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Surface and Groundwater Quality
Water quality standards define water quality goals of rivers and lakes in Nevada. Standards are set and revised through a regulatory process that starts with detailed analysis and a proposal by NDEP, which must be adopted by the State Environmental Commission.
Two types of standards are in use. One type is the general "narrative" standard, assigned to all water bodies in the state to set a minimum level of protection. In addition, detailed "numeric" standards have been set for major rivers, streams, lakes, and reservoirs. The latter take into account specific chemical and physical conditions necessary to maintain designated beneficial uses (e.g., drinking, swimming, fishing, and industrial processes). Stream reach specific numeric standards have been developed for water bodies in the Carson, Colorado, Humboldt, Snake, Truckee, and Walker River Basins and many smaller streams.
To ensure standards are being maintained, the NDEP periodically monitors water quality in 80 river reaches and 10 lakes and reservoirs. Water bodies identified in the agency's Water Quality Monitoring Plan are sampled 3 to 12 times each year. The state's surface water monitoring network was established in 1967. Modifications are periodically made based on review of the database, resource constraints, and opportunities to coordinate and utilize other government agencies monitoring activities. The monitoring network is used to assess compliance with water quality standards, conduct trend analysis, validate water quality models and set total maximum daily loads (TMDL's). The data also is used for nonpoint source assessments, the 303 (d) List, 208 Plan Amendments, and the 305(b) report.
Selection of the more than 100 sampling sites in the monitoring network is based on land use intensity, water quality, hydro-modifications, and topography. Samples are analyzed for nutrients, sediment, metals, temperature, dissolved oxygen, pH, and other chemical and physical parameters. In general, if twenty-five percent of the samples for a pollutant exceed the water quality standard, then the water body may be classified as impaired. Impaired water bodies placed on the Clean Water Act 303(d) List. The 303(d) List is intended to draw more attention to water bodies in need of water quality improvement. A new listing will be published by NDEP in 2002, incorporating new methods of determining impairment.
Beginning in Summer 2000, the NDEP began a preliminary bio-assessment monitoring program to supplement physical and chemical quality assessments. The bio-assessment monitoring involves investigation of the presence of macro-invertebrates (i.e., insects, such as stone, caddis, and mayfly larvae), channel shape and dimensions, flow conditions, and riparian plant cover. Fifty initial sampling sites were established on the Truckee, Carson, and Walker rivers. In 2001, additional bio-assessment sampling sites will be established on the Muddy and Virgin rivers, and tributaries of the Humboldt.
River Water Quality Status
A summary of the water quality status of major rivers in Nevada and streams tributary to Lake Tahoe is shown in Figure 2-11. All rivers, except streams flowing from the Nevada side of Lake Tahoe, show slight to serious signs of impaired water quality in a number of reaches.
Each receives runoff from land developed for urban, industrial, mining, and/or agricultural uses. Of 1,213 river miles periodically assessed, water quality standards were not met for one or more pollutants on 825 miles (Nevada Division of Environmental Protection, 2001a). Nutrients, sediment, and metals are the most widespread pollutants contributing to exceeded standards (Table 2-5).
Phosphorus is the most widespread nutrient found at elevated levels. Human sources are probably fertilizer use and animal feedlots. However, many soil types and rock formations are naturally phosphorus rich. Historic mining and milling activities, as well as natural sources, such as metal-bearing rock formations and geothermal springs, are associated with high metal levels in monitored water bodies
in addition to various others located throughout the state. Abandoned mine land (AML) sites that are or have the potential to degrade water quality are numbered in the thousands according to a report produced by the U.S. Bureau of Land Management (BLM) and the Nevada Division of Mines (NDOM) as part of a federal-state task force. The Task Force identified and prioritized AML sites where contamination is present or possible. Thirty-three priority reclamation sites are identified in the Nevada Abandoned Mine Lands Report (Interagency Abandoned Mine Land Environmental Task Force, 1999). (Links to 2001 Report)
Water quality standards exceeded on other water bodies also include boron in reaches of the Humboldt and Colorado rivers; suspended solids, or sediment, in the lower Walker and lower Truckee rivers; and, mercury in the Carson River, below Carson City. The elevated nutrient level in the Truckee River occurred below the outfall from the Truckee Meadows Water Reclamation Facility. Operational improvements and more stringent permit limits have lowered the amount of nitrogen in the discharge. More recent water quality data show the total nitrogen standard is being met. Where mercury or other toxic metals reach levels in fish that could pose a threat to human health, the State Heath Division issues advisories. The only fish consumption advisory in the state is the result of mercury in the lower Carson River, below the historic Comstock-era mill sites.
The process to identify water quality improvement measures for the purpose of attaining the standard(s) begins with establishment of the Total Maximum Daily Load (TMDL). A TMDL is equivalent to calculating a budget for pollution. In the TMDL process, scientists estimate the total amount of a pollutant that could be released by all point and nonpoint sources to a specific water body without exceeding the beneficial use standards. After pollution sources are identified, the NDEP works with local government and interested parties to allocate pollution reduction responsibility.
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| An indication of low pH and high concentrations of heavy metals in surface water is the presence of orange iron oxyhydroxide, often associated with acid mine drainage. This water quality condition also occurs naturally by weathering of altered rock in association with subsurface water. The photo shows a streambed next to a tailing pile at the Rio Tinto Mine in Elko County. A remediation plan has been developed for the mine site 1995. Courtesy of Jon Price, Nevada Bureau of Mines and Geology. |
The TMDL process has been implemented on several water bodies. Included are: 1) total phosphorous in seven segments of the Carson River; 2) total suspended solids in two segments of the Walker River; 3) total nitrogen, total phosphorous, and total dissolved solids in a segment of the Truckee River; 4) total phosphorous and total suspended solids in three segments of the Humboldt River, and total dissolved solids in two segments; and, 5) total phosphorous and total ammonia in Las Vegas Wash and Bay. Priorities for TMDL review and revision include the Las Vegas Wash and Bay, Humboldt River, and Walker River.
Because discharges from wastewater treatment plants, industrial facilities, mines, and other large point sources are regulated and monitored, much is known about the types and amount of pollution released. For most rivers in Nevada, all point source discharges have been removed. Nonpoint sources are the major causes for substandard quality in Nevada's impaired water bodies. Pollutant discharges from nonpoint sources are much more difficult to assess and control.
Nonpoint pollution is associated with serious impacts to native and endangered fishes, accelerated ageing of lakes (eutrophication), increased drinking water treatment requirements and costs, and general unsightliness that lowers scenic value, especially important to recreation-based tourism. In urban areas, runoff from streets and parking lots, construction sites, lawns and golf courses, and eroding channels contribute to elevated nutrients, heavy metals or sediment loads. In rural areas, nonpoint sources include intensive agricultural activities, irrigation, abandoned mine sites, and unpaved roads, eroding channels and barren stream embankments. Artificially low streamflow or lake levels and loss of wetlands and riparian plant communities can amplify the affects of nonpoint source pollution.
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