The Answer to Erroneous Readings from Landfill Gas and PID Meters

Gas Data of Coventry (UK) have launched a new landfill gas meter, the GFM436, for use in geoenvironmental appraisals and site investigations. The meter can attempt to answer the question of unexpectedly high methane results being recorded when the Phase I desk study, and possibly the Phase 2 investigation, which suggest that methane should not be present. It does this by allowing the operator to switch to a second infra-red scale referenced to hexane. Hexane closely matches the infra-red absorption characteristics of fuel and oil and should significant readings be obtained on the hexane scale then the erroneous methane record can begin to be explained by the presence of fuel. This can then be verified by using a PID meter and/or by obtaining a bag sample for lab analysis.

Conversely the GFM436 can also assist the use of conventional PID meters. PID meters have an inherent weakness in that their calibration is greatly affected by the presence of methane. The GFM436 can be used to arrive at a PID Compensation Factor which can then be applied to the PID readings to enable them to be accurately corrected (generally upwards) for the error caused by the presence of methane. This ability is of great benefit where PID meters are used in the control or remediation of fuel spills and the cleanup of petrol station forecourt sites.