Evaluation of fluorocarbon compounds as ground water tracers : soil column studies

Abstract

Fluorocarbon compounds have potential value as hydrologic tracers. The compounds are easily detectable in small amounts, and background hydrologic concentrations are usually small. This thesis documents soil column studies which were designed to test the mobility of fluorocarbon compounds in a controlled saturated flow regime. The fluorocarbon compounds were passed, in aqueous solutions, through columns filled with Ottowa sand, Yolo sandy loam, and crushed coal. Salt tracers were used as control substances. The fluorocarbon tracer effluent concentrations were compared to the salt tracer effluent concentrations so that relative tracer mobilities could be analyzed. In all tests, the fluorocarbon tracers exhibited delayed breakthrough characteristics. Delays were least in the Ottowa sand, significant in the Yolo sandy loam, and severe in the crushed coal. Longitudinal dispersion coefficients (D(L)) were calculated for the various tests. Fluorocarbon tracer D(L) values averaged 3.9 times higher than the salt tracer D(L) values. Distribution coefficient analysis yielded fluorocarbon tracer values that averaged 8.0 times the salt tracer values. Nonspecific electrical phenomena probably caused the fluorocarbon tracer delays, and related parameters such as polarizability and aqueous solubility are speculated to be predictive parameters for qualitatively determining fluorocarbon delay times.