From July through November 2018, 48 environmental samples and four quality-control samples were collected throughout the Lower Hudson, Chemung, and Eastern Lake Ontario River Basins. Samples were collected from seven production wells and eight domestic wells in the Eastern Lake Ontario Basin, 13 production wells and 12 domestic wells in the Lower Hudson River Basin, and four production wells and four domestic wells in the Chemung River Basin. Of the wells sampled, 27 were completed in bedrock and 21 were completed in sand and gravel. Approximately 20 percent of samples were collected from wells that were previously sampled in 2003, 2008, and 2013. Groundwater samples were collected prior to any treatment or filtration systems, from existing domestic and production wells equipped with permanently installed pumps. Samples were collected and processed using standard USGS methods and were analyzed for 372 constituents including physicochemical properties, dissolved gases, major ions, nutrients, trace elements, pesticides, volatile organic compounds (VOCs), radiological activity, and indicator bacteria. All analytes are listed in the data release, along with the associated method detection and reporting limits, some of which changed over time. About 68 percent of constituents analyzed were not detected at concentrations greater than the method detection limit. Samples were analyzed at the USGS National Water Quality Laboratory (NWQL) in Denver, Colorado, and other certified laboratories following published methods. Quality assurance and quality control samples were collected and assessed in each of the sampled basins. In the Lower Hudson River Basin, one replicate was collected at well U4469 and analyzed for all constituents. A replicate analyzed for dissolved gases, radiological activity, and indicator bacteria was collected at well SV4356, as was a field blank analyzed for organics and inorganics. In the Chemung River Basin, one replicate was collected at well SB392 and analyzed for all constituents. In the Eastern Lake Ontario Basin, a replicate analyzed for dissolved gases, radiological activity, and indicator bacteria was collected at OW622, as was a field blank analyzed for organics and inorganics. The VOC 1,2,4-Trimethylbenzene was detected in blank samples and most of the groundwater samples, and contamination is suspected from the scintillation liquid in the radon sampling kits. Due to the potential for contamination bias, results for 1,2,4-Trimethylbenzene are not included.

This data release contains analytical results from 52 groundwater samples and six quality assurance and quality control samples collected from western New York and the Mohawk River basin. Samples were collected between July and September, 2021 from 11 production wells and 10 domestic wells in the Mohawk River basin, and 15 production wells and 16 domestic wells in western New York. Of the total wells sampled, 25 were completed in bedrock and 27 were completed in sand and gravel. Samples were collected prior to any treatment or filtration systems, from existing domestic and production wells equipped with permanently installed pumps. Samples were collected and processed using standard USGS methods (see References.csv) and were analyzed for constituents including physicochemical properties, dissolved gases, major ions, nutrients, trace elements, pesticides, volatile organic compounds (VOCs), radiological activity, and indicator bacteria. All analytes are listed with the associated method detection and reporting limits. Samples were analyzed at the USGS National Water Quality Laboratory (NWQL) in Denver, Colorado, and other certified laboratories following published methods (see References.csv).

From May to December 2017, 48 environmental samples and six quality control samples were collected throughout the Upper Hudson and Central New York River Basins. Samples were collected from nine production wells and 11 domestic wells in the Upper Hudson River Basin, and 14 production wells and 14 domestic wells in the Central New York River Basin. Of the total wells sampled, 22 were completed in bedrock and 26 were completed in sand and gravel. Approximately 20 percent of samples were collected from wells that were previously sampled as in 2007 and 2012. Groundwater samples were collected prior to any treatment or filtration systems, from existing domestic and production wells equipped with permanently installed pumps. Samples were collected and processed using standard USGS methods and were analyzed for 372 constituents including physicochemical properties, dissolved gases, major ions, nutrients, trace elements, pesticides, volatile organic compounds (VOCs), radiological activity, and indicator bacteria. All analytes are listed in the data release, along with the associated method detection and reporting limits, some of which changed over time. About 73 percent of constituents analyzed were not detected at concentrations greater than the method detection limit. Samples were analyzed at the USGS National Water Quality Laboratory (NWQL) in Denver, Colorado, and other certified laboratories following published methods. Quality assurance and quality control samples were collected and assessed in each of the sampled basins. In the Upper Hudson River Basin, one replicate was collected at well SA1091, and in the Central New York River Basin, one replicate was collected at well OW1677, and both were analyzed for all constituents. Replicates analyzed for dissolved gases, radionuclides, and indicator bacteria were collected at well RE4784 of the Upper Hudson River Basin and well OT1821 of the Central New York River Basin. Field blanks analyzed for major ions, dissolved solids, nutrients, organic carbon, trace elements, pesticides, and VOCs were collected at well OT1821 and well RE4784. The VOC 1,2,4-Trimethylbenzene was detected in blank samples and most of the groundwater samples, and contamination is suspected from the scintillation liquid in the radon sampling kits. Due to the potential for contamination bias, results for 1,2,4-Trimethylbenzene are not included.

From May to December 2017, 48 environmental samples and six quality control samples were collected throughout the Upper Hudson and Central New York River Basins. Samples were collected from nine production wells and 11 domestic wells in the Upper Hudson River Basin, and 14 production wells and 14 domestic wells in the Central New York River Basin. Of the total wells sampled, 22 were completed in bedrock and 26 were completed in sand and gravel. Approximately 20 percent of samples were collected from wells that were previously sampled as in 2007 and 2012. Groundwater samples were collected prior to any treatment or filtration systems, from existing domestic and production wells equipped with permanently installed pumps. Samples were collected and processed using standard USGS methods and were analyzed for 372 constituents including physicochemical properties, dissolved gases, major ions, nutrients, trace elements, pesticides, volatile organic compounds (VOCs), radiological activity, and indicator bacteria. All analytes are listed in the data release, along with the associated method detection and reporting limits, some of which changed over time. About 73 percent of constituents analyzed were not detected at concentrations greater than the method detection limit. Samples were analyzed at the USGS National Water Quality Laboratory (NWQL) in Denver, Colorado, and other certified laboratories following published methods. Quality assurance and quality control samples were collected and assessed in each of the sampled basins. In the Upper Hudson River Basin, one replicate was collected at well SA1091, and in the Central New York River Basin, one replicate was collected at well OW1677, and both were analyzed for all constituents. Replicates analyzed for dissolved gases, radionuclides, and indicator bacteria were collected at well RE4784 of the Upper Hudson River Basin and well OT1821 of the Central New York River Basin. Field blanks analyzed for major ions, dissolved solids, nutrients, organic carbon, trace elements, pesticides, and VOCs were collected at well OT1821 and well RE4784. The VOC 1,2,4-Trimethylbenzene was detected in blank samples and most of the groundwater samples, and contamination is suspected from the scintillation liquid in the radon sampling kits. Due to the potential for contamination bias, results for 1,2,4-Trimethylbenzene are not included.

From July through December 2016, 56 environmental samples were collected from the Mohawk and Western New York River Basins. Samples were collected from nine production wells and 13 domestic wells in the Mohawk River Basin, and 17 production wells and 17 domestic wells in the Western New York River Basins. Samples were collected and processed using standard USGS methods and analyzed for 320 constituents including physicochemical properties, dissolved gases, major ions, nutrients, trace elements, pesticides, volatile organic compounds, radionuclides, and indicator bacteria. Analytical methods are described and referenced in Gaige and others (2023). Five of the Mohawk River Basin wells (HE 622, HE 624, OE1468, SA1501, and MT 406) were also sampled in 2002, 2006, and (or) 2011. Seven of the Western New York River Basins wells (AG 265, CU2131, E1903, E1904, GS 216, WO 351, and OL 19) were also sampled in 2006 and (or) 2011. Results from these wells and years are tabulated for comparison.

From July through December 2016, 56 environmental samples were collected from the Mohawk and Western New York River Basins. Samples were collected from nine production wells and 13 domestic wells in the Mohawk River Basin, and 17 production wells and 17 domestic wells in the Western New York River Basins. Samples were collected and processed using standard USGS methods and analyzed for 320 constituents including physicochemical properties, dissolved gases, major ions, nutrients, trace elements, pesticides, volatile organic compounds, radionuclides, and indicator bacteria. Analytical methods are described and referenced in Gaige and others (2023). Five of the Mohawk River Basin wells (HE 622, HE 624, OE1468, SA1501, and MT 406) were also sampled in 2002, 2006, and (or) 2011. Seven of the Western New York River Basins wells (AG 265, CU2131, E1903, E1904, GS 216, WO 351, and OL 19) were also sampled in 2006 and (or) 2011. Results from these wells and years are tabulated for comparison.

From July to November 2019, 48 environmental samples and four quality assurance and quality control samples were collected throughout the Lake Champlain and Susquehanna River Basins. Samples were collected from 10 production wells and nine domestic wells in the Lake Champlain Basin, and 14 production wells and 15 domestic wells in the Susquehanna River Basin. Of the total wells sampled, 24 were completed in bedrock and 24 were completed in sand and gravel. Approximately 20 percent of samples were collected from wells that previously have been sampled as part of this study in 2005, 2009, and 2014. Groundwater samples were collected prior to any treatment or filtration systems, from existing domestic and production wells equipped with permanently installed pumps. Samples were collected and processed using standard USGS methods and were analyzed for 364 constituents including physicochemical properties, dissolved gases, major ions, nutrients, trace elements, pesticides, volatile organic compounds (VOCs), radiological activity, and indicator bacteria. All analytes are listed in the data release, along with the associated method detection and reporting limits, some of which changed over time. About 73 percent of constituents analyzed were not detected at concentrations greater than the method detection limit. Samples were analyzed at the USGS National Water Quality Laboratory (NWQL) in Denver, Colorado, and other certified laboratories following published methods. Quality assurance and quality control samples were collected and assessed in each of the sampled basins. In the Susquehanna River Basin, a replicate was collected at well SY1363, and in the Lake Champlain Basin a replicate was collected at well W1616, and both were analyzed for all constituents. An equipment blank and field blank were also analyzed for all constituents. The VOC 1,2,4-Trimethylbenzene was detected in the blank samples and all the groundwater samples, and contamination is suspected from the scintillation liquid in the radon sampling kits. Due to the potential for contamination bias, results for 1,2,4-Trimethylbenzene are not included.

From July to November 2019, 48 environmental samples and four quality assurance and quality control samples were collected throughout the Lake Champlain and Susquehanna River Basins. Samples were collected from 10 production wells and nine domestic wells in the Lake Champlain Basin, and 14 production wells and 15 domestic wells in the Susquehanna River Basin. Of the total wells sampled, 24 were completed in bedrock and 24 were completed in sand and gravel. Approximately 20 percent of samples were collected from wells that previously have been sampled as part of this study in 2005, 2009, and 2014. Groundwater samples were collected prior to any treatment or filtration systems, from existing domestic and production wells equipped with permanently installed pumps. Samples were collected and processed using standard USGS methods and were analyzed for 364 constituents including physicochemical properties, dissolved gases, major ions, nutrients, trace elements, pesticides, volatile organic compounds (VOCs), radiological activity, and indicator bacteria. All analytes are listed in the data release, along with the associated method detection and reporting limits, some of which changed over time. About 73 percent of constituents analyzed were not detected at concentrations greater than the method detection limit. Samples were analyzed at the USGS National Water Quality Laboratory (NWQL) in Denver, Colorado, and other certified laboratories following published methods. Quality assurance and quality control samples were collected and assessed in each of the sampled basins. In the Susquehanna River Basin, a replicate was collected at well SY1363, and in the Lake Champlain Basin a replicate was collected at well W1616, and both were analyzed for all constituents. An equipment blank and field blank were also analyzed for all constituents. The VOC 1,2,4-Trimethylbenzene was detected in the blank samples and all the groundwater samples, and contamination is suspected from the scintillation liquid in the radon sampling kits. Due to the potential for contamination bias, results for 1,2,4-Trimethylbenzene are not included.

This data release contains analytical results from 52 groundwater samples and six quality assurance and quality control samples collected from the Delaware, Genesee, and St. Lawrence River basins. Samples were collected between June and September, 2020 from six production wells and five domestic wells in the Delaware River basin, seven production wells and 10 domestic wells in the Genesee River basin, and 13 productions wells and 11 domestic wells in the St. Lawrence River basin. Of the total wells sampled, 33 were completed in bedrock and 19 were completed in sand and gravel. Samples were collected prior to any treatment or filtration systems, from existing domestic and production wells equipped with permanently installed pumps. Samples were collected and processed using standard USGS methods (see References.csv) and were analyzed for constituents including physicochemical properties, dissolved gases, major ions, nutrients, trace elements, pesticides, volatile organic compounds (VOCs), radiological activity, and indicator bacteria. All analytes are listed with the associated method detection and reporting limits. Samples were analyzed at the USGS National Water Quality Laboratory (NWQL) in Denver, Colorado, and other certified laboratories following published methods (see References.csv).

In June and July of 2020, 45 groundwater wells in McHenry County, Illinois, were sampled for water quality (field properties, major ions, nutrients, and trace metals) and 12 wells were sampled for contaminants of emerging concern (pharmaceuticals, pesticides, and wastewater indicator compounds). Quality-assurance and quality-control samples were collected during the June and July 2020 sampling that included equipment blanks, field blanks, and replicates. The results of these samples were used to understand the sources of bias and variability associated with sample collection, processing, storage, and shipping. This data release contains one comma separated values files containing the results of the quality-control sample collection for general water quality (metals, nutrients, and major ions) and contaminants of emerging concern (wastewater indicator compounds and pharmaceuticals). Water-quality data from the associated groundwater monitoring well data are available at the National Water Information System (NWIS) web database (https://doi.org/10.5066/F7P55KJN). Results and discussion of the water quality and contaminants of emerging concern can also be found in the associated scientific investigation report referenced.