WATER-QUALITY ASSESSMENT OF THE UPPER SNAKE RIVER BASIN, IDAHO AND WESTERN WYOMING ENVIRONMENTAL SETTING, 1980-92 By MOLLY A. MAUPIN U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 94-4221 Boise, Idaho 1995 FOREWORD The mission of the U.S. Geological Survey Describe how water quality is changing over time. (USGS) is to assess the quantity and quality of the Improve understanding of the primary natural and earth resources of the Nation and to provide informa­ human factors that affect water-quality conditions. tion that will assist resource managers and policymak- ers at Federal, State, and local levels in making sound This information will help support the develop­ decisions. Assessment of water-quality conditions and ment and evaluation of management, regulatory, and trends is an important part of this overall mission. monitoring decisions by other Federal, State, and local agencies to protect, use, and enhance water resources. One of the greatest challenges faced by water- resources scientists is acquiring reliable information The goals of the NAWQA Program are being that will guide the use and protection of the Nation's achieved through ongoing and proposed investigations water resources. That challenge is being addressed by of 60 of the Nation's most important river basins and Federal, State, interstate, and local water-resource aquifer systems, which are referred to as study units. agencies and by many academic institutions. These These study units are distributed throughout the Nation organizations are collecting water-quality data for a and cover a diversity of hydrogeologic settings. More host of purposes that include: compliance with permits than two-thirds of the Nation's freshwater use occurs and water-supply standards; development of remedia­ within the 60 study units and more than two-thirds of tion plans for a specific contamination problem; opera­ the people served by public water-supply systems live tional decisions on industrial, wastewater, or water- within their boundaries. supply facilities; and research on factors that affect National synthesis of data analysis, based on water quality. An additional need for water-quality aggregation of comparable information obtained from information is to provide a basis on which regional and the study units, is a major component of the program. national-level policy decisions can be based. Wise This effort focuses on selected water-quality topics decisions must be based on sound information. As a using nationally consistent information. Comparative society we need to know whether certain types of studies will explain differences and similarities in water-quality problems are isolated or ubiquitous, observed water-quality conditions among study areas whether there are significant differences in conditions and will identify changes and trends and their causes. among regions, whether the conditions are changing The first topics addressed by the national synthesis are over time, and why these conditions change from place pesticides, nutrients, volatile organic compounds, and to place and over time. The information can be used to aquatic biology. Discussions on these and other water- help determine the efficacy of existing water-quality quality topics will be published in periodic summaries policies and to help analysts determine the need for and of the quality of the Nation's ground and surface water likely consequences of new policies. as the information becomes available. To address these needs, the Congress appropriated This report is an element of the comprehensive funds in 1986 for the USGS to begin a pilot program in body of information developed as part of the NAWQA seven project areas to develop and refine the National Program. The program depends heavily on the advice, Water-Quality Assessment (NAWQA) Program. In cooperation, and information from many Federal, 1991, the USGS began full implementation of the pro­ State, interstate, Tribal, and local agencies and the pub­ gram. The NAWQA Program builds upon an existing lic. The assistance and suggestions of all are greatly base of water-quality studies of the USGS, as well as appreciated. those of other Federal, State, and local agencies. The objectives of the NAWQA Program are to: Describe current water-quality conditions for a large part of the Nation's freshwater streams, Robert M. Hirsch rivers, and aquifers. Chief Hydrologist Forewordi UK' CONTENTS Foreword ................................................................................................................................................................................ iii Abstract .................................................................................................................................................................................. 1 Introduction ............................. ............................................................................................................................................... 2 Purpose and scope.......................... ................................................................................................................................. 2 Acknowledgments........................................................................................................................................................... 2 Environmental setting ............................................................................................................................................................ 2 Location and physiography ............................................................................................................................................. 2 Population....................................................................................................................................................................... 4 Geology........................................................................................................................................................................... 5 Climate................................... ......................................................................................................................................... 8 Surface-water hydrology.......... ....................................................................................................................................... 12 Ground-water hydrology ................................................................................................................................................. 16 Soils...................................... ........................................................................................................................................... 18 Ecoregions............................. .......................................................................................................................................... 20 Land use and land ownership ................................................................................................................................................. 22 Water use .................................................................................................................................................................... 26 Offstream water use ........................................................................................................................................................ 27 Irrigated agriculture ................................................................................................................................................. 27 Industrial .................................................................................................................................................................. 28 Municipal................................................................................................................................................................. 28 Instream water use .......................................................................................................................................................... 28 Aquaculture........................ ...................................................................................................................................... 28 Hydroelectric power generation............................................................................................................................... 29 Sources of pollution ............................................................................................................................................................... 29 Point sources ................................................................................................................................................................... 29 Nonpoint sources............................................................................................................................................................. 30 Summary ................................................................................................................................................................................ 32 References cited ..................................................................................................................................................................... 34 ILLUSTRATIONS 1 -4. Maps showing: 1. Upper Snake River Basin study area................................................................................................................