Contaminated land planning guidance

If the development is situated within 250m of a landfill site, or is suspected of having the potential to generate ground gas, it will be necessary to assess the potential risk and, if required, to incorporate appropriate gas protection measures into the development design. To facilitate this, the following ground gas conditions are usually used:

1. A scheme detailing appropriate gas mitigation/protection measures

Prior to the start of the development, a scheme detailing appropriate gas mitigation/protection measures to be incorporated into the development shall be submitted to and approved by the Local Planning Authority in writing. This shall also include details on how the scheme will be tested/verified. Any scheme should have regard to the Building Research Establishment document ‘’BR414 Protective Measures for Housing on Gas Contaminated Land and CIRIA Report C735 Good practice on the testing and verification of protection systems for buildings against hazardous ground gases.

As a minimum the scheme should include (but not be limited to):

• a summary of the gas risk assessment
• the gas protection measures proposed (including reference to the appropriate guidance documents) and confirmation they will meet the gas protection requirements for the lifetime of the development
• technical drawings showing how the gas protection measures will be incorporated
• formal qualifications/experience/training of the person carrying out the installation
• formal qualifications/experience/training of the person carrying out the verification
• the manufacturer’s specification of the gas protection membrane to be used
• full details of what the verification process will comprise and at what stage verification will be carried out
• details of how any non-conformance will be dealt with
• details of the number of plots to be validated (deviation from verification of every plot will need to be justified and agreed with the Local Planning Authority)
• timeline of when during the build, each of the gas protection measures will be installed
• details of management measures proposed to ensure how damage to the membrane will be prevented prior to the floor being installed, post installation
• details of how all site personnel (including follow on trades) will be made aware of the presence of the membrane and that damage to the membrane must be prevented
• details of the extent of overlap and method of sealing (these must be in line with manufacturer’s instructions and evidence provided)
• confirmation that a signed (plot specific unless agreed otherwise) statement confirming that the gas protection measures were installed as agreed and that the membrane was free from tears and punctures and was lapped and sealed as agreed at joins and around services and sub floor voids were clear and free from debris will be included in the Verification Report
• confirmation that plot specific photographs showing the installed membrane will be included in the Verification Report.

2. Detailed ground gas verification report

Prior to occupation, a suitably detailed ground gas verification report shall be submitted and approved in writing by the Local Planning Authority prior to occupation. The verification report should include but not be limited to photographic evidence demonstrating the quality of works undertaken and be able to demonstrate the gas mitigation/protection measures have been installed and validated by a suitably qualified person(s).

The Verification Report should include a summary of all the works undertaken, relating to gas protection measures including all elements detailed within the Remediation Strategy discussed above. As a minimum the report should include (but not be limited to):

• site details
• planning application details
• summary of Gas Risk Assessment (including original CSM)
• details of who carried out installation (qualifications/experience/training)
• details of who carried out verification (qualifications/experience/training)
• description of protection measures installed with reference to method statements and drawings and manufacturers specification of the materials used
• details of the verification inspection regime
• supporting information, plans, air vent installation, photographs, as built drawings
• summary of verification data (completed proformas, test results)
• details of non-conformances and how they were rectified
• clear statement saying remedial objectives been achieved supported by lines of evidence including reference to CSM
• where necessary further works and/ or long term management

Guidance for assessment of the risks associated with the presence of methane and carbon dioxide within ground gas can be found in the following useful documents;

• Assessing Risks Posed by Hazardous Gas Ground Gases to Buildings (CIRIA C665)
• BRE Report 414 publication Protective Measures for Housing on Gas Contaminated Land Guidance on Evaluation of Development Proposals on Sites where Methane and Carbon Dioxide are present
• Code of practice for the design of protective measures for methane and carbon dioxide ground gases for new buildings
• Local Authority Guide to Ground Gas, and Development on Land Potentially Affected by Hazardous Ground Gas