of oil and gas development activities on groundwater quality near and overlying the Elk Hills and North Coles Levee Oil Fields, San Joaquin Valley, California Assessing potential effects of oil and gas development activities on groundwater quality near and overlying the Elk Hills and North Coles Levee Oil Fields, San Joaquin Valley, California
Groundwater resources are utilized near areas of intensive oil and gas development in California’s San Joaquin Valley. In this study, we examined chemical and isotopic data to assess if thermogenic gas or saline water from oil producing formations have mixed with groundwater near the Elk Hills and North Coles Levee Oil Fields in the southwestern San Joaquin Valley. Major ion...
Authors
John Warden, Matthew Landon, Michael Stephens, Tracy Davis, Janice Gillespie, Peter McMahon, Justin Kulongoski, Andrew G. Hunt, David Shimabukuro, Riley Gannon, Lyndsay Ball
Land-use interactions, Oil-Field infrastructure, and natural processes control hydrocarbon and arsenic concentrations in groundwater, Poso Creek Oil Field, California, USA Land-use interactions, Oil-Field infrastructure, and natural processes control hydrocarbon and arsenic concentrations in groundwater, Poso Creek Oil Field, California, USA
Like many hydrocarbon production areas in the U.S., the Poso Creek Oil Field in California includes and is adjacent to other land uses (agricultural and other developed lands) that affect the hydrology and geochemistry of the aquifer overlying and adjacent to oil development. We hypothesize that the distributions of hydrocarbons and arsenic in groundwater in such areas will be controlled...
Authors
Peter McMahon, Matthew Landon, Michael Stephens, Kimberly Taylor, Michael Wright, Angela Hansen, Tamara Kraus, Isabelle Cozzarelli, David Shimabukuro, Theron A. Sowers, Justin Kulongoski, Andrew G. Hunt, Ruta Karolyte, Darren Hillegonds, Chris Ballentine
Spectral characterization of dissolved organic matter in groundwater to assess mixing with oil-field water near selected oil fields, southern California Spectral characterization of dissolved organic matter in groundwater to assess mixing with oil-field water near selected oil fields, southern California
Samples of oil-field water (oil wells, injectate, disposal ponds) and groundwater near selected oil and gas fields in southern California were analyzed for dissolved organic carbon (DOC) concentration and by optical spectroscopic techniques (i.e., absorbance and fluorescence) to assess whether these measurements can be used to distinguish between oil-field water (Oil Field), native...
Authors
Angela Hansen, Tamara Kraus, Matthew Landon, Peter McMahon
Fluid migration pathways to groundwater in mature oil fields: Exploring the roles of water injection/production and oil-well integrity in California, USA Fluid migration pathways to groundwater in mature oil fields: Exploring the roles of water injection/production and oil-well integrity in California, USA
Mature oil fields potentially contain multiple fluid migration pathways toward protected groundwater (total dissolved solids, TDS, in nonexempted aquifer 10 m of uncemented annulus that straddles oil-well casing damage and/or the base of groundwater with TDS
Authors
Peter McMahon, Matthew Landon, Michael Stephens, Kimberly Taylor, Janice Gillespie, Tracy Davis, David Shimabukuro
Multiple-well monitoring site within the Poso Creek Oil Field, Kern County, California Multiple-well monitoring site within the Poso Creek Oil Field, Kern County, California
Introduction The Poso Creek Oil Field is one of the many fields selected for regional groundwater mapping and monitoring by the California State Water Resources Control Board as part of the Oil and Gas Regional Monitoring Program (RMP; California State Water Resources Control Board, 2015, 2022b; U.S. Geological Survey, 2022a). The U.S. Geological Survey (USGS), in cooperation with the...
Authors
Rhett Everett, Peter McMahon, Michael Stephens, Janice Gillespie, Mackenzie Shepherd, Nicole Fenton