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

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: