Applicability of the Multi-Channel Surface-soil CO2-concentration Monitoring (SCM) System as a Surface Soil CO2 Monitoring Tool

Monitoring of CO2 release through the ground surface is essential to confirm the safety of carbon storage projects. We conducted a feasibility study of the multi-channel surface-soil CO2-concentration monitoring (SCM) system as a soil CO2 monitoring tool with a small scale injection test. The background concentrations showed the distinct diurnal variation. The negative relation of CO2 with temperature and the low CO2 concentrations during the day imply that surface-soil CO2 depends on photosynthesis and respiration. After 4.2 kg of CO2 injection (1 m depth for 29 minutes), surface-soil CO2 concentrations increased in the all five chambers, which were located less than 2.8 m of distance from each other. The CO2 concentrations seem to be recovered to the background around 4 hours after the injection ended. To determine the leakage, the data from Chamber 2 and 5 with low increase rates were used for statistical analyses. Coefficient of variation for 30 minutes (CV30min.) is efficient to determine a leakage signal, with reflecting the fast change in CO2 concentrations. Consequently, SCM and CV30min could be applied for an efficient monitoring tool to detect CO2 release through the ground surface. Also, this study provides ideas for establishing action steps after leakage detection.