Ground gases can be produced from a variety of man-made sources such as landfills, in filled ponds and made ground as well as natural sources which include coal, peat and alluvial deposits.
GRM provides ground-gas risk assessments to identify and quantify ground-gas risks to specified receptors based on current guidance including:
- CIRIA C665
This usually involves the installation of monitoring installations in line with current good practice followed by a period of monitoring. Depending on the type of site proposed, proximity to gas sources (often landfills) and the strata revealed during the ground investigation the gas monitoring is targeted to investigate those issues and a suitable monitoring period arrived at. The design of ground gas investigation is based on guidance provided in CIRIA C665 and BS8576:2013.
Once gas monitoring is complete ground-gas protection measures can be designed and targeted accurately.
All gas protection measure are designed to comply with BS8485:2007 – Code of Practice for the Characterisation and Remediation from Ground Gas in Affected Developments. In general the majority of gas risks can be dealt with by specifying suitable below slab gas protection augmented if necessary with vented sub-floor voids.
On some occasions the concentration of landfill or soil gas is such that additional measures have to be taken in order to protect development. Typical additional measures might include:
- Vent trenches
- Venting boreholes
- Venting boreholes + Vent Trench
- Vibro-replacement columns
- Re-engineered cohesive layers
- Search and removal of source areas
GRM’s environmental experts can help design suitable gas monitoring schemes and subsequent gas protection measures.
Whilst gas monitoring is normally carried out via a number of visits over a period of usually 3 months, this timescale can be reduced by the use of continuous monitoring equipment in boreholes over a much reduced time period.
However, the costs of monitoring will increase significantly and whilst this is an attractive option on some occasions is not usually a cost effective option for our Clients.