Ground gas – Is your development site at risk and what action should you take?
When developing a site near a landfill, infilled ground or overlying coal, like the majority of the places in the North East, the development is at risk from ground gas.
The protection of the development and future users is regulated by the Local Authority through planning conditions, which are applied as part of a planning application. However, at Roberts Environmental we have found the expectations of Local Authorities with regards to the scope of Ground Gas Risk Assessments and Validation can vary depending upon location.
In general, the requirements of the Local Authorities appear to be becoming more stringent and less flexible, as they look for assessments and validation which follow more closely available guidance. This is not often a pragmatic or commercially viable course of action for a developer.
There are four stages of ground gas management;
- data collection,
- risk assessment process,
- installation of gas mitigation measurements
- validation of these measures
In the UK, the principal sources of guidance for Ground Gas Risk Assessment are based on the industry led and semi-authoritative documentation CIRIA C665 and BS8485.
CIRIA C665
CIRCA C665 outlines the methodology required when scoping up a ground gas monitoring investigation and outlines the gas risk assessment.
C665 also provides the ‘Typical Scope’ of gas protection required for the various ground gas classifications referred to as ‘Characteristic Situations’, however a more stringent and prescriptive scope is provided in BS8485.
BS8485
Some Local Authorities will accept the ‘Typical Scope’ of gas protection presented in C665 when deciding on Planning Applications, however others insist on the more stringent and prescriptive requirements outlined in BS8485.By following C665, there is a danger that the protective measures installed into the final development would not be considered to fall in line with BS8485, as there are slight differences and ambiguities. Therefore, to avoid problems moving forward it would be prudent to adopt the Gas Protection requirements of BS8485 up front, although this could have commercial implications from increased development costs and extended timescales from validation requirements.All gas protection systems should undergo some level of validation to confirm they are suitable for use. However, Local Authorities are more frequently adopting the requirements outlined in a third guidance document named as CIRIA C735.
CIRCA C735
C735 sets out what Validation should entail, and includes details of what should be examined during validation inspections, a requirement to obtain for proof of qualifications and experience from the installer and depending upon the type of protection system installed, specialist integrity testing.The validation inspection should be carried out immediately after installation when the protection measures are still visible and we would recommend that when selecting an installation contractor, they provide proof of qualifications.Should appropriate validation fail to be carried out and the development advances towards completion, should the Local Authority request proof of validation, this can cause significant difficulties.
As can be seen there is no all-encompassing guidance documentation which can cause significant issues for both the regulatory authorities and developers alike. Until such government led policy is adopted problems will continue.
References:
• CIRIA C665: Assessing risks posed by hazardous ground gases to buildings
• British Standard BS8485: Code of practice for the characterization and remediation from ground gas in affected developments
• CIRIA C735: Good practice on the testing and verification of protection systems for buildings against hazardous ground gases