Sulfur Hexafluoride Gas Tracer Studies in Streams

The air-water mass transfer coefficients, dispersion coefficients, and mean residence times in two experimental streams and one natural stream are measured using a variation of the standard volatile tracer-dye technique. Sulfur hexafluoride (SF6) is used as the volatile tracer and rhodamine WT is used as the conservative tracer. The low limit of quantification of SF6 makes it possible to inject SF6-rich water into many streams and avoid complications with dosing a stream with a gaseous tracer. The experimental methods are described in detail. The SF6 measurements were extremely precise, producing smooth concentration time curves. The SF6 measurements collected in side-by-side experimental channels yielded similar values of the gas transfer coefficient.