This chapter presents an overview of the international regulations and guidelines related to potential leakage events of CO2 from a geological storage site, an overview of the international regulations and guidelines related to leakage, as well as the effects of CO2 reaching the biosphere.

The chapter starts with a review of the main international acts and agreements that regulate the risk of CO2 leakage, the London Convention and Protocol, OSPAR, EU Directives on Geological Storage of CO2 and ETS. These international agreements were elaborated at different times and differ mostly on their focus (e.g. OSPAR focuses only on the effects of CO2 leakage in the marine environment whereas EU Directive on Geological Storage of CO2 refers to CO2 leakage in all environments) and geographical coverage (although they overlap to some extent with regards to this). Still, all regulations require that storage operations are conducted in a safe manner, taking corrective measures in case of leakage. For this reason, they also stipulate the necessity of conducting a thorough risk assessment in each step of a storage project (starting with the pre-operational phase) in order to prevent and mitigate the identified hazards.

In this context, another important part of the chapter refers to guidelines for risk assessment, especially the ones developed under OSPAR (FRAM) and EU CCS Directive (Guidance Document 1). These guidelines comprise several stages for risk assessment, covering the entire cycle of a CO2 storage project, starting from site characterisation to risk management (including monitoring and corrective measures).

A first step in the risk assessment for a CO2 geological storage site is to identify all of the potential risks related to the site, especially the potential leakage pathways, presented within this chapter, such as permeable caprock, faults and fractures, wells and other anthropogenic pathways (e.g. hydraulic fracturing of reservoir possibly connected to a CO2 storage site or extension of fractures to the CO2 storage complex).

The final part of the chapter presents the effects of a potential CO2 leakage on the environment and on human safety and health through a few studies made on this topic using natural analogues (e.g. Laacher See, Germany; Panarea Island, Italy) and some incidents and regulations related to human and animal exposure to increased levels of CO2. Although the exact effects of a CO2 leakage are not yet known (as the composition of CO2 stream and the re-actions of co-injected elements play an important role in this issue and there is still a research need for controlled CO2 leakage), it is commonly accepted that CO2 leakage can cause acidification of sea or groundwater, mobilisation of toxic elements (due to pH change in soils), adverse effects on plants, animals and humans.  

The risks of leakage are regulated through several acts and international agreements such as the London Convention and Protocol, OSPAR, EU directives on Geological storage of CO2 and the ETS Directive. The regulatory regimes require that storage operations are conducted in such a manner that any hazards are prevented or mitigated and also that necessary corrective measures must be taken in the case of leakage.

According to the EC directive a storage site shall not be chosen if there is significant risk of leakage of the stored CO2.The risk of leakage from a site with a storage permit has therefore been restricted and the site conditions delimited from the very beginning. Site characterisation is the first step in the process of choosing the most appropriate storage site with no significant risk of leakage. During this process all potential leakage pathways should be identified and their implications then assessed during the risk assessment process. The risk analysis is a major part of this assessment process and is important when deciding on an appropriate storage site.

The second step in leakage prevention is the implementation of a comprehensive, site-specific monitoring plan covering the storage site and the surrounding area (including the seal and overlying marker formations) (i.e. the storage complex). The main purpose of monitoring is to permit control of the CO2 plume behaviour and to discover and prevent any potential leakage at an early stage. The data acquisition performed during monitoring will also provide new high quality information that will continuously improve the static and dynamic characterisation of the storage complex. Further details on monitoring can be found in CGS Key Report 1 (Rütters et al., 2013).

The effects of CO2 reaching the biosphere are not yet fully understood. However, it is widely known that CO2 leakage may cause acidification of sea water, groundwater resources and soils. The change in pH also mobilises environmentally toxic elements in soils such as lead. An important issue with respect to the effects of leakage is the composition of CO2 stream and the reactions of the co-injected substances. There are many lessons to be learned from natural analogues of CO2 leakage and from laboratory experiments as well as the catastrophic events of Lake Nyos and Monoun in Africa which demonstrated the importance of understanding potential hazards in order to mitigate them fully.


in depth

3.1 International agreements regulating CO2 leakage

There are several national and international regulatory regimes that currently cover the impact of a leakage event from ...

3.2 CO2 storage risk assessment

There are several recently published studies and recommendations concerning risk analysis of CO2 storage....

3.3 Leakage pathways

Five different leakage events are identified in Guidance Document 1 of the EU CCS Directive....

3.5 Occupational guidelines regulating CO2 levels in the environment

Currently there are no general guidelines or regulations for CO2 levels in the environment....

3.6 Conclusions

The main purpose of CCS technology is to prevent any further emissions of CO2 to the atmosphere from fossil fuel based e...