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

Report collating current practice in local authorities 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.

6. Conclusions and recommendations

Key findings

6.1 The initial and detailed consultation undertaken in this project with local authority officers in Planning and Building Standards and in EHO/ CLO roles has revealed the following key findings.

6.2 There is a good level of awareness of issues relating to mine gas risk to development following the Gorebridge incident and the 2019 research report (SG, 2019a), which is important for effective regulation in this area.

6.3 All of the local authorities consulted have processes in place for assessing mine gas issues for specific planning and building warrant applications. These are generally not formal written procedures but they have typically developed over time. Written procedures for interdisciplinary working are not necessarily considered to be required.

6.4 Key elements to an effective working relationship between disciplines were found to be trust between colleagues, relationships established over time and the ease with which officers were able to communicate and share information. It was found that there are usually strong links between Planning and EHO/ CLO staff but sometimes weaker links between these disciplines and Building Standards staff who tend to operate more independently.

6.5 With a planning application typically preceding a building warrant application, the identification of sites potentially affected by mine gas normally falls in the first instance to the Planning department.

6.6 Some LAs have a process for 'screening' applications for mine gas (and other land contamination related issues). The approaches adopted included selection of specific applications by Planning Department staff for review by EHO/ CLO staff; review of weekly lists of planning applications by EHO/ CLO staff; or consulting with EHO/ CLO staff on all non-householder applications. Depending on the data source(s) used when 'screening sites', the first two approaches could lead to sites where there is a potential mine gas issue not being identified.

6.7 Other LAs have taken the decision to require desk study reports for all planning applications, which are then peer reviewed (internally or externally) to make sure mine gas issues have been addressed. This reduces the likelihood of mine gas issues not being identified but is potentially more onerous in time and cost for peer review resources.

6.8 Where the interdisciplinary working was less effective at a LA, the 'screening' of sites was undertaken separately by Building Standards with limited oversight of decisions that may have already been undertaken by Planning and/or the EHO/ CLO. This leads to potential inconsistency between requirements for the two regimes as well as potential duplication of effort to screen applications and peer review reports. A shared document management system, linked to a property gazetteer, and accessible by all disciplines is preferable for effective sharing of resources and efficient regulation.

6.9 There is a clear understanding of relevant technical guidance for peer review of mine gas related reports (e.g. BS8576, BS8485, CIRIA C665) particularly amongst EHO/ CLO staff leading reviews of relevant reports. Use and knowledge of BS8485 (BSI, 2019) by Building Standards officers is more limited. This represents a potential gap, particularly in those LAs where Building Standards officers review remediation strategies, design reports and verification reports independently of the EHO/ CLO resource. It should be noted that the CL:AIRE 2021 good practice guidance would now be considered among the relevant technical guidance noted above but knowledge and awareness of this cannot be commented on.

6.10 Standard planning conditions used by individual LAs (as informed by PAN 33), were considered to be adequate to achieve effective regulation of mine gas issues in most cases. Where specific mine gas planning conditions were required, these were already in use by a small number of LAs. A number of the consultees commented that the current trend is toward simplifying the use of generic conditions and Planning Departments can be resistant to application-specific conditions.

6.11 Verification was identified as the weakest part of the regulatory process. At least one LA consulted was not proactively requesting verification reports to discharge outstanding planning conditions, and other LAs are concerned about the quality of such reports when received. The implication is that the mine gas protection measures may not have been installed appropriately and there will be a residual risk to site occupiers and building structures. There were differences of opinion amongst LAs as to whether reliance should be placed on verification reports, site inspections or a combination of the two to support acceptance of completion certificates for building warrants.

6.12 Responses on the value of external peer reviews varied widely suggesting there is a need to improve the consistency and quality of this.

6.13 Training of LA staff on mine gas issues, for effective regulation was considered to be required by the majority of respondents. Training is required specifically in relation to BS8485 (BSI, 2019) design reports to ensure they are reviewed by an officer with the appropriate technical competency and specialism. CL:AIRE has been offering training on the mine gas guidance since its publication.

6.14 Although it is good practice for the decommissioning and sealing of gas monitoring wells to form part of the remediation strategy, not all LAs consulted are managing to regulate this effectively; in some cases the issue is not being considered during peer review of remediation strategy and verification reports, while in others cases developers are not complying with the requirement. Supporting guidance on decommissioning of monitoring wells to address gas migration pathways would also be beneficial as well as raising awareness of this issue to all parties. This is noted to have been included within the CL:AIRE 2021 good practice guidance and also the NHBC NF94 (2023) guidance report for housebuilders.

6.15 Where a design change is made to building foundations that could have implications for the mine gas risk assessment, this should be covered under an Application for Amendment to the Building Warrant. The consultation revealed that this change should be identified at that point as needing further peer review to assess the implications for mine gas risk assessment and mitigation. However, gaps in the screening process discussed above could lead to this being missed.

6.16 There was consensus that updating the EPS (2019) 'Land contamination and development guidance', and where relevant LA-specific Supplementary Planning Guidance that has been published, to cover mine gas specifically would be beneficial to all parties involved in the development process.

6.17 The LA consultees agreed unanimously that additions to the two Building Standards technical handbooks (SG, 2023) were required in relation to mine gas (and ground gas more generally). Some consultees commented that the lack of specific reference to ground gas in the technical handbooks has led to push back from developers when more information is requested in support of a building warrant, such as a verification report. The consultees acknowledged that there was a balance to be achieved between being overly prescriptive and ensuring the required information was submitted in relation to mandatory standard 3.1.

Proposal for good practice for processing applications

6.18 A proposed process has been developed for good practice in the regulation of mine gas risk to development under planning and building standards. This takes account of the findings of the consultation with respect to areas of current good practice and areas for improvement.

6.19 It is acknowledged that it is the responsibility of the developer to undertake an adequate risk assessment of a site, and to propose measures to ensure that these risks are appropriately addressed. However, the proposed good practice approach, including technical peer review of submitted reports, is recommended to improve the consistency of regulation to help avoid a recurrence of the Gorebridge incident at other localities across Scotland.

6.20 The process is supported by the flowchart in Annex C. The flow chart identifies when engagement between disciplines should be undertaken to achieve effective, efficient and consistent regulation. Suggested key elements and a proposed format for the peer review process in relation to all report types to support the good practice recommendations, are presented in Annex D.

6.21 Key elements of the process to be adopted by local authorities include:

  • Agreed roles and responsibilities and good working relationships between all disciplines involved with regular dialogue occurring.
  • Use of a shared document management system and GIS to facilitate information sharing and avoiding the duplication of effort.
  • Use of an effective and consistent method of screening applications for mine gas based on access to CA and relevant LA-held data, and with reference to the CL:AIRE 2021 good practice guide's decision tool.
  • 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.
  • Review of design reports and verification reports is undertaken through input from both EHO/ CLO and Building Standards officers.
  • Identification of where specialist external resources for peer review may be required, and
  • Where key elements such as decommissioning of monitoring wells should be considered.

Additional recommendations

6.22 The following additional recommendations are made:

  • The previous mine gas research report (SG, 2019a) recommended that PAN 33 should be updated to make reference to key issues relating to mine gas and relevant standards and guidance to be followed. In the absence of an update to PAN 33, the EPS (2019) guidance and LA-specific guidance should be updated to cover mine gas issues specifically.
  • The Building Standards Technical Handbooks (domestic and non-domestic) need to be updated to cover mine gas (and wider ground gas issues). This was a recommendation of the 2019 research report (SG, 2019a) but has not yet been acted upon.
  • Additional training of EHO/ CLO and Building Standards on mine gas issues should be undertaken to increase competency in peer reviews of submitted reports.
  • An approved register should be developed of suitably qualified and experienced consultants to undertake external peer review of mine gas related reports, for example through the Scotland Excel engineering and technical consultancy framework.

6.23 With respect to the Building Standards Technical Handbooks (domestic and non-domestic, the following sections are considered to require updating:

  • Section 3.1.3 on hazard identification should include reference to both ground gas and mine gas, with examples of land likely to be impacted (e.g. development over coal working or areas of non-coal mining, CA Development High Risk Areas, proximity to mine shafts etc.)
  • Table 3.1 'Possible contaminants and actions' should be updated to include an entry for permanent gases with specific reference to mine gas.
  • Section 3.1.6 'Risk management techniques' should be updated in relation to gas mitigation measures in building design or ground enabling works.
  • Reference should be made to decommissioning of gas monitoring wells, that could represent a preferential pathway for mine gas to migrate to the surface or into permeable strata.
  • Additional section relating to the importance of verification reporting in relation to land contamination and ground gas protection measures.



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