TRENDS IN QUALITY OF WATER FROM THE MISSISSIPPI RIVER VALLEY ALLUVIAL AQUIFER AND SPARTA AQUIFER OF ARKANSAS, 1952-2000

Relatively few wells in Arkansas have long-term water-quality data associated with them. However, the U.S. Geological Survey (USGS) established a small “master well” network of wells (and springs) for data dating back to the mid-1950s. Each site in the network is sampled at 5-year intervals for several water-quality characteristics and constituents. Sixteen of these wells are located in the Mississippi River Valley alluvial aquifer (hereafter referred to as alluvial aquifer) and Sparta aquifer of eastern Arkansas and occurs as part of the Mississippi Embayment of the Coastal Plain Province. Potentiometric surfaces of these two aquifers have declined substantially in some places since the mid-1950s. The existence of this network of wells allows investigation of water-quality time trends and their relation to changes in potentiometric surfaces in two of the major water producing aquifers in Arkansas. Irrigation of rice and fish farming are the two main uses of water withdrawn from the alluvial aquifer. Industry and municipalities are the heaviest users of water withdrawn from the Sparta aquifer.

Data from seven alluvial wells and nine Sparta wells (1952-2000) will be analyzed for water-quality trends in specific conductance, major ions, and total dissolved solids. The water-quality trends will then be compared to trends in water levels. Preliminary analyses of water-quality data using the USGS-developed computer program S-ESTREND to test for time trends using the seasonal Kendall procedure and/or various exploratory data analysis procedures indicate that water-quality associated with the wells in this network does not appear to have been affected by declines in water levels.