LAND-USE AND GROUNDWATER QUALITY IN THE TRINITY GROUP OUTCROP OF NORTH-CENTRAL TEXAS, USA

Concentrations of nitrate, chloride, and bromide in groundwater were o btained for 57 wells in a rural, three-county area of north-central Te xas. The counties straddle the outcrop of the Trinity Group, an import ant source of groundwater in the region. Predominant land uses in the area are cropland/pasture and rangeland. The highest nitrate concentra tions were associated with cropland/pasture. In general, nitrate conce ntrations increased as well depth decreased. However, well depth did n ot 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 c hloride and bromide concentrations. Neither chloride nor bromide was c orrelated with nitrate, but they were strongly correlated with each ot her. Dry farming and scant precipitation recharge may account for an a bsence 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 st udy area, (C) 1997 Elsevier Science Ltd.