High resolution techniques for geoenvironmental characterization of a site with methane in the subsoil

The risks associated with gas and vapor intrusion and accumulation in buildings are gaining increasing attention in our society, mainly because of the possible harm to human health or even explosion. In São Paulo Metropolitan Area, environmental studies have frequently reported methane (CH₄) in the subsoil, causing social, political and economic concerns. These risks highlight the need to foment the debate and the improvement of technical knowledge for establishing guidelines for the assessment and management of these cases. An innovative approach to optimize site assessment and generate more consistent conceptual site models (CSM), allowing better decision making, is through the application of high resolution site characterization (HRSC). Among many techniques currently adopted, the Membrane Interface Probe (MIP) is a very useful and reliable tool due to its ability to detect volatile compounds and gases in subsurface. The equipment has a Flame Ionization Detector (FID/MIP), which enables the detection of CH₄ with high precision (Christy, 1996). Furthermore, the Electrical Conductivity sensor (EC), attached to the probe, allows a centimetric characterization of the lithostratigraphy (Schulmeiter et al., 2003). In this context, this study has evaluated the application of the MIP, with other HRSC techniques, for the characterization of a site with methane gas occurrence in the subsurface. (author)