The specific objectives of this paper include using existing hydrogen and oxygen isotopic data to generate a LMWL for recharge areas to the eastern Snake River Plain aquifer. We also compare several reported LMWLs to the GMWL (Craig, 1961) and to the LMWL calculated for this report.
Several investigators (Bartholomay and others, 1994, 1995, 1996; Busenberg and others, 2000; Knobel and others, 1999; Ott and others, 1994; and Wood and Low, 1988) have reported [[delta].sup.2]H and [[delta].sup.18]O data from ground-water samples that were collected from the eastern Snake River Plain aquifer.
Within the uncertainty of the methods used to calculate a basin-wide water budget, all water within the eastern Snake River Plain aquifer system is reported to be derived from precipitation (Kjelstrom, 1986).
The water line generated from the ground-water data, [[delta].sup.2]H = 5.49 [[delta].sup.18]O -38, has a slope (5.49) and a resultant deuterium-intercept value (-38) that also are indicative of extensive secondary evaporative effects encountered partly during precipitation fallout and partly from evaporation during infiltration into the Snake River Plain aquifer (figure 1).
The results presented here suggest that recharge to the eastern Snake River Plain aquifer is dominated by winter precipitation between the months of October and April.
The Snake River Plain aquifer underlies approximately 11,000 square miles of southeast Idaho.
In the case of the Snake River Plain aquifer, this may be one hundred years or more for pumping occurrin g at great distances from the river.
Four sets of steady state response functions have been determined for each grid cell of the Snake River Plain aquifer model (1183 cells) used by the Idaho Department of Water Resources.
Taken separately, neither upgradient ESP site is truly representative of ambient groundwater chemistry in this region of the Eastern Snake River Plain aquifer. Taken together, both help document an important transition in water chemistry as waters from the Yellowstone Plateau mix with waters from the Paleozoic and Mesozoic sedimentary rocks of the Centennial Range directly north of Mud Lake and waters impacted by anthropogenic sources in the Mud Lake region.
Key Words: Groundwater, water quality, major-ion chemistry, trilinear diagram, Mud Lake, Eastern Snake River Plain aquifer, Idaho National Engineering and Environmental Laboratory, State of Idaho INEEL Oversight Program, Environmental Surveillance Program, U.S.
This study was undertaken to find an explanation for the differences in the chemistry of major ions seen in samples from USGS 27 and Mud Lake WS, and to determine how this difference fits into the larger context of water quality and aquifer flow in this portion of the Eastern Snake River Plain aquifer.
The Wood and Low (1988) study of the Snake River Plain aquifer, reported that dissolved calcium, magnesium, sodium, potassium, chloride, sulfate, and bicarbonate ions compose more that 95% of all dissolved constituents observed in the Snake River Plain aquifer, and concluded that the major ion chemistry is primarily a function of the geology of the recharge areas: changes in ion concentrations as the groundwater reacts with the aquifer matrix, and mixing with waters from other sources (for example, irrigation).