Assessment of biogeochemical processes and transformations at the aquifer-estuary interface and measurement of the chemical flux from submarine groundwater discharge (SGD) zones to coastal water bodies are critical for evaluating ecosystem service, geochemical budgets, and eutrophication status. The U.S. Geological Survey and the University of Delaware measured rates of SGD and concentrations of dissolved constituents, including nitrogen species, from recirculating ultrasonic and manual seepage meters, and in nearshore groundwater, on the southern shore of Guinea Creek, an estuarine tributary of Rehoboth Bay, in Millsboro, Delaware, in June, August, and October of 2015. A novel oxygen- and light-regulated seepage meter and a standard seepage meter were deployed as an adjacent pair and sampled at 0.5- to 2-hour intervals across the majority or entirety of single tidal cycles (8 to 12 hours). SGD rate was measured within an attached collection bag (0.5- to 2-hour intervals), or with an ultrasonic flow sensor (1-second intervals). Groundwater samples were collected at multiple depths (5 to 83 centimeters) in shore-perpendicular transects extending across the nearshore subtidal SGD zone. Constituents and other parameters measured in seepage meters and groundwater included: dissolved oxygen, salinity, pH, oxidation/reduction potential, temperature, nitrate, ammonium, phosphate, dissolved organic and inorganic carbon, stable isotopic ratios of carbon species, trace elements, and alkalinity. These data can be used to evaluate biogeochemical conditions and extent of chemical transformation in the upper coastal aquifer and surface sediments and to calculate fluxes of nitrogen and other constituents carried by SGD across the aquifer-estuary interface.

This U.S. Geological Survey (USGS) data release contains stream water chemistry and streamflow data collected in late August and early September, 2021 from 28 sites located throughout Colorado, USA. The sampled streams all drain high-elevation mountain watersheds in areas where the bedrock is hydrothermally altered and contains abundant sulfide minerals. Most sampled streams are therefore affected by natural acid-rock drainage. All sites had been sampled in prior years so that the 2021 data could be used to evaluate potential changes in stream water chemistry in recent decades. Streamflow was also quantified at most sites using data from a sodium chloride slug addition wherein specific conductivity readings were used as a surrogate for the tracer concentration.

This U.S. Geological Survey (USGS) data release contains stream water chemistry and streamflow data collected in late August and early September, 2021 from 28 sites located throughout Colorado, USA. The sampled streams all drain high-elevation mountain watersheds in areas where the bedrock is hydrothermally altered and contains abundant sulfide minerals. Most sampled streams are therefore affected by natural acid-rock drainage. All sites had been sampled in prior years so that the 2021 data could be used to evaluate potential changes in stream water chemistry in recent decades. Streamflow was also quantified at most sites using data from a sodium chloride slug addition wherein specific conductivity readings were used as a surrogate for the tracer concentration.

This U.S. Geological Survey (USGS) data release contains data from stream water, groundwater, and soil samples collected in 2019 and 2020 in the North Quartz Creek watershed in central Colorado. Fourteen streambank wells were installed in pairs at seven locations in August 2020 to capture the emerging groundwater from the left bank and right banks (relative to downstream-facing direction) and a synoptic sampling campaign was conducted to quantify metal contributions to the stream. A continuous, instream injection of sodium bromide (NaBr) was initiated at the head of the 5 km study reach several days prior to the synoptic sampling campaign and maintained throughout the duration of the study. Bromide concentrations were subsequently used to determine streamflow in the primary study reach (upper 1.3 km) using the tracer-dilution method, and as an indicator of hydrologic connections between North Quartz Creek and subsurface water. Streamflow was quantified in a secondary study reach (lower 3.7 km) using data from a series of sodium chloride slug additions wherein specific conductivity readings were used as a surrogate for the tracer concentration. Surface water samples were collected along North Quartz Creek including inflows from the left (LBI) and right (RBI) banks. Soil and sediment samples were collected along the transport path from source material (natural weathering and mine tailings/mine drainage) to the stream.

This U.S. Geological Survey (USGS) data release contains data from stream water, groundwater, and soil samples collected in 2019 and 2020 in the North Quartz Creek watershed in central Colorado. Fourteen streambank wells were installed in pairs at seven locations in August 2020 to capture the emerging groundwater from the left bank and right banks (relative to downstream-facing direction) and a synoptic sampling campaign was conducted to quantify metal contributions to the stream. A continuous, instream injection of sodium bromide (NaBr) was initiated at the head of the 5 km study reach several days prior to the synoptic sampling campaign and maintained throughout the duration of the study. Bromide concentrations were subsequently used to determine streamflow in the primary study reach (upper 1.3 km) using the tracer-dilution method, and as an indicator of hydrologic connections between North Quartz Creek and subsurface water. Streamflow was quantified in a secondary study reach (lower 3.7 km) using data from a series of sodium chloride slug additions wherein specific conductivity readings were used as a surrogate for the tracer concentration. Surface water samples were collected along North Quartz Creek including inflows from the left (LBI) and right (RBI) banks. Soil and sediment samples were collected along the transport path from source material (natural weathering and mine tailings/mine drainage) to the stream.

This dataset contains measurements of dissolved hydrocarbons in from various water sources, as well as ancillary raw calibration data showing the stability of the gas chromatograph with an atomic emission detector and flame ionization detector (GC-AED-FID) analytical system over time. Across multiple studies, samples from tap water, groundwater, surface water, springs, mine outflows, and blank materials were analyzed using this system over a period from 2014 to 2017, comprising 172 samples analyzed. In addition to water samples, 183 calibrations conducted over the same period of time are included to document the stability of the GC-AED-FID system over time. The target analytes in this study were: methane (CH4), ethane (C2H6), ethene (C2H4), ethyne (C2H2), propane (C3H8), propene (C3H6), i-butane (C4H10), n-butane (C4H10), 1-butene (C4H8), propyne (C3H4), i-pentane (C5H12), n-pentane (C5H12), 2-methyl-pentane (C6H14), 3-methyl-pentane (C6H14), hexane (C6H14), and benzene (C6H6).

This dataset contains measurements of dissolved hydrocarbons in from various water sources, as well as ancillary raw calibration data showing the stability of the gas chromatograph with an atomic emission detector and flame ionization detector (GC-AED-FID) analytical system over time. Across multiple studies, samples from tap water, groundwater, surface water, springs, mine outflows, and blank materials were analyzed using this system over a period from 2014 to 2017, comprising 172 samples analyzed. In addition to water samples, 183 calibrations conducted over the same period of time are included to document the stability of the GC-AED-FID system over time. The target analytes in this study were: methane (CH4), ethane (C2H6), ethene (C2H4), ethyne (C2H2), propane (C3H8), propene (C3H6), i-butane (C4H10), n-butane (C4H10), 1-butene (C4H8), propyne (C3H4), i-pentane (C5H12), n-pentane (C5H12), 2-methyl-pentane (C6H14), 3-methyl-pentane (C6H14), hexane (C6H14), and benzene (C6H6).

This data release documents four tables that contain data for assessing the susceptibility of groundwater using environmental tracers collected from public-supply wells located in the Northern Atlantic Coastal Plain (NACP) Aquifer System and Piedmont and Blue Ridge Crystalline-Rock Aquifers of Eastern United States. Results for two modeling support studies located within the NACP are also included. Table 1 provides the primary results of this study and it contains condensed results from dissolved gas modeling and calculated environmental tracer concentrations, as well as results of the tritium age classification, susceptibility index, the mean groundwater age, fraction of Modern water (water that was recharged after 1952), and detailed lumped parameter model calibration results of each sample in this study. Mean groundwater ages were determined by calibration of environmental tracers (tritium, tritiogenic helium-3, sulfur hexafluoride, carbon-14 and radiogenic helium-4) to lumped parameter models for 231 public-supply wells. Calibrated lumped parameter models provide the optimal mean age and mixing parameter(s) used to compute the distribution of ages that explain the measured tracer concentrations in a sample. Tables two, three, and four provide results in support of table 1. Table two reports detailed results for the calibration of dissolved gas models to neon, argon, krypton, xenon, and nitrogen. Calibrated dissolved gas models provide the optimal water temperature, excess air, entrapped air, fractionation of gases, and excess nitrogen gas (mainly from denitrification) that explain the measured dissolved gases in a sample. Table three reports measured concentrations and the detailed calculations of environmental tracer concentrations derived from the dissolved gas modeling results reported in table 2. The dry-air mixing ratio is the atmospheric concentration (assuming the water has a single age) at the time of gas-water equilibration and is calculated for transient atmospheric gas tracers such as sulfur hexafluoride and chlorofluorocarbons. Tritiogenic helium-3 is the concentration of helium-3 that resulted from the decay of tritium and radiogenic helium-4 is the amount of helium generated from the decay of uranium and thorium in aquifer sediments. Table 4 reports results of calculated carbon-14 corrections caused by dissolution of carbonate minerals in the soil and saturated zone. Calculated carbon-14 corrections can be determined from analytical models of carbonate dissolution or from inverse geochemical modeling of the evolution of groundwater chemistry of a sample. The corrected carbon-14 concentration can be compared directly to carbon-14 atmospheric records, otherwise, dilution of the atmospheric record was inferred from Modern groundwater sample with 2 or more environmental tracers. In addition to these four tables, two ancillary tables are included to provide more detailed information about the fields and the abbreviations used in tables one through four. Please see processing steps in the general metadata file for more detailed information about the methods used to create the tables.

This data release documents four tables that contain data for assessing the susceptibility of groundwater using environmental tracers collected from public-supply wells located in the Northern Atlantic Coastal Plain (NACP) Aquifer System and Piedmont and Blue Ridge Crystalline-Rock Aquifers of Eastern United States. Results for two modeling support studies located within the NACP are also included. Table 1 provides the primary results of this study and it contains condensed results from dissolved gas modeling and calculated environmental tracer concentrations, as well as results of the tritium age classification, susceptibility index, the mean groundwater age, fraction of Modern water (water that was recharged after 1952), and detailed lumped parameter model calibration results of each sample in this study. Mean groundwater ages were determined by calibration of environmental tracers (tritium, tritiogenic helium-3, sulfur hexafluoride, carbon-14 and radiogenic helium-4) to lumped parameter models for 231 public-supply wells. Calibrated lumped parameter models provide the optimal mean age and mixing parameter(s) used to compute the distribution of ages that explain the measured tracer concentrations in a sample. Tables two, three, and four provide results in support of table 1. Table two reports detailed results for the calibration of dissolved gas models to neon, argon, krypton, xenon, and nitrogen. Calibrated dissolved gas models provide the optimal water temperature, excess air, entrapped air, fractionation of gases, and excess nitrogen gas (mainly from denitrification) that explain the measured dissolved gases in a sample. Table three reports measured concentrations and the detailed calculations of environmental tracer concentrations derived from the dissolved gas modeling results reported in table 2. The dry-air mixing ratio is the atmospheric concentration (assuming the water has a single age) at the time of gas-water equilibration and is calculated for transient atmospheric gas tracers such as sulfur hexafluoride and chlorofluorocarbons. Tritiogenic helium-3 is the concentration of helium-3 that resulted from the decay of tritium and radiogenic helium-4 is the amount of helium generated from the decay of uranium and thorium in aquifer sediments. Table 4 reports results of calculated carbon-14 corrections caused by dissolution of carbonate minerals in the soil and saturated zone. Calculated carbon-14 corrections can be determined from analytical models of carbonate dissolution or from inverse geochemical modeling of the evolution of groundwater chemistry of a sample. The corrected carbon-14 concentration can be compared directly to carbon-14 atmospheric records, otherwise, dilution of the atmospheric record was inferred from Modern groundwater sample with 2 or more environmental tracers. In addition to these four tables, two ancillary tables are included to provide more detailed information about the fields and the abbreviations used in tables one through four. Please see processing steps in the general metadata file for more detailed information about the methods used to create the tables.

The U.S. Geological Survey National Real-Time Water Quality (NRTWQ) Data Service (https://nrtwq.usgs.gov) provides computed concentrations and loads for sediment, nutrients, bacteria, and many additional constituents; uncertainty values and probabilities for exceeding drinking water or recreational criteria; frequency distribution curves; and all historical in-stream sensor measurements.