Julian
Natural soils produce carbon monoxide as a result of chemical oxidation of small quantities of organic matter. It is regularly detected in natural soils and unless there is an external source such as a smouldering landfill it does not pose a risk to development. The production is transient and is probably dependent on rainfall. The carbon monoxide sensor on the most commonly used gas meters is also cross sensitive with hydrogen. Soils are also a sink for atmospheric carbon monoxide. It could also be present in groundwater, which would affect the results in a sealed headspace (for information there is a Ground Gas Information Sheet on our website that discusses the influence of dissolved methane on gas monitoring results and the principles in it can be applied to any gas including carbon monoxide).
My question to you is , given the conditions you describe, why were you gas monitoring in the first place? If there is no source of gas in the ground you do not need to install gas monitoring wells.
In your test the carbon monoxide may be coming from the water. It is also a thermal decomposition product of polyethylene - although all the info I have seen has been at very high temperatures. HDPE will also include fillers. One of those may be calcium carbonate which may influence the CO results?
Steve
Steve Wilson, Technical Director
The Environmental Protection Group Ltd
Tel 07971 277869
www.epg-ltd.co.uk
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-----Original Message-----
From: Contaminated Land Management Discussion List <[log in to unmask]> On Behalf Of Julian Puzyna
Sent: 08 October 2018 00:48
To: [log in to unmask]
Subject: Carbon Monoxide and HDPE Well Pipes
Dear List
I have a Monday query for anyone with knowledge of plastics. We expect that the black HDPE well pipes we install in boreholes around the country to be largely inert, i.e. not giving of plasticiser vapours or other trapped hydrocarbons.
A round of gas monitoring from wells installed in June and July showed significant concentrations of Carbon Monoxide (no methane or Hydrogen Sulphide and low levels of Carbon Dioxide). At least two of the boreholes showing high CO concentrations had water levels above the well pipe response zone (slotted pipe).
Given the rural backdrop, lack of landfills and London Clay geology (with a sprinkle of superficial gravel) I was rather alarmed by the gas meter readings. By August however, return visits showed the Carbon Monoxide values had fallen to zero and have not been seen again.
To eliminate the potential for the well pipe material to be the source of the CO, I set up a metre-long section of pipe with an end cap on the base and a bung with a gas value in the top. After adding a little water, I left the pipe out in the August sun for an afternoon.
On attaching the gas meter and puncturing the base cap I saw the CO and CO2 levels rise (about 20ppm CO and 2.9% CO2). The PID meter plugged into the gas meter output read volatiles at about 25ppm. I appreciate that water vapour is the Achilles heel of PID meters however, I had recently cleaned the PID bulb its electrodes.
When I un-bunged the pipe and offered up my nose, all I could smell was a strong odour of ‘plastic’.
I am reluctant to dismiss the initial readings as being due to the well pipes however, gas membranes in all the new dwellings in this area will be a costly recommendation.
Am I blaming pipework when I should be looking for a smouldering pit of burning tyres somewhere?
Has anyone else experienced CO being given off by plastic well pipes?
Julian Puzyna
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