Ground-water quality and preliminary assessment of the potential for contamination beneath agricultural lands in central Lonoke County, Arkansas

Abstract

As part of an effort to monitor ground-water quality and to assess the potential for ground-water contamination on a statewide basis ground-water quality was studied in central Lonoke County, an agricultural area with heavy pesticide and fertilizer use. Ground water from 21 wells in the alluvial aquifer and 1 well each in the Sparta aquifer and Wilcox aquifer was sampled and analyzed for physical properties, major inorganic constituents, nutrients, trace inorganic constituents, total organic carbon, and selected pesticides. With the exception of iron and manganese, the water in the alluvial aquifer generally did not exceed U.S. Environmental Protection Agency primary and secondary maximum contaminant levels for drinking water. High iron and manganese concentrations, although suitable for irrigation purposes, indicate that some treatment for iron and manganese removal might be desirable for drinking water use. Dissolved-solids concentrations in the alluvial aquifer ranged from 88 to 536 milligrams per liter with the higher concentrations occurring in the southern one-half of the study area. Of the pesticides tested for, none were detected in the alluvial aquifer. The potential for widespread ground-water contamination in the study area is low because of the relatively impermeable clay and silt deposits of the alluvial confining unit that overlie the alluvial aquifer in most of, if not all, of the study area. Locally, however, potential contaminants could enter the aquifer from streams incised into and in hydraulic connection with the