Perched Ground Water in Zeolitized-Bedded Tuff, Rainier Mesa and Vicinity, Nevada Test Site, Nevada

A process to estimate net infiltration using a site-scale water-budget approach, Rainier Mesa, Nevada National Security Site, Nevada, 2002–05

“…Because discharge decreased with time, it was concluded that the fractures were disconnected. This conclusion is supported by Thordarson (1965), who noted that only 2 percent of roughly 5,000 fractures in 19 km of exposed tunnel yielded water.…”

“…These rises are interpreted as a response to episodic pulses of recharge resulting from substantially above-average precipitation during the 2004-05 winter (Soule, 2006;Mirus and Nimmo, 2013). These rapid rises are consistent with preferential flow paths that allow recharge to reach the water table quickly (Thordarson, 1965;Ebel and Nimmo, 2009). Previous estimates of recharge to the water table on Rainier Mesa range from 5 (Belcher and others, 2004) to 50 millimeters per year (mm/yr) (Russell and Minor, 2002).…”

“…This volcanic upland is preserved, in part, by a dense cap of welded tuff identified as the Timber Mountain welded-tuff formation (Fenelon and others, 2008). The Tertiary-age heavily fractured welded-tuff caprock extends from land surface to 80-170 m below land surface (bls) and overlies a thick sequence (>900 m) of bedded tuffs (Thordarson, 1965;Fenelon and others, 2010). Precipitation periodically percolates beyond the influence of the dynamic near-surface ET zone and recharges the water table about 450 m bls (Fenelon and others, 2010).…”

“…Contrarily, flow is extremely limited through the welded-tuff matrix because the saturated hydraulic conductivity is less than 5 × 10 -9 m/s (Thordarson, 1965;Ebel and Nimmo, 2009). Various investigators used tunnels mined into the mesa to study the recharge process.…”

“…Underground nuclear tests were done near or below the water table in 11 tunnels ranging from 0.06-to 24-km long (Ebel and Nimmo, 2009). Groundwater discharged to some of the tunnels through fractures and faults exposed during mining (Clebsch, 1960;Thordarson, 1965). Because discharge decreased with time, it was concluded that the fractures were disconnected.…”