CO2 mine gas - site investigation and risk assessment: best practice

Executive Summary

1. This research project follows on from and implements some of the findings of a 2019 Scottish Government research project on the prevalence of carbon dioxide (CO₂) mine gas derived from disused coal mines and the implications for residential buildings.

2. The aim of the project is to collate current practice and provide a summary assessment of options to deliver a standardised 'good practice' approach to risk assessment, reporting, mitigation and verification of mitigation measures for mine gas. The proposed good practice approach should consider interdepartmental relationships between Environmental Health officers (EHO)/ Contaminated Land officers (CLO), Planning, and Building Standards staff with the aim of achieving a scientifically robust and consistent approach to the risks posed by mine gas to development.

3. This work has been supported and informed by engagement with the 23 local authorities located within coal or oil shale mining affected areas of Scotland. In an initial consultation phase, an online survey was sent to 130 participants from the 23 local authorities by email in December 2020. This was followed by detailed engagement interviews with staff from six local authorities undertaken in January and February 2021.

4. Detailed analysis of the consultation findings was undertaken to examine all aspects of the current regulation of potential risks from mine gas to development under the planning and building standards regimes. Areas of good practice, and areas where there are potential gaps, that could be improved were identified.

5. A review and update of the report findings was commissioned in December 2023 in light of additional industry and regulatory guidance published since the report was originally drafted in February 2021.

6. A proposed process has been developed for good practice to be adopted across all 23 local authorities affected by coal/ oil shale mine gas risk. This focuses on:

a. Agreed roles and responsibilities and good working relationships between all disciplines involved with regular dialogue occurring.

b. Use of an effective and consistent method of screening applications for mine gas based on access to Coal Authority and relevant local authority (LA)-held data and with reference to the decision tool contained in the CL:AIRE 2021 good practice guidance.

c. Use of a shared document management system and data held in Geographical Information Systems (GIS) to facilitate information sharing and avoiding the duplication of effort.

d. Peer reviews of reports submitted under planning should also consider Building Warrant requirements in terms of complying with mandatory standard 3.1 in relation to harmful and dangerous substances.

e. Review of BS8485 design reports and verification reports should be undertaken with input from both EHO/ CLO and Building Standards officers.

7. A process flow chart describing the good practice process was developed. This is supported by an example template for LA peer review of mine gas related reports. The draft process and supporting materials were issued to staff from the six local authorities from the detailed consultation phase for comment. The responses received were broadly supportive and where improvements were suggested, the process and supporting materials were updated accordingly. In updating this report subsequently, the flow chart has also been evaluated with regard to information within the CL:AIRE 2021 good practice guide with minor amendments being made.

8. Additional recommendations identified over the course of the research include:

a. The Building Standards Technical Handbooks, last updated in June 2023, need to be updated to cover mine gas (and ground gas more generally) and associated reporting. A number of local authority consultees expressed the view during the consultations that this should be undertaken as a matter of urgency.

b. Additional training of EHO/ CLO and Building Standards on mine gas issues and peer review of reports in relation to mine gas issues should be undertaken to increase staff competency in peer reviews of submitted reports.

c. In the absence of an update to PAN 33 or Scotland-wide supplementary planning guidance, the EPS (2019) guidance and/ or LA-specific guidance should be updated to cover mine gas issues specifically.