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Water Quality in the Great Salt Lake Region Affected by Land Use
Released: 6/22/2004

Contact Information:
U.S. Department of the Interior, U.S. Geological Survey
Office of Communication
119 National Center
Reston, VA 20192
Susan Thiros 1-click interview
Phone: 801-908-5063

Water samples collected by the U.S. Geological Survey (USGS) in areas surrounding the Great Salt Lake in parts of Utah, Idaho, and Wyoming generally meet existing guidelines for drinking water and the protection of aquatic life, although water quality in some specific areas have elevated concentrations of pesticides, volatile organic compounds (VOCs), nutrients, chloride, and elements such as arsenic and lead, according to the results of a 5-year study of water quality by the USGS.

This study provides a large dataset to area water managers that can serve as a baseline of water-quality conditions because components are being monitored for trends over time.

Water quality and biological conditions are generally better in streams that drain forests and rangeland (undeveloped areas) than in streams that drain agricultural and urban areas, said Susan Thiros, a USGS hydrologist and project leader. In developed areas, including those affected by mining, study results indicate elevated concentrations of pesticides, volatile organic compounds (VOCs), nutrients, chloride, and trace elements such as arsenic and lead.

Rivers and Streams

More than 80 percent of the samples USGS scientists collected from streams affected by agricultural and by a combination of mixed land uses had phosphorus concentrations that exceeded the U.S. Environmental Protection Agency (EPA) desired goal of 0.1 mg/L (milligrams per liter) to prevent nuisance plant growth in streams. Although nutrients occur naturally in streams, additional and potentially elevated sources include agricultural and urban runoff and wastewater discharge. Thiros noted that an elevated nutrient concentration in water can cause excessive growth of aquatic vegetation and reduced dissolved-oxygen concentrations, which can adversely affect the aquatic community.

In many streams near the mountain front, aquatic communities have been negatively affected by increased water temperature and nutrient and dissolved-solid concentrations as a result of water diversion, mainly for irrigation. Continued drought conditions and increasing demands for water in the areas surrounding the Great Salt Lake make this an ongoing water-quality issue, said Thiros.

At least one pesticide was detected in all but one of the 24 streams sampled. Insecticides — most commonly carbaryl, diazinon, and malathion — were detected more frequently in urban streams than in agricultural streams. Diazinon was detected in about 90 percent of 42 samples from the urbanized Little Cottonwood Creek, but in only about 4 percent of 26 samples from Cub River, classified as agricultural. Thiros said that this is most likely because storm runoff in urbanized areas can carry substantial amounts of nutrients, pesticides, and VOCs to streams. These contaminants accumulate between storms on impervious surfaces in urban areas and are transported to streams in storm runoff. During the winter of 1999, for example, chloride concentrations in Little Cottonwood Creek often exceeded the EPA aquatic-life guideline following winter storms and the application of salt to area roads.

Aquatic-life guidelines for arsenic, cadmium, copper, lead, mercury, silver, and zinc were exceeded in sediment samples from streams that were affected by mine-tailing deposits and smelters (including some on urbanized streams). The most heavily affected streams sampled were Little Cottonwood Creek, Silver Creek, and the Weber River below the Silver Creek confluence. In areas with little mining or urban influence, such as the Bear River basin, trace-elements concentrations were low compared to those measured in other parts of the nation.

Ground Water

The USGS study revealed that the median concentration (6.8 mg/L) of nitrate in shallow ground water underlying residential and commercial land in Salt Lake Valley was almost 5 times the national median (1.4 mg/L) for ground-water studies in similar urban areas and was the highest measured in 34 urban studies done across the nation. Thiros said that although nitrate does occur naturally in ground water, elevated concentrations in urban and agricultural areas could result from leaking septic systems and sewer pipes, as well as from fertilizer applications. Even though this shallow water is not currently used for drinking, Thiros said the potential exists for contaminated water in the shallow aquifer to move downward to the underlying aquifer that is used for public supply.

VOCs and pesticides were detected, mostly at very low concentrations, in water from 23 of 31 public-supply wells sampled in Salt Lake Valley. The widespread occurrence of the VOC chloroform in Salt Lake Valley is likely a result of chlorinated public-supply water used to irrigate lawns and gardens in residential areas that then recharges the deeper aquifer. Although the concentration of these compounds measured in ground water used for public supply is not a known health concern according to current standards, the occurrence of these compounds in the deeper ground water presents the possibility that water with a higher concentration may enter this used aquifer in the future.

Copies of the USGS report, "Water Quality in the Great Salt Lake Basins, Utah, Idaho, and Wyoming, 1998-2001," published as USGS Circular 1236 are available free of charge by writing the USGS Branch of Information Services, Box 25286, Denver Federal Center, Denver, CO 80225 (or by calling 1-888-ask-usgs). The report also can be accessed on the World Wide Web at http://water.usgs.gov/nawqa/nawqa_sumr.html. The water-quality conditions summarized in this report are discussed in detail in other reports that can be accessed at http://ut.water.usgs.gov/nawqa/pubs.htm.

The USGS assessment is part of a national program currently releasing results on streams and ground water in 14 additional major river basins and aquifer systems. Findings of regional and national interest are highlighted in a separate report, "Water Quality in the Nation’s Streams and Aquifers—Overview of Selected Findings, 1991-2001." Check the status and availability of these reports on the NAWQA website, as well as accessibility to other publications and national data sets and maps.

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