Sara,
Because gas concentrations can vary depending on the time of year for a variety of reasons, a six-week period of monitoring cannot guarantee that that highest concentrations (or flows) have been encountered. Because there are so many variables, it would be difficult to say that any particular period during the year would be likely to encompass worse-case conditions. In flood risk and drainage assessments it is usual to consider 1 in 100 years events and even 1 in 1000 years. The chances of covering an equivalent gassing event in an arbitrary 6-week period seems vanishingly low.
We need a little more sophistication in how we assess risks from gassing sites.
Gas can migrate through the ground (e.g. a band of sand in predominately clay strata) in an episodic fashion rather than continuously.
Regards,
Mike Smith
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Mike Smith
M A Smith Environmental Consultancy
Farthing Hill
Browns Springs
Potten End
BERKHAMSTED
HP4 2SQ
01442-872968
07961-312790
[log in to unmask]
www.michael.a.smith.btinternet.co.uk
-----Original Message-----
From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of Sara Ball
Sent: 31 January 2012 13:34
To: [log in to unmask]
Subject: Continuous Monitoring using Gas Clam
I have a site where the houses have been put up without the required gas monitoring being undertaken before hand. I now need to determine whether the gas protection measures incorporated into the dwellings is sufficient. The developer is proposing to employ a firm who will use the GasClam system to undertake 6 weeks of continuous monitoring in Boreholes to be installed in the gardens. In addition they will be doing continous monitoring inside the dwellings near a service entry point or other potential weak spot in the construction.
Has anyone had this method submitted to them as the only form of gas monitoring to determine protection measures and what were their experiences? What would be considered an adequate period of monitoring for a residential site next to an extensive area of made ground? How would you compare this to the CIRIA/NHBC guidance tables?
I've already read the literature provided on the companies case studies and the CL:AIRE research bulletin RB13.
Thanks, in advance, for any advice.
Sara Ball
EHO - Nottingham City Council
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