The U.S. Geological Survey collected groundwater samples from 49 wells used for domestic and small system drinking water supplies in Amador, Placer, Sutter, and Sacramento Counties, California in 2017. The wells were sampled for the Sacramento Metropolitan (SacMetro) Shallow Aquifer Study Unit of the California State Water Resources Control Board Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project’s assessment of the quality of groundwater resources used for domestic and small system drinking water supplies. Domestic and small-system wells are commonly screened at shallower depths than public-supply wells. The SacMetro study unit consisted of three “study areas” corresponding to three California Department of Water Resources groundwater subbasins: the North American and South American subbasins of the Sacramento Valley groundwater basin, and the Cosumnes subbasin of the San Joaquin Valley groundwater basin. Wells in the SacMetro study unit were in alluvial aquifers composed of sediments derived from the Sierra Nevada Mountains east of the study unit. The study unit was divided into 56 approximately 58 square kilometer grid cells, and a domestic or small-system well was sampled in 49 of those cells. Groundwater samples from all 49 wells were analyzed for field water-quality parameters, volatile organic compounds, pesticides and pesticide degradates, nutrients, major ions and trace elements, arsenic speciation, chromium (VI), perchlorate, gross alpha and gross beta particle activities, sulfur hexafluoride, tritium, carbon-14 in dissolved inorganic carbon, noble gases, stable isotopic ratios of water and dissolved nitrate, and microbial indicators. Groundwater levels were measured in 44 of the 49 wells. All results are presented in this data release, except results for pesticide and pesticide degradates. In 2017, the U.S. Geological Survey National Water-Quality Assessment (NAWQA) Program sampled 22 monitoring wells located in the SacMetro study unit as part of ongoing NAWQA studies of groundwater quality in different land-use settings. Of the 22 wells, 21 were part of an urban land-use network and 1 was part of a rice land use network. Results for analyses of perchlorate, chromium (VI), and stable isotopic ratios are presented in this data release, and results for analyses of field water-quality parameters, volatile organic compounds, pesticide and pesticide degradates, nutrients, major ions and trace elements, dissolved organic carbon, and tritium will be presented in a data release to be published separately by NAWQA. This data release supports the following publication: Groundwater Quality in the Sacramento Metropolitan shallow aquifer, California: U.S. Geological Survey Open-File Report 2019-1047, 4p., https://doi.org/10.3133/ofr20191047.

The U.S. Geological Survey collected groundwater samples from 49 wells used for domestic and small system drinking water supplies in Amador, Placer, Sutter, and Sacramento Counties, California in 2017. The wells were sampled for the Sacramento Metropolitan (SacMetro) Shallow Aquifer Study Unit of the California State Water Resources Control Board Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project’s assessment of the quality of groundwater resources used for domestic and small system drinking water supplies. Domestic and small-system wells are commonly screened at shallower depths than public-supply wells. The SacMetro study unit consisted of three “study areas” corresponding to three California Department of Water Resources groundwater subbasins: the North American and South American subbasins of the Sacramento Valley groundwater basin, and the Cosumnes subbasin of the San Joaquin Valley groundwater basin. Wells in the SacMetro study unit were in alluvial aquifers composed of sediments derived from the Sierra Nevada Mountains east of the study unit. The study unit was divided into 56 approximately 58 square kilometer grid cells, and a domestic or small-system well was sampled in 49 of those cells. Groundwater samples from all 49 wells were analyzed for field water-quality parameters, volatile organic compounds, pesticides and pesticide degradates, nutrients, major ions and trace elements, arsenic speciation, chromium (VI), perchlorate, gross alpha and gross beta particle activities, sulfur hexafluoride, tritium, carbon-14 in dissolved inorganic carbon, noble gases, stable isotopic ratios of water and dissolved nitrate, and microbial indicators. Groundwater levels were measured in 44 of the 49 wells. All results are presented in this data release, except results for pesticide and pesticide degradates. In 2017, the U.S. Geological Survey National Water-Quality Assessment (NAWQA) Program sampled 22 monitoring wells located in the SacMetro study unit as part of ongoing NAWQA studies of groundwater quality in different land-use settings. Of the 22 wells, 21 were part of an urban land-use network and 1 was part of a rice land use network. Results for analyses of perchlorate, chromium (VI), and stable isotopic ratios are presented in this data release, and results for analyses of field water-quality parameters, volatile organic compounds, pesticide and pesticide degradates, nutrients, major ions and trace elements, dissolved organic carbon, and tritium will be presented in a data release to be published separately by NAWQA. This data release supports the following publication: Groundwater Quality in the Sacramento Metropolitan shallow aquifer, California: U.S. Geological Survey Open-File Report 2019-1047, 4p., https://doi.org/10.3133/ofr20191047.

The U.S. Geological Survey collected groundwater samples from 49 wells used for domestic and small system drinking water supplies in Amador, Placer, Sutter, and Sacramento Counties, California in 2017. The wells were sampled for the Sacramento Metropolitan (SacMetro) Shallow Aquifer Study Unit of the California State Water Resources Control Board Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project’s assessment of the quality of groundwater resources used for domestic and small system drinking water supplies. Domestic and small-system wells are commonly screened at shallower depths than public-supply wells. The SacMetro study unit consisted of three “study areas” corresponding to three California Department of Water Resources groundwater subbasins: the North American and South American subbasins of the Sacramento Valley groundwater basin, and the Cosumnes subbasin of the San Joaquin Valley groundwater basin. Wells in the SacMetro study unit were in alluvial aquifers composed of sediments derived from the Sierra Nevada Mountains east of the study unit. The study unit was divided into 56 approximately 58 square kilometer grid cells, and a domestic or small-system well was sampled in 49 of those cells. Groundwater samples from all 49 wells were analyzed for field water-quality parameters, volatile organic compounds, pesticides and pesticide degradates, nutrients, major ions and trace elements, arsenic speciation, chromium (VI), perchlorate, gross alpha and gross beta particle activities, sulfur hexafluoride, tritium, carbon-14 in dissolved inorganic carbon, noble gases, stable isotopic ratios of water and dissolved nitrate, and microbial indicators. Groundwater levels were measured in 44 of the 49 wells. All results are presented in this data release, except results for pesticide and pesticide degradates. In 2017, the U.S. Geological Survey National Water-Quality Assessment (NAWQA) Program sampled 22 monitoring wells located in the SacMetro study unit as part of ongoing NAWQA studies of groundwater quality in different land-use settings. Of the 22 wells, 21 were part of an urban land-use network and 1 was part of a rice land use network. Results for analyses of perchlorate, chromium (VI), and stable isotopic ratios are presented in this data release, and results for analyses of field water-quality parameters, volatile organic compounds, pesticide and pesticide degradates, nutrients, major ions and trace elements, dissolved organic carbon, and tritium will be presented in a data release to be published separately by NAWQA. This data release supports the following publication: Groundwater Quality in the Sacramento Metropolitan shallow aquifer, California: U.S. Geological Survey Open-File Report 2019-1047, 4p., https://doi.org/10.3133/ofr20191047.

The U.S. Geological Survey collected groundwater samples from 44 wells used for domestic and small system drinking water supplies in the western Central Valley, California in 2023. The wells were sampled for the Western Central Valley domestic-supply aquifer study unit of the State Water Resources Control Board Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project’s assessment of the quality of groundwater resources used for domestic and small system drinking water supplies. The study unit consists of two study areas. The western Sacramento Valley study area comprises the Corning, Colusa, Yolo, and Solano subbasins of the Sacramento Valley groundwater basin, and the western San Joaquin Valley study area comprises the East Contra Costa, Tracy, Delta-Mendota, and Westside subbasins of the San Joaquin Valley groundwater basin. The study unit was divided into 49 grid cells and one domestic or small system well was sampled to represent 44 of the grid cells; the remaining 5 grid cells has no accessible wells. Groundwater levels were measured in 28 of 44 wells. Table 1 contains sample and site information. Groundwater samples were analyzed for field water-quality parameters, microbial indicators, volatile organic compounds, pesticides and pesticide degradants, nutrients, major ions and trace elements, hexavalent chromium, perchlorate, per- and polyfluoroalkyl substances (PFAS), stable isotopes, and groundwater age tracers. Results from these analyses are reported in Tables 2 through 8. Tables 9 and 10 report results from quality control samples. This data release contains two supplementary tables that define abbreviations (Table 11) and provide additional context for the information presented in Tables 1 through 10 (Table 12). A zipfile is included containing geospatial data (study unit boundaries, grid cell boundaries, site locations) as shapefiles.

The U.S. Geological Survey collected groundwater samples from 67 wells and 1 spring used for domestic and small system drinking water supplies in Placer, El Dorado, Amador, and Calaveras Counties, California in 2016-2017. The sites were sampled for the Mokelumne, Cosumnes, and American River Watersheds (MCAW) Shallow Aquifer Study Unit of the California State Water Resources Control Board Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project’s assessment of the quality of groundwater resources used for domestic and small system drinking water supplies. Domestic and small-system wells commonly are screened at shallower depths than public-supply wells. The MCAW study unit covered the parts of the Upper Mokelumne, Upper Cosumnes, and South and North Fork American River watersheds [8-digit hydrologic unit codes (HUC8) 18040012, 18040013, 18020129, and 18020128] in the Sierra Nevada hydrogeologic province. Wells in the MCAW study unit generally tap hard-rock aquifer systems composed of volcanic, granitic, or metamorphic rocks. The study unit was divided into equal area grid cells and one well or spring was sampled in each cell. Groundwater samples were analyzed for field water-quality parameters, volatile organic compounds, pesticides and pesticide degradates, nutrients, major ions and trace elements, hexavalent chromium, perchlorate, gross alpha and gross beta particle activities, tritium, carbon-14 in dissolved inorganic carbon, stable isotopic ratios of water and dissolved nitrate, and microbial indicators. These data support the following publication: Fram, M.S., and Shelton, J.L., 2018, Groundwater Quality in the Mokelumne, Cosumnes, and American River Watersheds, Sierra Nevada, California: U.S. Geological Survey Open-File Report 2018-1047, 4p., https://doi.org/10.3133/ofr20181047.

The U.S. Geological Survey collected groundwater samples from 67 wells and 1 spring used for domestic and small system drinking water supplies in Placer, El Dorado, Amador, and Calaveras Counties, California in 2016-2017. The sites were sampled for the Mokelumne, Cosumnes, and American River Watersheds (MCAW) Shallow Aquifer Study Unit of the California State Water Resources Control Board Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project’s assessment of the quality of groundwater resources used for domestic and small system drinking water supplies. Domestic and small-system wells commonly are screened at shallower depths than public-supply wells. The MCAW study unit covered the parts of the Upper Mokelumne, Upper Cosumnes, and South and North Fork American River watersheds [8-digit hydrologic unit codes (HUC8) 18040012, 18040013, 18020129, and 18020128] in the Sierra Nevada hydrogeologic province. Wells in the MCAW study unit generally tap hard-rock aquifer systems composed of volcanic, granitic, or metamorphic rocks. The study unit was divided into equal area grid cells and one well or spring was sampled in each cell. Groundwater samples were analyzed for field water-quality parameters, volatile organic compounds, pesticides and pesticide degradates, nutrients, major ions and trace elements, hexavalent chromium, perchlorate, gross alpha and gross beta particle activities, tritium, carbon-14 in dissolved inorganic carbon, stable isotopic ratios of water and dissolved nitrate, and microbial indicators. These data support the following publication: Fram, M.S., and Shelton, J.L., 2018, Groundwater Quality in the Mokelumne, Cosumnes, and American River Watersheds, Sierra Nevada, California: U.S. Geological Survey Open-File Report 2018-1047, 4p., https://doi.org/10.3133/ofr20181047.

The U.S. Geological Survey collected groundwater samples from 50 wells used for domestic and small system drinking water supplies in Shasta and Tehama Counties, California in 2018-2019. The wells were sampled for the Redding-Red Bluff Shallow Aquifer Study Unit of the California State Water Resources Control Board Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project’s assessment of the quality of groundwater resources used for domestic and small system drinking water supplies. Domestic and small-system wells are commonly screened at shallower depths than public-supply wells. Wells in the study unit generally tap unconsolidated to moderately consolidated coarse and fine-grained sediments derived from the northern Coast Ranges to the west and the Cascade Range to the east. The Redding-Red Bluff Shallow Aquifer study unit included 11 groundwater subbasins of the Sacramento Valley groundwater basin (California Department of Water Resources, 2003) and was divided into two study areas: Redding (Enterprise, Millville, South Battle Creek, Bowman, Rosewood, and Anderson) and Red Bluff (Bend, Antelope, Dye Creek, Los Molinos, and Red Bluff). In each study area, the collective area of all one-mile square sections estimated to contain domestic wells (Johnson and Belitz, 2015) was divided into equal-area grid cells, and a well was sampled in each cell: Redding, twenty-five 48-square kilometer cells, and Red Bluff, twenty-five 43 square kilometer grid cells. Groundwater samples from all 50 wells were analyzed for field water-quality parameters and microbial indicators, volatile organic compounds, pesticides and pesticide degradates, major ions and trace elements, chromium (VI), perchlorate, nutrients, gross alpha and gross beta particle activities, carbon-14 in dissolved inorganic carbon, stable isotopic ratios of water, tritium, sulfur hexafluoride, and noble gases. Groundwater levels were measured in 41 of the 50 wells. All results are presented in this data release, except results for sulfur hexafluoride and noble gases. This data release supports the following publication: Groundwater quality in the Redding-Red Bluff Shallow Aquifer Study Unit of the Northern Sacramento Valley, California: U.S. Geological Survey Fact Sheet 2020–3025, 4 p., https://doi.org/10.3133/fs20203025.

The U.S. Geological Survey collected groundwater samples from 50 wells used for domestic and small system drinking water supplies in Shasta and Tehama Counties, California in 2018-2019. The wells were sampled for the Redding-Red Bluff Shallow Aquifer Study Unit of the California State Water Resources Control Board Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project’s assessment of the quality of groundwater resources used for domestic and small system drinking water supplies. Domestic and small-system wells are commonly screened at shallower depths than public-supply wells. Wells in the study unit generally tap unconsolidated to moderately consolidated coarse and fine-grained sediments derived from the northern Coast Ranges to the west and the Cascade Range to the east. The Redding-Red Bluff Shallow Aquifer study unit included 11 groundwater subbasins of the Sacramento Valley groundwater basin (California Department of Water Resources, 2003) and was divided into two study areas: Redding (Enterprise, Millville, South Battle Creek, Bowman, Rosewood, and Anderson) and Red Bluff (Bend, Antelope, Dye Creek, Los Molinos, and Red Bluff). In each study area, the collective area of all one-mile square sections estimated to contain domestic wells (Johnson and Belitz, 2015) was divided into equal-area grid cells, and a well was sampled in each cell: Redding, twenty-five 48-square kilometer cells, and Red Bluff, twenty-five 43 square kilometer grid cells. Groundwater samples from all 50 wells were analyzed for field water-quality parameters and microbial indicators, volatile organic compounds, pesticides and pesticide degradates, major ions and trace elements, chromium (VI), perchlorate, nutrients, gross alpha and gross beta particle activities, carbon-14 in dissolved inorganic carbon, stable isotopic ratios of water, tritium, sulfur hexafluoride, and noble gases. Groundwater levels were measured in 41 of the 50 wells. All results are presented in this data release, except results for sulfur hexafluoride and noble gases. This data release supports the following publication: Groundwater quality in the Redding-Red Bluff Shallow Aquifer Study Unit of the Northern Sacramento Valley, California: U.S. Geological Survey Fact Sheet 2020–3025, 4 p., https://doi.org/10.3133/fs20203025.

The U.S. Geological Survey collected groundwater samples from 67 wells and 1 spring used for domestic and small system drinking water supplies in Placer, El Dorado, Amador, and Calaveras Counties, California in 2016-2017. The sites were sampled for the Mokelumne, Cosumnes, and American River Watersheds (MCAW) Shallow Aquifer Study Unit of the California State Water Resources Control Board Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project’s assessment of the quality of groundwater resources used for domestic and small system drinking water supplies. Domestic and small-system wells commonly are screened at shallower depths than public-supply wells. The MCAW study unit covered the parts of the Upper Mokelumne, Upper Cosumnes, and South and North Fork American River watersheds [8-digit hydrologic unit codes (HUC8) 18040012, 18040013, 18020129, and 18020128] in the Sierra Nevada hydrogeologic province. Wells in the MCAW study unit generally tap hard-rock aquifer systems composed of volcanic, granitic, or metamorphic rocks. The study unit was divided into equal area grid cells and one well or spring was sampled in each cell. Groundwater samples were analyzed for field water-quality parameters, volatile organic compounds, pesticides and pesticide degradates, nutrients, major ions and trace elements, hexavalent chromium, perchlorate, gross alpha and gross beta particle activities, tritium, carbon-14 in dissolved inorganic carbon, stable isotopic ratios of water and dissolved nitrate, and microbial indicators. These data support the following publication: Fram, M.S., and Shelton, J.L., 2018, Groundwater Quality in the Mokelumne, Cosumnes, and American River Watersheds, Sierra Nevada, California: U.S. Geological Survey Open-File Report 2018-1047, 4p., https://doi.org/10.3133/ofr20181047.

The U.S. Geological Survey collected groundwater samples from 67 wells and 1 spring used for domestic and small system drinking water supplies in Placer, El Dorado, Amador, and Calaveras Counties, California in 2016-2017. The sites were sampled for the Mokelumne, Cosumnes, and American River Watersheds (MCAW) Shallow Aquifer Study Unit of the California State Water Resources Control Board Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project’s assessment of the quality of groundwater resources used for domestic and small system drinking water supplies. Domestic and small-system wells commonly are screened at shallower depths than public-supply wells. The MCAW study unit covered the parts of the Upper Mokelumne, Upper Cosumnes, and South and North Fork American River watersheds [8-digit hydrologic unit codes (HUC8) 18040012, 18040013, 18020129, and 18020128] in the Sierra Nevada hydrogeologic province. Wells in the MCAW study unit generally tap hard-rock aquifer systems composed of volcanic, granitic, or metamorphic rocks. The study unit was divided into equal area grid cells and one well or spring was sampled in each cell. Groundwater samples were analyzed for field water-quality parameters, volatile organic compounds, pesticides and pesticide degradates, nutrients, major ions and trace elements, hexavalent chromium, perchlorate, gross alpha and gross beta particle activities, tritium, carbon-14 in dissolved inorganic carbon, stable isotopic ratios of water and dissolved nitrate, and microbial indicators. These data support the following publication: Fram, M.S., and Shelton, J.L., 2018, Groundwater Quality in the Mokelumne, Cosumnes, and American River Watersheds, Sierra Nevada, California: U.S. Geological Survey Open-File Report 2018-1047, 4p., https://doi.org/10.3133/ofr20181047.