Introduction

Great Basin National Park encompasses about 120 mi² of the highest parts of the southern Snake Range in eastern White Pine County, Nevada, near the border with Utah (fig. 1). The Southern Nevada Water Authority has applied for rights to withdraw large quantities of ground water from adjacent Spring Valley and Snake Valley. The National Park Service is concerned that pumping of ground water could adversely affect water resources of the park and in particular, the discharge of Cave Springs. Additionally, Cave Springs are near two popular camping areas and park managers are concerned about potential sources of contamination to the springs.

Description of Cave Springs

Cave Springs are in the Lehman Creek drainage about 1 mi upstream of Lehman Caves and four of the larger springs are diverted at the source into a water-collection system that is used as the water supply for the Lehman Caves Visitor Center (fig. 2). The springs discharge from alluvial and glacial deposits near the contact between Proterozoic Prospect Mountain Quartzite and Tertiary granite (fig. 2). The granite west of Lehman Caves was called an aplitic granitoid rock by Lee and Van Loenen, 1971, p. 40. The discharge from Cave Springs is about 0.1 ft³/s (Gretchen Baker, National Park Service, Great Basin National Park, written commun., 2004). A recently completed study (Elliott and others, 2006) indicated that the Lehman Creek drainage near and downstream of Cave Springs likely is susceptible to ground-water withdrawals farther downstream in Snake Valley because ground water in the alluvial and glacial deposits are connected with similar deposits in the valley.

Discharge at Cave Springs could be shallow ground water from alluvial and glacial deposits associated with Lehman Creek, from Prospect Mountain Quartzite, from middle Cambrian Pole Canyon Limestone that might be buried beneath the alluvial and glacial deposits, or from a mixture of water flowing through these different formations (Elliott and others, 2006). The susceptibility of a decreasing discharge to Cave Springs due to ground-water pumping partly depends on the formations that provide water to the springs. If the water source is from alluvial and glacial deposits or Pole Canyon Limestone that are connected to alluvial deposits farther downstream, then drawdown of water levels from downstream pumping sites could propagate upstream and decrease the flow of Cave Springs. If the source of water was from Prospect Mountain Quartzite near the contact with the Tertiary granite, however, then drawdown of water levels from downstream pumping sites would not likely decrease flow of the springs because the granite would be an effective barrier that would restrict the upstream propagation of drawdown farther upstream. Furthermore, if the source of Cave Springs is from ground water in the shallow alluvial and glacial deposits, Great Basin National Park may need to expand their present fenced area to minimize contamination to the springs.

The Tertiary granite intruded and assimilated the Pioche Shale that separates the Prospect Mountain Quartzite from the Pole Canyon Limestone (Lee and Van Loenen, 1971, p. 40). Although the nearest outcrop of Pole Canyon Limestone is about 2,000 ft southeast of Cave Springs (fig. 2), the limestone might be present beneath the alluvial and glacial deposits at Cave Springs if the granite split the limestone as illustrated in figure 3. This concept was invoked by Elliott and others (2006, p. 33) because the specific conductance of Cave Springs during 2003 and 2004 was much greater than that in Lehman Creek and greater than the specific conductance from Marmot Spring (name of spring provided by Gretchen Baker, National Park Service, Great Basin National Park, written commun., 2008) at the contact between Prospect Mountain Quartzite and the Tertiary granite in the adjacent Baker Creek drainage (fig. 2). Conversely, if the limestone is absent beneath Cave Springs then the discharge from Cave Springs could be from the Prospect Mountain Quartzite at the contact with the Tertiary granite, and the higher specific conductance has some other cause.

Purpose and Scope

This report describes the geochemical investigation of Cave Springs to determine the source of water discharging from the springs and to determine if the water has been in contact with carbonate rocks. Water samples were collected in September 2007 from Cave Springs, a spring discharging from alluvial and glacial deposits near upper Lehman Creek campground, a permanent pool in Lehman Caves within the Middle Cambrian Pole Canyon Limestone, and Marmot Spring at the contact between Prospect Mountain Quartzite with Tertiary granite in the Baker Creek drainage (fig. 2). The samples were analyzed for major ions, selected trace elements, nutrients, stable isotopes (carbon, hydrogen, oxygen, and strontium), dissolved gases, and chlorofluorocarbons. Samples of Prospect Mountain Quartzite, Tertiary granite, and Pole Canyon Limestone were collected from outcrops near Cave Springs and analyzed for stable isotopes of strontium. The limestone also was analyzed for stable isotopes of carbon and oxygen. The source of water to Cave Springs was investigated by using the geochemical analyses of the water and rock samples and the geochemical models PHREEQC (Parkhurst, 1995; Parkhurst and Appelo, 1999) and NETPATH (Plummer and others, 1994; Parkhurst and Charlton, 2008).