Chloride and nitrate distributions in the Hickory aquifer, Central Texas, USA

Abstract

Nitrate and chloride concentrations were compiled for 53 water wells in a rural, six-county area of central Texas. The counties reside above the Hickory Aquifer, an important source of ground-water in the region. Farming is the predominant land use in the study area. Consequently, fertilizer and animal waste are potential sources of contamination to the underlying groundwater. Some parts of the aquifer contain above-background nitrate levels, but no spatial trends were evident for chloride. Observations from four wells exceeded the primary drinking water standard of 44.27 mg/L for nitrate (10 mg/L for NO 3-N), and two wells surpassed the secondary standard of 250 mg/L for chloride. Rank correlations between nitrate and well depth were statistically significant, consistent with nitrate contamination originating at the land surface. However, no significant correlation was observed between nitrate and chloride, nor between chloride and well depth. A low recharge rate may contribute to the absence of pervasive nitrate contamination in the aquifer.