Monitoring is essential for the approval and control of geological storage of carbon dioxide and to judge the effectiveness of the technology in mitigating CO2 emissions and climate change. We present a strategy for monitoring the atmosphere in the vicinity of a geological storage project that is designed to detect and quantify potential emissions. The strategy includes measurements of CO2, CO2 fluxes and tracers, combined with model simulations of atmospheric dispersion and ecosystem CO2 fluxes. We applied an atmospheric monitoring program to the CO2CRC Otway Project where large amounts of CO2 have been stored in a deep depleted natural gas reservoir. The sensitivity of the monitoring is tested by detecting emissions from surface activities at the Otway facility, including a scheduled release of injected gas.