This data release codifies and attributes explanatory factors that could potentially impact groundwater quality at 142 groundwater sites (wells or developed springs) used for domestic water supply and 310 groundwater sites used for public water supply in the northern Sierra Nevada foothills. Water quality from domestic groundwater sites was assessed as part of the California State Water Resources Control Board’s Groundwater Ambient Monitoring and Assessment (GAMA) program in 2015-2017. Domestic groundwater sites from two of the U.S. Geological Survey’s Priority Basin Project Shallow Aquifer Assessment study units are attributed here: The Yuba-Bear Watersheds (YBW) study unit (sampled in 2015-2016) and the American-Cosumnes-Mokelumne Watersheds (ACMW) study unit (sampled in 2016-2017). The YBW and ACMW study units include domestic well and spring sites within watersheds overlying fractured rock aquifer systems of the Sierra Nevada hydrogeologic province of California in Nevada, Yuba, Sierra, Placer, El Dorado, Amador, and Calaveras Counties. Study design and site selection for the YBW and ACMW study units are detailed by Jasper and others (2017) and Shelton and others (2018), respectively.

Potential explanatory factors are attributed to domestic groundwater sites relating to: aquifer lithology, land use (percent agricultural, urban, and natural land use), underground storage and septic tank densities, hydrologic conditions (aridity index, elevation of the groundwater site), well construction (well depth, depth to the top of the open or perforated interval, well depth classification), groundwater age classification, geochemical condition (pH, dissolved oxygen, groundwater redox classification), recharge condition (deuterium-excess, normalized recharge temperature), and saturation indices (Langelier saturation index, calcite saturation index). A subset of these potential explanatory variables (aquifer lithology, land use, elevation of the groundwater site) were attributed to 310 public groundwater sites within the YBW and ACMW study units that were used to compare the quality of groundwater resources used for domestic and public supply. This data release contains a tab-delimited text file containing locations and potential explanatory factors for domestic groundwater sites (Table 1), a tab-delimited text file containing locations and potential explanatory factors for public groundwater sites (Table 2), and a tab-delimited text file containing explanations for abbreviations used in this data release (Table 3). Additionally, an extensible markup language (XML) metadata file is included detailing process steps and references for attribution of potential explanatory factors to the groundwater sites.

Jasper, M., Bennett, G.L., and Fram, M.S., 2017, Groundwater-Quality Data in the Yuba and Bear Watersheds Shallow Aquifer Study Unit, 2015-2016: Results from the California GAMA Priority Basin Project: U.S. Geological Survey data release, https://doi.org/10.5066/F73F4MS9.

Shelton, J.L., Fram, M.S., Goldrath, D.A., Bennett, G.L., V, and Jasper, M., 2018, Groundwater-quality data in the Mokelumne, Cosumnes, and American River Watersheds Shallow Aquifer Study Unit, 2016-2017: Results from the California GAMA Priority Basin Project: U.S. Geological Survey data release, https://doi.org/10.5066/F78G8JXP.

Levy, Z.F., and Fram, M.S., 2021, Status and understanding of groundwater quality in the northern Sierra Nevada foothills domestic-supply aquifer study units, 2015–17—California GAMA Priority Basin Project: U.S. Geological Survey Scientific Investigations Report 2021–5019, 120 p., https://doi.org/10.3133/sir20215019.