GROUND-WATER SENSITIVITY AND VULNERABILITY MAPS FOR THE STATE OF UTAH

Contamination from pesticides poses a potential threat to human health and the environment in agricultural areas of Utah where ground water is the primary source of drinking water. Using geographic information system (GIS) technology and readily available GIS data, we mapped ground-water sensitivity and vulnerability to pesticides for the state of Utah. This mapping was performed as part of U.S. Environmental Protection Agency-required management plans for four agricultural pesticides (alachlor, atrazine, metolachlor, and simazine).

Sensitivity to pesticides was determined by assessing natural factors favorable or unfavorable to the degradation of ground water by pesticides applied or spilled on the land surface. We selected hydrostratigraphy (based on primary and secondary permeability of geologic units), soil hydraulic conductivity, retardation of pesticides, attenuation of pesticides, depth to ground water, and land-surface slope as the six factors primarily determining ground-water sensitivity to pesticides in Utah. Vulnerability to pesticides was determined by assessing the effects of human-induced factors on ground-water sensitivity to pesticides. We selected irrigated versus non-irrigated agriculture, and crop type (corn or sorghum versus other crop types), as the two principal human-related factors that, when combined with pesticide sensitivity, determine ground-water vulnerability to pesticides.

We compiled two GIS maps by applying a combined process-based and index-based model to determine ground-water sensitivity and vulnerability to pesticides, and then combining the numerical rankings to produce low, moderate, and high GIS map categories. In terms of land area, the low, moderate, and high categories respectively cover 13, 79, and 8 percent of the state for sensitivity, and 13, 86, and 1 percent for vulnerability.