Professional Paper 1781
The National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey has been conducting a regional analysis of water quality in the principal aquifer systems in the southwestern United States (hereinafter, “Southwest”) since 2005. Part of the NAWQA Program, the objective of the Southwest Principal Aquifers (SWPA) study is to develop a better understanding of water quality in basin-fill aquifers in the region by synthesizing information from case studies of 15 basins into a common set of important natural and human-related factors found to affect groundwater quality.
The synthesis consists of three major components:
1. Summary of current knowledge about the groundwater systems, and the status of, changes in, and influential factors affecting quality of groundwater in basin-fill aquifers in 15 basins previously studied by NAWQA (this report).
2. Development of a conceptual model of the primary natural and human-related factors commonly affecting groundwater quality, thereby building a regional understanding of the susceptibility and vulnerability of basin-fill aquifers to contaminants.
3. Development of statistical models that relate the concentration or occurrence of specific chemical constituents in groundwater to natural and human-related factors linked to the susceptibility and vulnerability of basin-fill aquifers to contamination.
Basin-fill aquifers occur in about 200,000 mi2 of the 410,000 mi2 SWPA study area and are the primary source of groundwater supply for cities and agricultural communities. Four of the principal aquifers or aquifer systems of the United States are included in the basin-fill aquifers of the study area: (1) the Basin and Range basin-fill aquifers in California, Nevada, Utah, and Arizona; (2) the Rio Grande aquifer system in New Mexico and Colorado; (3) the California Coastal Basin aquifers; and (4) the Central Valley aquifer system in California. Because of the generally limited availability of surface-water supplies in the arid to semiarid climate, cultural and economic activities in the Southwest are particularly dependent on supplies of good-quality groundwater. Irrigation and public-supply withdrawals from basin-fill aquifers in the study area account for about one quarter of the total withdrawals from all aquifers in the United States.
Many factors influence the quality of groundwater in the 15 case-study basins, but some common factors emerge from the basin summaries presented in this report. These factors include the chemical composition of the recharge water, consolidated rock geology and composition of aquifer materials derived from consolidated rock, and land and water use. The major water-quality issues in many of the developed case-study basins are increased concentrations of dissolved solids, nitrate, and VOCs in groundwater as a result of human activities.
The information presented and the citations listed in this report serve as a resource for those interested in the groundwater-flow systems in the NAWQA case-study basins. The summaries of water-development history, hydrogeology, conceptual understanding of the groundwater system under both predevelopment and modern conditions, and effects of natural and human-related factors on groundwater quality presented in the sections on each basin also serve as a foundation for the synthesis and modeling phases of the SWPA regional study.
First posted December 17, 2010
For additional information contact:
Part or all of this report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge.
Thiros, S.A., Bexfield, L.M., Anning, D.W., and Huntington, J.M., eds., 2010, Conceptual understanding and groundwater quality of selected basin-fill aquifers in the Southwestern United States: U.S. Geological Professional Paper 1781, 288 p.
Additional information about this study is available at http://water.usgs.gov/nawqa/studies/praq/swpa/
Conceptual Understanding and Groundwater Quality of Selected Basin-Fill Aquifers in the United States
Section 1.—Background and Study Approach.
Section 2.—Conceptual Understanding and Groundwater Quality of the Basin-Fill Aquifer in Salt Lake Valley, Utah.
Section 3.—Conceptual Understanding and Groundwater Quality of the Basin-Fill Aquifer in Truckee Meadows, Nevada.
Section 4.—Conceptual Understanding and Groundwater Quality of the Basin-Fill Aquifers in Eagle and Carson Valleys, Nevada.
Section 5.—Conceptual Understanding and Groundwater Quality of the Basin-Fill Aquifer in Spanish Springs Valley, Nevada.
Section 6.—Conceptual Understanding and Groundwater Quality of the Basin-Fill Aquifer in Las Vegas Valley, Nevada.
Section 7.—Conceptual Understanding and Groundwater Quality of the Basin-Fill Aquifer in the West Salt River Valley, Arizona.
Section 8.—Conceptual Understanding and Groundwater Quality of the Basin-Fill Aquifer in the Upper Santa Cruz Basin, Arizona.
Section 9.—Conceptual Understanding and Groundwater Quality of the Basin-Fill Aquifer in the Sierra Vista Subbasin of the Upper San Pedro Basin, Arizona.
Section 10.—Conceptual Understanding and Groundwater Quality of the Basin-Fill Aquifer in the San Luis Valley, Colorado and New Mexico.
Section 11.—Conceptual Understanding and Groundwater Quality of the Basin-Fill Aquifer in the Middle Rio Grande Basin, New Mexico
Section 12.—Conceptual Understanding and Groundwater Quality of the Basin-Fill Aquifers in the Santa Ana Basin, California.
Section 13.—Conceptual Understanding and Groundwater Quality of the Basin-Fill Aquifer in the Central Valley, California.