The U.S. Geological Survey collected groundwater samples from 71 wells used for domestic and small system drinking water supplies in Stanislaus and Merced counties of California during 2020-2021. The wells were sampled for the Modesto-Turlock-Merced 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 was defined by the extent of the Modesto, Turlock, and Merced subbasins of the San Joaquin Valley groundwater basin. The study unit was divided into 62 grid cells and one or more domestic or small system well was sampled in 60 of the cells. Groundwater samples from a total of 71 sampled wells were analyzed for field water-quality parameters, volatile organic compounds, pesticides and pesticide degradants, stable isotopes of water, nutrients, major ions and trace elements, hexavalent chromium, perchlorate, per- and polyfluoroalkyl substances (PFAS), and microbial indicators. Groundwater levels were measured in 56 out 71 wells.
|Title||Groundwater-quality data in the Modesto-Turlock-Merced Domestic-Supply Aquifer Study Unit, 2020-2021: Results from the California GAMA Priority Basin Project|
|Authors||Mariia Balkan, Zeno F Levy, Danielle I Dupuy, Jennifer L Shelton, Elise Watson, Tyler Johnson|
|Product Type||Data Release|
|Record Source||USGS Digital Object Identifier Catalog|
|USGS Organization||California Water Science Center|
Quality of groundwater used for domestic supply in the Modesto, Turlock, and Merced Subbasins of the San Joaquin Valley, California
Quality of groundwater used for domestic supply in the Modesto, Turlock, and Merced Subbasins of the San Joaquin Valley, CaliforniaSummary More than 2 million Californians rely on groundwater from privately owned domestic wells for drinking-water supply. This report summarizes a water-quality survey of domestic and small-system drinking-water supply wells in the Modesto, Turlock, and Merced subbasins of the San Joaquin Valley where more than 78,000 residents are estimated to use privately owned domestic wells. Results indicat