Well U-20bg is open below the water table to about 60 ft of tuff. The initial five water levels show a rising trend following dewatering of the well after drilling. This rising trend is followed by a 4-yr declining trend as water levels equilibrated from well construction. From 1996 to present (2011), water levels are consistent and representative of steady-state conditions in the volcanic composite unit open to the well. Some of the small changes in water levels from 1996 to present may be caused by pumping in well U-20 WW (cased), located 1.5 mi northwest of well U-20bg (Fenelon, 2000). For example, the small (0.3 ft) rise from 1996 to 1998 followed by the 0.5-ft decline in late 1998 to mid 1999 correspond to decreasing and increasing pumpage in well U-20 WW (cased). These changes in water levels that potentially result from pumping are too small to definitively attribute to pumping because of water-level variation caused by measurement error and barometric-pressure changes. Well U-20bg was used as an observation well for an aquifer test in 2008-09, in which well U-20 WW (cased) was pumped. No response was seen in well U-20bg from this pumping. Continual data and interpretations for the aquifer test are available from the U.S. Geological Survey Nevada Water Science Center Aquifer Tests web page at http://nevada.usgs.gov/water/AquiferTests/index.htm. Continual water-level data are available for well U-20bg from October 2008 to June 2011 (U.S. Geological Survey data files, Henderson, Nev.). Three nuclear tests, near or below the water table, were detonated within 1 mi of U-20bg.Less
