A mine of information: Q&A with Dr Tom Henman

Ahead of this year’s Brownfield Land Scotland 2020 conference, which is taking place on 5 February in Edinburgh, UK, Environment Analyst caught up with RSK geosciences Director Dr Tom Henman, who shared his thoughts on the risks from mine related CO2 emissions.

Q. Have there been many other incidents of mine related CO2 emissions causing issues in properties?

Apart from the Gorebridge case that is well known, RSK’s research and consultation with local authorities and the Coal Authority has revealed that there were 15 recorded or anecdotally reported incidents in Scotland involving mine gas since the 1950s. Of these, 12 involved hazards from carbon dioxide emissions and three were related to methane. We also identified additional incidents that have occurred across coalfields in the rest of the UK, including a cluster of incidents known to have occurred in Northumberland in the 1990s.

Q. Is the drive to insulate buildings more creating conditions which give rise to more CO2 in buildings?

We examined this issue in detail through extensive consultation with stakeholders and industry experts. It is true that older draughty buildings are less prone to gas build-up due to the inherent increase in air exchange rate. In newer buildings, due to improved airtightness standards, gases able to enter a property are more likely to be retained, however the ingress of gas itself will also be reduced. Improved airtightness is of course needed to meet energy efficiency requirements and ultimately our climate change commitments. However, Government research on the effectiveness of indoor ventilation measures (and thus the assumed air exchange rate) indicates that improvements are needed to meet current building standards and inform residents of the importance of ventilation in homes. Therefore, the best option is to prevent gas ingress to properties in the first place.

Q. Are modern construction techniques which don’t create a sub ground void adding to the problem?

A ventilated void does help to provide a good basic level of defence against ingress of ground gases as gas concentrations are reduced before entry into properties. We found this construction method is used less commonly in Scotland now, as Modern Methods of Construction are adopted and due to Disability Discrimination Act (DDA) access requirements. However, other subfloor ventilation options are available and covered in relevant British Standards. Our work identified the potential need for further research to test the long-term effectiveness of granular fill and perforated pipe, commonly used as a passive ventilation technique, in areas affected by mine gas emissions.

Q. Is the current risk assessment process adequate in calculating potential future risks and construction impacts?

Our study concluded that existing standards and guidance for assessment of ground gas risk are generally adequate. Compliance was identified as the key issue as such assessments can be poorly implemented or have insufficient scrutiny by regulators. Despite recent changes to standards and guidance placing a greater emphasis on developing a robust conceptual site model and the use of quantitative risk assessment methods for complex sites, there can be an over-reliance by assessors on gas monitoring of boreholes and use of simple empirical approaches, e.g. gas screening values.

We made a series of recommendations to improve compliance, including use and enforcement of model planning conditions and changes to Scottish Planning and Building Standards and associated technical guidance. We also felt that applying the National Quality Mark Scheme (NQMS) to gas risk assessments would be of benefit in improving quality since there is a mandatory requirement for all reports registered under the scheme to consider data gaps/ uncertainties in land contamination assessments and their implications.

We also recommended further research and preparation of supplementary technical guidance to improve understanding of specific factors associated with mine gas emissions, including gas sources, relevant pathways, changes over time and the effect of cumulative development.

Q. Is the current scope of the guidance for mitigation measures tight enough?

Stakeholder views differed over the points-based system within British Standard BS 8485. We found some evidence of the standard being applied incorrectly as a prescriptive approach by consultants but also examples of some seeking to exploit loopholes in the guidance rather than using it to assist in the risk mitigation process. However, many expressed the view that if the gas risk assessment has been undertaken appropriately based on a robust conceptual site model then suitable recommendations for mitigation measures and implementation will follow. Appropriate verification of the installation of gas protection measures remains a key concern for many, although progress in this area is being made through various initiatives, such the British Verification Council, to improve the quality of workmanship and oversight.

Q. Is one of the problems the co-ordination between different departments in local authorities – Planning, Building Standards and Environmental Health?

This can be a challenge particularly where there is a ‘silo’ mentality but we found some excellent examples of good practice in some Scottish local authorities, which we felt could be adopted more widely. Planning staff are noted to be under increasing pressure to approve residential developments quickly, which can affect timescales for scrutiny of assessments. We also identified the need for additional funding requirements to enhance capabilities for local authorities to critically review ground gas assessments through training or the use of independent external specialist support.

Want to know more? Join Environment Analyst at the upcoming  Brownfield Land Scotland 2020 conference on 5 February in Edinburgh, where Tom and Andrew Gunning, RSK@Stirling Managing Director, will be going into detail about a project that RSK was appointed by the Scottish Government to carry out a research project into the prevalence of CO2 from disused mineral mines and the resulting risk to residential buildings. Book your place at the conference here.