Status of water levels and selected water-quality conditions in the Sparta and Memphis aquifers in eastern and south-central Arkansas, 1999

Abstract

During the spring of 1999, water levels were measured in the Sparta and Memphis aquifers in 321 wells in eastern and south-central Arkansas. Water samples were collected during the spring and summer of 1999 from wells completed in these aquifers. The specific conductance of the ground water was measured from 147 samples and dissolved chloride was measured from 98 samples. Maps of areal distribution of potentiometric surface and specific conductance generated from these data reveal spatial trends across the study area. The altitude of the potentiometric surface ranged from 214 feet below sea level in Union County to 332 feet above sea level in Grant County.The regional direction of ground-water flow in Arkansas is from the north and west to the south and east, away from the recharge zone in the outcrop and subcrop area, except near areas affected by intense ground-water withdrawals; such areas are characterized by large cones of depression centered in Columbia, Jefferson, and Union Counties. Heavy pumpage locally has altered or reversed the natural direction of flow in some areas. Flow in these areas is toward the cones of depression at the center of pumping. Comparison of potentiometric surface maps through time shows that the cones of depression in Columbia and Union Counties are coalescing at or near the Columbia and Union County line.Long-term hydrographs of 20 wells indicate trends of water-level decline over a 31-year period. During the period 1969-1999, average water-level declines generally were less than 0.7 foot per year in Craighead, Drew, Lee, Ouachita, and Phillips Counties, and between 0.7 and 1.1 feet per year in Bradley, Cleveland, Cross, Dallas, Poinsett, and Prairie Counties. Analysis of water-level data from Calhoun, Desha, Jefferson, Lonoke, Lincoln, and Union Counties indicates water levels declined between 1.1 and 2.0 feet per year since 1969. Water levels in Arkansas and Colum-bia Counties have declined more than 2.0 feet per year for the past 31 years.Water-level data from counties with cones of depressions indicate that water levels continued to decline in three cones of depression from 1995 to 1999; however, water levels increased in one cone of depression. Water levels declined an average of 2.5 feet per year in Union County, 1.4 feet per year in Jefferson County, and 1.7 feet per year in Cross County since 1995. One relatively new cone of depression has formed in Arkansas County. Water levels declined 4.0 feet per year in Arkansas County since 1995. However, water levels appear to be increasing in Columbia County where the same 11 wells were monitored in 1995 and 1999, and the water levels increased at a rate of 0.6 foot per year.Specific conductance measurements made on water samples collected during the study ranged from 44 microsiemens per centimeter at 25 degrees Celsius at a well in Ouachita County to 1,510 microsiemens per centimeter at 25 degrees Celsius at a well in Lee County. Dissolved chloride concentrations ranged from 1.1 milligram per liter at a well in Lincoln County to 2...