Sources and mechanisms of recharge for ground water in the west-central Amargosa Desert, Nevada– A geochemical interpretation

Abstract

Ground water in the west-central Amargosa Desert, Nevada, was recharged primarily by overland flow of snowmelt in or near the present-day stream channels, rather than by subsurface flow from highland recharge areas to the north. Geochemical arguments, including reaction mechanisms, are used to support these findings. Carbon-, hydrogen-, and oxygen-isotope data show that much of the recharge in the area occurred during late Wisconsin time. Absence of ground water recharged prior to late Pleistocene is considered to indicate that either climatic conditions were unfavorable for recharge or that ground-water velocities were such that they transported this earlier recharge away from the study area.

Groundwater chemistry at Yucca Mountain, Nevada, and vicinity

“…They used Isotopic data to conclude that groundwater from Pahute Mesa discharges through tuffaceous aquifers Into Oasis Valley, but not Into Fortymtle Wash. They also concluded that water In the alluvium In the upper north-central Amargosa Desert originated principally as groundwater In tuffs In Fortymlle Wash; this disagrees with the conclusion of Claassen (1985) that overland flow was more Important. White and Chuma (1986) Infer that, during passage through Oasis Valley, dissolved carbonate In the water Is exchanged with soil-zone carbon dioxide and carbonate In caliche; this exchange Is facilitated by the proximity of the water to ths ground surface In Oasis Valley.…”

“…The straight Hne through the origin, with a slope of 0.82, represents a least squares fit of all the data. Claassen (1985) shows a similar plot with a line representing evaporation of modern precipitation; the slope of that line is approximately 1.65, that 1s, twice the slope of the line In F1g. 13(a).…”

“…Two different proposals for the source of groundwater In the southern part of Fortymile Wash have been made. Claassen (1985) concluded that groundwater was recharged primarily by overland flow and local recharge, but White and Chuma (1986) considered subsurface flow more likely. In either case, the water would contact tuffaceous material in the aquifers or valley fill and have a similar overall composition.…”

“…13(a). Claassen (1985) also noted that groundwater in the Amargosa Desert contains less sulfate relative to chloride than modern precipitation. EQ3 calculations of gypsum log 1Q (Q/K) for about two-thirds of the samples 1n Figs.…”

Electrical conductivity images of Quaternary faults and Tertiary detachments in the California Basin and Range

“…Hydrogeochemical analyses of the formation waters in the carbonate aquifers reveal a narrow range of 13-16 ohm-m for the fluid resistivities from springs in the Ash Meadows discharge zone [Winograd and Thordarson, 1975]. From additional geochemical analyses of water sampled in boreholes near Ash Meadows [Claassen, 1985], we calculated a water resistivity of 9.4 ohm-m and therefore conclude that 10 ohm-m is a reasonable average resistivity for zones 2, 4, 6, and 7. Models relating fluid resistivity and rock resistivity have the form:…”