Abstract

Ground water is the most important source of drinking water in Utah, the second most arid state in the nation. Ground water can be extremely vulnerable to contamination, and remediating contaminated ground water is expensive and time consumptive. Aquifer classification is a relatively new and little known tool for local governments in Utah to use for managing potential ground-water contamination sources and protecting the quality of their ground-water resources. 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. Two other ground-water-quality classes, class 1B (Irreplaceable) and class 1C (Ecologically Important), are not based on total-dissolved-solids concentrations and are not addressed in our studies.

Cache Valley, Ogden Valley, and Tooele Valley are areas in northern Utah that are experiencing an increase in residential development. Most of the development is on unconsolidated deposits of the basin-/valley-fill aquifers, which provide the primary drinking-water supply for communities in those valleys. The purpose of our studies is to classify the ground-water quality of the principal aquifers to formally identify and document the beneficial use of each valley’s ground-water resource. 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 fall 1997 and winter/spring 1998-1999. Total-dissolved-solids concentrations in Cache Valley range from 178 to 1,010 mg/L. Ogden Valley ground water is classified as class 1 A, based on chemical analyses of water obtained from 87 wells sampled during 1985-86 and spring/fall 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.