Laboratory studies on hydrocarbon tracer gases

Laboratory studies were conducted to investigate two assumptions of the hydrocarbon gas tracer technique for measurement of reaeration rate coefficients. First, the assumption of constant ratios between the mass transfer rate coefficients was examined by measuring the relative transfer rates of oxygen, ethylene, and propane in an open mixing tank at the temperatures of 4°, 20°, and 32° C. In agreement with previous studies, the ratios were found to be constant and equal to 1.14 for oxygen/ethylene and 1.36 for oxygen/propane. Second, the assumption that dissolved ethylene and propane are not adsorbed on suspended sediments was investigated using the batch equilibrium method with five soils. The tests showed negligible adsorptive losses. In addition, previous studies on relative gas transfer rates were reviewed to gain insight into the physical process.