PROTECTING GROUND-WATER RESOURCES THROUGH GROUND-WATER-QUALITY CLASSIFICATION--EXAMPLES FROM THREE NORTHERN UTAH VALLEYS

Ground-water-quality classification is a relatively new tool for local governments in Utah to use for managing potential ground-water contamination sources and protecting the quality of their ground-water resources. Classifying the ground-water quality of the principal aquifers is a way to formally identify and document the beneficial use of the ground-water resource so that defendable land-use regulations can be enacted. Utah’s ground-water-quality classes are based mostly on total-dissolved-solids concentrations as follows: class 1A (Pristine), less than 500 mg/L; class 2 (Drinking Water Quality), 500 to less than 3,000 mg/L; class 3 (Limited Use), 3,000 to less than 10,000 mg/L; and class 4 (Saline), 10,000 mg/L and greater.

Cache Valley, Ogden Valley, and Tooele Valley are areas in northern Utah that are experiencing an increase in residential development on unconsolidated deposits of the basin-fill aquifers, the primary source of drinking water in those valleys. The quality of water is generally good for all three valleys. Cache Valley ground water is classified as class 1A (84 percent) and class 2 (16 percent), based on chemical analyses of water obtained from 164 wells sampled during 1997-1999. Total-dissolved-solids concentrations in Cache Valley range from 178 to 1,758 mg/L. Ogden Valley ground water is classified as class 1A, based on chemical analyses of water obtained from 87 wells sampled between 1985 and 1997. Total-dissolved-solids concentrations in Ogden Valley range from 42 to 629 mg/L. Tooele Valley has a more varied chemistry due to its proximity to Great Salt Lake. Ground-water quality classes there include class 1A (26 percent), class 2 (46 percent), class 4 (22.5 percent), and combined classes (5.5 percent). Total-dissolved-solids concentrations in Tooele Valley range from 256 to 37,800 mg/L, based on water-quality data collected between 1964 and 1995. Land-use planners may now use ground-water-quality classification to enact regulations to protect water resources in these valleys.