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The AAPG/Datapages Combined Publications Database

Utah Geological Association

Abstract


Geology of Northwest Utah, 2006
Pages 83-131

Ground Water Sensitivity and Vulnerability to Pesticides, Northern and Central Wasatch Front, Utah

Mike Lowe, Janae Wallace

Abstract

The U.S. Environmental Protection Agency recommends states develop Pesticide Management Plans for four agricultural chemicals—alachlor, atrazine, metolachlor, and simazine—herbicides used in Utah in the production of corn and sorghum. The maps presented in this document have been previously published as four separate publications by the Utah Geological Survey, but have been consolidated herein into one report covering the northern and central Wasatch Front; the original documents are intended to be used as part of the Utah Department of Agriculture and Food’s Pesticide Management Plans to provide local, state, and federal government agencies and agricultural pesticide users with a base of information concerning sensitivity and vulnerability of ground water to agricultural pesticides. We used existing data to produce pesticide sensitivity and vulnerability maps by applying an attribute ranking system specifically tailored to the western United States using Geographic Information System analysis methods. This is a first cut at developing pesticide sensitivity and vulnerability maps; better data and tools may become available in the future so that better maps can be produced.

Ground water sensitivity (intrinsic susceptibility) to pesticides is determined by assessing natural factors favorable or unfavorable to the degradation of ground water by any pesticides applied to or spilled on the land surface. Hydrogeologic setting (vertical ground water gradient and presence or absence of confining layers), soil hydraulic conductivity, retardation of pesticides, attenuation of pesticides, and depth to ground water are the factors primarily determining ground water sensitivity to pesticides in the basin-fill deposits of the northern and central Wasatch Front. Much of the northern and central Wasatch Front has low ground-water sensitivity to pesticides due to prevalent protective clay layers within the basin-fill deposits.

Ground water vulnerability to pesticides is determined by assessing how ground-water sensitivity is modified by the activities of humans. Ground-water sensitivity to pesticides, the presence of applied water (irrigation), and crop type are the three factors generally determining ground water vulnerability to pesticides in the basin-fill deposits of the northern and central Wasatch Front. Areas of high vulnerability are located primarily in areas where irrigation occurs and ground-water sensitivity to pesticides is high. Of particular concern are areas where influent (losing) streams originating in mountainous areas cross the basin margin; streams in these areas are the most important source of recharge to the basin-fill aquifer and efforts to preserve water quality in streams at these points would help to preserve ground-water quality in the northern and central Wasatch Front.

Because of relatively high retardation (long travel times of pesticides in the vadose zone) and attenuation (short half-lives) of pesticides in the soil environment, pesticides applied to fields in the northern and central Wasatch Front likely do not present a serious threat to ground-water quality. To verify this conclusion, the author’s recommend that future ground-water sampling by the Utah Department of Agriculture and Food in the northern and central Wasatch Front be concentrated in areas of moderate and high sensitivity or vulnerability, typically along basin margins. Sampling in the central areas of the Great Salt Lake and Utah Lake basins, characterized by low sensitivity and vulnerability, should continue, but at a lower density than in the areas of higher sensitivity and vulnerability.


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