APPLICATION OF BORON ISOTOPE RATIOS FOR IDENTIFYING NITRATE CONTAMINATION SOURCES IN THE GROUNDWATER OF AVRA VALLEY, ARIZONA

摘要

The stable isotopes of the conservative element boron, 11B and 1°B, have beenudemployed as co- migrating isotopic tracers to determine the origin of nitrate observed inudgroundwater from a large capacity (2500 gpm) irrigation well in the Avra Valley ofudsoutheastern Arizona. The isotopic ratios of the conservative element, boron, provided anudidentifying signature for various nitrate rich source waters. Additional chemicaludparameters were also examined to corroborate the isotopic indications.udFindings of this investigation indicate that most of the nitrate observed inudgroundwater from well CMID 18 at the beginning of the 1993 irrigation season was dueudto municipal wastewater contamination. As the irrigation season progressed, an increasingudproportion of nitrate was contributed by irrigation return flow from neighboringudagricultural fields.