Leading gas measurements in site investigations with the GFM 436
Land that has been previously occupied by or situated adjacent to industrial activities may be affected by contamination from chemicals and ground gas generation. Sometimes contaminants may even be present naturally.
A key role of development management with regard to land contamination is to ensure that land is made suitable for its intended use. Usually this requires commissioning of environmental consultant or specialist. These persons must be familiar with all elements of risk assessment and site investigations. They should also be familiar with current UK policy and the legislative framework surrounding land affected by contamination.
A risk assessment is a process that identifies all the potential contamination hazards and considers the likelihood of harm being caused to human health and the wider environment.
The assessment should be site specific, and a good environmental risk assessment should contribute to effective site development by providing a comprehensive and robust aid to decision-making. Usually, this requires commissioning of environmental consultants or specialists.
How Gas Data GFM 436 can help?
The Gas Data GFM436 is an ATEX, UKEx and IECEx accredited hand-held gas analyser designed specifically for monitoring and analysing soil gas parameters during site investigations of greenfield, brownfield and land affected by landfill operations or other industrial contamination.
Operation is extremely simple, yet the readings obtained are comprehensive and accurate. The instrument uses Gas Data’s proprietary NDIR (non-dispersive infra-red) sensors and a combination of industry standard sensors and transducers for the other parameters. It is lightweight, small, and robustly constructed with a weather resistant case making it perfect for use in the most challenging of field conditions. It first measures the proportion of methane (by volume and LEL), carbon dioxide, oxygen, hydrogen sulphide and carbon monoxide in the soil gas. Should the methane readings be above normal levels caused by biodegradation then it is likely that the soil gas contains other hydrocarbon vapours (from spilt fuels, oils, or other contaminants).
A standard analyser would be unable to evaluate these but the GFM436 has a second infra-red scale referenced to hexane vapour. This allows the GFM436 to respond in a more accurate and predictable way because hexane has an infra-red absorption characteristic that closely matches those of typical fuel and oil vapours. By reading from this second scale erroneous or even over-range methane results, that could be meaningless, are avoided and replaced with readings referenced to hexane instead. Leading the field for gas measurements in site investigations, landfill gas control and environmental regulation compliance monitoring
The GFM436 is designed to enhance the usefulness and accuracy of commonly used PID’s (photo-ionisation detectors). PID’s are the industry standard device for quantifying low level VOC’s (volatile organic compounds) in soil gas but they have an inherent weakness in that their calibration is greatly affected by the presence of methane. The GFM436 automatically reads out the necessary multiplication factor (PID Compensation Factor) that must be applied by the user to the readings taken from the PID before they are recorded. After this factor is applied, the PID reading is now accurately compensated for the error caused by the presence of methane. Without this compensation the PID readings may be grossly inaccurate and misleading.
A second group of measurements define the physical parameters of the gas such as its pressure, flow rate and temperature which can also be easily measured in the field using the GFM436. An internal high-precision thermal mass flow transducer directly measures the flow of gas either out of or into the monitoring borehole (bi-directional flow).
The flow is displayed as two readings. One is the instantaneous value, the other is the peak value. A secondary calibration of this transducer is used to dynamically indicate the precise difference between the gas pressure inside the borehole and the air pressure outside (Atmospheric pressure) down to only a few Pascals. This is done whilst the gas is still flowing. Two static silicone bridge pressure transducers are also built into the GFM436, one to determine atmospheric pressure and the other is used to measure the static pressure in the borehole in situations where the site utilises a network of vacuum pipes connected to the boreholes in order to safely extract the gases (gas extraction system). Using the static pressure channel to measure the vacuum at different points in the gas extraction system the GFM436 can also be used to assist in the setting of control valves and gas pumps (gas balancing). In keeping with a policy of continuous development, Gas Data Ltd. reserve the right to change any part of this specification without notice.
Finally, by using the multi-way connector on the top of the instrument, an optional temperature sensor can be plugged in for the general-purpose gas temperature measurements, or alternatively a vane anemometer to measure the velocity in a gas extraction system pipeline.
Using Gas Data’s SiteMan program data, it can easily be transferred to and from a PC via the supplied USB connection cable. Data storage can trigger manually, or the internal real time clock can be programmed to take and store readings automatically while the instrument is left unattended.