Selected hydrologic data for Salt Lake Valley, Utah, 1990-92, with emphasis on data from the shallow unconfined aquifer and confining layers

Abstract

Hydrologic data were collected from wells in the Salt Lake Valley, Utah, from 1990 to 1992, to better understand the hydrologic system in the valley. Most of the data collected are from 36 monitoring wells drilled in June and July 1990 and March and May 1991 using a hollow-stem auger. These wells range from 15.0 to 129.5 feet deep and are completed in the shallow unconfined aquifer, an underlying confining layer, or both. Data from public supply wells and other existing wells completed in aquifers below the confining layers near these monitoring wells are presented in order to compare data from those wells with data from the shallow unconfined aquifer and the underlying confining layers. Field data collected from selected wells and drill holes include well-completion information, lithologic logs, and water-level and field water-quality measurements. Water samples collected from monitoring wells drilled in 1990 and 1991 and from selected existing wells were analyzed for inorganic constituents, trace metals in unfiltered water, volatile organic compounds, organochlorine pesticides, polychlorinated biphenyls, and radionuclides. Core samples were collected from selected monitoring wells drilled in 1990 and 1991 and analyzed for geochemical and geotechnical properties. Cation exchange capacity, carbon concentration, and the concentration of selected elements in core material are presented. Particle size, dry density, moisture content, porosity, hydraulic conductivity, initial void ratio, specific storage, and other properties determined for material in cores from selected monitoring wells also are listed. INTRODUCTION This report contains hydrologic data collected in the Salt Lake Valley mainly from 1990 through 1992. The Salt Lake Valley (pi. 1) is bounded by the Wasatch Range on the east, the Oquirrh Mountains on the west, the Traverse Mountains on the south, and the boundary between Davis and Salt Lake Counties on the north. The saturated valley-fill material in Salt Lake Valley consists of a deep unconfined aquifer near the mountains, a confined (artesian) aquifer, a shallow unconfined aquifer overlying the confined aquifer, and locally unconfined or perched aquifers (Hely and others, 1971,p. 107-111). Less permeable layers of silt and clay overlie the confined aquifer, but the thickness, continuity, and permeability of these confining layers vary with location. Ground water in the deep unconfined and confined aquifers is used for public supply in many parts of the valley. The shallow unconfined aquifer is relatively close to activities and processes occurring at land surface. This makes the shallow unconfined aquifer more susceptible to many types of contamination, such as contamination from trace metals, organic compounds, and increased concentrations of dissolved solids as a result of evaporation. The extent of the confining layers separating the shallow unconfined aquifer from the deep confined aquifer and their effectiveness as a barrier to contaminant movement are not well known. Hydrologic data were collected by the U.S. Geological Survey in cooperation with the Utah Department of Natural Resources, Division of Water Rights, and the Utah Department of Environmental Quality, Division of Water Quality. The following public water suppliers also provided financial assistance for the collection of hydrologic data presented in this report: Salt Lake City Corporation, Salt Lake County Water Conservancy District, Taylorsville-Bennion Improvement District, Granger-Hunter Improvement District, Murray City, City of South Salt Lake, and Kearns Improvement District. Purpose and Scope The purpose of this report is to present hydrologic data for use by the general public and by officials who manage water resources. The U.S. Geological Survey began a study in 1990 to better define the ground-water-flow system in Salt Lake Valley. This report supplements an objective of this study, which is to better define the quality of water and hydraulic properties of the shallow unconfined aquifer and the underlying confining layers. Most of the data presented in this report are from 36 monitoring wells drilled in June and July 1990 and March and May 1991 using a hollow-stem auger. These monitoring wells range from 15.0 to 129.5 feet deep and penetrate the shallow unconfined aquifer, an underlying confining layer, or both. Data from public supply wells and other existing wells completed in the deep confined and unconfined aquifers near these monitoring wells are presented in order to compare data from those wells with data from the shallow unconfined aquifer and the underlying confining layers. Water levels in selected monitoring wells completed in the shallow unconfined aquifer in 1982 (Seiler and Waddell, 1984) were remeasured in 1990. Five existing seismic-data access holes also were converted to monitoring wells. Although depths of the converted access holes range from 168 to 248 feet, two of the wells on the east side of the valley are completed in an unsaturated zone. Information collected from monitoring wells drilled in 1990 and 1991 by the U.S. Geological Survey and from selected existing wells is presented in tables 1 through 13. Most of the data presented in this report were collected from 1990 through 1992. Selected water-level and waterquality data collected prior to 1990 also are included. Well locations are shown on plate 1. The well-numbering system used in Utah is shown in figure 1. Field data such as well-completion information, lithologic logs, and water-level measurements from wells and drill holes are listed in tables 1,2, 3, and 4. Methods and Types of Analysis Chemical analyses of water from wells sampled in 1990 and 1991 were made mainly by the Utah State Health Laboratory. Methods of analysis used by the Utah State Health Laboratory are listed in its quality assurance plan (Utah State Health Laboratory, 1988). Selected nitrite and nitrate plus nitrite values were determined by the U.S. Geological Survey National Water Quality Laboratory. Chemical analyses of water samples collected prior to 1990 but included in this report and water samples collected from selected public supply wells in 1990 also were made by the National Water Quality Laboratory. Methods of analysis used by the National Water Quality Laboratory are described by Fishman and Friedman (1989). The results of these analyses are listed in tables 5 and 6. The system of numbering wells in Utah is based on the cadastral land-survey system of the U.S. Government. The number, in addition to designating the well, describes its position in the land net. The land-survey system divides the State into four quadrants separated by the Salt Lake Base Line and the Salt Lake Meridian. These quadrants are designated by the uppercase letters A, B, C, and D, indicating the northeast, northwest, southwest, and southeast quadrants, respectively. Numbers designating the township and range, in that order, follow the quadrant letter, and all three are enclosed in parentheses. The number after the parentheses indicates the section, and is followed by three letters indicating the quarter section, the quarter-quarter section, and the quarter-quarter-quarter section generally 10 1 acres. The letters, a, b, c, and d indicate, respectively, the northeast, northwest, southwest, and southeast quarters of each subdivision. The number after the letters is the serial number of the well within the 10acre tract. Thus, (C-2-l)23dac-l designates the first well constructed or visited in the southwest 1/4, northeast 1/4, southeast 1/4, section 23, T. 2 S., R. 1 W. The numbering system is illustrated below. Sections within a township R. 1 W. Tracts within a section Sec. 23