Assessment of managed aquifer recharge from Sand Hollow Reservoir Washington County Utah updated to conditions in 2010: USGS Scientific Investigations Report 2011-5142

Sand Hollow Reservoir in Washington County Utah was completed in March 2002 and is operated primarily for managed aquifer recharge by the Washington County Water Conservancy District. From 2002 through 2009 total surface-water diversions of about 154000 acre-feet to Sand Hollow Reservoir have allowed it to remain nearly full since 2006. Groundwater levels in monitoring wells near the reservoir rose through 2006 and have fluctuated more recently because of variations in reservoir water-level altitude and nearby pumping from production wells. Between 2004 and 2009 a total of about 13000 acre-feet of groundwater has been withdrawn by these wells for municipal supply. In addition a total of about 14000 acre-feet of shallow seepage was captured by French drains adjacent to the North and West Dams and used for municipal supply irrigation or returned to the reservoir. From 2002 through 2009 about 86000 acre-feet of water seeped beneath the reservoir to recharge the underlying Navajo Sandstone aquifer. Water-quality sampling was conducted at various monitoring wells in Sand Hollow to evaluate the timing and location of reservoir recharge moving through the aquifer. Tracers of reservoir recharge include major and minor dissolved inorganic ions tritium dissolved organic carbon chlorofluorocarbons sulfur hexafluoride and noble gases. By 2010 this recharge arrived at monitoring wells within about 1000 feet of the reservoir.