Framework for a Ground-Water Quality Monitoring and Assessment Program for California

By Kenneth Belitz, Neil M. Dubrovsky, Karen Burow, Bryant Jurgens, and Tyler Johnson



Water Resources Investigation Report 03-4166

Sacramento, California 2003

Prepared in cooperation with

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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


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


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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