Abstract

The potential for contaminants entering ground-water flow systems in Utah varies in recharge areas, in areas of predominantly lateral ground-water movement, and in discharge areas. Some of the factors affecting contaminant movement in each of these areas also vary.

Utah is divided into three major physiographic areas that have distinct geologic and hydrologic characteristics. Ground water in two of the areas, the Basin and Range Province in western Utah and the Colorado Plateaus Province in eastern Utah, has been developed to varying degrees. Limited ground-water development has occurred in the Middle Rocky Mountains Province; however, because this province receives a large proportion of the annual precipitation in Utah, it is an important source of the water that eventually recharges the aquifers in the other two physiographic provinces. The Middle Rocky Mountains Province will be discussed mainly in terms of its importance as a recharge boundary to the other two provinces.

Potential or known contaminant sites in the Basin and Range Province of Utah include both point (landfills, burial pits, leaky storage tanks, mine and mill tailings, leaching ponds) and non-point (urban runoff and agricultural areas) sources. Most known sites are located in the center of basins away from the recharge areas, although a few are in the mountain areas (mines) or near mountain fronts (mine tailings and some military installations). Most contaminant sites in the Basin and Range Province of Utah are located in the basins near the Wasatch Range.

Contaminant sites in the Colorado Plateaus Province generally are point sources such as uranium-mill and coal-mine tailings, oil-field brine-disposal wells and pits, or leaky storage tanks. Non-point sources such as pesticide and fertilizer contamination in agricultural areas may become a future concern.

Proposed siting regulations for waste-disposal sites being formulated by the State of Utah will be principally based on geologic and hydrologic factors. Differences in the geologic and hydrologic character between the three provinces will be a main consideration for those writing or updating these regulations. Regulations that protect areas where the principal aquifer is unconsolidated basin-fill sediments may be overly restrictive for an area where the principal aquifer is a deep sandstone. Conversely, regulations designed for basin-fill aquifers may be inadequate to protect a highly fractured consolidated-rock aquifer exposed at land surface.