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

5. Proposal for good practice for processing applications

Introduction

5.1 A key output of the current research project is to develop a recommended approach to good practice with the aim of achieving a scientifically robust and consistent approach to the risks posed by mine gas to development under both planning and building standards regimes. LAs may find that some, or all of the good practice approach can be adopted.

5.2 The good practice approach developed relates specifically to new development in coal mining affected areas, and the appropriate assessment and mitigation of risks relating to mine gas. It does not consider other mine related risks such as unsealed mine entries or subsidence. There may be further coal mining related risks that should be considered over and beyond mine gas, which are not covered by the proposed good practice approach.

5.3 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.

5.4 The proposed good practice approach has been written on the assumption the proposed updates to the 2023 Building Standards Technical Handbooks recommended in Section 6 are completed.

5.5 The principles of the good practice approach presented may have wider applicability to the regulation of ground gas from other sources and wider land contamination issues, although it has been developed specifically in the context of CO₂ mine gas.

5.6 Annex C presents a flow chart setting out a proposed process for good practice in the regulation of mine gas risk to development under planning and building standards. The process presented in the flowchart (see Note 9) occurs in parallel to consultation with the CA as a statutory consultee under the planning regime. The flow chart is focused towards non-householder applications. Applications for small domestic extensions to existing buildings are not specifically covered but some of the principles may be relevant to such applications. For householder extensions, consideration should be given to available information on existing gas protection measures at the property.

5.7 Based on the findings of the consultation undertaken in this and the previous project (SG, 2019a), EHO/ CLO are identified as the discipline with the greatest expertise in the area of mine gas risk assessment. Building Standards officers typically have the greater expertise in reviewing detailed design drawings and specifications.

5.8 On this basis, this good practice approach assumes that the EHO/ CLO would lead on 'screening' sites for mine gas and in undertaking peer review of desk study and SI reports assessing mine gas risks to development. Building Standards officers would typically lead the review of design reports for gas protection measures, possibly with support from EHO/ CLO. Verification reports are likely to be reviewed by both EHO/ CLO and Building Standards officers (where submitted as part of the supporting evidence for a Completion Certificate submission).

5.9 As noted in the findings of the consultation, there are differences in some local authorities in terms of where this expertise may lie, and it is acknowledged that the roles and responsibilities proposed on Annex C and discussed in Section 5 may be a simplification.

5.10 The process described does not specifically cover consultation with the CA, which is likely to be occurring in parallel as they are a statutory consultee for all developments in areas of former or proposed coal workings. Although CA comments are focused primarily on geotechnical risks, there may be relevant information on mine gas provided. Also, mitigation undertaken to address geotechnical risks, e.g. grouting of shallow workings or sealing of mine entries, will have implications for the assessment and mitigation of mine gas risks. The two processes therefore need to be linked.

5.11 Each of the key stages is discussed in detail below.

Receipt of planning application – screening for mine gas risks

5.12 On receipt of a planning application, initial validation checks are undertaken by Planning/ Development Management officers. Some local authorities require desk studies and/ or site investigation reports for all sites under local plans or supplementary planning guidance therefore the screening step is not required.

5.13 Screening of applications for mine gas should be undertaken alongside potential land contamination risks in a consistent manner. The identification of sites with potential mine gas (or land contamination) issues is undertaken by either Planning or the EHO/ CLO. The designated person responsible for the screening is clearly identified and known to all disciplines. Where the screening is undertaken by Planning staff, input from the EHO/ CLO and/or any Minerals Officers, is likely to be valuable due to their technical expertise and local knowledge.

5.14 The datasets used for the screening are relevant and up to date. In relation to mine gas these include, as a minimum, Coal Mining Reporting Areas and Development High Risk Areas, which are publicly available on the CA interactive viewer, and relevant local information held by the LA. The Coal Mining Reporting Area is the entire coalfield area, made up of Development High Risk and Development Low Risk areas. A Development Low Risk Area (85% of the coalfield area, UK-wide) is the part of the Coal Mining Reporting Area which contains no recorded coal mining legacy risks to the surface (CA, 2021). The Development High Risk Area (15% of the coalfield area, UK-wide) is the part of the Coal Mining Reporting Area where coal mining risks are present at shallow depth which are likely to affect new development (CA, 2021). Consideration of mine gas issues is needed for both Development High Risk and Development Low Risk areas. Reference to the CL:AIRE 2021 good practice guide's decision tool can be made for screening of sites for mine gas risk.

5.15 Table 5-1 summarises key information relevant to screening of planning applications for mine gas risk.

Notes

¹ 50 m is taken as a pragmatic distance and that viewable on a GIS layer

² Areas where the CA believes there to be unrecorded coal workings that exist at or close to the surface (less than 30 metres deep).

³ 500 m is that reported in a CA Consultants Report

5.16 A decision record should be kept of the outcome of the screening, such as on the planning application record or shared document management system.

Submission and review of desk study and site investigation report

5.17 The good practice approach presented recommends that a desk study report should always be submitted prior to the decision being made as to whether to grant planning permission. Where the site is located in a Coal Mining Reporting Area, the desk study report should always incorporate a Consultants Coal Mining Report procured from the CA with the findings interpreted in the report. The Consultants Coal Mining Report provides additional information over and beyond a CA CON29M report, which is intended for conveyancing only. Additional information from the CA may be relevant including details of mine entries, mine abandonment plans and gas or groundwater monitoring data. Information from the Desk Study and CA consultant's coal mining report should always be considered against the CL:AIRE 2021 good practice guide's decision tool to apply a risk zone to the site.

5.18 Where the desk study report identifies the potential for mine gas risks to the proposed development, an SI report incorporating a mine gas risk assessment shall be required before development commences. This should apply irrespective of development type, e.g. residential, public amenity, commercial etc.

5.19 The SI report should preferably be submitted prior to the decision being made on whether to grant planning permission. This is because the SI report and associated mine gas risk assessment need to be able to demonstrate that the risks can be suitably mitigated for the proposed development prior to planning permission being granted. Land contamination (including mine gas) is noted to be a material planning consideration. Also, the peer review may identify the need for further site investigation or monitoring which can be time consuming.

5.20 Reports submitted are peer reviewed by the CLO/EHO against current and relevant standards and technical guidance. Depending on the complexity of the mine gas / land contamination issues identified in the desk study/ site investigation report, external peer review support may be required. The report(s) is either a) accepted and recommendations regarding relevant planning conditions to include are made by the CLO/EHO to Planning or b) subject to on-going review until review comments have been addressed to the satisfaction of the CLO/EHO.

5.21 The findings of the review(s) are documented and retained on a shared document management system, and directly linked to a property gazetteer. The shared document management system is accessible to all three disciplines (Planning, EHO/ CLO and Building Standards). Where applicable, acceptance of the report(s) leads to discharge of the relevant planning condition (or part thereof).

5.22 The peer review of submitted reports should follow a structured and clearly documented process. The review should consider suitability for use under PAN 33 and the recommendations of supplementary guidance (e.g. EPS). This could include publications by the Scottish Government. And specific LAs. The EPS (2019) guidance is also of value in this regard. 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.

5.23 For efficiency purposes it is recommended that the peer reviews of reports also consider Building Warrant requirements in terms of complying with mandatory standard 3.1 in relation to harmful and dangerous substances.

5.24 The peer review considers if a remediation strategy is required before the application can be determined, or if submission of the remediation strategy report can be conditioned. Recommendations are made for relevant planning conditions to be agreed between the Planning Officer and the EHO/ CLO.

Planning decision and setting conditions

5.25 Where the decision is made by the LA to grant planning permission, the planning conditions should be attached to the Decision Notice to address the remaining requirements in relation to mine gas. Standard conditions used for assessment and remediation of land contamination risks are likely to be suitable to encompass mine gas risks on many sites. These reflect the report(s) submitted prior to the decision on whether to grant planning permission, and the further submissions required. Such conditions would normally require the submission of a SI report if not required at the application stage, and where applicable, a remediation strategy including a verification plan, and a verification report.

5.26 Where there are specific considerations for mine gas on a particular development the use of bespoke planning conditions should be considered. Examples could include the impact of mine grouting or decommissioning of boreholes. Where development-specific conditions are required, there should be input from EHO/ CLO staff to agree the appropriate wording.

5.27 Where the peer review, if undertaken in advance of the decision to grant planning permission, indicates that mine gas risks cannot be suitably mitigated for the proposed development then the application should be refused. An example would be for Characteristic Situation 4 (CS4). BS8485 (BSI, 2019) states that 'residential buildings should not be built on CS4 or higher [risk] sites unless the type of construction or site circumstances allow additional levels of protection to be incorporated, e.g. high‑performance ventilation or pathway intervention measures, and an associated sustainable system of management of maintenance of the gas control system, e.g. in institutional and/or fully serviced contractual situations.'

Submission and review of remediation strategy

5.28 The remediation strategy, if identified as being required, is typically submitted after the granting of planning permission. If the remediation strategy has been prepared in advance of the grant of planning permission, it may be reviewed earlier in the development control process.

5.29 Where applicable, the report will describe measures to be taken to decommission boreholes that could represent a preferential pathway for mine gas to migrate to the surface or into permeable strata.

5.30 The submitted report is peer reviewed by the CLO/EHO, in the context of the previously reviewed desk study and SI reports. Depending on the complexity of the remediation being proposed, external peer review support may be required. The report is either a) accepted and recommendations regarding relevant planning conditions to include are made by the CLO/EHO to Planning or b) subject to on-going review until review comments have been addressed to the satisfaction of the CLO/EHO. The findings of the review(s) are documented and retained on a shared document management system, and directly linked to a property gazetteer. Where applicable, acceptance of the report leads to discharge of the relevant planning application (or part thereof).

5.31 The peer review follows a structured and clearly documented process. Suggested key elements of the peer review process in relation to all report types are presented in Annex D. The key elements of the report types requiring peer review are those that would be expected to be presented in a report prepared by a suitably qualified geo-environmental consultant where mine gas is a potential issue. The review should consider suitability for use under PAN 33 and mandatory standard 3.1 in relation to harmful and dangerous substances.

Aspects specific to building warrant applications

5.32 On receipt of a building warrant application, a check should be made by Building Standards for an existing planning application and its status. These applications should be linked.

5.33 If mine gas-related reports have been submitted directly in connection with the building warrant application, they should be cross referenced with those previously submitted earlier in connection with the linked planning application. Where there is a shared document management system, directly linked to a property gazetteer, all previous documents and correspondence can be viewed. Checks are made with the CLO/EHO in relation to reports directly relevant to mandatory standard 3.1 have previously been submitted. Such reports will additionally consider mandatory standard 3.2 for radon gas. These checks should identify if the previously submitted reports are considered to be sufficiently up to date at the time of the building warrant application.

5.34 If there is no linked planning application, the initial Building Standards application validation checks should include screening for potential land contamination risks, including mine gas. The datasets used in the screening are those used by planning and/or the CLO/EHO to screen a planning application submission. Table 5-2 summarises key information relevant to screening of building warrant applications for mine gas risk.

5.35 Screening of building warrant applications for mine gas should be undertaken alongside potential land contamination risks in a consistent manner. The identification of sites with potential mine gas (or land contamination) issues is undertaken by either Building Standards or the EHO/ CLO. The designated person responsible for the screening is clearly identified and known to all disciplines. Where the screening is undertaken by Planning staff, input from the EHO/ CLO and/or any Minerals Officers, is likely to be valuable due to their technical expertise and local knowledge.

Notes

¹ 50 m is taken as a pragmatic distance and that viewable on a GIS layer

² Areas where the CA believes there to be unrecorded coal workings that exist at or close to the surface (less than 30 metres deep).

³ 500 m is that reported in a CA Consultants Report

5.36 The criteria for needing a desk study, SI report and remediation strategy to address mine gas issues should be the same as for a planning application. Peer review of these reports should be undertaken desk study by the CLO/EHO as detailed above, seeking external peer review if required.

Review of design report for gas protection measures

5.37 Where gas protection measures are required for the development and outlined in the remediation strategy, the detailed design and specification of the protection measures should be recorded in a design report. For standard construction details or lower risk sites there may be sufficient information in the remediation strategy report. Information in the remediation strategy should, however, include that required in BS8485 (BSI, 2019) in relation to a design report, but does not necessarily need to be presented as a standalone report. However, for non-standard construction details for a CS2 site or for higher risk sites (CS3 or above), it is recommended that a design report should be submitted.

5.38 The design report is specific to the design and construction of the gas protection measures and how these tie into the detailed design of the proposed buildings. The design report will additionally provide a verification plan for the installation of the gas protection measures in accordance with BS8485 (BSI, 2019) and CIRIA C735 (CIRIA, 2014). BS8485 (BSI, 2019) makes reference to C735 in relation to verification. The reports are therefore directly applicable to address mandatory standard 3.1 for a building warrant. They may also need to be considered as part of discharge of relevant planning conditions and this is likely to need to be agreed on a case by case basis between the EHO/ CLO and Planning officer.

5.39 The report is reviewed by the CLO/EHO or building standards officer, depending on the technical complexity of the gas protection measures and the technical competency of either discipline. Depending on the complexity of the gas protection measures external peer review support may be required. Examples of this include complex ventilation calculations or non-standard design of gas protection measures. The discipline reviewing the report should do so in the context of the previously reviewed (and accepted) desk study, SI and remediation strategy reports.

5.40 The design report (and associated drawings) is either a) accepted by the designated reviewer and recommendations are made to Planning or Building Standards or b) subject to on-going review until review comments have been addressed to the satisfaction of the reviewer. The findings of the review(s) are documented and retained on a shared document management system, and directly linked to a property gazetteer.

Building warrant approval

5.41 Building warrant approval is granted following acceptance of the relevant reports, each of which have been subject to peer review by the designated officer(s) at the LA.

5.42 Applications for amendments to the building warrant, which have potential implications for mine gas risks or the previously agreed design of gas protection measures, are considered (see Annex D). The CLO/EHO is consulted on the amendment application, following the same review process of submitted reports as for the original application.

Installation and verification of gas protection measures

5.43 The installation and verification of the approved gas protection measures is undertaken by an independent party on behalf of the developer, to inform the verification report. The third party may hold accreditation under the CL:AIRE Gas Protection Verification Accreditation Scheme (GPVS). The scheme applies to both the practical installation of the gas mitigation measures and to the verification reporting process. The GPVS is not mandatory but seeks to raise standards in membrane inspection, verification and reporting. Use of the scheme is intended to provide all stakeholders involved in land contamination management with confidence that risks associated with ground gases have been adequately managed.

5.44 Independent checks may be undertaken by Building Standards officers, depending on the approach taken by the LA, and as set out in the Construction Compliance and Notification Plan (CCNP).

Review of verification report

5.45 A verification report is submitted by, or on behalf of, the developer/ applicant as part of an application to discharge relevant planning conditions.

5.46 The Relevant Person signing and submitting the building warrant Completion Certificate should have a copy of the verification report and have satisfied themselves of its adequacy. The verification report should provide the evidence that the proposed gas protection measures have been installed appropriately. In relation to the building warrant, the verification report should ideally accompany the completion certificate, although there is no legal requirement for this. It would however be beneficial if the Building Standards Technical Handbooks were to be updated to make specific reference to the importance of ground gas verification reports.

5.47 The submitted verification report in connection with the planning application is peer reviewed by the CLO/EHO, in the context of the previously reviewed remediation strategy and/ or design report, where applicable. Depending on the complexity of the gas protection measures being verified, external peer review support may be required. Where applicable, the report will include measures taken to decommission boreholes that could represent a preferential pathway for mine gas to migrate to the surface or into permeable strata.

5.48 The report is either a) accepted and recommendations regarding discharging relevant planning conditions are made by the CLO/EHO to Planning or b) subject to on-going review until review comments have been addressed to the satisfaction of the CLO/EHO. The findings of the review(s) are documented and retained on a shared document management system, and directly linked to a property gazetteer. If the verification report is not considered adequate in relation to gas protection measures and planning conditions, it is good practice that this opinion is shared with Building Standards prior to Building Standards accepting the Completion Certificate.

5.49 All disciplines are in agreement of the acceptability of the verification report in relation to suitability for use under PAN 33 and mandatory standard 3.1 in relation to harmful and dangerous substances. Where applicable, acceptance of the report leads to discharge of the relevant planning application (or part thereof).

Acceptance of building warrant completion certificate

5.50 Following acceptance by the CLO/EHO and/or Building Standards of the verification report, the Completion Certificate is accepted by Building Standards. Acceptance of gas protection measures may be for individual plot(s), with an overarching verification report submitted in relation to the entire site/ or specific phases once development is completed. If using the peer review template in Annex D, relevant review points within Table 2d can be used to support a peer review of gas protection measures as the sample principles apply.