Good morning all,

 

Bumping this thread along with some recent experience and a couple of questions.

 

We’ve monitored (GFM portable) two sites in the last twelve months (centre of Leeds and Huddersfield respectively) where the overall gas risk situation has been low (shallow demo fill, Till, no landfills etc) but boreholes installed deep into the bedrock (installed for groundwater studies) have recorded high CO and H2S concentrations (up to 2000ppm CO and 160 H2S).  Both sites have no known coal mining locally and no evidence on the sites themselves although there is reason to suspect unrecorded workings locally to both (I understand it wasn’t uncommon for large industrial sites back in the day to dig their own pits) and so it appears to be leaning towards a mine gas source.  Worth noting that the sewers have not been surveyed and are present within 50m of installs. 

 

Bag samples seems to be the way to go again but I was wondering if anyone else had experienced this and also, what the residence times of these gases are in the ground – could this be Victorian mine gas trapped in fissures?  On the latter, I could imagine the CO remaining trapped (unreactive) and that the H2S could be produced by more recent phenomena.

 

Thanks in advance for your thoughts.

 

Russell

 

Russell Bowman  
Curtins
T. 0113 274 8509 | F. 0113 274 8496 | [log in to unmask]"> [log in to unmask]
 

 

Dear All,

 

Steve’s comment may be a little misleading.

 

The reaction that produces foaming in concrete and other cementitious materials is between metallic aluminium (added as powder) and the alkali in the cement. This reaction is used in the production of aerated concrete blocks such as Celcon & Thermalite. It can also be a problem when ash derived from burning refuse is used with cement because this ash will usually contain some aluminium.

 

The aluminium in pulverised fuel ash (PFA) and cement is bound in crystalline aluminates, aluminosilicates and ferroaluminosilicates or in aluminosilicate glass and is therefore not free to react with alkali to yield hydrogen.

 

PFA and cement clinker are formed under highly oxidising conditions so sulfide concentrations are either zero or very low (I don’t have any analyses to hand).

 

Rusting of iron and steel also produces hydrogen and is thus another possible (more likely?) source.

 

Incidentally, it is believed that it was the ignition of hydrogen due to reaction between aluminium and alkali that caused a major explosion in a waste disposal shaft at Dounreay a few decades ago.

 

 

Regards,

 

 

Mike Smith

 

 

+++++++++++++++++++++++++

Mike Smith

M A Smith Environmental Consultancy

Farthing Hill

Browns Springs

Potten End

BERKHAMSTED

HP4 2SQ

 

01442-872968

07961-312790

 

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www.masmithenvironmental.co.uk

 

 

 

 

 

 

 

 

 

Russell

 

Lime in the cement could react with aluminium in the PFA and generate hydrogen.  Hydrogen was also the gas generated in some foamed concrete grouts to act as the foaming agent.  I think from memory that hydrogen can cause interference on the CO channel of the monitor.  I would check with the manufacturer and also take samples for lab testing.

 

The H2S could be from sulphides in the sandstone reacting with acid water. 

 

You need to understand the chemistry of the ground and groundwater.  However in both cases the gas release is probably a short term effect due to installation of the monitoring well.

 

 

 

Dear all,

 

Quick query regarding non-coal mine gas.

 

I’m currently looking at a site upon which hydrogen sulphide and carbon monoxide have been recorded within a borehole whose response zone bridges a historic shallow (3m to 7m bgl) sandstone mine.  The mine is believed to have been grouted and the borehole logs appear to reflect this (possible PFA:Cement grout) however void spaces are present within which these gases are believed to have accumulated. 

 

First round of monitoring record; 90ppm CO and 30ppm H2S within 1 of 3 boreholes advanced through the relic seam.  No H2S and CO were recorded on a subsequent visit at comparable environmental conditions.

 

First gas generation scenario is a historic mine fire (mine shut in 1950s) leading to the generation of CO and then subsequent generation of H2S from limited sulphates (~1%) present in the mine grout (PFA).  The non-detection on the second visit suggests the well and possibly the void has been purged of these gasses. 

 

A side-line question from this is whether anyone has known mine grout (PFA type) to generate H2S?

 

The alternative gas generation scenario is sewerage leaking into surrounding soils from a sewer recorded in relatively close proximity to the ‘gassing’ borehole. The localized nature of the gasses leans towards this conclusion.

 

Any comments/thoughts the group has would be appreciated.

 

Russell