THE STATE OF WYOMING Water Development Office 6920 YELLOWTAIL ROAD TELEPHONE: (307) 777-7626 CHEYENNE, WY 82002 FAX: (307) 777-6819 TECHNICAL MEMORANDUM TO: Water Development Commission DATE: December 13, 2013 FROM: Keith E. Clarey, P.G. REFERENCE: Snake/Salt River Basin Plan Update, 2012 SUBJECT: Available Groundwater Determination – Tab XI (2012) Contents 1.0 Introduction .............................................................................................................................. 1 2.0 Hydrogeology .......................................................................................................................... 4 3.0 Groundwater Development .................................................................................................... 15 4.0 Groundwater Quality ............................................................................................................. 21 5.0 Geothermal Resources ........................................................................................................... 22 6.0 Groundwater Availability ...................................................................................................... 22 References ..................................................................................................................................... 23 Appendix A: Figures and Table ....................................................................................................... i 1.0 Introduction This 2013 Technical Memorandum is an update of the September 10, 2003, Tab S – “Available Groundwater Determination Technical Memorandum” (Hinckley, 2003) and focuses on the changes in the Snake/Salt River Basin groundwater resources from approximately 2003 to 2013. The population of the Basin and real estate values in the Basin has continued to increase over the past 10 years with a corresponding increase in groundwater use. The Snake/Salt River Basin is located in northwestern Wyoming and covers an area of approximately 5,096 square miles (3,261,440 acres). Private lands only comprise 256,340 acres (7.8%) of the Snake/Salt River Basin, which means 92.2% of this Basin is public land. Most of the private land is located in the river valleys, hill sides, and stream/river drainages within the Basin. The Snake/Salt River Basin has several unique features compared to the other six major river basins located in Wyoming, including: • The highest percentage of public land (92.2%) and the lowest percentage (7.8%) of private land. • The highest rates (62+ inches) of annual precipitation. • The highest potential for large earthquakes (magnitude 5.0 or greater) to occur, including earthquakes in the 7 to 8+ magnitude range. • The highest concentration of landslide deposits. Technical Memorandum Available Groundwater Determination Wyoming Water Development Office Page 1 The Wyoming Framework Water Plan was completed in 2007 and included updated data on the groundwater resources of the Snake/Salt River Basin: • The Framework Plan (WWC Engineering, 2007; Table 5-6, p. 5-11) listed the average Basin demand factor as 223 gallons per capita per day (surface and groundwater combined); with municipal groundwater use as 5,875,140 gallons per day (18.0 acre- feet/day or 6,581 acre-feet/year) and domestic groundwater use as 2,241,000 gallons per day (6.9 acre-feet/day or 2,510 acre-feet/year). • The Framework Plan (WWC Engineering, 2007; Table 5-7, p. 5-12) listed municipal and domestic groundwater depletions combined as approximately 9,100 acre-feet per year. • The Framework Plan (WWC Engineering, 2007; Table 5-8, p. 5-14) listed industrial (manufacturing) groundwater use as 140 acre-feet per year. There are a total of sixty-eight (68) GIS geologic units shown on the Geologic Map of the Snake/Salt River Basin (Figure A-1) and these units are included in Table A-1. Figure A-2 illustrates the Major Aquifer Groups of the Basin. These groups include the Cenozoic, Mesozoic, Paleozoic, and Precambrian Aquifer Groups and the Volcanic and Intrusive Formations. The Volcanic and Intrusive Formations (Middle Eocene and younger age) are actually a subgroup within the Cenozoic Aquifer Group. Figure A-3 shows spring locations that are mapped on the U.S. Geological Survey (USGS) 1:24,000-scale topographic maps within Wyoming. The locations of 418 springs in the Snake/Salt River Basin are shown on Figure A-3. In the October 2012 database provided by the Wyoming State Engineer’s Office (WSEO), there are a total of 6,161 groundwater permit entries in the Snake/Salt River Basin (Figure A-4). Not all of these 6,161 permit entries represent one single water well. Some wells and springs have more than one permit. These WSEO groundwater permits include water wells and small springs of 25 gallons per minute (gpm) or less yield. Larger yielding (greater than 25 gpm) springs have a surface water permit from the WSEO. The total calculated area of the Snake/Salt River Basin using the GIS Wyoming Geologic Map data (1:500,000-scale digital Geologic Map of Wyoming) is 5,108.70 square miles, which is a difference of 12.70 square miles compared to the basin area of 5,096 square miles as calculated by using a digital GIS method. There are 4,212 digital polygons for the Snake/Salt River Basin as part of the 1:500,000-scale state-wide GIS geologic map of Wyoming. A very small mapped GIS polygon of geologic unit “Tcs” is reportedly located in the northern part of the Teton Range and is mapped as Conglomerate of the Sublette Range (Tcs). This is apparently an error in the GIS database for the 1:500,000-scale digital GIS geologic map of Wyoming. Using the 5,108.70 square mile area from the 1:500,000 scale digital Wyoming Geologic Map, the following Basin areas are calculated: Technical Memorandum Available Groundwater Determination Wyoming Water Development Office Page 2 Water/Reservoir 70.47 square miles (1.4%) Volcanic and Intrusive Formations 825.50 square miles (16.2%) Cenozoic Aquifer Group 2,044.77 square miles (40.0%) Mesozoic Aquifer Group 1,218.74 square miles (23.8%) Paleozoic Aquifer Group 789.65 square miles (15.5%) Precambrian Aquifer Group 159.57 square miles (3.1%) TOTAL 5,108.70 square miles (100%) Cenozoic Aquifer Group The Cenozoic Aquifer Group is the most heavily used aquifer group for groundwater supplies in the Snake/Salt River Basin. The various units of this aquifer group and the corresponding surface areas within the Basin are listed below: Qal – Quaternary alluvium and colluvium 540.34 square miles (10.6%) Qg – Quaternary glacial deposits 429.87 square miles (8.4%) Qls – Quaternary landslide deposits 369.73 square miles (7.2%) Qt – Quaternary gravel deposits 155.93 square miles (3.1%) Qu – Quaternary, undivided 106.69 square miles (2.1%) QTg – Tertiary-Quaternary conglomerate 5.75 square miles (0.1%) Approximately 15.9% (808.71 square miles) of the Snake/Salt River Basin is covered by the “alluvial aquifer,” which combines the alluvium/colluvium, gravel deposits, undivided deposits, and conglomerate into one larger unit of similar hydrogeologic characteristics. Hinckley (2003, p. 30) considered the “alluvial aquifer” to cover approximately 400 square miles. Please note that the “Volcanic and Intrusive Formations” are actually of Cenozoic age (Middle Eocene and younger) and therefore may be considered a subgroup of an expanded Cenozoic Aquifer Group that covers a total area of 2,870.27 square miles (56.2%). There are 12 units listed in Table A-1 that are considered primarily “volcanic” (also includes intrusive igneous rock units). When these Yellowstone-related igneous rock formations are included in the Cenozoic Aquifer Group, all of the geologic formations of Cenozoic age cover a total area of 56.2% of the Snake/Salt River Basin in Wyoming. Previous Studies – Since 2003 The 2003 Hinckley Consulting, Snake/Salt River Basin Plan Technical Memorandum listed the older hydrogeologic studies in the Basin. Since 2003, many additional studies have been conducted. The Wyoming Water Development Commission (WWDC) has funded the following water development studies and projects during the time period from 2003 to 2013: • Hinckley Consulting (2003), Available Groundwater Determination, Snake/Salt River Basin Plan, Technical Memorandum. • Keller Associates, Inc. (2003), Kennington Springs Pipeline Company, Level I Water System Reconnaissance Study. • Nelson Engineering (2006), Hoback Junction Water Supply Study, Level I, Final Report. Technical Memorandum Available Groundwater Determination Wyoming Water Development Office Page 3 • Sunrise Engineering (2006), Siting, Construction and Testing of the Town of Afton New Municipal East Alley Well. • Rendezvous Engineering, P.C. (2007), Final Report, Level II – Alta Groundwater Supply Study. • WWC Engineering (2007), Wyoming Framework Water Plan. • Forsgren Associates, Inc. (2008), Star Valley Ranch Master Plan. • Rendezvous Engineering, P.C. (2009), Final Report, Level II – Alpine Master Plan Update. • Sunrise Engineering (2009), Star Valley Regional Master Plan, Final Report. • Sunrise Engineering (2009), Star Valley Regional Master Plan, Water System Investigation & Evaluations, Book 1 of 2. • Sunrise Engineering (2009), Star Valley Regional Master Plan, Water System Investigation & Evaluations, Book 2 of 2. • Weston Engineering (2009), Final Report, Star Valley Ranch Groundwater Level II Study. • Jorgensen Associates, PC (2012), Thayne Storage – Level II Study, Final Report. The more complete references for these listed WWDC studies are included in the reference