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of the Interior
The Las Vegas Wash is a natural drainage channel providing the only surface water outlet for the entire 2,193 square miles of Las Vegas Valley. The Las Vegas Valley in Clark County in southern Nevada contains the largest population center in the state. Studies evaluating salinity contributed by the Las Vegas Wash are concerned mainly with the 10-mile reach upstream of Las Vegas Bay.
Before urban water development in the valley, the Las Vegas Wash was a generally barren, sandy channel which contained discharge only during brief periods of major storm runoff. As communities in the valley grew, increasing amounts of wastewater was discharged to the Las Vegas Wash until the flow became perennial. Return flows to the Las Vegas Wash now include sewage treatment plant effluent, industrial cooling water, and urban irrigation as well as natural flows. Solute load (tons) of this wastewater has been increasing as discharge continues to increase.
The Las Vegas Wash conveys storm runoff and wastewater from Las Vegas Valley to Las Vegas Bay, an arm of Lake Mead. Located in Clark County in southern Nevada, the Las Vegas Valley contains the largest population center in the State. Studies evaluating salinity contributed by the Las Vegas Wash are concerned mainly with the 10-mile reach upstream of Las Vegas Bay.
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The project was originally planned to be constructed in phases.
Phase 1 of the project is a 4 mile long pipeline that reduces groundwater flow. This Pittman Bypass Pipeline separates wastewater discharge from highly saline soils by diverting industrial return flow from an open, unlined ditch. This has reduced groundwater flow and consequent pickup of salts leached from the soil, resulting in an estimated decline in salt loading to the Colorado River of 3,800 tons per year.
A monitoring system to establish an accurate record of conditions prior to project operation. A subsurface barrier, an intake pumping plant, a brine reject pipeline, and evaporation ponds was also planned.
Other phases were found to be not cost effective. Reclamation continues to monitor once a year.
Early explorers moved up Las Vegas Wash toward an oasis of spring-fed meadows at the present site of Las Vegas. After the Mormons settled in the 1850`s, cattle ranches occupied much of the valley and artesian springs were used to cultivate crops of hay. Rapid population growth and commensurate increased ground-water use since the 1930`s have resulted in a rapid and continuing decline in ground-water levels. Surface water was no longer flowing by the late 1940`s and few springs in Las Vegas Valley are now active. However, rapid municipal growth has also resulted in a continuous increase in waste water processed through sewage treatment plants and discharged to the lower portions of Las Vegas Wash. Increased urban irrigation along the east side of the valley has resulted in increased ground-water return flows.
Rising local concern over the pollution of Lake Mead began in the early 1960`s, and Clark County and various political subdivisions took the first steps toward controlling polution in 1964. This effort was centered around the development of a plan to reuse effluent water for irrigation and other nondrinking purposes.
In 1966, a water pollution control board was formed for the Clark County area, and in 1968, a local interagency water pollution task force was organized to function as a technical committee on water pollution control for the Clark County Regional Planning Council. On the recommendation of this task force, two consulting firms were hired by Clark County to develop a long-range water resource management program for optimization of the beneficial uses of the total water resources in the valley and the protection of the quality of these resources for future generations. Discussed in the consultants` report are four programs for controlling the salinity and pollution problems affecting Las Vegas Wash and Lake Mead.
During the 1971 State legislative session, the Las Vegas Valley Water District was delegated the responsibility for developing a plan to control the Las Vegas Wash pollution. The district was given until December 1972 to complete its studies and have a report ready for the 1973 legislative session. In accomplishing its assigned task, the district awarded several contracts for special studies that have contributed significantly to the development of a solution to the Las Vegas Wash salinity problem. The Nevada legislature enacted the County Sewage and Wastewater Law (chapter 790, statutes of Nevada, 1973) which empowered Clark County as the master agency for the collection, disposal, and treatment of sewage and wastewater. As master agency, the county became responsible for the pollution abatement problem in the Las Vegas Wash-Lake Mead area.
On August 9, 1973, the Colorado River Commission of Nevada issued resolution 73-5 which urged the Department of the Interior, through the Bureau of Reclamation, to immediately initiate reviews and studies and to produce an early report leading to construction of a Federal salinity control project for Las Vegas Wash flows. On August 31, 1973, the Clark County Board of County Commissioners approved a similar resolution in support of a Federal salinity control project. Federal funds were budgeted in October 1973 to initiate studies on the Las Vegas Wash Unit.
Construction of Phase 1 was begun in 1977, but delayed in 1978 to allow time to re-evaluate changing groundwater conditions. Several salinity control strategies were addressed during the re-evaluation period. One strategy would have prevented seepage of wastewater and minor storm runoff by placing it in a bypass channel running parallel to the Las Vegas Wash for about 4 miles, circumventing salt deposits in the Las Vegas Wash alluvium. The bypass channel was viewed by some local entities as being in conflict with nutrient control and wildlife habitat improvement objectives, and a consensus of local support was not obtained.
Another strategy to reduce groundwater flow proposed constructing detention dikes across the Las Vegas Wash. The hypothesis was that groundwater detained behind the dikes would stratify, with relatively high quality water collecting at the top. This higher quality water would then spill to the Las Vegas Wash channel. However, simulation of the concept by USGS using computer models indicated that stratification would not occur, and the groundwater detention strategy would not be effective in reducing salinity in the Las Vegas Wash.
Reclamation has discontinued efforts for developing and implementing further salt-reduction strategies for the Las Vegas Wash Unit. Apparently, a cost effective, technically feasible, and publicly acceptable strategy is not available at this time. A final report was published in September 1989. Quarterly water quality monitoring is continuing. Salinity levels appear to be increasing in the Wash.
Early studies showed that a significant portion of the highly saline flows in Las Vegas Wash occurred from surfacing ground-water returns, which qualified it as a point source of salinity under the Bureau of Reclamation studies on the Colorado River Water Quality Improvement Program. In January 1974, Reclamation issued a special report, `Las Vegas Wash Unit, Point Source Division, Colorado River Water Quality Improvement Program.`
The environmental statement was prepared as an authorized unit under Title II of the Colorado River Basin Salinity Control Act of 1974 and published as a part of the environmental statement on the Colorado River Water Quality Improvement Program of May 19, 1977.
Advance planning studies were initiated in 1976. The Las Vegas Wash was included in the May 19, 1977 environmental statement on the Colorado River Water Quality Improvement Program.
Studies were terminated in September 1989. The Las Vegas Wash is part of an ongoing water quality monitoring program with the Las Vegas Water Quality Program. The map below shows some of the monitoring stations at Lake Mead.
Title II of the Salinity Control Act (Public Law 93-320) authorized the Secretary and the Secretary of Agriculture to implement the Colorado River Salinity Control Program. This program includes a broad range of specific and general salinity control measures--including the Las Vegas Wash-- in an ongoing effort to prevent further degradation of water quality in theUnited States.
Construction of the first stage was initiated in 1977 on the Las Vegas Wash Collection System and construction of the access road to the site was completed in 1977. Construction was deferred in 1978 pending the results of additional hydrologic studies of the ground-water and surface-water conditions of the Las Vegas Wash area. Additional studies showed that cost effective measures were not available and construction has stopped.
The Pittman Bypass pipeline removes 3,800 tons of salt per year, for a total capital cost of $1,757,000 and an annual O&M cost of $50,000--for a cost of $51 per ton.