1. © NERC All rights reserved Task 3: Review of findings from experimental and natural seepage sites and modelling Comparison with onshore sites

2. © NERC All rights reserved Experimental test and natural sites ZERT and Mississippi (aquifer), USA: 2m, 50m Ginninderra, Australia: 2m Denmark (aquifer): 10 m CO2 Field Lab & Grimsrud Farm, Norway: 20m, 1m ASGARD, UK: <1m Natural sites e.g. Latera, Laacher See, Florina, Ste Marguerite Lakes (e.g. Laacher See, Rotomahana)

3. © NERC All rights reserved Relevance of onshore General monitoring strategies (e.g. from physical size and flux rates) – large areas, small targets Once locate leakage need to prove source and quantify amounts Difficult to predict where leakage will occur (may be indications from deeper monitoring) Similar issues with dispersion (air v water) Mix of survey and continuous modes Some evidence of low-level seepage (difficult to detect but could be significant) Deeper techniques and downhole methods similar Lakes – similar techniques used

4. © NERC All rights reserved Examples of seepage CO 2 Field Lab Florina Similar flux rates and areas

5. © NERC All rights reserved Similarities with offshore techniques Lake monitoring multibeam and other sonar techniques flux measurements multi-parameter probes Deeper focussed methods Seismic and other geophysical methods Downhole and cross-hole geophysics Downhole sampling, geochemistry, pH, T, P etc Aquifer studies (but not drinking water issues) Analytical methods on samples

6. © NERC All rights reserved Differences to offshore techniques Physical manifestation (vegetation effects v bubbles, pH changes) Different near surface approaches (remote sensing, atmospheric monitoring) cf multibeam etc Flux measured directly cf from bubbles (displacement or acoustic + gas analysis) EC possible in theory (need fast CO 2 sensors) Same techniques need different deployment Gas sampling for analysis easier onshore, other methods easier offshore (e.g. seismic)

7. © NERC All rights reserved Baselines Some major differences but… Variations over different timescales similar (diurnal, days to weeks, seasonal, interannual) Similar strategies possible Surveys to define ‘typical’ or vulnerable sites for continuous monitoring (care in site selection) Choice of parameters to be measured (not just CO 2 ) Timing of surveys (autumn/winter best onshore) Length of baselines (Schlömer et al., 3 years) Use of control/reference sites