GasClam: Continuous Ground-Gas Monitoring Becomes a Reality
12 October 2009, News release from Shawcity Ltd
Ground-gas monitoring is an important aspect of contaminated land site investigation and landfill management as the data is critical to the risk assessment process.
The objectives of gas monitoring programs are to determine the true subsurface gas regime and predict how this may change in the future. This is currently achieved by discrete periodic static measurements of gas concentrations from which the gas regime is inferred.
Flaws in the current approach to quantifying and predicting risk arising from ground-gas are identified explicitly in the literature and are implicit in the continuing evolution of guidance notes. The underlying cause of flaws is that whilst accurate quantification of risk should require accurate measurement of ground-gas concentration and of ground-gas fluxes, neither is measured directly and both are likely to be temporally variable.
Measurement is indirect because ground-gas concentration is inferred from periodic sampling of gas accumulated within a borehole and flux is then inferred from these borehole gas concentrations. The unit of flux is volume/time, therefore it can not be measured directly without time series data.
With the ability to collect time series data, an improved measurement of flux can be made and temporal variability can be quantified and accounted for. This will improve understanding of processes, thereby reducing the uncertainty which is inherent in the inferences required in using measurements that are indirect and lacking in temporal resolution.
Contaminated land and landfill industry regulators recognise the need for more representative data but cost has prevented the collection of continuous records of ground-gas measurements. However, the availability of reliable miniature infra-red sensors has recently been combined with innovative engineering to produce a new instrument; GasClam, which will allow the collection of continuous data to become widely used.
The GasClam allows secure, unmanned collection of continuous ground-gas data. It is manufactured from stainless steel, is intrinsically safe with ingress protection rated IP-68. It is designed to fit in a 50 mm borehole and measures methane, carbon dioxide, oxygen and hydrogen sulphide concentrations, as well as atmospheric pressure, borehole pressure and temperature. Water level can also be measured with an optional pressure transducer.
The device fits securely within a borehole, whilst also allowing for controlled venting of the borehole. Sampling frequency is variable from 2 minutes to once daily and this can be set and data downloaded through a notebook PC using an RS 232 communication cable. It can be powered for 3 months by two alkaline D-cells based on hourly sampling.
GasClam is exclusively available in the UK through Shawcity Ltd and for details contact Paul Walton:
Tel: 01367 2461675
For further information please email Shawcity Ltd