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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2007–5261

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Introduction

A study initiated by Federal legislation (Lincoln County Conservation, Recreation, and Development Act of 2004; PL 108-424) directed the Secretary of the Interior, through the U.S. Geological Survey (USGS), the Desert Research Institute (DRI), and a designee from the State of Utah, to evaluate the basin-fill and carbonate-rock aquifers in White Pine County, Nevada, and adjacent areas in Nevada and Utah. The final report was transmitted to Congress in December 2007. The congressionally mandated study is termed the Basin and Range carbonate-rock aquifer system (BARCAS) study, and was completed in cooperation with the Bureau of Land Management.

White Pine County in east-central Nevada (fig. 1) is a sparsely populated area, with less than 10,000 residents in 2006, most of which reside in and adjacent to the city of Ely, Nevada, the county seat. The area within the county is characterized by typical basin and range topography—north-south trending valleys and mountains that range in altitude from 5,000 to 7,000 ft above sea level for valley floors, and above 10,000 ft for most mountain ranges. Precipitation on the mountain ranges is the principal source of recharge to four regional ground-water flow systems in the study area (fig. 1). Most ground water in White Pine County is used for irrigation and mining purposes. Lesser amounts of ground water are used for municipal and domestic purposes in and adjacent to the city of Ely.

The Colorado River system is currently the principal source of water supply for southern Nevada. The prospect of obtaining additional allotments of water from the Colorado River system are confounded by the legal and socio-political issues derived from the competition for those scarce resources. Proposed ground-water development is based, in part, on concerns that water from the Colorado River Basin is not a resource capable of supporting future growth in southern Nevada and elsewhere in the southwestern United States due to a persistent drought in the Basin. Water purveyors in southern Nevada have proposed to develop in-state ground-water resources in rural basins north of Clark County, including basins in White Pine County, Nevada. Municipal and regulatory agencies have expressed concerns about potential impacts on water quantity and quality, existing water rights, sensitive wildlife habitats, and other beneficial uses from developing these ground-water resources. As a first step in assessing the potential impacts of any proposed large-scale ground-water development, agencies and stakeholders have recognized the need for additional hydrologic data and an improved understanding of hydrogeologic processes that control the rate and direction of ground-water flow in eastern and central Nevada.

Purpose and Scope

The purpose of this report is to summarize hydrogeologic factors affecting the occurrence and movement of ground water in the study area. Ground-water resources were evaluated by focusing on the following hydrogeologic characteristics: (1) the extent, thickness, and hydrologic properties of aquifers, (2) subsurface geologic structures controlling ground-water flow, (3) ground-water flow directions and gradients, (4) the volume and quality of water stored in aquifers, and (5) the distribution and rates of recharge and discharge. Moreover, geologic, hydrologic, and geochemical information were evaluated to determine ground-water budgets in the study area. Finally, hydrogeologic characteristics were compiled and integrated to develop a three-dimensional hydrogeologic framework and conceptual understanding of ground-water flow in the study area.

Description of Study Area

The study area encompasses about 13,500 mi² and covers about 80 percent of White Pine County, Nevada, and smaller areas of adjacent counties in Nevada and Utah (fig. 1). White Pine County lies within the eastern half of the Great Basin—a unique internally drained physiographic feature of the Western United States. Basin and Range topography—north-south trending valleys and adjacent mountain ranges—dominates the region.

The study area encompasses 13 hydrographic areas (HAs)¹ (fig. 2). For most figures and tables in this report, water-budget components were estimated independently for the northern and central parts of Little Smoky Valley, and then were combined and reported as one value. Past studies have combined HAs to delineate intermediate or regional ground-water flow systems, primarily based on the direction of interbasin ground-water flow in the underlying carbonate-rock aquifer and the location of major recharge and terminal discharge areas (Harrill and Prudic, 1998). Although most boundaries between HAs coincide with topographic basin divides, some are arbitrary divisions that have no topographic basis. In this report, HAs also are referred to as basins, and ground-water flow within a basin is referred to as intrabasin ground-water flow. Moreover, HAs were further divided into subbasins that are separated by areas where pre-Cenozoic rocks are at or near the land surface. For purposes of this report, areas that separate subbasins are referred to as intrabasin divides. Subbasins are the subdivision used to estimate recharge and discharge in this study. HAs are the subdivision used to report summed and tabulated subbasin water budgets. HAs within this report refer to formal HAs of Harrill and others (1988) with two exceptions: (1) ‘Little Smoky Valley’ refers to both HAs 155A and 155B, which are the northern and central parts of Harrill and others’ description of Little Smoky Valley, respectively, and (2) ‘Butte Valley’ refers only to HA 178B, which is the southern part of Harrill and others’ description of Butte Valley.

Precipitation in the study area provides recharge to four regional ground-water flow systems—the Newark Valley, Goshute Valley, Great Salt Lake Desert, and Colorado regional flow systems (fig. 1)—that headwater in White Pine County. These regional flow systems are characterized by flow across HA boundaries and discharge as warm springs. All these regional flow systems extend to areas outside of White Pine County. As perceived by Harrill and others (1988), the Newark Valley and Goshute Valley flow systems are relatively small, internally drained flow systems, whereas the Great Salt Lake Desert and Colorado flow systems terminate in areas hundreds of miles from their source area in White Pine County. The Great Salt Lake Desert regional flow system terminates at the Great Salt Lake, with intermediate discharge at Fish Springs in Juab County, Utah. The Colorado regional flow system terminates at Lake Mead and the Colorado River, with a principal intermediate discharge area at Muddy River Springs in Lincoln County, Nevada. In addition to these and other perennial valley-floor springs, numerous high-altitude ephemeral and perennial springs are found in the study area. Many of these perennial and ephemeral springs support native vegetation; and some springs support protected aquatic or wildlife species, such as the Pahrump poolfish (Empetrichthys latos) in southeastern Spring Valley, and the White River spinedace (Lepidomeda albivallis) in White River Valley near Lund.

Regional ground-water flow in the study area primarily is through the carbonate rocks. Much of the carbonate-rock aquifer is fractured and these fractured rocks, where continuous, form a regional flow system that receives recharge in high-altitude mountain ranges in the study area where these rocks are exposed. Some water flows from the carbonate-rock aquifer into basin-fill aquifers. This regional discharge sustains many of the larger, perennial low-altitude springs in the study area. The basin-fill aquifers that overlie the carbonate-rock aquifer typically are more than 1,000-ft-thick deposits of volcanic rocks, gravel, sand, silt and clay (Harrill and Prudic, 1998). Basin-fill deposits locally can exceed 10,000 ft in thickness. Gravel and sand deposits yield water readily to wells and form the aquifers most commonly developed for agricultural, domestic, and municipal water supply.

¹Formal hydrographic areas in Nevada were delineated systematically by the U.S. Geological Survey and Nevada Division of Water Resources in the late 1960s (Cardinalli and others, 1968; Rush, 1968) for scientific and administrative purposes. The official hydrographic-area names, numbers, and geographic boundaries continue to be used in U.S. Geological Survey scientific reports and Division of Water Resources administrative activities.

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