Southwest Environmental Limited

Ground Gas Risk Assessment

We can offer ground gas risk assessments based on desk studies, and primary data collection. We have done both many times since 2009. A desk study may very occasionally close out risks, whilst RB17 method can prove useful in some situations and avoid 3 (typical) or 6 (extreme) months of monitoring.

If you need a ground gas risk assessment we are willing and able to assist, please contact us for a quotation.

Understanding the Ground Gas Risk Assessment Process

A ground gas risk assessment in the UK typically involves several key steps:

Ground Gas Desk Study

This involves gathering information about the site, including its history, surrounding land use, geology, and potential sources of ground gas (landfills, infilled ground, etc.). You can consult historical maps, environmental reports, and seek relevant local authority information.

This uses the information gathered in the preliminary assessment to identify potential risks and determine if a detailed ground gas investigation is necessary. Guidance documents like CIRIA C665 and BS 8485 can help guide this step.

Ground Gas Monitoring

If your desk study indicates potential risks there are two option moving forward:

• RB17 Method - Using results from soil samples we can determine a "character" for the site and suggest mitigation. This isn't always possible but if it is, the results are obtain far faster than full GI.
• Full GI - Gas monitoring wells are installed at the site to measure gas concentrations and flow rates. The monitoring duration and frequency depend on the identified risks and local regulations.

Ground Gas Risk Assessment and Mitigation

Based on the monitoring results and desk study findings, a qualified professional like a Chartered Engineer or a geotechnical consultant assesses the level of risk and recommends appropriate mitigation measures. These can include gas protection membranes, ventilation systems, or even redesigning the development if necessary.

Reporting and Validation

Whilst mitigation measures are installed it is very important to make thorough records. Lots of photos, and video should be taken as evidence that gas membrane etc. are installed correctly. Warranties from the NHBC etc. will not be given unless evidence can be provided. These records are added to a comprehensive report documenting the assessment process, findings, and recommended mitigation measures is prepared. Depending on the project and local regulations, validation by a qualified professional might be required.

The below section was written by a machine: Google Gemini

Ground Gas Risk Assessment: Protecting New Developments

Ground gas risk assessment is a vital component of the planning process, particularly for sites located near former landfills, filled ground, or areas with naturally occurring geological hazards. Southwest Environmental Limited provides technical expertise in monitoring and assessing Methane (CH4), Carbon Dioxide (CO2), and Radon to ensure the long-term safety of building occupants.

The Assessment Process

Our methodology follows current UK best practices, including CIRIA C665 and BS 8485, to provide a robust data set for planning approval.

• Monitoring Well Installation: Strategic placement of gas monitoring standpipes during the Environmental Site Investigation.
• Data Collection: Periodic monitoring of gas concentrations and flow rates under varying atmospheric pressures.
• Gas Screening Values (GSV): Calculation of GSVs to determine the site's Characteristic Situation (CS1 to CS6).
• Mitigation Design: Specification of gas membranes and sub-floor venting where required to protect the building envelope.

Technical Compliance for Planning

A professional gas risk assessment prevents costly delays and ensures that your project meets the requirements of Local Planning Authorities and Building Control. By integrating these findings with a Phase 1 Desktop Study, we provide a seamless path from site characterization to the final Phase 4 Verification of gas protection measures.

Expert Geo-Environmental Guidance

With over 900 projects completed across the UK, our consultants leverage extensive experience in complex geology and contaminated land. Whether you are dealing with coal mining legacy issues or biodegradable fill, SWEL delivers the accredited technical authority needed to secure your development's future.