The potential for groundwater contamination along basin margins in the arid west: Alluvial fans and lake features

Many towns of the arid west were built upon alluvial fans and upon sites underlain by Pleistocene lake deposits. The objective of this study was to assess the potential impact of these activities of man upon groundwater quality within these geological features. Emphasis was placed on shallow groundwater quality after it was determined that deep groundwater is rarely contaminated at such sites. A reconnaissance of Utah and Nevada was made and four sites underlain by alluvial fans (Willard, Manti, Elsinore, and Spring City) and four sites underlain by lake shore deposits (Hyde Park, Fielding, Providence and Richmond) were selected in Utah for more detailed geologic, hydrologic, and water quality studies. Samples for water quality analyses were taken from existing wells and springs where available. At Hyde Park a shallow, small diameter well was constructed. Three groundwater sampling wells were constructed on the Willard Creek fan. Sites were selected to represent various degrees and types of land use. It was concluded that septic effluents, agricultural wastes, and other sources of man-made contamination can be hazards to shallow groundwater quality in alluvial fans and lake shore sediments. Mercury was found in concentrations exceeding the EPA drinking water standards at a few of the sites, but its source was probably natural. Nitrates and phosphates usually were the observable indicators of shallow groundwater contamination at the sites investigated, while coliform bacteria evidently are not transported appreciable distances underground and made poor indicators. The conclusions reached in this report are believed to be applicable to other areas of the arid west where similar geologic features and basin margin sediments occur