New Mexico Geological Society Annual Spring Meeting — Abstracts

In groundwater investigations involving multiple sources of water, or in cases where measurements are repeated over time, several unique tracers which can be used simultaneously are required. A group of fluorinated benzoic acid derivatives has previously been shown to be effective as soil and groundwater tracers. In this study, four related fluorobenzoates were examined in an attempt to enlarge the suite of proven tracers. The organic anions being studied are 2, 3-difluorobenzoic acid (2,3-DFBA), 2,S-difluorobenzoic acid (2,5-DFBA), 3,4-difluorobenzoic acid (3, 4-DFBA) and 3, 5-difluorobenzoic acid, (3-5 DFBA). A high pressure liquid chromatography (HPLC) separation was developed for simultaneous detection of the four anions being evaluated, as well as bromide anion which was used as a standard against which the others were measured. The laboratory phase of this evaluation consisted of batch studies to measure these compounds' resistance to degradation and affinity for sorption on soil surfaces, as well as column studies to measure the mobility and stability of the compounds. The batch study using a low organic content sand showed no loss of concentration of any of the fluoro-organics over a 90-day period, while the study using a high organic matter silty clay loam is still underway. Both ponded and ,trickle irrigation column flow conditions indicated no loss of mass as well as similar mobility of the fluora-organics' compared to bromide. The field portion of this evaluation will consist of a single-well tracer test to measure their stability , under saturated conditions, and a trickle irrigation tracer test to evaluate their behavior under unsaturated natural conditions. These two experiments are now underway, with results expected by May.