Water Quality in the Las Vegas Valley Area and Carson and Truckee River Basins, Nevada and California, 1992-96

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Environmental Subareas Were Identified for Investigation

The NVBR Study Unit was divided into subareas representing important combinations of natural and human factors. A conceptual model of basin and range hydrology was used to develop a framework of primary subareas (headwater and basin areas). Headwater areas (fig. 3) were defined as mountains and adjacent areas where precipitation is adequate to provide ground-water recharge and streamflow (yielding 0.2 inch or more of annual runoff [59]). Basin areas do not receive adequate precipitation for appreciable ground-water recharge and streamflow, but can receive recharge and streamflow from upstream headwater areas. Natural discharge in the Study Unit is by stream outflow from and evapotranspiration in the Las Vegas Valley and by only evapotranspiration in the Carson and Truckee River Basins (hydrologically closed basins characterized by internal drainage).

Secondary subareas were developed by subdividing the two primary subareas (headwater and basin areas) into land uses that represent more natural conditions (forest and range) or human activities (urban and agricultural land use; fig. 5). Water resources in the environmental subareas were then identified for study. Principal surface-water resources included in the investigation were Las Vegas Wash and Lake Mead, the Carson River, and the Truckee River (fig. 3). Principal aquifers (fig. 3) were defined as unconsolidated deposits beneath valleys with 100 ft or more of saturated thickness [60,61,62] and containing ground water with less than 1,000 mg/L of dissolved solids [63,64].

Headwater areas are primarily forest and basin areas are primarily range. The principal headwater urban area is Reno-Sparks and the principal headwater agricultural area is Carson Valley. The principal basin urban area is the Las Vegas urban area and the principal basin agricultural area is Carson Desert.

Effects of Urban and Agricultural Activities Were Focus of Investigations

Stream-chemistry data collection included a Bottom Sediment and Tissue Study, Basic and Intensive Fixed-Site networks, and a Surface-Water Synoptic Study (fig. 13). The Bottom Sediment and Tissue Study was done early in the Study Unit investigation and included sites being considered for selection as Basic and Intensive Fixed Sites. Basic Fixed Sites were located on streams downstream from forested headwater areas, urban and agricultural headwater areas, urban and agricultural basin areas, major sources of treated sewage effluent, and at downstream sites that integrate streamflow from throughout the study basins. An Intensive Fixed Site was operated to sample drainage from the Las Vegas urban area. The Surface-Water Synoptic Study increased the areal coverage of the Fixed-Site networks and provided additional data on pesticides and trace elements. 

Stream-ecology activities included Fixed-Site Reach Assessments and Ecological Synoptic Studies (fig. 13). Fixed-Site Single-Reach Assessments were made at all Basic Fixed Sites in the Carson and Truckee River Basins. Fixed-Site Three-Reach Assessments were made at the farthest upstream Carson and Truckee River Basic Fixed Sites, to serve as reference sites, and at one downstream integrator site on each stream, to serve as trend sites. Ecological Synoptic Studies of benthic invertebrates and algae were completed in the Carson Valley agricultural area and the Reno-Sparks urban area to evaluate land-use effects.

study unit map 
(click for full-size figure; 74 K) 

Figure 13. Study unit stream-chemistry, stream-ecology, and ground-water-chemistry sites, and areas of special studies were chosen to represent environmental subareas characterized by selected natural conditions and human activities.

Ground-water-chemistry activities included Land-Use Studies and Study-Unit Surveys (fig. 13). Land-Use Studies of shallow ground water were completed in the Las Vegas basin urban area, the Carson Valley headwater agricultural area, the Carson Desert basin agricultural area, and the Reno-Sparks headwater urban area. The Study-Unit Surveys sampled principal aquifers in the Las Vegas urban area, Carson Valley, and Reno-Sparks urban area.

Special studies of irrigation drainage and endocrine disruption were made with assistance from cooperating agencies (fig. 13). The Department of the Interior National Irrigation Water Quality Program provided financial resources for a joint investigation with the NVBR NAWQA to quantify loads of potentially toxic constituents and to document contributing source areas in irrigated lands of the Carson Desert [9]. The National Park Service provided financial assistance and participated with the U.S. Fish and Wildlife Service in a joint investigation with the NVBR NAWQA to identify synthetic organic compounds in Las Vegas Wash and Las Vegas Bay of Lake Mead and to evaluate carp endocrine systems with respect to estrogenic effects that could be caused by synthetic organic compounds [42].

Summary of data collection in the Nevada Basin and Range Study Unit, 1992-96

What data were 
collected and why
Types of 
sites sampled
of sites
Sampling frequency 
and period
Stream chemistry 
Basic Fixed Sites Streamflow, major chemical constituents, nutrients, organic carbon, suspended sediment, pH, temperature, and specific conductance to describe areal and temporal differences. Stream sites representing hydrologic conditions, land use (forest, urban, and agriculture), and treated sewage effluent.
Monthly (Apr. 1993- Mar. 1995).
Intensive Fixed Sites In addition to Basic Fixed Site data, dissolved pesticides and trace elements to describe concentrations from urban activities. Stream site representing runoff from urban land use.
Biweekly and during storm runoff (Apr. 1993-Mar. 1995).
Synoptic Study Intensive Fixed Site data to determine areal and temporal variability of pesticides and trace elements during spring runoff and irrigation. All basic and intensive sites and seven additional sites to improve areal coverage.
Biweekly (2 sites) and monthly (15 sites); May-Aug. 1994.
Bottom Sediment and Tissue Study Organochlorine compounds, semivolatile compounds, and trace elements to determine occurrence. Basic and Intensive Fixed Sites and seven additional sites. 
Once in 1992.
Stream ecology
Fixed-Site Reach Assessment Fish, benthic invertebrates, algae, and aquatic and riparian habitat to assess conditions. Stream reaches at Basic Fixed Sites.
Once in 1993; annually for trend sites (1994-96).
Synoptic Study Benthic invertebrates and algae to assess effects of urban and agricultural land use. Carson (Carson Valley) and Truckee (Reno-Sparks) River.
Once in 1994 and once in 1995.
Ground-water chemistry 
Study-Unit Survey Major chemical constituents, nutrients, trace elements, radon-222, volatile organic compounds, dissolved organic carbon, pesticides, phenols, and MBAS(a) to assess principal aquifer systems. Existing supply wells in principal aquifers in Las Vegas area, Reno-Sparks area, and Carson Valley.
Once in 1995.
Land-Use Studies Study-Unit Survey data to assess effects of urban and agricultural land use on shallow ground water. Shallow observation wells in urban (Las Vegas and Reno-Sparks) and agricultural (Carson Valley, and Carson Desert) areas.
Once in Las Vegas (1993), and once in Reno-Sparks, Carson Valley and Carson Desert (1994).
Special studies
Irrigation Drainage Streamflow, major chemical constituents, nutrients, trace elements, and pesticides in water and trace elements in bottom sediment to determine major sources and loads. Irrigation drains in Carson Desert.
Water chemistry (3 times), pesticides and bottom sediment (once); Feb.- Sept. 1995.
Endocrine Disruption Organochlorine pesticides, PCBs, dioxins, furans, and semivolatile organic compounds in water, bottom sediment, semi-permeable membrane devices, and carp to determine occurrence. Sex-steroid hormones in carp to assess endocrine systems. Las Vegas Wash and Las Vegas Bay, Callville Bay, Colorado River inlet, Virgin River inlet, and Muddy River inlet of Lake Mead.
Once, 6 sites in 1995 and 10 sites in 1996.
MBAS (methylene blue active substances), synthetic detergents or surfactants, occur in natural water almost exclusively as a result of pollution.
Additional data from a pilot NAWQA study of the Carson River Basin were used to help determine land-use effects on shallow ground water in Carson Valley and Carson Desert [19].

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Suggested citation:
Bevans, H.E., Lico, M.S., and Lawrence, S.J., 1998, Water Quality in the Las Vegas Valley Area and the Carson and Truckee River Basins, Nevada and California, 1992-96, on line at <URL:>, updated 19 March 1998

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Last modified: Tue Mar 17 17:53:42 1998