This data release codifies and attributes explanatory variables that could potentially influence groundwater quality at 50 groundwater wells used for domestic water supply and 43 groundwater sites used for public water supply in the U.S. Geological Survey’s Priority Basin Project Redding-Red Bluff shallow aquifer (NSV-SA) study unit in 2018-2019 and Northern Sacramento Valley public-supply (NSV-PA) study unit in 2007, respectively. Water quality from domestic and public-supply groundwater sites was assessed as part of the California State Water Resources Control Board’s Groundwater Ambient Monitoring and Assessment (GAMA) program. The NSV-SA and NSV-PA study units include domestic and public-supply wells within sedimentary aquifers of the Central Valley province of California in Shasta and Tehama Counties. Study design and site selection for the NSV-SA and NSV-PA study units are detailed by Shelton and others (2020) and Bennett and others (2007), respectively. Potential explanatory factors are attributed to groundwater sites relating to: aquifer lithology, land use (percent agricultural, urban, and natural land use), septic tank and underground storage densities, distance to geothermal sites, hydrologic conditions (aridity index, elevation of the groundwater site), well construction (well depth, depth to the top of the open or perforated interval), groundwater age (tritium, carbon-14 and age classification), geochemical condition (pH, dissolved oxygen, groundwater redox classification). 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 data dictionary. These data support the following publications: Harkness, J.S.., 2022, Status and understanding of groundwater quality in the northern Sacramento Valley domestic-supply aquifer study unit, 2018–19—California GAMA Priority Basin Project: U.S. Geological Survey Scientific Investigations Report