Ground-water geochemistry of the near-surface Wasatch Formation, northern Green River basin, Sublette County, Wyoming

Content Provider	Semantic Scholar
Author	Chafin, Daniel T. Kimball, Briant A.
Copyright Year	1992
Abstract	In 1981, the U.S. Geological Survey began a study of ground water of the Upper Colorado River Basin as part of the Regional Aquifer-System Analysis (RASA) Program. The near-surface Wasatch Formation of the northern Green River Basin was selected for study because of the importance of the ground water in this area for stock and domestic use. This report provides general information about the hydrologic system and detailed information about the chemical quality of the water and its evolution in this system. The near-surface ground water in the arkosic sandstones of the Wasatch Formation of the northern Green River Basin primarily is fresh, sodium carbonate water with an alkaline pH. Dissolved solids generally increase down flow paths. The potentiometric surface in this area indicates that the ground water is providing base flow to the major streams in the central and eastern parts of the study area. Chemical-reaction modeling indicates dissolution of carbonate minerals by water that is exposed to large carbon dioxide partial pressures in the soil of recharge areas. Below the soil zone, ground water quickly becomes isolated from the atmosphere, indicating that the Wasatch Formation is a confined aquifer system. Incongruent dissolution of dolomite predominates after the water flows a few miles into the basin. Incongruent dissolution of feldspars occurs throughout the study area; smectite precipitation dominates near recharge areas, and analcime and saponite precipitation dominate farther into the basin. Ion exchange of calcium and magnesium for sodium is a major reaction believed to affect the composition of the ground water in the Wasatch Formation throughout most of the study area. Sulfate is provided by gypsum (or anhydrite) dissolution throughout most of the basin but is reduced to sulfide by organic matter near the southern boundary of the study area. Sulfide is precipitated as pyrite, although, at greater depths in the Wasatch Formation, hydrogen sulfide gas is present because of a limited iron supply. Final reaction models were used to calculate three carbon-14 ages for the ground water, and average ground-water velocities were computed from the calculated ages. Ground water near the recharge areas at the base of the Wind River Range in the northern part of the study area had a calculated age of about 4,700 years. The resulting estimated ground-water velocity is about 0.01 foot per day; the corresponding hydraulic day. A calculated age of 21,000 years for ground part of the study area indicates an estimated 0.017 foot per day from the recharge area by spending hydraulic conductivity is 0.3 foot ground water in the central part of the study in an estimated average ground-water velocity recharge area along the Wyoming Range to the conductivity is 0.8 foot per day. These values the value of 6.5 feet per day derived from a other investigators and the median of measured differences between calculated and measured from uncertainties in carbon-14 age calculations Sulfate sulfur isotopes exhibit a progressive lightening basinward except for those samples that have undergone sulfate conductivity is 0.2 foot per water in the south-central average ground-water velocity of Wind River Range; the correday. The calculated age of area is 12,700 years, resulting of 0.025 foot per day from the ; the corresponding hydraulic are considerably smaller than gional ground-water model by values (8.7 feet per day). The do not appear to result for ground water. the per
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Alternate Webpage(s)	https://pubs.usgs.gov/wri/1991/4069/report.pdf
Alternate Webpage(s)	https://doi.org/10.3133/wri914069
Language	English
Access Restriction	Open
Content Type	Text
Resource Type	Article