Gas and groundwater level monitoring surveys are often undertaken as part of the Phase 2 contaminated land site investigation works where the Phase 1 desk study has identified a potential gas risk to a property.
Gas monitoring is undertaken using a calibrated geotechnical instruments GA2000 for oxygen, carbon dioxide, methane, carbon monoxide and hydrogen sulphide. Pressure differential and gas flow rate measurements are also made and the weather and ground conditions recorded.
Where interference to the gas monitoring results from organic vapours is suspected on contaminated sites, gas samples are often taken for analysis at an accredited testing laboratory. Laboratory analysis of gas samples can also be undertaken to attempt to determine the source of the gas (e.g. is the gas recorded derived from landfilling or shallow coal mining).
Upon completion of the monitoring period recommendations are typically made as to the level of gas protection measures which need to be incorporated into the proposed development to reduce the risk to end users from ground gases.
Gas monitoring is completed in accordance with CIRIA C665 'Assessing risks posed by hazardous ground gases to buildings'.