Comparison of surface and near-surface geochemical methods for detection of gas microseepage from carbon dioxide sequestration

► Detection and quantification of gas microseepage above the land surface is difficult. ► Detection of gas microseepage below the land surface is easier. ► Surface methods provide a means to screen larger areas for locations of interest. ► Constituents or parameters with low concentrations and low variance are most definitive. ► A combination of approaches must fit the local climatic, cultural, and other interferences.