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 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.

Groundwater-quality data were collected from 748 wells as part of the National Water-Quality Assessment Project of the U.S. Geological Survey National Water-Quality Program from May 2012 through December 2013. The data were collected from four types of well networks: principal aquifer study networks, which assess the quality of groundwater used for public water supply; land-use study networks, which assess land-use effects on shallow groundwater quality; major aquifer study networks, which assess the quality of groundwater used for domestic supply; and enhanced trends networks, which evaluate the time scales during which groundwater quality changes. Groundwater samples were analyzed for a large number of water-quality indicators and constituents, including major ions, nutrients, trace elements, volatile organic compounds, pesticides, and radionuclides. These groundwater quality data are tabulated in a U.S. Geological Survey Data Series Report DS-997 which is available at http://dx.doi.org/10.3133/ds997 and in this data release. Quality-control samples also were collected; data from blank and replicate quality-control samples are included in the related report (DS-997) and this data release. This compressed file contains 28 files of groundwater-quality data in ASCII text tab-delimited format and 28 corresponding metadata in xml format for wells sampled for the U.S. Geological Survey National Water-Quality Assessment Project, May 2012 through December 2013.

Groundwater-quality data were collected from 748 wells as part of the National Water-Quality Assessment Project of the U.S. Geological Survey National Water-Quality Program from May 2012 through December 2013. The data were collected from four types of well networks: principal aquifer study networks, which assess the quality of groundwater used for public water supply; land-use study networks, which assess land-use effects on shallow groundwater quality; major aquifer study networks, which assess the quality of groundwater used for domestic supply; and enhanced trends networks, which evaluate the time scales during which groundwater quality changes. Groundwater samples were analyzed for a large number of water-quality indicators and constituents, including major ions, nutrients, trace elements, volatile organic compounds, pesticides, and radionuclides. These groundwater quality data are tabulated in a U.S. Geological Survey Data Series Report DS-997 which is available at http://dx.doi.org/10.3133/ds997 and in this data release. Quality-control samples also were collected; data from blank and replicate quality-control samples are included in the related report (DS-997) and this data release. This compressed file contains 28 files of groundwater-quality data in ASCII text tab-delimited format and 28 corresponding metadata in xml format for wells sampled for the U.S. Geological Survey National Water-Quality Assessment Project, May 2012 through December 2013.

Groundwater-quality data were collected from 502 wells as part of the National Water-Quality Assessment Project of the U.S. Geological Survey National Water-Quality Program and are included in this report. Most of the wells (500) were sampled from January through December 2015 and 2 of them were sampled in 2013. The data were collected from five types of well networks: principal aquifer study networks, which are used to assess the quality of groundwater used for public water supply; land-use study networks, which are used to assess land-use effects on shallow groundwater quality; major aquifer study networks, which are used to assess the quality of groundwater used for domestic supply; enhanced trends networks, which are used to evaluate the time scales during which groundwater quality changes; and vertical flow-path study networks, which are used to evaluate changes in groundwater quality from shallower to deeper depths. Groundwater samples were analyzed for a large number of water-quality indicators and constituents, including major ions, nutrients, trace elements, volatile organic compounds, pesticides, radionuclides, and some special interest constituents (arsenic speciation, chromium [VI] and perchlorate). These groundwater quality data are tabulated in a U.S. Geological Survey Data Series Report DS-XXXX which is available at https://dx.doi.org/XXXXXX and in this data release. Data from the environmental and QC samples from the 2012-2013 sampling period were presented in Arnold and others (2016a,b) and those from the 2014 sampling period were presented in Arnold and others (2017a,b). There are 20 data tables included in this data release and they are referenced as tables 1-12 and appendix tables 3.3-3.10 in the larger work citation. There are 25 tables that are part of the larger work citation; the 5 tables not included in the data release are summary tables derived from some of the other 20 tables. A version of table 1 is included in both the text and data release. This compressed file contains 20 files of groundwater-quality data in ASCII text tab-delimited format and 20 corresponding metadata in xml format for wells sampled for the U.S. Geological Survey National Water-Quality Assessment Project.

Groundwater-quality data were collected from 502 wells as part of the National Water-Quality Assessment Project of the U.S. Geological Survey National Water-Quality Program and are included in this report. Most of the wells (500) were sampled from January through December 2015 and 2 of them were sampled in 2013. The data were collected from five types of well networks: principal aquifer study networks, which are used to assess the quality of groundwater used for public water supply; land-use study networks, which are used to assess land-use effects on shallow groundwater quality; major aquifer study networks, which are used to assess the quality of groundwater used for domestic supply; enhanced trends networks, which are used to evaluate the time scales during which groundwater quality changes; and vertical flow-path study networks, which are used to evaluate changes in groundwater quality from shallower to deeper depths. Groundwater samples were analyzed for a large number of water-quality indicators and constituents, including major ions, nutrients, trace elements, volatile organic compounds, pesticides, radionuclides, and some special interest constituents (arsenic speciation, chromium [VI] and perchlorate). These groundwater quality data are tabulated in a U.S. Geological Survey Data Series Report DS-XXXX which is available at https://dx.doi.org/XXXXXX and in this data release. Data from the environmental and QC samples from the 2012-2013 sampling period were presented in Arnold and others (2016a,b) and those from the 2014 sampling period were presented in Arnold and others (2017a,b). There are 20 data tables included in this data release and they are referenced as tables 1-12 and appendix tables 3.3-3.10 in the larger work citation. There are 25 tables that are part of the larger work citation; the 5 tables not included in the data release are summary tables derived from some of the other 20 tables. A version of table 1 is included in both the text and data release. This compressed file contains 20 files of groundwater-quality data in ASCII text tab-delimited format and 20 corresponding metadata in xml format for wells sampled for the U.S. Geological Survey National Water-Quality Assessment Project.

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-quality data were collected from 559 wells as part of the National Water-Quality Assessment Project of the U.S. Geological Survey National Water-Quality Program from January through December 2014. The data were collected from four types of well networks: principal aquifer study networks, which assess the quality of groundwater used for public water supply; land-use study networks, which assess land-use effects on shallow groundwater quality; major aquifer study networks, which assess the quality of groundwater used for domestic supply; and enhanced trends networks, which evaluate the time scales during which groundwater quality changes. Groundwater samples were analyzed for a large number of water-quality indicators and constituents, including major ions, nutrients, trace elements, volatile organic compounds, pesticides, radionuclides, and some special interest constituents (arsenic speciation, chromium (VI) and perchlorate). These groundwater quality data are tabulated in a U.S. Geological Survey Data Series Report DS-1063 which is available at https://dx.doi.org/10.3133/ds1063 and in this data release. Quality-control samples also were collected and select data from 2012-2014 are included in the report DS1063 and this data release. Data from the environmental and QC blank and replicate samples from the 2012-2013 sampling period were presented in Arnold and others (2016). Data from spike QC samples have not previously been published Data from VOC spike QC data from May 2012-December 2014 are published in this report (see larger work citation) and data release along with an analysis of QC data where detections in field blank samples, variability in replicate samples, and recoveries in VOC spike samples are described for the entire sampling period through the date covered in this report (May 2012-December 2014). Pesticide spike samples and analysis of recoveries will be presented in a later report. There are 42 tables that are part of the larger work citation. There are 9 tables in the text of the larger work citation and 33 external tables included in this data release. The 9 tables not included in the data release are summary tables derived from some of the other 33 tables. Tables in the text include table 1, Appendix 1 tables 1-1 and 1-2; Appendix 2 table 2-1, and Appendix 4 tables 4-1 through 4-6. Tables that are external files are tables 1 through 12; Appendix 4 tables 4-7 through 4-27. This compressed file contains 33 files of groundwater-quality data in ASCII text tab-delimited format and 33 corresponding metadata in xml format for wells sampled for the U.S. Geological Survey National Water-Quality Assessment Project.

Groundwater-quality data were collected from 559 wells as part of the National Water-Quality Assessment Project of the U.S. Geological Survey National Water-Quality Program from January through December 2014. The data were collected from four types of well networks: principal aquifer study networks, which assess the quality of groundwater used for public water supply; land-use study networks, which assess land-use effects on shallow groundwater quality; major aquifer study networks, which assess the quality of groundwater used for domestic supply; and enhanced trends networks, which evaluate the time scales during which groundwater quality changes. Groundwater samples were analyzed for a large number of water-quality indicators and constituents, including major ions, nutrients, trace elements, volatile organic compounds, pesticides, radionuclides, and some special interest constituents (arsenic speciation, chromium (VI) and perchlorate). These groundwater quality data are tabulated in a U.S. Geological Survey Data Series Report DS-1063 which is available at https://dx.doi.org/10.3133/ds1063 and in this data release. Quality-control samples also were collected and select data from 2012-2014 are included in the report DS1063 and this data release. Data from the environmental and QC blank and replicate samples from the 2012-2013 sampling period were presented in Arnold and others (2016). Data from spike QC samples have not previously been published Data from VOC spike QC data from May 2012-December 2014 are published in this report (see larger work citation) and data release along with an analysis of QC data where detections in field blank samples, variability in replicate samples, and recoveries in VOC spike samples are described for the entire sampling period through the date covered in this report (May 2012-December 2014). Pesticide spike samples and analysis of recoveries will be presented in a later report. There are 42 tables that are part of the larger work citation. There are 9 tables in the text of the larger work citation and 33 external tables included in this data release. The 9 tables not included in the data release are summary tables derived from some of the other 33 tables. Tables in the text include table 1, Appendix 1 tables 1-1 and 1-2; Appendix 2 table 2-1, and Appendix 4 tables 4-1 through 4-6. Tables that are external files are tables 1 through 12; Appendix 4 tables 4-7 through 4-27. This compressed file contains 33 files of groundwater-quality data in ASCII text tab-delimited format and 33 corresponding metadata in xml format for wells sampled for the U.S. Geological Survey National Water-Quality Assessment Project.

Groundwater-quality data were collected from 648 wells as part of the National Water-Quality Assessment Project of the U.S. Geological Survey National Water-Quality Program and are included in this report. Most of the wells (514) were sampled from January through December 2016 and 60 of them were sampled in 2013 and 74 in 2014. The data were collected from seven types of well networks: principal aquifer study networks, which are used to assess the quality of groundwater used for public water supply; land-use study networks, which are used to assess land-use effects on shallow groundwater quality; major aquifer study networks, which are used to assess the quality of groundwater used for domestic supply; enhanced trends networks, which are used to evaluate the time scales during which groundwater quality changes; vertical flow-path study networks, which are used to evaluate changes in groundwater quality from shallow to deeper depths; flow path study networks, which are used to evaluate changes in groundwater quality from shallow to deeper depths over a horizontal distance; and modeling support studies, which are used to provide data to support groundwater modeling. Groundwater samples were analyzed for a large number of water-quality indicators and constituents, including major ions, nutrients, trace elements, volatile organic compounds, pesticides, radionuclides, and some special interest constituents (arsenic speciation, chromium [VI] and perchlorate). These groundwater quality data are tabulated in a U.S. Geological Survey Data Series Report DS-1124 which is available at https://dx.doi.org/XXXXXX and in this data release. Some data from environmental samples collected in 2013-14 and quality-control samples collected in 2012-15 also are included in the associated data release. Data from samples collected in 2016 are associated with networks described in this report and have not been published previously; data from samples collected between 2012 and 2015 are associated with networks described in previous reports in this data series (Arnold and others, 2016a,b, 2017a,b, 2018a,b). There are 23 data tables included in this data release and they are referenced as tables 1-13 and appendix tables 4.10-4.19 in the larger work citation. There are 36 tables that are part of the larger work citation; the 13 tables not included in the data release are summary tables derived from some of the other tables (tables 1.1, 2.2-2.3, 3.1, 4.1-4.9). A version of table 1 is included in both the text and data release. This compressed file contains 23 files of groundwater-quality data in ASCII text tab-delimited format and one corresponding metadata in xml format that describes all the tables and attributes.