Associations between rural land uses and ground water quality in the ogallala aquifer, Northwest Texas

Recent nitrate, chloride, and bromide concentrations were studied in the Ogallala Aquifer of northwest Texas. The study included 361 wells with a median depth of 92 m in a rural area dominated by agricultural activity and oil and gas production. Only five observations surpassed the 44.3 mg/L standard for nitrate (10 mg/L NO3-N). Four other observations, and one from the preceding set, exceeded the secondary standard of 250 mg/L for chloride. Maximum concentrations were 91.2 mg/L, 1530 mg/L, and 0.70 mg/L for nitrate, chloride, and bromide, respectively. Chloride/bromide ratios covered a broad range, from 30.4 to 10930, but medians were <160 for each of two years analyzed. There were statistically significant correlations between nitrate and chloride, and chloride and well depth. Results of this study suggest that agricultural activity has locally impacted ground water in northwest Texas. Regionally, low aquifer recharge rates have curtailed ground water contamination from potentially adverse land uses.