Vol.19 No.1 CHINESE JOURNAL OF GEOCHEMISTRY 2000 Major Ion Geochemistry of Groundwaters from Southern Nevada and Eastern California, USA ZHOU XIAOPING' ) () J /i'F) , KLAUS J. STETZENBACHI , KEVIN H. JOHANNESSON2) , AND IRENE M. FARNHAM' 1) (Grounduxiter Geochemistry Group, Harry Reid Center for Environmental Studies, University of Nevada, Las V egas, Las V egas, Nevada 89154 -4009, USA ) 2) (Department of Ocean, Earth, and Atmospheric Sciences, Old Dominion University, Norfolk, V irginia 23529-0276, USA ) Abstract: The dissolved ionic constituents of groundwaters are, in part, a record of the miner- als and rocks in aquifers through which the water has flowed. The chemical composition and association of these major ions in groundwaters have been used to trace groundwater flow paths and sources. In general, the chemical composition of water in carbonate-rock aquifers is domi- nated by calcium, magnesium, and bicarbonate, whereas sodium, chloride, and sulfate can be dominant ions in the water that comes from volcanic aquifers or clay minerals. Since the 1990' s, we have dealt with the geochemistry of groundwaters from more than 100 springs and wells in southern Nevada and eastern California, USA for major solutes and trace elements. This paper compiles the hydrochemical data of major ions of these groundwaters. Based on ma- jor ion geochemistry, groundwaters from southern Nevada and eastern California can be classi- fied as carbonate aquifer water, volcanic aquifer water, and mixing water (either mixing of carbonate and volcanic aquifer waters or mixing with local recharges) . Piper and Stiff diagrams of major ions have graphically shown the general chemical characteristics, classifications, and mixing relationships of groundwaters from southern Nevada and eastern California. Key words: geochemistry; major ion, groundwater; Nevada and California Introduction The dissolved ionic constituents of groundwater are, in part, a record of theminerals and rocks with which the water has reacted (either dissolving or precipitating) as it moves through aquifer materials. In general, the chemical composition of water in carbonate-rock aquifers is dominated by calcium, magnesium, and bicarbonate, whereas sodium, chloride, and sulfate can be dominant ions in the water that comes from volcanic aquifers or clay minerals ( Thomas et al . , 1996) . The movement of water from a volcanic aquifer into a regional carbonate aquifer in southern Nevada can be deduced in large part by an increase in sodium concentration in the carbonate aquifer groundwater sampled down gradient from the recharge area (Schof f and Moore, 1964) . Thus, the geochemical characteristics of the water can be used to facilitate tracing groundwater sources and flow paths . The geochemistry of groundwater from the Neva- da Test Site (NTS) and adjacent areas in southern Nevada and eastern Cafifornia, has been in- strumental to the development of the fundamental groundwater flow hypotheses for the region (Schoff and Moore, 1964 ; Blankennagel and Weir, 1973 ; Winograd and Thordarson, 1975; White, 1979; Chapman and Lyles, 1993; Thomas et al . , 1996) . ISSN 1000-9426