This data table includes the data source, identifiers for sampled wells, properties in the vicinity of San Juan Coal Mine where wells are located, sampling date, and results of groundwater chemistry analyses for arsenic, calcium, chloride, sodium, sulfate, sulfide and dissolved solids in milligrams per liter.

This product "Predicted nitrate and arsenic concentrations in basin-fill aquifers of the Southwest Principal Aquifers study area" is a 1:250,000-scale vector dataset and was developed as part of a regional Southwest Principal Aquifers (SWPA) study. The study examined the vulnerability of basin-fill aquifers in the southwestern United States to nitrate contamination and arsenic enrichment. Statistical models were developed by using the random forest classifier algorithm to predict concentrations of nitrate and arsenic across a model grid that represents local- and basin-scale measures of source, aquifer susceptibility, and geochemical conditions. Separate classifiers were developed for nitrate and arsenic because each constituent was expected to be affected by a different set of factors, and each factor could have a different magnitude or directional influence (increase/decrease) on concentration. For each constituent, two different classifiers were developed; a prediction classifier and a confirmatory classifier. The prediction classifiers were developed specifically to predict nitrate and arsenic concentrations in basin-fill aquifers across the SWPA study area and were based on explanatory variables representing source and susceptibility conditions. These explanatory variables were available throughout the entire SWPA study area and, therefore, did not pose a limitation for using the classifiers to predict concentrations. The confirmatory classifiers were developed to supplement the prediction classifiers in the evaluation of the conceptual model. The name, "confirmatory," reflects the classifier's purpose for evaluation of a-priori hypotheses and contrasts other general types of statistical models, such as those used for prediction or exploratory purposes. The confirmatory classifiers included the explanatory variables used in the prediction classifiers, as well as additional variables representing geochemical conditions and basin groundwater budget components. The inclusion of the geochemical and basin groundwater budget variables in the confirmatory classifiers allowed for further evaluation of the conceptual models, which was not possible with the prediction classifiers alone. The geochemical data, however, were only available at specific well locations, and consistent water-budget data were not available for every basin in the study area. The limited availability of the data for these variables constrained the confirmatory classifiers to observations from 16 case-study basins and precluded use of the confirmatory classifier for predicting concentrations across the SWPA study area. To contrast the scope of the two classifiers, the confirmatory classifiers were developed by using all available explanatory variables but with observations restricted to the 16 case-study basins, whereas the prediction classifiers were unrestricted with respect to spatial extent because these were developed by using a subset of the explanatory variables that were available throughout the study area.

Groundwater arsenic concentrations in the San Joaquin Valley have varied over the decades from 1980 to 2019. This report was compiled to determine whether arsenic concentrations are increasing or decreasing and the mechanism controlling the trends. The San Joaquin Valley contains 4,979 wells with arsenic analyses and possible co-detections of any of the following constituents: dissolved oxygen, field-measured pH, iron, manganese, sulfate, nitrate, or water level. Water quality data comes from two sources: 3,302 wells from with California State Water Resources Control Board - Division of Drinking Water and 1,448 wells from the U.S. Geological Survey National Water Information System (California State Water Resources Control Board – Division of Drinking Water, 2019; U.S. Geological Survey, 2020). There are an additional 229 wells with data from both sources. Other data compiled in addition to the constituents analysed are well type, water use, status, and depth. Well location in relation to the regions defined in the study unit, the El Nido and Pixley subsidence areas, and lateral position from the valley center were also collected (Hansen et al., 2018; Faunt and Sneed, 2015; Faunt, 2009; Voss et al., 2019). The co-detections of constituent trends with arsenic trends was used to determine possible mechanisms controlling arsenic variability in addition to the location and depth of the wells.

Arsenic (As) toxicity is a global environmental and health problem. There are both natural (eg volcanic activity) and anthropogenic sources of As (eg lead arsenate and copper arsenate were commonly used pesticides in the 1900’s). Aqueous levels of arsenic in the Klamath Basin (CA, OR), which has a volcanic origin, can exceed at some locations both the Oregon Department of Environmental Quality human health water quality criteria (2.1 ug/L) (Sturdevant, 2011) and the US EPA drinking water limit (10 ug/L) (US EPA., 2001). In this study, dissolved concentrations of As, copper (Cu) and lead (Pb) were measured in more than 30 sites within the Klamath Basin between May and October. Results from samples collected between 2018 and 2022 are reported in this data release. References: Sturdevant, Debra., 2011. Water Quality Standards Review and Recommendations: Arsenic (Draft Report). State of Oregon Department of Environmental Quality. https://www.oregon.gov/deq/FilterDocs/AppEArsenicIssuePaper.pdf US EPA., 2001. Drinking Water Standard for Arsenic (Report No. EPA 815-F-00-015). United States Environmental Protection Agency. https://www.epa.gov/dwreginfo/chemical-contaminant-rules

These data are comprised of measurements of elements (e.g., uranium, cobalt, nickel, copper, zinc, cadmium, lead, etc.), major anions (chloride, nitrite+nitrate as nitrogen, sulfate, etc.), dissolved organic carbon, and general water quality characteristics in Canyon Mine containment pond water samples collected in calendar year 2018.

These data are comprised of measurements of elements (e.g., uranium, cobalt, nickel, copper, zinc, cadmium, lead, etc.), major anions (chloride, nitrite+nitrate as nitrogen, sulfate, etc.), dissolved organic carbon, and general water quality characteristics in Canyon Mine containment pond water samples collected in calendar year 2018.

The map graphic image at https://www.sciencebase.gov/catalog/file/get/63140561d34e36012efa2b7f?name=arsenic_map.png illustrates arsenic values, in micrograms per liter, for groundwater samples from about 31,000 wells and springs in 49 states compiled by the United States Geological Survey (USGS). The map graphic illustrates an updated version of figure 1 from Ryker (2001). Cited Reference: Ryker, S.J., Nov. 2001, Mapping arsenic in groundwater-- A real need, but a hard problem: Geotimes Newsmagazine of the Earth Sciences, v. 46 no. 11, p. 34-36 at http://www.agiweb.org/geotimes/nov01/feature_Asmap.html. An excel tabular data file, a txt file, along with a GIS shape file of arsenic concentrations (20,043 samples collected by the USGS) for a subset of the sites shown on the map. Samples were collected between 1973 and 2001 and are provided for download.

This data release contains total dissolved solids (TDS) concentrations and specific conductance (SC) measurements collected at surface-water monitoring locations and groundwater monitoring wells within the Upper Colorado River Basin (UCRB) between 1894 and 2022. Discrete TDS and SC results were obtained from the Water Quality Portal (WQP). Continuous SC monitoring results were obtained from the USGS National Water Information System (NWIS). The data set includes 127,294 TDS results that were collected at 12,339 sites between 1900 and 2022, and 705,918 SC results that were collected at 19,630 sites between 1894 and 2022. The SC results represented 244,784 discrete measurements at 19,625 sites and 461,134 mean daily values from continuous monitoring at 193 sites. The data retrieved from the WQP were harmonized to create a standardized and readily usable dataset. The harmonization process included the synthesis of parameter names and fractions, the reconciliation of remarks and other data qualifiers, the resolution of duplicate records, and basic checks of the data quality. The harmonized results at 230 sites were selected for additional data processing because those sites were potential calibration targets for TDS watershed modeling for the UCRB using the USGS Spatially Referenced Regression on Watershed attributes (SPARROW) model. The 230 sites met the minimum criteria for the number and seasonal distribution of samples, the length of the sampling period, and the amount of overlap with the streamflow record at a nearby gage. The measured TDS concentrations at those sites were supplemented with estimated TDS concentrations that were determined from relations between measured TDS and SC results within the UCRB. A site-specific regression of TDS on SC was used to estimate TDS from SC at 143 sites, while a regional conversion factor between TDS and SC was used to estimate TDS from SC at 87 sites. The final TDS data for the 230 sites included 50,003 measured values from the WQP, 378,147 values estimated using the equation from a site-specific regression of TDS on SC (with 350,840 based on mean daily SC values), and 30,880 values estimated using a regional median ratio between TDS and SC.

This data release provides total and aqueous arsenic (As) determinations and associated field readings collected from groundwater sampled from 254 newly constructed private residential wells from 2014-2016. The study focuses on three regions of Minnesota that differ geologically: south-central (herein called central), northwest, and northeast. These study regions were chosen due to their prevalent elevated As concentrations in drinking water. Each of the 254 wells were sampled in three rounds by the Minnesota Department of Health (MDH). The timing of the three sampling rounds was (1) immediately or shortly after well construction (round 1); (2) 3-6 months after initial sample collection (round 2); and (3) 12 months after initial sample collection (round 3). During each round, samples were collected for both total and aqueous As. Physicochemical characteristics, including specific conductance, pH, dissolved oxygen, oxidation reduction potential, and temperature, were also measured to gage the well water stability prior to sample collection. Round 1 sampling was timed to co-occur and mimic well driller regulatory sampling. Drillers collected samples after well development from the drill rig groundwater pump or from the residential plumbing and the MDH sampler replicated the sample location and timing used by the driller. Sampling from the drill rig's groundwater pump occurred after the well was drilled and developed, when the water was visibly clear, with little visible sediment particles. Samples from plumbing were collected after the plumbing was flushed out and physicochemical characteristic readings stabilized. Round 2 and round 3 by MDH staff were collected only from plumbing. Samples collected from plumbing were taken from faucets, hydrants, or pressure tanks prior to filters or treatment systems.

This dataset provides aqueous nitrate+nitrite, aqueous manganese, aqueous iron, and total sulfate measurements in groundwater samples from 254 newly constructed private residential wells between 2014 and 2016. The study focuses on three geologically distinct regions of Minnesota: central, northwest, and northeast. These study regions were chosen due to their prevalent elevated As concentrations in drinking water. Each of the 254 wells were sampled in three rounds by the Minnesota Department of Health (MDH). The timing of the three sampling rounds was (1) immediately or shortly after well construction (round 1); (2) 3-6 months after initial sample collection (round 2); and (3) 12 months after initial sample collection (round 3). During each round, samples were collected for both total and aqueous As, aqueous nitrate+nitrite, aqueous manganese, aqueous iron, and total sulfate. Physiochemical characteristics, including specific conductance, pH, dissolved oxygen, oxidation reduction potential, and temperature, were also measured to gage the well water stability prior to sample collection. Round 1 sampling was timed to co-occur and mimic well driller regulatory sampling. Drillers collected samples after well development from the drill rig groundwater pump or from the residential plumbing, and the MDH sampler replicated the sample location and timing used by the driller. Sampling from the drill rig’s groundwater pump occurred after the well was drilled and developed, when the water was visibly clear, with little visible sediment particles. Samples from plumbing were collected after the plumbing was flushed out and physiochemical characteristic readings stabilized. Round 2 and round 3 by MDH staff were collected only from plumbing. Samples collected from plumbing were taken from faucets, hydrants, or pressure tanks prior to filters or treatment systems.