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Groundwater Data & Monitoring

Southern Region
Groundwater Quality Monitoring

Groundwater quality data consisting primarily of inorganic mineral analyses are available for more than 18,000 wells. There are about 88,000 analyses made by the Department and other agencies during 1900 to 1991. These data are organized by State Well Number.

Water Quality Evaluations

Program Overview

Under this program, technical assessments are conducted that provide unique and consistent information on the status, trends, and causes of groundwater and surface water quality conditions.

The program complements the Department's water supply planning programs by providing a cohesive framework to examine quality aspects of water resources. Interpretive and technical information is provided, and coordination is maintained with other State, federal, and local agencies. Assessment of water quality conditions and trends is an integral part of the Department's overall mission to protect, conserve, develop, and manage the water resources of California.


The water quality evaluation and advisory activities of this program started in 1950 with the Dickey Water Pollution Act, which gave the Department responsibility to investigate quality conditions of the State's water resources. The Porter-Cologne Water Quality Control Act and subsequent federal and State acts have reaffirmed the Department's water quality role in the area of water resource protection, planning, and management.


Quality considerations have consequential effects on the quantity of water available for use. Therefore, it is appropriate that the Department exercise its responsibility to assess water quality conditions and provide sound, consistent information that can be used for protection and management of the resource. The information developed in this program, which is made available to water agencies, policy makers, and the public, gives a scientific basis for understanding, making decisions, and evaluating the effectiveness of water quality management plans. By providing for coordination with the Regional Water Quality Control Boards, the program ensures that appropriate regulatory measures are enacted to protect the State's water supply.


   To assess the status, trends, and causes of quality conditions of surface and groundwater supplies of the State, pursuant to the Department's responsibilities specified in Water Code Section 229, and to incorporate water quality considerations into water resource management plans.

   To assist agencies in identifying water quality conditions and developing solutions to problems.

   To provide advice, in accordance with the Department's needs, to Regional Water Quality Control Boards for use in formulating water quality control plans and in prescribing controls for significant waste discharges that may affect receiving water supplies.

Water Quality Assessments

Regional, subregional, and local water quality assessments are conducted on a continuing basis by the Southern District in response to the needs of the Department and other government agencies. This information provides an improved scientific basis not only for evaluating the effectiveness of water quality management programs, but also for predicting the likely effects of contemplated changes in land and water management practices. Assessments are closely coordinated with other State, federal, and local agencies to reduce duplication of efforts, ensure proper distribution of information, and ensure that assessments of high priority are undertaken.

The assessments: (1) describe current water quality conditions on a watershed basis and in problem areas, (2) define long-term trends or lack of trends in water quality, and (3) identify, describe, and explain, as possible, the major factors that affect observed quality conditions and trends.

Each watershed assessment consists of two to three years of intensive data collection, interpretation, and analysis, followed by a year to complete a report on the findings.

These assessments consist of: (1) reviewing previous studies; (2) collecting, compiling, screening, and interpreting available water quality data; (3) defining data needs and taking and analyzing water samples; (4) using a GIS to query and present the information; (5) assessing hydrologic and hydrogeologic conditions; (6) making a statistical evaluation of quality conditions and trends; (7) determining sources of quality impairment; and (8) preparing a report in a format suitable for posting on the Internet, as well as in hardcopy.

Water Quality Reports

   Water Resources of the Arroyo Grande - Nipomo Mesa Area, 2002

For further information contact:

Bob Pierotti
Phone: 818 500-1645 x238