Ground gas and volatile organic compound (VOC) monitoring, gas protection measures and verification

A F Howland Associates undertake ground gas and vapour investigations in accordance with CIRIA C665, BS8576 and NHBC recommendations.

A preliminary conceptual model formulated by the Phase I study or the initial stages of the ground gas risk assessment will determine the likely sources of ground gas (landfill, peat, coal mine or fill strata derived). This allows a site specific gas monitoring regime to be designed for the site with the gas monitoring period determined by the anticipated source of ground gas.

We utilise a fully calibrated MiniRAE 3000 photo-ionisation detector (PID) for VOC monitoring and Geotechnical Instruments GA5000 for ground gas monitoring. The GA5000 records oxygen, carbon monoxide, carbon dioxide, hydrogen sulphide and methane in addition to flow via an internal flow pod. The PID is best applied for screening of soils and waters on-site via head space testing of samples or through monitoring gas standpipe installations.

GA5000 gas monitor and MiniRAE 3000 PID

Continuous monitoring of ground gas has been recently developed. The method allows gas standpipes to be continuously monitored rather than a ‘snapshot’ of gas levels that can sometimes occur with spot monitoring. Thus, changes in gas levels are recorded together with atmospheric and temperature changes.

Continuous monitoring device “Gas Clam” being deployed in a borehole

The results of the ground gas investigation are assessed using CIRIA C665, BS8576 and NHBC guidance and the appropriate mitigation measures recommended by AFHA.

We can also provide detail of the gas protection measures to be installed in a building together with testing and verification of the suitability of the measures. This is carried out in accordance with CIRIA C735, BS8485 and the Local Authority Guide to Ground Gas.