Analysis of Environmental Tracer Data to Help Determine Sources of High Nitrate Ground Water in Sanpete and Central Sevier Valleys, Central Utah
Nitrate concentrations for water samples from 76 water wells and 19 springs in the study area range from less than 0.1 mg/L to 39 mg/L, with an average of 6.7 mg/L, and a median of 5.2 mg/L; 19% of these samples yield nitrate values exceeding the EPA standard of 10 mg/L. Sixty-two percent of samples have nitrate concentrations that exceed 3 mg/L; ground water having values exceeding 3 mg/L is typically associated with human- or animal-derived sources. Possible sources of nitrate include fertilizer, feed lots, septic tanks, and natural sources. Most nitrogen and oxygen isotope data plot in overlapping fields characteristic of septic tank/manure, soil, and ammonia fertilizer/rain. Tritium ages plot as pre-bomb(1952), bomb water, post bomb, and mixed water. CFC data ages range from 1943 to 2000. Carbon isotope data ages range from modern to 19,000 years. Environmental tracer data show three samples are categorized as modern-age water (<1981) with remaining samples showing mixed-age ground water. Based on the environmental tracer data, nitrate contamination is from multiple sources in mixed ground-water systems.