Conceptual Understanding and Groundwater Quality of the Basin-Fill Aquifers in the Santa Ana Basin, California
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Section 12.—Conceptual Understanding and Groundwater Quality of the Basin-Fill Aquifers in the Santa Ana Basin, California By Susan A. Thiros in Conceptual Understanding and Groundwater Quality of Selected Basin- Fill Aquifers in the Southwestern United States Edited by Susan A. Thiros, Laura M. Bexfield, David W. Anning, and Jena M. Huntington National Water-Quality Assessment Program Professional Paper 1781 U.S. Department of the Interior U.S. Geological Survey ii Contents Basin Overview .........................................................................................................................................219 Water Development History .....................................................................................................................220 Hydrogeology .............................................................................................................................................221 Conceptual Understanding of the Groundwater Flow System ...........................................................221 Groundwater Quality ................................................................................................................................223 San Jacinto Basin of the Santa Ana Basin ..........................................................................................225 Conceptual Understanding of the Groundwater System in the San Jacinto Basin .............225 Water Budget and Groundwater Flow .................................................................................228 Effects of Natural and Human Factors on Groundwater Quality ..............................................230 General Water-Quality Characteristics and Natural Factors ...........................................230 Potential Effects of Human Factors ......................................................................................233 Inland Basin of the Santa Ana Basin ......................................................................................................235 Conceptual Understanding of the Groundwater System in the Inland Basin .........................235 Groundwater Budget ...............................................................................................................238 Groundwater Flow ...................................................................................................................243 Effects of Natural and Human Factors on Groundwater Quality ..............................................244 General Water-Quality Characteristics and Natural Factors ...........................................244 Potential Effects of Human Factors .....................................................................................245 Coastal Basin of the Santa Ana Basin ...................................................................................................248 Conceptual Understanding of the Groundwater System in the Coastal Basin ......................250 Water Budget ...........................................................................................................................250 Groundwater Flow ...................................................................................................................254 Effects of Natural and Human Factors on Groundwater Quality ..............................................254 General Water-Quality Characteristics and Natural Factors ...........................................257 Potential Effects of Human Factors ......................................................................................257 Summary......................................................................................................................................................261 References Cited........................................................................................................................................262 Figures Figure 1. View to the northwest of the San Jacinto, Inland, and Coastal Basins in the Santa Ana drainage basin, California ……………………………………………220 Figure 2. Dissolved-solids concentrations in groundwater in the San Jacinto, Inland, and Coastal Basins and in surface water in the Santa Ana Basin, California ……222 Figure 3. Physiography, land use, and generalized geology of the San Jacinto Basin, California …………………………………………………………………………226 Figure 4. Generalized diagrams for the San Jacinto Basin, California, showing the basin-fill deposits and components of the groundwater system under predevelopment and modern conditions …………………………………………227 Figure 5. Groundwater levels and generalized flow directions in 1973 and in 2006 in the San Jacinto Basin, California ……………………………………………………231 Figure 6. Locations of and chemical characteristics of water in wells sampled in the San Jacinto Basin, California, by the NAWQA Program, 2001 ……………………232 iii Figures—Continued Figure 7. Detection frequencies of tritium, volatile organic compounds, and pesticides in water samples from wells in the San Jacinto Basin, California ……………………234 Figure 8. Physiography, land use, and generalized geology of the Santa Ana Inland Basin, California …………………………………………………………………236 Figure 9. Generalized diagrams for the Bunker Hill subbasin, California, showing the basin-fill deposits and components of the groundwater system under predevelopment and modern conditions …………………………………………237 Figure 10. Generalized diagrams for the Chino subbasin, California, showing the basin-fill deposits and components of the groundwater system under predevelopment and modern conditions ……………………………………………………………239 Figure 11. Groundwater levels and generalized flow directions in 1997 in the Inland Basin, California …………………………………………………………………240 Figure 12. Locations of and chemical characteristics of water in wells sampled in the Inland Basin, California, by the NAWQA Program, 2000 …………………………246 Figure 13. Detection frequencies of tritium, volatile organic compounds, and pesticides in water samples from wells in the Inland Basin, California …………………………248 Figure 14. Physiography, land use, and generalized geology of the Coastal Santa Ana Basin, California …………………………………………………………………249 Figure 15. Generalized diagrams for the Coastal Basin, California, showing the basin-fill deposits and components of the groundwater system under predevelopment and modern conditions ……………………………………………………………251 Figure 16. Groundwater levels and generalized flow directions in the Coastal Basin, California, in 2005, and artesian areas in 1904 and under predevelopment conditions …………………………………………………………………………255 Figure 17. Locations of and chemical characteristics of water in wells in the Coastal Basin, California, sampled by the NAWQA Program, 1999–2001 …………………256 Figure 18. Detection frequencies of tritium, volatile organic compounds, and pesticides in water samples from wells in the Coastal Basin, California ………………………258 Figure 19. Public-supply wells sampled in the Coastal Basin, California, and the number of volatile organic compounds detected at concentrations above the laboratory reporting level in each well ……………………………………………260 Tables Table 1. Summary of physical and water-quality characteristics of wells in the Santa Ana Basin, California, sampled by the NAWQA Program, 1999–2001 ……………224 Table 2. Estimated groundwater budget for the basin-fill aquifer system in the San Jacinto Basin, California, under predevelopment and modern conditions ………229 Table 3. Estimated groundwater budget for the basin-fill aquifer system in the Bunker Hill subbasin, California, under predevelopment and modern conditions …………241 Table 4. Estimated groundwater budget for the basin-fill aquifer system in the Chino subbasin, California, under predevelopment and modern conditions ……………242 Table 5. Estimated groundwater budget for the basin-fill aquifer system in the Coastal Basin, California, under predevelopment and modern conditions …………………252 iv This page intentionally left blank. Section 12.—Conceptual Understanding and Groundwater Quality of the Basin-Fill Aquifers in the Santa Ana Basin, California By Susan A. Thiros Basin Overview The climate of the Santa Ana Basin is Mediterranean, with hot, dry sum¬mers and cool, wet winters. Average annual precipitation ranges from 10 to 24 in. in the coastal plain and The hydrologic cycles of the groundwater basins in the inland valleys and from 24 to 48 in. in the San Gabriel and San Santa Ana Basin are greatly affected by human activities as Bernardino Mountains (Belitz and others, 2004, p. 3). Most of a result of the semiarid climate and the water demands of the the precipitation occurs between November and March in the large urban population (Belitz and others, 2004). Pumping form of rain, but with variable amounts of snow in the higher from the basin-fill aquifers and changes in the sources and elevations. This seasonal precipitation pattern can result in distribution of recharge that have accompanied development high streamflow in the spring, followed by low flow during the have accelerated the rate of groundwater flow and the transport dry season. of dissolved constituents through the aquifers. The quality of The Santa Ana Basin is drained by the Santa Ana groundwater in parts of these aquifers reflects the quality of River, which has the largest drainage area of any stream in the surface water used for recharge during the past 50 years. southern California. The Santa Ana River begins in the San Groundwater recharged before any substantial human effects Bernardino Mountains and flows westward more than 100 on water quality or the flow