This report provides background information about the Ginninderra controlled release Experiment 3 including a description of the environmental and weather conditions during the experiment, the groundwater levels and a brief description of all the monitoring techniques that were trialled during the experiment. The Ginninderra controlled release facility is designed to simulate CO2 leakage through a fault, with CO2 released from a horizontal well 2 m underground. Two previous subsurface CO2 release experiments have been conducted at this facility in early and late 2012, which have helped guide and develop the techniques that have been applied herein. The aim of the third Ginninderra controlled release experiment was to further the development of detection and quantification techniques, and investigate seasonal effects on gas migration. Particular focus was given to plant health as a diagnostic detection method, via physical, biochemical and hyperspectral changes in plant biomass in response to elevated CO2 in the shallow root zone. Release of CO2 began 8 October 2013 at 4:45 PM and stopped 17 December 2013 at 5:35 PM. The CO2 release rate during Experiment 3 was 144 kg/d CO2. Several monitoring and assessment techniques were trialled for their effectiveness to quantify and qualify the CO2 that was released. The methods are described in this report and include: - soil gas - eddy covariance - mobile surveys - Line CO2 concentrations - groundwater levels and chemistry - plant biochemistry - airborne hyperspectral - soil flux - electromagnetic (EM-31 and EM-38) - meteorology This report is a reference guide to describe the Ginninderra Experiment 3 details. Only methods are described in this report, with the results of the experiment published in conference papers and journal articles.

Following the drilling of a shallow natural CO₂ reservoir at the Qinghai research site, west of Haidong, China, it was discovered that CO₂ was continuously leaking from the wellbore due to well-failure. The site has become a useful research facility in China for studying CO₂ leakage and monitoring technologies for application to geological storage sites of CO₂. During an eight day period in 2014, soil gas and soil flux surveys were conducted to characterise the distribution, magnitude and likely source of the leaking CO₂ . Two different sampling patterns were utilised during soil flux surveys. A regular sampling grid was used to spatially map out the two high-flux zones which were located 20–50 m away from the wellhead. An irregular sampling grid, with higher sampling density in the high-flux zones, allowed for more accurate mapping of the leak distribution and estimation of total field emission rate using cubic interpolation. The total CO₂ emission rate for the site was estimated at 649-1015 kgCO₂/d and there appeared to be some degree of spatial correlation between observed CO₂ fluxes and elevated surface H₂O fluxes. Sixteen soil gas wells were installed across the field to test the real-time application of Romanak et al.’s (2012) process-based approach for soil gas measurements (using ratios of major soil gas components to identify the CO₂ source) using a portable multi-gas analyser. Results clearly identified CO₂ as being derived from one exogenous source, and are consistent with gas samples collected for laboratory analysis. Carbon-13 isotopes in the centre of each leak zone (−0.21‰ and −0.22‰) indicate the underlying CO₂ is likely sourced from the thermal decomposition of marine carbonates. Surface soil mineralisation (predominantly calcite) can be used to infer prior distribution of the CO₂ hotspots and as a consequence highlighted plume migration of 20m in 11 years. The broadening of the affected area beyond the wellbore at the Qinghai research site markedly increases the area that needs surveying at sufficient density to detect a leak. This challenges the role of soil gas and soil flux in a CCS monitoring and verification program for leak detection, suggesting that these techniques may be better applied for characterising the source and emission rate of a CO₂ leak, respectively. <b>Citation:</b> I.F. Schroder, H. Zhang, C. Zhang, A.J. Feitz, The role of soil flux and soil gas monitoring in the characterisation of a CO2 surface leak: A case study in Qinghai, China, International Journal of Greenhouse Gas Control, Volume 54, Part 1, 2016, Pages 84-95, ISSN 1750-5836, https://doi.org/10.1016/j.ijggc.2016.07.030.