HR: 11:50h
AN: H42C-07    [Abstracts]
TI: Multivariate Analysis of Amargosa Desert, NV Groundwater Chemistry
AU: * Woocay, A
EM: awoocay@utep.edu
AF: University of Texas at El Paso, 500 W. University Ave., El Paso, TX 79968 United States
AU: Walton, J C
EM: walton@utep.edu
AF: University of Texas at El Paso, 500 W. University Ave., El Paso, TX 79968 United States
AB: Major ion and isotopic chemistry from 203 wells located in the vicinity of the Amargosa Desert, Nevada was analyzed using Principal Component Analysis (PCA). PCA is a multivariate method that allows for a better understanding of the chemical evolution of the groundwater, potential flow paths, and groundwater flow rates. The PCA of the major ion chemistry was used to reduce the number of variables that describe the groundwater chemistry from seven to three principal axes which are then rotated to better interpret the systems variation. A cluster analysis of the reduced system produced nine separate groups of wells. The derived axes and well groups are presented as biplots and overlaid on a digital elevation model of the region giving a visual picture of potential interactions and flow paths. A distinct signature of the groundwater chemistry along the extended flow path of Fortymile Wash can be observed along with some potential interaction at possible fault lines near Highway 95. The signature from Fortymile Wash is believed to represent the relict of water that infiltrated during past pluvial periods when the amount of runoff in the wash was significantly larger than during the current drier period. This hypothesis appears to be supported by 14C and 18O data which indicate that younger groundwater is found in the upper part of wash near Yucca Mountain and older groundwater is found in the lower region of the wash near Amargosa Valley. Corrected 14C dating along Fortymile Wash present ages between 8 thousand years in the upper region and 14 thousand years in the lower region. This range in ages corresponds to the end of the Pleistocene and early Holocene, marking the end of the Wisconsin glaciation and beginning of the current interglacial period. The range of the 18O data correspond to a relatively cold clime precipitation and have a similar spatial signature to the 14C data. 18O values in the upper part of Fortymile Wash correspond to the warmer climate of the cold clime range, but still cold relative to the present; whereas values found in the lower portion of the wash correspond to colder climates. Plots of 2H versus 18O compared with the Global Meteoric Water Line (GMWL), demonstrate a humid climate type of precipitation with very little surface evaporation before infiltration, which along with a cold climate, suggest snowmelt infiltration.
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1833 Hydroclimatology
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting