Embracing professional judgement: NHBC's Hazardous Ground Gas Guidance redefines best practice

Embracing Professional Judgement: NHBC’s Hazardous Ground Gas Guidance redefines best practice

As specialist geo-environmental consultants, GGS plays a crucial role in ensuring safety and mitigating risks associated with hazardous ground gases. The recently published NHBC Hazardous Ground Gas Guidance document marks a welcome shift in approach, emphasizing the importance of professional judgement over undue over-conservatism. In this blog, we will explore the main points of the guidance and how it aims to promote higher standards, better workmanship, and more efficient verification processes.

1. Moving away from over-conservatism

The NHBC guidance recognizes the issue of over-conservatism prevailing in the industry, where some practitioners tend to escalate precautionary measures from Characteristic Situation 1 (CS1) to CS2 without sufficient grounds. Such a “better safe than sorry” approach may lead to unnecessary expenses and an increased burden on developers, without necessarily providing additional benefits. By encouraging a more nuanced and professional judgment-based assessment, the guidance aims to strike a balance between safety and pragmatic solutions.

2. The downside of over-conservatism

Overly conservative practices might inadvertently lower the overall standards within the industry. When measures are escalated without valid justifications, it can create a culture of complacency and neglect towards accurate risk assessments and installation procedures. This kind of approach might result in an unnecessary financial burden for developers, leading to a lack of incentive for maintaining high standards of workmanship and verification.

4. Importance of a comprehensive desk study and walk over survey

The guidance stresses the significance of conducting a thorough desk study and a comprehensive walk over survey as the initial steps in any ground gas protection project. A desk study helps in identifying potential sources of contamination, historical land uses, and ground conditions, while a walk over survey provides valuable visual and site-specific information that contributes to a more accurate risk assessment.

5. Variability in made ground and ground gasses

Not all made ground is the same; some may contain hazardous ground gases, while others may not pose such risks. It is essential to recognize the variability in ground conditions and tailor the site investigation and ground gas protection measures accordingly. Site-specific assessments are vital to determine the presence and potential risks associated with ground gasses effectively.

6. Dissolved gas in groundwater

Dissolved gas in groundwater may not always present a problem; however, it can lead to high gas concentrations and flows from flooded monitoring wells. Understanding the behaviour of dissolved gases is crucial in interpreting monitoring data accurately and planning appropriate gas protection measures.

7. Utilizing tertiary plots

The use of tertiary plots is an effective way of presenting ground gas data. Tertiary plots can help demonstrate the source of ground gases and provide valuable insights into migration pathways. They enhance the overall understanding of the ground gas dynamics and facilitate better decision-making during risk assessment and mitigation planning.

10. The worst case scenario: Misallocated resources

Failing to follow the principles of professional judgement can result in the following:

a. Unnecessary mas Monitoring: Conducting gas monitoring in areas where there is no credible contaminant linkage is a wasteful practice. It adds to the project’s costs without providing meaningful data or insights.

b. Improper gas membrane installations: Installing gas membranes where they are not needed or without adhering to industry best practices can lead to compromised effectiveness, rendering them practically useless.

c. Costly and unnecessary verification: Carrying out excessive and poor-quality verification processes, especially when the risk does not warrant it, results in unnecessary expenses and a diversion of resources from critical tasks. It also squanders material resources and unsustainable.

d. Poor detailing of the gas barrier installation: This can have severe consequences, leading to moisture ingress back into a property. When moisture tracks back along the top of the gas barrier, it can lead to mould and rot inside the property. Such issues result in property damage and/or health risks, leading to potential claims against NHBC and legal disputes. Proper detailing and installation are crucial to preventing these problems and ensuring the gas protection system functions as intended.