Detection of diesel fuel plumes using methane data in Guadalajara, Mexico

This paper examines the detection of diesel fuel in the subsoil by means of measurements of biogenerated methane. Once a link between methane and diesel fuel was established at the laboratory scale, the authors applied this concept to the field scale. Methane causes asphyxia, it is flammable and explosive, and it is quickly and economically feasible to measure in soil gas. A flame ionization detector was used to measure hydrocarbon vapors during the field research. This study was performed in the Moderna neighborhood in Guadalajara, Mexico, with a methane concentration ranging from 0 to 220,000 ppmv, and a diesel fuel thickness ranging from 0 to 83 cm. Benzene, toluene, ethylbenzene, and xylene were also measured in soil gas with maximum concentration of 4000 ppmv. From our statistical analysis, the correlation between methane and diesel fuel was 0.89 and there was no correlation with other measured vapors. Since methane distribution showed spatial variability, geostatistical techniques were applied yielding maps, which described zones with different gas concentrations. Experimental variograms were built using 1263 measurements and the theoretical variograms were of the exponential type. If we already know the positive high correlation between methane and diesel fuel, plume, sources, and sinks of diesel fuels can be located. The results of the case analysis imply pollution under 50 of the 114 city blocks we studied, with methane concentrations higher than the 2000 ppmv threshold value and a diesel fuel thickness higher than 28.90 cm.