Detailed Hydrogeologic Evaluation of the Hurricane Fault Zone and the Pah Tempe Hot Springs Hydrothermal System, Washington County, Utah
Tom Marston and Bert Stolp
14 May 18
Pah Tempe Springs, also known as Dixie Hot Springs or La Verkin Springs, are located along the Virgin River where the river cuts through Timpoweap Canyon in Washington County, Utah. The average concentration of dissolved solids in discharge from these springs is 9,100 mg/L and the springs contribute about 95,000 tons of dissolved solids (salt) annually to the Virgin River. The Bureau of
Reclamation (BOR) Colorado River Basin Salinity Control Program (CRBSCP) continues to evaluate the feasibility of desalinizing the discharge of Pah Tempe Springs to improve water quality in the Virgin River. The most viable plan identified by the BOR in early
studies for mitigating the salt discharge to the Virgin River from Pah Tempe Springs is to capture and treat the spring flow by withdrawing (pumping) thermal groundwater from within the Hurricane Fault damage zone to lower the groundwater pressure head and thereby reducing or eliminating discharge from the springs into the river. To understand the interaction between the hydrothermal groundwater system and the Virgin River locally around Pah Tempe Hot Springs, the U.S. Geological Survey (USGS) and Washington County Water Conservancy District (WCWCD) conducted three stress tests where thermal groundwater was pumped at rates up to 7 cubic feet per second from a shallow subsurface cistern under different flow conditions in the adjacent Virgin River during 2013-2014. During each test, changes in spring and pumping discharge, chemistry, and temperature were continuously monitored. The USGS and WCWCD are currently drilling two exploration wells that will: 1) investigate groundwater stratification associated with Pah Tempe Springs and the Virgin River using general water chemistry and age-dating tracers, 2) assess hydrologic conditions associated with the Hurricane Fault in relation to the location of Pah Tempe Springs, 3) examine hydraulic characteristics of the shallow stream channel deposits, Toroweap Limestone, and Queantoweap Sandstone, and 4) refine a preliminary numerical model of the groundwater flow system.