The U.S. Geological Survey collected groundwater samples from 49 wells used for domestic and small system drinking water supplies and 10 monitoring wells in San Bernardino County, California in 2018. The wells were sampled for the Mojave Basin (MOBS) 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 MOBS study unit covered the Upper, Middle, and Lower Mojave River groundwater basins, the El Mirage groundwater basin, and part of the Harper groundwater basin [California Department of Water Resources, CA DWR basin designations 6-42, 6-41, 6-40, 6-43, 6-47] in the Desert hydrogeologic province (California Department of Water Resources, 2003; Johnson and Belitz, 2003). Wells in the MOBS study unit generally tap unconsolidated alluvial aquifers composed of sediment eroded from granitic and metamorphic rocks, with portions of aquifer material in the northeast part of the study unit eroded from volcanic rock. The MOBS study unit was divided into two study areas, the floodplain study area along the course of the Mojave River, and the regional study area covering the rest of the study unit. The study areas were further divided into equal area grid cells, with 35 grid cells of 85 square-kilometers each in the regional study area, and 15 grid cells of 29 square-kilometers in the floodplain study area. Domestic or small-system wells were sampled in 48 of the 50 grid cells. The 11 understanding wells (10 monitoring wells and 1 domestic well) were selected to provide additional data for evaluation of the effect of septic systems on groundwater resources used for domestic drinking water supply. 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, noble gases, tritium, carbon-14 in dissolved inorganic carbon, stable isotopic ratios of water and dissolved nitrate, and microbial indicators. Groundwater levels were measured in nearly all of the sampled wells. All results are presented in this data release, except results for pesticide and pesticide degradates, sulfur hexafluoride, and noble gases.

The U.S. Geological Survey collected groundwater samples from 49 wells used for domestic and small system drinking water supplies and 10 monitoring wells in San Bernardino County, California in 2018. The wells were sampled for the Mojave Basin (MOBS) 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 MOBS study unit covered the Upper, Middle, and Lower Mojave River groundwater basins, the El Mirage groundwater basin, and part of the Harper groundwater basin [California Department of Water Resources, CA DWR basin designations 6-42, 6-41, 6-40, 6-43, 6-47] in the Desert hydrogeologic province (California Department of Water Resources, 2003; Johnson and Belitz, 2003). Wells in the MOBS study unit generally tap unconsolidated alluvial aquifers composed of sediment eroded from granitic and metamorphic rocks, with portions of aquifer material in the northeast part of the study unit eroded from volcanic rock. The MOBS study unit was divided into two study areas, the floodplain study area along the course of the Mojave River, and the regional study area covering the rest of the study unit. The study areas were further divided into equal area grid cells, with 35 grid cells of 85 square-kilometers each in the regional study area, and 15 grid cells of 29 square-kilometers in the floodplain study area. Domestic or small-system wells were sampled in 48 of the 50 grid cells. The 11 understanding wells (10 monitoring wells and 1 domestic well) were selected to provide additional data for evaluation of the effect of septic systems on groundwater resources used for domestic drinking water supply. 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, noble gases, tritium, carbon-14 in dissolved inorganic carbon, stable isotopic ratios of water and dissolved nitrate, and microbial indicators. Groundwater levels were measured in nearly all of the sampled wells. All results are presented in this data release, except results for pesticide and pesticide degradates, sulfur hexafluoride, and noble gases.

The U.S. Geological Survey collected groundwater samples from 49 wells used for domestic and small system drinking water supplies and 10 monitoring wells in San Bernardino County, California in 2018. The wells were sampled for the Mojave Basin (MOBS) 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 MOBS study unit covered the Upper, Middle, and Lower Mojave River groundwater basins, the El Mirage groundwater basin, and part of the Harper groundwater basin [California Department of Water Resources, CA DWR basin designations 6-42, 6-41, 6-40, 6-43, 6-47] in the Desert hydrogeologic province (California Department of Water Resources, 2003; Johnson and Belitz, 2003). Wells in the MOBS study unit generally tap unconsolidated alluvial aquifers composed of sediment eroded from granitic and metamorphic rocks, with portions of aquifer material in the northeast part of the study unit eroded from volcanic rock. The MOBS study unit was divided into two study areas, the floodplain study area along the course of the Mojave River, and the regional study area covering the rest of the study unit. The study areas were further divided into equal area grid cells, with 35 grid cells of 85 square-kilometers each in the regional study area, and 15 grid cells of 29 square-kilometers in the floodplain study area. Domestic or small-system wells were sampled in 48 of the 50 grid cells. The 11 understanding wells (10 monitoring wells and 1 domestic well) were selected to provide additional data for evaluation of the effect of septic systems on groundwater resources used for domestic drinking water supply. 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, noble gases, tritium, carbon-14 in dissolved inorganic carbon, stable isotopic ratios of water and dissolved nitrate, and microbial indicators. Groundwater levels were measured in nearly all of the sampled wells. All results are presented in this data release, except results for pesticide and pesticide degradates, sulfur hexafluoride, and noble gases.

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 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 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 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.