Land use and groundwater quality in the trinity group outcrop of north-central Texas, USA

Concentrations of nitrate, chloride, and bromide in groundwater were obtained for 57 wells in a rural, three-county area of north-central Texas. The counties straddle the outcrop of the Trinity Group, an important source of groundwater in the region. Predominant land uses in the area are cropland/pasture and rangeland. The highest nitrate concentrations were associated with cropland/pasture. In general, nitrate concentrations increased as well depth decreased. However, well depth did not influence chloride or bromide concentrations. Outliers were as high as 1.3 g/L for chloride and 8.40 mg/L for bromide, There are numerous oil and gas wells in the study area, which may account for elevated chloride and bromide concentrations. Neither chloride nor bromide was correlated with nitrate, but they were strongly correlated with each other. Dry farming and scant precipitation recharge may account for an absence of nitrate levels above the drinking water standard (45 mg/L). Collectively, the results suggest that agricultural fertilizer and oil field brine are likely sources of groundwater contamination in the study area, (C) 1997 Elsevier Science Ltd.