During the spring of 2000, water levels were measured in 735 wells completed in the Mississippi River Valley Alluvial aquifer in eastern Arkansas. Water samples were collected during the summer of 2000 from 151 wells completed in the alluvial aquifer. All samples were measured for specific conductance, and samples from 104 wells were analyzed for dissolved chloride concentrations.
The regional direction of ground-water flow is generally to the south and east except where affected by ground-water withdrawals. In 2000, the highest water-level altitude measured was 289 feet above sea level in northeastern Clay County. The lowest water-level altitude measured was 78 feet above sea level in southwestern Ashley County. A large depression in the potentiometric surface is located in Arkansas, Lonoke, and Prairie Counties. Two shallower depressions are located in Craighead, Cross, and Poinsett Counties and Lee, Monroe, St. Francis, and Woodruff Counties. Potentiometric depressions seem to be forming in four new areas in Ashley, Chicot, Desha, Greene, and Lincoln Counties. Comparisons of water-level changes in cones of depression from 1994 to 2000 show increases in depth and areal extent. Water-level data from 25 wells with 26 or more years of record indicate long-term water levels in the alluvial aquifer declined an average of about 0.6 foot per year from 1975 to 2000.
Specific conductance measurements made on water samples collected during the study ranged from 190 microsiemens per centimeter at 25 degrees Celsius at a well in Drew County to 1,690 microsiemens per centimeter at 25 degrees Celsius at a well in Ashley County. Dissolved chloride concentrations ranged from 2.2 milligrams per liter at wells in Crittenden and St. Francis Counties to 550 milligrams per liter at a well in Chicot County. The areas of high chloride concentrations generally coincide with areas of high specific conductance.
