Soil vapour and ground gas - often forgotten risks

Soil vapour and ground gas are often the forgotten media in contaminated land investigation; as the contamination cannot be ‘seen’. However, when present, soil vapour and ground gas present one of the key risks posed to human health.

Soil vapours can be present in the sub-surface at many sites where volatile contaminants are, or have been, utilised (e.g. industrial and manufacturing facilities; petroleum retail and depot facilities; dry cleaners, and former gas works).

Ground gas (as methane and carbon dioxide), also commonly known as landfill gas (LFG) are formed from the degradation of organic matter, and are often associated with active and former landfills / waste disposal facilities; and in areas of organic rich soils (such as peat).

If soil vapour or ground gas are present beneath a site, intrusion into indoor air is the most likely pathway to pose a risk to human health. Using improved and reliable soil vapour and ground gas investigation technologies developed in the USA and Europe, we are able to assess whether soil vapour and/or ground gas is present in the sub-surface at concentrations that could pose a risk to human health. These investigation techniques can be partnered with indoor air monitoring to further assess actual risk poses by soil vapour and/or ground gas.

By utilising the most applicable and reliable investigation method for the site and project, we are able to provide cost effective and schedule efficient strategies tailored to the site and contaminant. The ‘no one size fits all’ approach, allows us to be dynamic in assessing actual risk. Rapidly assessing the risk posed to Site users assists decision makers in understanding whether measures to mitigate the risk are required (e.g. further investigation or remediation); or whether no imminent risk is present and attention and resources can be focused elsewhere.

We have experience in the collection of soil vapour samples utilising a number of technologies, including: traditional soil vapour bores, and sub-slab monitoring using the Cox Colvin & Associates Inc. Vapor Pin®. Soil vapour samples can typically be collected using either gas sampling bags (e.g. Tedlar®) or gas sampling cannisters (e.g. SUMMATM or SiloniteTM). Discrete passive soil vapour sampling techniques are also easily used to assess actual risk over a known period of time.

Sampling technique selection is based on the type of site, type of contamination and ultimate goals and objectives of the study. We have developed relationships and partnerships with New Zealand-based suppliers and laboratories who can provide required sampling equipment, and conduct required analysis in a timely and cost competitive manner.

We also have extensive experience in the assessment of ground gas (methane and carbon dioxide) affected sites, including the design and installation of gas monitoring infrastructure; surface emissions monitoring; and continuous monitoring strategies. Ground gas concentrations and flow are particularly influenced by atmospheric conditions, such as: temperature, rainfall and atmospheric pressure. Understanding the optimal timing of sampling and monitoring is key to obtaining useful data upon which to draw reliable conclusions.  

As a rapidly developing field, 4Sight remain committed to providing the most efficient investigation strategies, taking advantage of innovative cutting-edge technologies to provide the best project outcomes.

For more information on 4Sight’s Soil Vapour and Ground Gas investigation services, please get in touch with James Blackwell.