Section 6-Las Vegas Valley, Nevada
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Section 6.—Conceptual Understanding and Groundwater Quality of the Basin-Fill Aquifer in Las Vegas Valley, Nevada By Jena M. Huntington 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 ............................................................................................................................................83 Water Development History .......................................................................................................................83 Hydrogeology ...............................................................................................................................................85 Conceptual Understanding of the Groundwater System ......................................................................86 Water Budget and Groundwater Flow ............................................................................................88 Effects of Natural and Human Factors on Groundwater Quality .........................................................92 General Water-Quality Characteristics and Natural Factors ......................................................92 Potential Effects of Human Factors .................................................................................................94 Summary........................................................................................................................................................96 References Cited..........................................................................................................................................97 Figures Figure 1. Physiography, land use, and generalized geology of Las Vegas Valley, Nevada … 84 Figure 2. Historical population estimates for Las Vegas Valley, Nevada …………………… 85 Figure 3. Generalized cross-sections for Las Vegas Valley, Nevada, showing the basin-fill deposits and components of the groundwater flow system under predevelopment conditions and modern conditions ……………………………… 87 Figure 4. Approximate potentiometric surface in the principal basin-fill aquifer in Las Vegas Valley, Nevada, under predevelopment conditions ………………………… 89 Figure 5. Groundwater-level declines from predevelopment conditions to 1990 in Las Vegas Valley, Nevada …………………………………………………………… 90 Figure 6. Location of wells sampled in Las Vegas Valley, Nevada, by the NAWQA Program …………………………………………………………………………… 93 Figure 7. Concentrations of dissolved solids in groundwater in Las Vegas Valley, Nevada … 95 Tables Table 1. Estimated groundwater budget for the basin-fill aquifer in Las Vegas Valley, Nevada, under predevelopment and modern conditions ………………………… 91 Table 2. Summary of selected constituents in groundwater in Las Vegas Valley, Nevada, and sources or processes that affect their presence or concentration … 96 Section 6.—Conceptual Understanding and Groundwater Quality of the Basin-Fill Aquifer in Las Vegas Valley, Nevada By Jena M. Huntington Basin Overview that formerly were rangeland. The city of Henderson is on a piedmont surface. Further expansion of the urban areas is towards the pediment/mountain contact in the Las Vegas Valley in southern Nevada is characteristic of western, southern, and eastern parts of Las Vegas Valley. basin and range topography. The valley is bounded by high The population in the Las Vegas area increased from about mountain peaks surrounding a valley floor underlain by thick 795,000 in 1990 to about 1,367,000 in 2000. By 2005 the unconsolidated sediments that contain a basin-fill aquifer. The population had increased by an additional 28 percent, to valley is about 30 mi wide and 50 mi long (approximately about 1,752,000 (fig. 2) (Nevada State Demographer’s Office, 1,640 mi2) (fig. 1). The Spring Mountains to the west and 2009). Corresponding gross water use in the valley, almost northwest of the valley rise to an altitude of about 11,900 ft all of which was for public supply, was about 325,100 acre-ft at Mount Charleston. The altitude of the valley floor sits at in 1990 (Coache, 1990, p. 5), about 529,800 acre-ft in about 1,600 ft and drains southeastward through Las Vegas 2000 (Coache, 2000, p. 5), and about 541,300 acre-ft in Wash into Lake Mead on the Colorado River, at about 1,200 ft. 2005 (Coache, 2005, p. 5). Surface water from Lake Mead Other mountain ranges bordering Las Vegas Valley include contributed at least 80 percent of the water used in the valley the Sheep Range to the north, the Las Vegas Range to the during this same period (1990–2005) for each of these years. northeast, the McCullough Range to the south, the River Mountains to the southeast, and Frenchman Mountain and Sunrise Mountain to the east. Plume (1989, p. A2) divided Las Vegas Valley into three Water Development History physiographic units: mountains, piedmont surfaces, and valley lowlands. The mountain blocks are separated from the The earliest known people to use water in Las Vegas valley lowlands by long, gently sloping, laterally continuous Valley were the Anasazi, Mojave, and Paiute tribes (Wood, piedmont surfaces. These sloped surfaces were interpreted 2000, p. 2). Near the Old Spanish Trail (Mendenhall, 1909, as coalescing alluvial fans in early investigations (Longwell p. 26), the area was named Las Vegas, which is Spanish for and others, 1965, p. 6; Malmberg, 1965, p. 11), but have “the meadows”, due to the lush grassy vegetation surrounding since been interpreted as pediment surfaces of older basin-fill large springs near the center of the valley. In 1844, John C. deposits (Bell, 1981, p. 10). Fremont described the area as having “…two narrow streams The climate of Las Vegas Valley is considered arid, of clear water, 4 or 5 ft deep, with a quick current, from two with about 4.5 in/yr of precipitation on the valley floor singularly large springs” (Mendenhall, 1909, p. 92). The next (period of record 1971–2000; National Oceanic and few years saw failed lead mining and farming attempts, but Atmospheric Administration, 2002, p. 12). Higher altitudes by 1865 the first productive ranch was established. A railroad in the Spring Mountains can receive more than 24 in/yr. was built to the valley in 1905 because of its location between Mean annual temperature is 68°F on the valley floor (period Los Angeles and Salt Lake City and its readily available of record 1971– 2000; National Oceanic and Atmospheric water supply to operate the steam locomotives. Growth of the Administration, 2002, p. 8), although typically daily high railroad increased the demand for water, and in 1905 the first temperatures are 90°F or warmer on more than 125 days each well was drilled by the Las Vegas & Tonopah Railroad (Maxey year (Houghton and others, 1975, fig. 22). and Jameson, 1948, p. 5; Wood, 2000, p. 8). By 1912, about In the past, most of the valley’s population has resided 125 wells had been drilled in Las Vegas Valley, of which more in the lowlands, although recent expansion to the west, than half were flowing-artesian wells (Pavelko and others, northwest, and southwest has been onto the sloping pediments 1999, p. 52). 84 Conceptual Understanding and Groundwater Quality of Selected Basin-Fill Aquifers in the Southwestern United States Study area Sheep Range 36°30' Las Vegas Range 95 119°33'20" Spring Mountains 115°00' Las Mt Charleston North Vegas Las Vegas 15 Wash 93 Sunrise Mountain Las Vegas Frenchman Mountain Red Rock Wash Lake Mead Spring Mountains Wash Flamingo 159 Wash River Mountains Tropicana 515 215 Henderson 160 Duck 36°00' Creek 15 EXPLANATION 146 McCullough Urban land use Range Geology Carbonate rocks Metamorphic or intrusive igneous rocks Sedimentary-dominated rocks Volcanic rocks Basin-fill sediments Approximate boundary of basin-fill sediments Study area boundary Fault Shear line 0 2 4 6 8 Miles Base compiled from U.S. Geological Survey digital data, 1:100,000 scale, 1977, 1978 0 2 46 8 Kilometers National Elevation Data 1:24,000 scale, 2005 Albers Equal-Area Conic Projection, standard parallels 29˚30', 45˚30', central meridian 115˚15' Land use data from U.S. Geological Survey, 2003 Geology derived from Truner and Bawic, 1996 Figure 1. Physiography, land use, and generalized geology of Las Vegas Valley, Nevada. SWPALasVegas01 IP–005215 Section 6.—Conceptual Understanding and Groundwater Quality of the Basin-Fill Aquifer in Las Vegas Valley, Nevada 85 2,000,000 1,800,000 References:1910–1960 data from http://www.lasvegasnevada.gov/FactsStatistics/history.htm, 1,600,000 accessed 7/28/2009 and 1980–2005 data from Nevada State Demographer’s Office, 2009 1,400,000 1,200,000 1,000,000 800,000 POPULATION 600,000 400,000 200,000 0 1900 1910 1920 1930 1940 1950 1960 1970 1980 1999 2000 2010 Figure 2. Historical population estimates for Las Vegas Valley, Nevada. The construction of Boulder Dam (later named Hoover Hydrogeology Dam) and Lake Mead began on the Colorado River in 1932. This large-scale project, which provides water and power Basin and Range extensional faulting during the to Las Vegas, brought in workers from all over the country, Pliocene epoch broke up Precambrian- and Paleozoic-age thereby accelerating growth in the valley. Industry, including carbonate rocks, Permian- through Jurassic-age clastic military and gambling, were attracted to Las Vegas throughout rocks, and early Tertiary-age