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U.S. GEOLOGICAL SURVEY
Data Series 285 (ver 1.1, August 2018)

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Introduction

The U.S. Geological Survey (USGS) is collaborating with the California State Water Resources Control Board (hereinafter, referred to in its abbreviated form as the State Water Board), and partnering with the California Department of Health Services (CADHS) and Lawrence Livermore National Laboratory (LLNL), in the implementation of the GAMA Program. The GAMA Program was developed in response to the Ground-Water Quality Monitoring Act of 2001 (Sections 10780-10782.3 of the Water Code) and addresses a growing concern about ground-water quality throughout the state of California. The program has three main objectives: (1) status—assess the current quality of the ground-water resource; (2) trends—detect changes in ground-water quality; and (3) understanding—identify the natural and human factors affecting ground-water quality (Kulongoski and Belitz, 2004).

To achieve the program goals, the USGS developed a systematic approach to sampling (Belitz and others, 2003, http://water.usgs.gov/pubs/wri/wri034166/) that will provide a comprehensive, unbiased, spatially distributed assessment of statewide ground-water quality. This was achieved through the development of a randomized well-selection routine within a grid framework that covers distinct study areas. Samples collected by the GAMA Program must be representative of the wide range of geologic, hydrologic, and climatic conditions found within the state of California (Belitz and others, 2003). On the basis of these conditions, the state has been separated into 10 hydrogeologic provinces (fig. 1), each with its own distinct physical and geographic characteristics. Each province contains ground-water basins primarily composed of unconsolidated deposits of alluvial or volcanic origin (California Department of Water Resources, 2003). Eighty percent of public-supply wells in the state of California were located within ground-water basins, whereas the other 20 percent were located in relatively low permeability hard rock areas. The GAMA Program will provide a full assessment of the quality of ground-water used for drinking-water supply within each area of the state. Analysis of a broad suite of chemical constituents at detection levels lower than those currently required by CADHS will result in a database that can aid in the early identification and understanding of contamination issues throughout the state.

Purpose and Scope

The purpose of this report is to present the analytical results and quality-control (QC) analyses for organic, inorganic, and microbial constituents, and general water-quality parameters for ground-water samples collected from 83 wells in the Southern Sacramento Valley GAMA study unit (figs. 2 and 3). A total of 87 samples were collected from public-supply, domestic, irrigation, and monitoring wells. Sampled wells were located in Placer, Sacramento, Solano, Sutter, and Yolo counties, and water samples were collected between March 2005 and June 2005 (fig. 3). General water-quality parameters measured included alkalinity, dissolved oxygen (DO), pH, specific conductance (SC), and water temperature. Chemical constituents analyzed included 88 volatile organic compounds (VOCs), 118 pesticides, 5 nutrients, dissolved organic carbon (DOC), 9 major ions, 25 trace elements, 4 constituents of special interest (N-nitrosodimethylamine [NDMA], 1,2,3-trichloropropane, chromium(VI), and perchlorate), 8 isotopic constituents, 5 dissolved noble gases, and the microbial constituents coliform and coliphage. Detections of regulated constituents in samples collected for this program do not represent the quality of water delivered to consumers; after withdrawal from the ground, water typically is treated, disinfected, and (or) blended with other waters to maintain water quality. Regulatory 
thresholds apply to treated water, not to raw ground water.

Acknowledgments

The authors want to thank the State Water Board who funded and supported this study. We thank the following partners for their support: California Department of Health Services, California Department of Water Resources, and Lawrence Livermore National Laboratory. We also thank the well owners and water purveyors for their generosity in 
allowing the USGS to collect samples from their wells.

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