Ground Gas Assessments : Geotechnical, Environmental & Ecological Services

Ground Gas Investigations

Ground gas investigations are typically undertaken as part of a Phase II geo-environmental assessment or occasionally as a stand-alone investigation where proposed development sites/existing structures are potentially affected by ground gas from landfills, made ground or mine workings.

In terms of development, an appropriate site specific gas investigation, particularly on brownfield sites, is inevitably a planning condition. Environmental Health Officers currently use CIRIA C665 as guidance which recommends a minimum of 3 months monitoring for sensitive uses such as residential properties with gardens for a site with a very low potential of source gas generation. NHBC also recommends this guidance. It is therefore essential that this is included in the development programme to avoid delays and determine the most appropriate gas protection measures (if required).

Existing structures may also be at risk from ground gas and if the gas is from an off-site source the Environmental Protection Act 1990 Part 2A legislation could determine that the polluter or landowner from an adjacent site is liable for the remedial measures required.  The potential source could be determined by a Phase I Desk Study with a subsequent ground gas investigation to confirm this.

GEG undertake cost effective thorough ground gas investigations in accordance with current industry guidance, such as CIRIA C665, which have always been approved by the regulators.

A typical investigation will comprise the installation of a suitable number of appropriately positioned gas monitoring wells (the number is dependant on the size and complexity of the site)  with a subequent series of monitoring visits (according to the potential for ground gas and sensitivity of the exist/proposed development), at least one targeting low / falling atmospheric pressure conditions.  The monitoring will include gas flow measurements, which together with methane and carbon dioxide concentrations will be used to calculate gas screening values and hence allow the determination of any necessary gas protective measures. Additional monitoring of other gases such as carbon monoxide and hydrogen sulphide are also undertaken as appropriate on a site specific basis to determine whether these gases pose a health risk.