There are over 10,000 hydrothermal features in Yellowstone National Park (YNP), where waters have pH values ranging from about 1 to 10 and surface temperatures up to 95 °C. Active hydrothermal areas in YNP provide insight into a variety of processes occurring at depth, such as water-rock and oxidation-reduction (redox) reactions, the formation of alteration minerals, and microbial (thermophile) metabolism in extreme environments, and possible indications of volcanic unrest. Investigations into the water chemistry of hydrothermal features, streams, and rivers in YNP have been conducted by the U.S. Geological Survey (USGS) and other earth-science organizations and academic institutions since 1883 (Gooch and Whitfield, 1888; Price and others, 2024). More recently, USGS researchers have sampled hydrothermal features in YNP at least annually since 1994 (McCleskey and others, 2014, and references within). In this Data Release, the chemical and isotopic analyses of 845 water samples collected beginning in 2009 are reported for numerous thermal and non-thermal features in YNP. This report combines water chemistry data presented in McCleskey and others (2014) with data collected after 2014. These water samples were collected and analyzed as part of research investigations in YNP on and as part of the Yellowstone Volcano Observatory monitoring plans (Yellowstone Volcano Observatory, 2006); arsenic, iron, nitrogen, and sulfur redox species in hot springs and overflow drainages; the occurrence and distribution of dissolved mercury and arsenic; and general hydrogeochemistry of hot springs throughout YNP. For most samples, data includes water temperature, pH, specific conductance, dissolved oxygen, and concentrations of major cations, anions, trace metals, alkalinity, sulfur redox species (hydrogen sulfide and thiosulfate), nutrients, silica, boron, arsenic and iron redox species, acidity, dissolved organic carbon, and hydrogen and oxygen isotope ratios. For select samples, tritium (3H), stable carbon isotopes of the dissolved inorganic carbon, and sulfur isotopes of sulfate are presented. In addition, chemical data for river, stream, and lake waters were obtained to determine input of different solutes from thermal areas throughout YNP. References Cited Gooch, F.A., and Whitfield, J.E., 1888, Analyses of waters of the Yellowstone National Park with an account of the methods of analysis employed: Bulletin 47, p. 84. McCleskey, R.B., Chiu, R.B., Nordstrom, D.K., Campbell, K.M., Roth, D.A., Ball, J.W., and Plowman, T.I., 2014, Water-Chemistry Data for Selected Springs, Geysers, and Streams in Yellowstone National Park, Wyoming, Beginning 2009: doi:10.5066/F7M043FS. Price, M.B., McCleskey, R.B., Oaks, A., Hurwitz, S., and Nordstrom, D.K., 2024, Historic Water Chemistry Data for Thermal Features, Streams, and Rivers in the Yellowstone National Park Area, 1883-2021: U.S. Geological Survey data release, https://doi.org/10.5066/P9KSEVI1. Yellowstone Volcano Observatory, 2006, Volcano and earthquake monitoring plan for the Yellowstone Volcano Observatory, 2006-2015: U.S. Geological Survey Scientific Investigations Report 2006-5276, http://pubs.usgs.gov/sir/2006/5276/. First posted - September 19, 2022 (available from author) Revised - March 4, 2025 (version 2.0) NOTE: While previous versions are available from the author, all the records in previous versions can be found in version 2.0.

Water analyses are reported for 66 samples collected from numerous thermal and non-thermal (rivers and streams) features in the southwestern areas of Yellowstone National Park (YNP) during 2009, 2017, and 2018. Water samples were collected from sources near Boundary Creek, Bechler River, Falls River, Mountain Ash Creek, Upper Snake River, Spirea Creek, and Lewis Lake. These water samples were collected and analyzed as part of research investigations on the chemistry of Yellowstone’s hydrothermal system and on the distribution of dissolved arsenic and mercury. Most samples were analyzed for major cations and anions, trace metals, redox species of arsenic, iron, nitrogen, and sulfur, and isotopes of hydrogen and oxygen. Radiogenic isotopes of strontium and tritium concentrations were also determined in selected samples. In addition, river and stream discharge data were obtained to determine the flux of chloride and other solutes from thermal areas in the southwest YNP.

Water analyses are reported for 66 samples collected from numerous thermal and non-thermal (rivers and streams) features in the southwestern areas of Yellowstone National Park (YNP) during 2009, 2017, and 2018. Water samples were collected from sources near Boundary Creek, Bechler River, Falls River, Mountain Ash Creek, Upper Snake River, Spirea Creek, and Lewis Lake. These water samples were collected and analyzed as part of research investigations on the chemistry of Yellowstone’s hydrothermal system and on the distribution of dissolved arsenic and mercury. Most samples were analyzed for major cations and anions, trace metals, redox species of arsenic, iron, nitrogen, and sulfur, and isotopes of hydrogen and oxygen. Radiogenic isotopes of strontium and tritium concentrations were also determined in selected samples. In addition, river and stream discharge data were obtained to determine the flux of chloride and other solutes from thermal areas in the southwest YNP.

Yellowstone National Park (YNP; Wyoming, Montana, and Idaho, USA) contains more than 10,000 hydrothermal features, several lakes, and four major watersheds. For more than 140 years, researchers at the U.S. Geological Survey and other scientific institutions have investigated the chemical compositions of hot springs, geysers, fumaroles, mud pots, streams, rivers, and lakes in YNP and surrounding areas. Water chemistry studies have revealed a range of compositions including waters with pH values ranging from about 1 to 10, surface temperatures from ambient to superheated values of 95°C, and elevated concentrations of silica, lithium, boron, fluoride, mercury, and arsenic. Hydrogeochemical data from YNP research have led to insights on subsurface conditions of temperature and chemistry, water-rock-gas interactions and processes of high-temperature mineral alteration with dissolution and precipitation, redox processes, thermophilic microbial metabolism under extreme conditions and effects of thermal water chemistry on river systems. In this Data Release, water chemistry data for 4,918 water samples are reported for numerous thermal features, rivers, streams, lakes, drillholes, and precipitation in and around YNP. The data for these samples were originally located in 38 reports published between 1888 and 2022 and in multiple unpublished documents. Spanning more than 600 unique sampling sites throughout the YNP region, this dataset includes samples collected as early as 1883 (Gooch & Whitfield, 1888) and as recently as 2021 (McCleskey, et al, 2022). The thermal features sampled most frequently include Cistern Spring (180 samples) and Echinus Geyser (73 samples) in Norris Geyser Basin and Ojo Caliente Spring (143 samples) in the Lower Geyser Basin, while more than 500 sites have 5 samples or fewer. Water chemistry data from thermal features, rivers, and streams are most represented, comprising 75% (thermal) and 17% (rivers/streams) of the dataset. Across all major areas of the park, Norris Geyser Basin has been sampled more than any other basin, with more than 1,100 samples reported in this dataset.

Yellowstone National Park (YNP; Wyoming, Montana, and Idaho, USA) contains more than 10,000 hydrothermal features, several lakes, and four major watersheds. For more than 140 years, researchers at the U.S. Geological Survey and other scientific institutions have investigated the chemical compositions of hot springs, geysers, fumaroles, mud pots, streams, rivers, and lakes in YNP and surrounding areas. Water chemistry studies have revealed a range of compositions including waters with pH values ranging from about 1 to 10, surface temperatures from ambient to superheated values of 95°C, and elevated concentrations of silica, lithium, boron, fluoride, mercury, and arsenic. Hydrogeochemical data from YNP research have led to insights on subsurface conditions of temperature and chemistry, water-rock-gas interactions and processes of high-temperature mineral alteration with dissolution and precipitation, redox processes, thermophilic microbial metabolism under extreme conditions and effects of thermal water chemistry on river systems. In this Data Release, water chemistry data for 4,918 water samples are reported for numerous thermal features, rivers, streams, lakes, drillholes, and precipitation in and around YNP. The data for these samples were originally located in 38 reports published between 1888 and 2022 and in multiple unpublished documents. Spanning more than 600 unique sampling sites throughout the YNP region, this dataset includes samples collected as early as 1883 (Gooch & Whitfield, 1888) and as recently as 2021 (McCleskey, et al, 2022). The thermal features sampled most frequently include Cistern Spring (180 samples) and Echinus Geyser (73 samples) in Norris Geyser Basin and Ojo Caliente Spring (143 samples) in the Lower Geyser Basin, while more than 500 sites have 5 samples or fewer. Water chemistry data from thermal features, rivers, and streams are most represented, comprising 75% (thermal) and 17% (rivers/streams) of the dataset. Across all major areas of the park, Norris Geyser Basin has been sampled more than any other basin, with more than 1,100 samples reported in this dataset.

Surface water, springs and wells in Pinnacles National Park (San Benito and Monterey Counties, CA) were sampled in the Fall of 2016 and Spring of 2017. Field parameters such as in situ pH, TDS/conductivity, and temperature were assessed. GPS coordinates for all samples were taken. Comprehensive groundwater chemistry, including major and minor elements, alkalinity, nutrients (and other parameters), Sr isotopes and REE concentrations, was analyzed at the National Water Quality Lab, USGS, Denver CO; and in USGS labs in Menlo Park, CA. One field visit on 8/20/2017 was made to obtain rock samples from the volcanic and sedimentary rocks in and around the park, which were digested and analyzed for whole rock chemistry (XRF, OES, ICP MS) by the Analytical Chemistry Lab (Mineral Resources Program, USGS, Denver CO). Sr isotopes for these samples were analyzed in the Menlo Park Metal Isotope Lab at the USGS. Precipitation was collected in a bulk collector during the winter of 2016-2017 and the chemistry and Sr isotopes of bulk samples was analyzed by ICP-MS or TIMS at the USGS Metal Isotope Lab in Menlo Park, CA.

Surface water, springs and wells in Pinnacles National Park (San Benito and Monterey Counties, CA) were sampled in the Fall of 2016 and Spring of 2017. Field parameters such as in situ pH, TDS/conductivity, and temperature were assessed. GPS coordinates for all samples were taken. Comprehensive groundwater chemistry, including major and minor elements, alkalinity, nutrients (and other parameters), Sr isotopes and REE concentrations, was analyzed at the National Water Quality Lab, USGS, Denver CO; and in USGS labs in Menlo Park, CA. One field visit on 8/20/2017 was made to obtain rock samples from the volcanic and sedimentary rocks in and around the park, which were digested and analyzed for whole rock chemistry (XRF, OES, ICP MS) by the Analytical Chemistry Lab (Mineral Resources Program, USGS, Denver CO). Sr isotopes for these samples were analyzed in the Menlo Park Metal Isotope Lab at the USGS. Precipitation was collected in a bulk collector during the winter of 2016-2017 and the chemistry and Sr isotopes of bulk samples was analyzed by ICP-MS or TIMS at the USGS Metal Isotope Lab in Menlo Park, CA.

Historical water and gas chemistry data from geothermal areas are important for detecting long-term patterns, informing geothermal energy exploration, development, and use, and for contextualizing more recent data. The U.S. Geological Survey has published water and gas chemistry data from geothermal areas in the western United States, which is primarily available as scanned PDF files. This makes the data difficult to access or include in large-scale data analysis. This data release provides digitized and reformatted data from 20 previously published U.S. Geological Survey Open-File reports and journal articles, representing 1867 water chemistry samples and 313 gas chemistry samples. All data have been standardized to the same units, geographic coordinates, and file format. Description of sample site location was improved. Many reports do not report geographic location coordinates; those that do are frequently inaccurate, as latitude and longitude were interpolated from a map, or in some cases, estimated in the field before the common use of global positioning systems (GPS). Collection dates for individual samples range from 1930 to 2005, although most samples were collected between the years 1970 and 2000. Samples are primarily from California, Oregon, and Washington, although some reports include data from sites in Montana, Idaho, Nevada, Utah, Arizona, and New Mexico. Attributes for both water and gas chemistry are: Sample name, Sample ID, Type, Collection date, Collection time, Reported location, Reported latitude, Reported longitude, Reported Easting, Reported Northing, Location description, Region, State, County, Latitude, Longitude, Location resolution, Location error, Elevation, Source, Author comment, and Digitizer comment. Attributes for water chemistry are: Well depth, Collection depth, Discharge, Temperature, pH (field), pH (lab), pH, Aluminum (Al), Arsenic (As), Boron (B), Barium (Ba), Bromide (Br), Calcium (Ca), Chloride (Cl), Carbonate (CO3), Alkalinity as carbonate (CO3), Cesium (Cs), Copper (Cu), Dissolved Organic Carbon as Carbon (DIC as C), Fluoride (F), Iron (Fe), Hydrogen sulfide (H2S), Bicarbonate (HCO3), Alkalinity as bicarbonate (HCO3), Carbonic acid (H2CO3), Mercury (Hg), Iodide (I), Potassium (K), Lithium (Li), Magnesium (Mg), Manganese (Mn), Molybdenum (Mo), total Nitrogen (N), Sodium (Na), Ammonium (NH4), Nickel (Ni), Nitrate (NO3), total Phosphorus (P), Lead (Pb), Phosphate (PO4), Rubidium (Rb), Silica (SiO2), Sulfate (SO4), Strontium (Sr), Uranium (U), Vanadium (V), Zinc (Zn), Reported cations, Reported anions, Cations, Anions, Reported total dissolved solids, Salinity, Charge balance, Specific conductance, isotopic composition of hydrogen (Delta 2H), isotopic composition of oxygen in water (Delta 18O (H2O)), Oxygen shift, isotopic composition of oxygen in sulfate (Delta 18O (SO4)), isotopic composition of carbon (Delta 13C), isotopic composition of carbon in dissolved inorganic carbon (Delta 13C (DIC)), Tritium (3H), and 14C. Attributes for gas chemistry are: Temperature, Total gas, argon (Ar), oxygen and argon (O2 + Ar), ethane (C2H6), methane (CH4), carbon dioxide (CO2), hydrogen (H2), hydrogen sulfide (H2S), helium (He), nitrogen (N2), ammonia (NH3), oxygen (O2), dissolved argon (Ar dissolved), dissolved methane (CH4 dissolved), dissolved carbon dioxide (CO2 dissolved), dissolved hydrogen (H2 dissolved), dissolved helium (He dissolved), dissolved nitrogen (N2 dissolved), dissolved ammonia (NH3 dissolved), dissolved oxygen (O2 dissolved), isotopic ratio of helium (3He/4He), isotopic ratio of helium corrected for the atmospheric isotopic composition of helium (3He/4He corrected), isotopic composition of nitrogen (Delta 15N), and isotopic composition of carbon in carbon dioxide (Delta 13C (CO2)).

Historical water and gas chemistry data from geothermal areas are important for detecting long-term patterns, informing geothermal energy exploration, development, and use, and for contextualizing more recent data. The U.S. Geological Survey has published water and gas chemistry data from geothermal areas in the western United States, which is primarily available as scanned PDF files. This makes the data difficult to access or include in large-scale data analysis. This data release provides digitized and reformatted data from 20 previously published U.S. Geological Survey Open-File reports and journal articles, representing 1867 water chemistry samples and 313 gas chemistry samples. All data have been standardized to the same units, geographic coordinates, and file format. Description of sample site location was improved. Many reports do not report geographic location coordinates; those that do are frequently inaccurate, as latitude and longitude were interpolated from a map, or in some cases, estimated in the field before the common use of global positioning systems (GPS). Collection dates for individual samples range from 1930 to 2005, although most samples were collected between the years 1970 and 2000. Samples are primarily from California, Oregon, and Washington, although some reports include data from sites in Montana, Idaho, Nevada, Utah, Arizona, and New Mexico. Attributes for both water and gas chemistry are: Sample name, Sample ID, Type, Collection date, Collection time, Reported location, Reported latitude, Reported longitude, Reported Easting, Reported Northing, Location description, Region, State, County, Latitude, Longitude, Location resolution, Location error, Elevation, Source, Author comment, and Digitizer comment. Attributes for water chemistry are: Well depth, Collection depth, Discharge, Temperature, pH (field), pH (lab), pH, Aluminum (Al), Arsenic (As), Boron (B), Barium (Ba), Bromide (Br), Calcium (Ca), Chloride (Cl), Carbonate (CO3), Alkalinity as carbonate (CO3), Cesium (Cs), Copper (Cu), Dissolved Organic Carbon as Carbon (DIC as C), Fluoride (F), Iron (Fe), Hydrogen sulfide (H2S), Bicarbonate (HCO3), Alkalinity as bicarbonate (HCO3), Carbonic acid (H2CO3), Mercury (Hg), Iodide (I), Potassium (K), Lithium (Li), Magnesium (Mg), Manganese (Mn), Molybdenum (Mo), total Nitrogen (N), Sodium (Na), Ammonium (NH4), Nickel (Ni), Nitrate (NO3), total Phosphorus (P), Lead (Pb), Phosphate (PO4), Rubidium (Rb), Silica (SiO2), Sulfate (SO4), Strontium (Sr), Uranium (U), Vanadium (V), Zinc (Zn), Reported cations, Reported anions, Cations, Anions, Reported total dissolved solids, Salinity, Charge balance, Specific conductance, isotopic composition of hydrogen (Delta 2H), isotopic composition of oxygen in water (Delta 18O (H2O)), Oxygen shift, isotopic composition of oxygen in sulfate (Delta 18O (SO4)), isotopic composition of carbon (Delta 13C), isotopic composition of carbon in dissolved inorganic carbon (Delta 13C (DIC)), Tritium (3H), and 14C. Attributes for gas chemistry are: Temperature, Total gas, argon (Ar), oxygen and argon (O2 + Ar), ethane (C2H6), methane (CH4), carbon dioxide (CO2), hydrogen (H2), hydrogen sulfide (H2S), helium (He), nitrogen (N2), ammonia (NH3), oxygen (O2), dissolved argon (Ar dissolved), dissolved methane (CH4 dissolved), dissolved carbon dioxide (CO2 dissolved), dissolved hydrogen (H2 dissolved), dissolved helium (He dissolved), dissolved nitrogen (N2 dissolved), dissolved ammonia (NH3 dissolved), dissolved oxygen (O2 dissolved), isotopic ratio of helium (3He/4He), isotopic ratio of helium corrected for the atmospheric isotopic composition of helium (3He/4He corrected), isotopic composition of nitrogen (Delta 15N), and isotopic composition of carbon in carbon dioxide (Delta 13C (CO2)).

During October 1995 through March 2014, the U.S. Geological Survey in cooperation with the National Park Service, Luray, Virginia Station collected and analyzed samples of selected springs, air and unsaturated-zone gases in Shenandoah National Park, Virginia. The 19-year record of measurements of chemical and isotopic composition of water discharging from 34 springs located along the crest of the Blue Ridge Mountains in Shenandoah National Park, Virginia, is reported. These data include field measurements of water temperature, specific conductance, concentrations of dissolved oxygen (O2), and pH. Laboratory measurements included major-, minor-, and trace-element chemistry; concentrations of dissolved gases (nitrogen, [N2] argon [Ar], oxygen, and carbon dioxide [CO2]); concentrations of dissolved trace atmospheric gases, including trichlorofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12), and trichlorotrifluoroethane (CFC-113) and sulfur hexafluoride (SF6); and hydrogen stable isotopic composition (δ2H) and oxygen isotopic composition (δ18O) of water. The data include an up to 14-year time series record of monthly sampling at five springs collected between 1995 and 2013. The measurements included temperature, specific conductance, pH, and discharge recorded at 30-minute intervals. Atmospheric mixing ratios of CFC-11, CFC-12, CFC-113, trifluorobromomethane (CF3Br), SF6, and trifluoromethyl sulfur pentafluoride (SF5CF3) in air from the Big Meadows Air Monitoring Station, Shenandoah National Park, were measured at approximately weekly intervals from September 1995 through March 2014. Additional data include monthly (between May 2001 and August 2003) measurements of temperature, N2, O2, Ar, CO2, CFC-12, CFC-11, CFC-113, and SF6 concentrations in unsaturated-zone air from seven multilevel piezometers in Shenandoah National Park and at the U.S. Geological Survey National Center in Reston, Virginia. All samples were analyzed at the U.S. Geological Survey Laboratories in Reston, Virginia.