This report determines the magnitude and extent of saltwater contamination in the Sparta Sand, the region's most important potable water aquifer, and the possible sources and avenues of contamination. The study is restricted to Union County, with emphasis on the area around El Dorado.

The report includes

• A discussion of the geology, geohydrology, and water quality of the aquifers in the study area
• A generalized geologic column for the study area
• Typical electric log for the sub-surface units
• A tabulation of wells used for sampling water in units deeper than the El Dorado aquifer (lowermost Sparta Sand) in the study area
• A tabulation of chemical and physical analyses of water in units below the El Dorado aquifer
• A table of 136 wells in the El Dorado, Greensand, and Cockfield aquifers in Union County
• A table of chemical and physical analyses of water from 81 wells in the El Dorado, Greensand, and Cockfield aquifers in Union County
• Discussion of potential sources of saltwater contamination in the Sparta Sand, including brine in surface ponds, saltwater-bearing units below the El Dorado aquifer, and the presence of the El Dorado aquifer in a graben structure
• A fold out geologic map of Union County
• Four cross sections of the subsurface geology
• Structural maps of the Arkadelphia Marl (Cretaceous), Cane River Formation, and El Dorado aquifer
• Potentiometric surface map of the El Dorado aquifer
• Location map of selected wells in the study area
• Map of chloride concentrations in water from the El Dorado aquifer
• Structure map of the Greensand aquifer
• Potentiometric surface map of the Greensand aquifer

*Includes: 47 pages, 11 figures, 13 plates, 6 tables

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