## 2 Monitoring Protocols and Methods
### Regulatory Aspects
#### 2.7.3 Regulations Governing Post-Injection Monitoring  
The threshold levels were redefined in relation with third-party expert assessment of the injection-period data. This third-party expertise concerned the whole project and not only the soil-gas measurements, and was requested by the French authorities when injection stopped. As mentioned before, such adaptations of the monitoring protocol were foreseen from the beginning of the project, at the request of the French authorities or at the request of the site operator. The third-party expert used the soil gas concentration and flux data to calculate new thresholds. These new threshold levels were only valid for \"low season\" monitoring the frequency of which was reduced to one campaign per year, ideally in December. These new levels applied only to the post-injection monitoring data. The authorities approved a new scheme. Monitoring is restricted to 35 monitoring points: the third-party expert recommended one point to be discarded as it is too frequently water-saturated and thus no monitoring of the soil-gas concentrations is possible (point 23-B, Figure 1). There, of the 10 \"low season\" surveys between December 2008 and March 2013, no soil-gas concentrations could be measured 5 times because of flooding, and a further 3 campaigns gave CO\({}_{2}\) concentrations at atmospheric level. Only 2 campaigns allowed measuring a concentration well below the \"vigilance\" threshold (max. concentration of 1.9% vol.). Removal of this point thus had very little influence on the overall dataset. The set of monitored gas species was reduced to the sole monitoring of CO\({}_{2}\) and CH\({}_{4}\) (both soil-gas concentration and flux). In addition, the acquisition of O\({}_{2}\) soil-gas concentrations continued as the IRGA provides the opportunity to obtain this information at no extra cost. The \"vigilance\" mode was redefined and is now activated if 3 different locations of the 35 show CO\({}_{2}\) gas concentrations >3.6% vol. and CO\({}_{2}\) fluxes >5.9 cm\({}^{3}\cdot\)min\({}^{-1}\cdot\)m\({}^{-2}\). The third-party expert assessment--referring to the methodology initially used--helped calculating the new threshold level, which now corresponds to the mean value plus twice the standard deviation of the CO\({}_{2}\) concentration and the CO\({}_{2}\) flux measured in December 2008, 2009, 2010 and 2011 (M + 2\(\sigma\)). If repeated measurements show exceeding of the \"vigilance\" mode, a sample is taken for measuring the \(\delta^{13}\)C isotope ratio of CO\({}_{2}\) gas in the soil. The \"anomaly\" mode was also redefined and is now activated if, at a single location, CO\({}_{2}\) gas concentration is >4.7% vol. and CO\({}_{2}\) flux is >7.3 cm\({}^{3}\cdot\)min\({}^{-1}\cdot\)m\({}^{-2}\). The thresholds were calculated from the mean value plus three times the standard deviation of the December data (M + 3\(\sigma\)). An \"isotopic\" mode was introduced. It implies determination of the \(\delta^{13}\)C isotope ratio of the CO\({}_{2}\) gas phase in soil for 7 monitoring points. One of these points (Point 28-C, Figure 1) was surveyed during 11 campaigns out of 13 and a good estimate of its isotope signature is available together with its variability (-23.7 \(\pm\) 1.3\(\%\)). Some of the other points showed--since the start of measurements--more depleted isotope ratios together with gas concentrations over 2% vol. Therefore, for each CO\({}_{2}\) soil-gas concentration \(>\)2% vol., a sample must be taken for laboratory measurement of this isotope ratio. The third expertise evaluated indicative levels based on the \(\delta^{13}\)C isotope ratio in the injected CO\({}_{2}\) (\(-\)39.6\(\%\)). These suggested levels are \(-\)26\(\%\) (\"vigilance\") and \(-\)28.4\(\%\) (\"anomaly\"), respectively. The site operator set its own levels at \(-\)29\(\%\) and \(-\)31\(\%\), respectively, but none of these levels is part of the regulatory scheme so that the values are only given as indicative.