California's Central Valley

Delta-Mendota Canal: Water Quality Data

Groundwater is being sampled at many locations across California in order to characterize its constituents and identify trends in groundwater quality by the Groundwater Ambient Monitoring and Assessment (GAMA) Program. As part of this program, the following wells are being sampled:

  • 29 grid wells in Delta-Mendota area
  • 10 grid wells in Westside study area
  • 19 understanding wells, including 15 monitoring wells in 6 well clusters (5 of these include 13 wells from this study) and 4 other wells that were domestic, irrigation, or public-supply wells
Map of San Joaquin Valley GAMA Wells

For more Central Valley water quality data, please visit the following links:

Central Valley Water Quality Publications

National Water-Quality Assessment (NAWQA) Program

In 1991, the U.S. Geological Survey began a full-scale National Water-Quality Assessment (NAWQA) Program, to address the need for consistent and scientifically sound information for managing the Nation's water resources. This program is unique compared to other national water-quality assessment studies in that it integrates the monitoring of the quality of surface- and ground-waters with the study of aquatic ecosystems.

USGS NAWQA study units in the Central Valley:

San Joaquin Valley

Sacramento Valley

Delta-Mendota Canal Study

Study Home

Land Subsidence

Goundwater Model

Water Quality

Well Sites


Sneed, M., Brandt, J., Solt, M., 2013,Land Subsidence along the Delta-Mendota Canal in the Northern Part of the San Joaquin Valley, California, 2003-10: U.S. Geological Survey Scientific Investigations Report 2013-5142, 87 p.

Faunt, Claudia C. (editor), 2009,Groundwater Availability of the Central Valley Aquifer, California: U.S. Geological Survey Professional Paper 1766, 227 p.


Groundwater  Claudia Faunt

Phone  619.225.6142


Subsidence  Michelle Sneed

Phone  916.278.3000



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U.S. Bureau of Reclamation

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San Luis & Delta-Mendota Water Authority