Status of water levels and selected water-quality conditions in the Mississippi River Valley alluvial aquifer in eastern Arkansas, 1994-96

During the spring of 1994 and 1996, water levels were measured in more than 600 wells completed in the Mississippi River Valley alluvial aquifer in eastern Arkansas. Water samples were collected during the summer of 1995 from about 375 wells completed in the alluvial aquifer and measured for specific conductance. Concentrations of dissolved chloride were analyzed in 314 of the samples, and concentrations of dissolved calcium, magnesium, and sodium were analyzed in 18 of the samples.
The regional direction of ground-water flow is generally to the south and east except where affected by ground-water withdrawals. A large depression in the potentiometric surface is located in Arkansas, Lonoke, and Prairie Counties. The comparison of water-level altitudes from 1994 to 1996 reveals that water levels declined and the cone of depression became larger. The water-level altitudes did not decline in every well monitored from 1994 to 1996; however, most water-level altitudes declined during this period and cones of depression became deeper. Shallower depressions are located in Poinsett, Lee, St. Francis, and Woodruff Counties. Potentiometric depressions in this aquifer generally are a result of long-term pumping and probably are affected by variations in aquifer characteristics such as thickness and hydraulic conductivity. Long-term water levels typically declined an average rate of about 1.2 feet per year in the areas of potentiometric depression.
Specific conductance ranged from 81 microsiemens per centimeter at 25 degrees Celsius in Drew County to 4,640 microsiemens per centimeter at 25 degrees Celsius in Chicot County. The lowest ground-water specific-conductance values generally occur along the western border of the study area. Several areas exhibited increased specific conductance with the most prominent areas centered in Chicot, Desha, and northern Arkansas County.