If I could favourite this post I would!
Ruth
Ruth Willcox
Environmental Protection Officer
Office of the Director of Public Health
Plymouth City Council
Civic Centre
Plymouth
PL1 2AA
T +441752304154
E [log in to unmask]
www.plymouth.gov.uk
-----Original Message-----
From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of Chris Swainston
Sent: 16 May 2014 09:45
To: [log in to unmask]
Subject: Re: Soil vapour assessment of stockpiles
Exactly so Steve,
Andre, even with the best will in the world unless the PID is set up exactly right using the correct bulb, draws from a suitable headspace, has time to equalise and the correct calibration and span gas for the single most meaningful gaseous VOC or SVOC compound you are measuring (lets ignore possible cross contamination, interference and other effects such as moisture and temperature for sake of argument) you will be very lucky to see any correlation between it and any subsequent chemical analysis result of perhaps greater than about 20-30%.
As a screening tool, a PID has some very limited field use but it is not a magic box that gives a definitive answer, despite the fact that even some top consultants seem to think it does. At best it may give a relative one, for a given value of relative. Even then, not only are you removing the very thing you actually want to measure, but also changing the conditions by exposing it and taking a sample of it. In a limited, mixed and relatively open material such as a stockpile, frankly I would be amazed if you get any meaningful correlation at all between the gas/PID result and general soil concentrations of VOC and SVOC by GCFID following extraction for example.
Sad to say this general opinion that a PID gives a definitive and meaningful result is down to ignorance mainly and a general lack of understanding about what a VOC/SVOC actually is, how it reacts in the general or specific environment as a consequence of what it is and what a PID actually genuinely measures and especially how it does. I still chuckle when I remember the consultant asked me if 15ppm was significant compared to 10ppm on their PID results. Probably still gets paid a lot more than I do :)
Regards,
Chris Swainston
Principal Engineer
The Geotechnical Centre
203 Torrington Avenue | Tile Hill | Coventry | CV4 9AP
Tel: 02476 694664 Direct Dial: 02476 629013
Email: [log in to unmask]
This email has been scanned for viruses by Netshield MXSweep.
Geotechnics Limited, Registered in England No. 1757790 at The Geotechnical Centre, 203 Torrington Avenue, Tile Hill, Coventry CV4 9AP www.geotechnics.co.uk
********************************************************************************************************************************************
IMPORTANT: This e-mail (including any attachments to it) is strictly confidential and intended solely for the person or organisation to whom it is addressed. It may contain privileged, confidential or sensitive information. If you are not the intended recipient, you must not copy or distribute it to any other person or take any action in reliance. If you have received it in error, please notify your system manager and the sender as soon as possible and then delete it from your system.
|