By Kenneth Belitz, Neil M. Dubrovsky, Karen Burow, Bryant Jurgens, and Tyler Johnson
U.S. GEOLOGICAL SURVEY
Water Resources Investigation Report 03-4166
Sacramento, California 2003
The State of California uses more ground water than any other State in the Nation. With a population of over 30 million people, an agricultural economy based on intensive irrigation, large urban industrial areas, and naturally elevated concentrations of some trace elements, there is a wide range of contaminant sources that have the potential to contaminate ground water and limit its beneficial uses. In response to the many-and different-potential sources of ground-water contamination, the State of California has evolved an extensive set of rules and programs to protect ground-water quality, and agencies to implement the rules and programs. These programs have in common a focus on compliance with regulations governing chemical use and (or) ground-water quality. Although appropriate for, and successful at, their specific missions, these programs do not at present provide a comprehensive view of ground-water quality in the State of California.
In October 2001, The California Assembly passed a bill, AB 599, establishing the Ground-Water- Quality Monitoring Act of 2001." The goal of AB 599 is to improve Statewide comprehensive ground-water monitoring and increase availability of information about ground-water quality to the public. AB 599 requires the State Water Resources Control Board (SWRCB), in collaboration with an interagency task force (ITF) and a public advisory committee (PAC), to develop a plan for a comprehensive ground-water monitoring program. AB 599 specifies that the comprehensive program should be capable of assessing each ground-water basin in the State through direct and other statistically reliable sampling approaches, and that the program should integrate existing monitoring programs and design new program elements, as necessary. AB 599 also stresses the importance of prioritizing ground-water basins that provide drinking water.
The United States Geological Survey (USGS), in cooperation with the SWRCB, and in coordination with the ITF and PAC, has developed a framework for a comprehensive ground-water-quality monitoring and assessment program for California. The proposed framework relies extensively on previous work conducted by the USGS through its National Water-Quality Assessment (NAWQA) program. In particular, the NAWQA program defines three types of ground-water assessment: (1) status, the assessment of the current quality of the ground-water resource; (2) trends, the detection of changes in water quality, and (3) understanding, assessing the human and natural factors that affect ground-water quality.
A Statewide, comprehensive ground-water quality-monitoring and assessment program is most efficiently accomplished by applying uniform and consistent study-design and data-collection protocols to the entire State. At the same time, a comprehensive program should be relevant at a variety of scales, and therefore needs to retain flexibility to address regional and local issues. Consequently, many of the program components include a predominant element that will be consistently applied in all basins, and a secondary element that may be applied in specific basins where local conditions warrant attention.
Executive Summary
Hydrogeologic Provinces of California
Ancillary Data
Utility of Existing Data for Ground-Water-Quality Assessment
Network Design
Target Constituents
Trend Assessment
Assessment for Understanding
Prioritization of Basins and Other Study Areas
Scope of the Proposed Comprehensive Monitoring and Assessment Program
Introduction
Objectives and Overview of the Proposed Program
Hydrogeologic Provinces of California
Ancillary Data Needed for a Comprehensive Assessment
Case Study: Using Drillers' Logs from the Modesto Area
Utility of Existing Data for Ground-Water-Quality Assessment
Case Study: MTBE Occurrence in Several Southern California Ground-Water Basins
Network Design
Case Study: Spatially-Distributed, Randomized Well Selection in the Santa Ana Basin
Selection of Target Constituents
Data Collected by Existing Programs
Balancing Spatial Coverage and Analytical Intensity
Iterative Analytical Strategy
Quality Assurance and Quality Control
Trend Assessment
Case Study: Nitrate Concentrations in the San Joaquin Valley
Assessment for Understanding: Relating Water Quality to Human and Natural Factors
Case Study: Tritium, Chloroform and MTBE in the Southern California Coastal Plain
Prioritization of Basins and Other Study Areas
Ranking the Basins
Examine the Location of Highly Ranked Basins
Define the Criteria for Identifying Four Categories of Priority Basins
Apply the Criteria: Priority Study Areas Consisting of Basins
Two Additional Categories Are Identified
Scope of the Proposed Comprehensive Monitoring and Assessment Program
Estimate the Total Number of Samples to be Collected in Priority Basins
Estimate the Total Number of Samples to be Collected in Low-Use Ground-Water Basins
Other Types of Wells that Might be Sampled
Summary
References Cited
Appendix A. Arsenic in the San Joaquin Valley: Evaluating the Utility of Existing Data
Appendix B. Digital Map of Hydrogeologic Provinces
Appendix C. Category 1 Priority Ground-Water Basins, California
Appendix D. Category 2 Priority Ground-Water Basins, California
Appendix E. Category 3 Priority Ground-Water Basins, California
Appendix F. Category 4 Priority Ground-Water Basins, California
Appendix G. Category 6 Low-Use Ground-Water Basins, California
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