This data release contains two spatial datasets and a data table in support of an evaluation of arsenic and uranium occurrence in Connecticut groundwater through spatially weighted and bedrock geology assessments. Spatial datasets include 1) a shapefile of 130 equal-area grid cells with associated arsenic attribute data, and 2) a shapefile of 110 equal-area grid cells with associated uranium attribute data. The State of Connecticut was divided based on a set of randomized equal-area grid cells based on the method of Scott (1990); one grid was created for arsenic, with 130 grid cells, and one was created for uranium, with 110 grid cells. Arsenic and uranium attribute data associated with the equal-area grid cells include the number of wells in each grid cell, the number of wells with constituent concentrations above three selected thresholds, the fraction of wells with constituent concentrations above three selected thresholds, and the percentage of wells with constituent concentrations above three selected thresholds. The three selected thresholds for arsenic include 3, 5, and 10 micrograms per liter (ug/L), with 10 ug/L representing the maximum contaminant level (MCL) established by the U.S. Environmental Protection Agency (EPA) for human health for arsenic. The three selected thresholds for uranium include 1, 10, and 30 ug/L, with 30 ug/L representing the EPA MCL for human health for uranium. The bedrock geology data table is table 4 from Gross and others (2020) formatted so that it can easily be joined with Connecticut's bedrock geology dataset (Connecticut Department of Environmental Protection, 2000) using the geologic unit abbreviation (UNIT attribute) in order to recreate figure 3 from Gross and others (2020). The data table includes counts and percentages of arsenic and uranium concentrations that exceed maximum contaminant levels from private wells in Connecticut, by geologic unit and major bedrock category, 2013-18.

This dataset contains the water-quality results from the testing of unfiltered water samples (environmental samples) collected from 674 private wells in Connecticut for the analysis of arsenic and (or) uranium, using EPA method 200.8. All of the environmental water-quality data and georeferenced locations of the sampled wells were provided by the Connecticut Department of Public Health (CT-DPH). The water samples, collected from 2013 to 2015, were analyzed by the CT-DPH Laboratory in Hartford, CT. This dataset also contains information on the town and county location for each well and information on the geologic setting for each well. Latitude and longitude coordinate data are not provided in this data release in order to maintain the confidentiality of the well owner's identities.

This dataset contains the water-quality results from the testing of unfiltered water samples (environmental samples) collected from 674 private wells in Connecticut for the analysis of arsenic and (or) uranium, using EPA method 200.8. All of the environmental water-quality data and georeferenced locations of the sampled wells were provided by the Connecticut Department of Public Health (CT-DPH). The water samples, collected from 2013 to 2015, were analyzed by the CT-DPH Laboratory in Hartford, CT. This dataset also contains information on the town and county location for each well and information on the geologic setting for each well. Latitude and longitude coordinate data are not provided in this data release in order to maintain the confidentiality of the well owner's identities.

This data release contains groundwater-quality data for three parameters of interest (arsenic, manganese, and pH) and well information for sample sites for aquifers in the conterminous U.S. Water-quality data and well information were derived from a dataset compiled from three sources: the U.S. Geological Survey (USGS) National Water Information System (NWIS), the U.S. Environmental Protection Agency (USEPA) Safe Drinking Water Information System (SDWIS), and numerous agencies and organizations at the state, regional, and local level. The data compilation of the National Water Quality Program’s groundwater assessment team is an internal dataset informally referred to as the National Groundwater Aggregation (NGA). The current study of groundwater quality in the conterminous U.S. augments data compiled by others globally. Only geochemical parameters of interest (arsenic, manganese, pH) from wells in the national groundwater aggregation are presented—data from springs were not used. A table of site information includes attributes for each well, such as the state, water use code, depth, open interval (if available) and aquifer (if available). The provider of the water-quality data and well information in also in this table.

This data release contains groundwater-quality data for three parameters of interest (arsenic, manganese, and pH) and well information for sample sites for aquifers in the conterminous U.S. Water-quality data and well information were derived from a dataset compiled from three sources: the U.S. Geological Survey (USGS) National Water Information System (NWIS), the U.S. Environmental Protection Agency (USEPA) Safe Drinking Water Information System (SDWIS), and numerous agencies and organizations at the state, regional, and local level. The data compilation of the National Water Quality Program’s groundwater assessment team is an internal dataset informally referred to as the National Groundwater Aggregation (NGA). The current study of groundwater quality in the conterminous U.S. augments data compiled by others globally. Only geochemical parameters of interest (arsenic, manganese, pH) from wells in the national groundwater aggregation are presented—data from springs were not used. A table of site information includes attributes for each well, such as the state, water use code, depth, open interval (if available) and aquifer (if available). The provider of the water-quality data and well information in also in this table.

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.

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.

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.

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 data used to develop models and maps that estimate probabilities of exceeding various thresholds of arsenic concentrations in private domestic wells throughout the conterminous United States. Three boosted regression tree (BRT) models were developed separately to estimate the probability of private well arsenic concentrations exceeding 1, 5, and 10 micrograms per liter (µg/L). A random forest (RF) model was developed to estimate the most probable arsenic concentration category (≤5, >5 to ≤10, or >10 µg/L). The models use arsenic concentration data from private domestic wells located throughout the conterminous United States and independent variables that are available as geospatial data. The models were used to produce maps that are included in this data release. The model input data (predictor variables) that were used to make the maps are within a zipped folder (Map_Input_Data.zip) that contains 85 tif-raster files, one for each model predictor variable. The map probability estimates that are outputs from the model are in a zipped folder (Map_Output_Data.zip) that contains 13 tif-raster files, one model estimate map for each of the BRT models and four for the RF model, as well as 2 confidence interval maps for each BRT model.