Hi Rowan,
Composite sampling of “surface-soils” on your allotment plots could well be appropriate and is a sensible way of determining the average concentration if that is what is considered most relevant. However, it must be done with care and the objectives carefully worked through. BS ISO 18400-104 when eventually published (hopefully by the end of the year) will provide guidance on the application of composite sampling to determine average concentrations of surface soils and stockpiled soils.
The guidance is too extensive to summarise here but key points are:
* the area to be investigated should be divided into at least two zones (in your case each plot should be split),
* a number of composite samples (say 3) should be taken from each zone using an appropriate sampling pattern (a ”w” is probably best),
* the composite samples must only be formed from increments of roughly equal size drawn only from material that is similar in character and from the same depth,
* each composite sample should be formed from at least 25 increments (this is based on UK research in 1973 by MAFF),
* each composite sample must be thoroughly homogenised before being sub-sampled in the laboratory.
Composite sampling cannot usually be used to detect contamination although as indicated in USEPA guidance a number of spot samples of equal mass can be combined in the laboratory to save money when looking for more exotic compounds especially when the normal background is essentially zero – if five samples are combined then the normal assessment criteria must be divided by at least 5 which might take it below the LOD. If contamination is detected in a particular zone this can then be investigated in more detail. If there is a variable background concentration, then the sensitivity is further reduced.
If you decide to use spot samples rather than composite samples then there are advantages in taking “cluster samples” – numerous increments from an area of about 1 m2 at each sampling location – obviously not possible at depth.
I am awaiting the FDIS (final draft international standard) version of BS ISO 18400-104 from ISO but could probably let you have a copy of a near-final version of for “personal use” if you decide the pursue the idea of composite sampling. I cannot at present circulate this more widely for copyright reasons.
Regards,
Mike
+++++++++++++++++++++
Mike Smith
M A Smith Environmental Consultancy
Farthing Hill
Browns Springs
Potten End
Berkhamsted
Hertfordshire
HP4 2SQ
Tel. 01442-872968
Mobile 07961-312790
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From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of Willcox, Ruth
Sent: 27 June 2018 09:14
To: [log in to unmask]
Subject: OFFICIAL: RE: Composite sampling
Some interesting points of view.
Good to see uncertainty being appropriately discussed.
I personally agree that composite sampling is not suitable for contaminated land main ground investigation. It may be useful for due diligence on relatively low risk sites however. What do others think?
We have accepted composite sampling for stockpiles from sources that have been subject to full ground investigation. Most Local authorities I suspect would in these circumstances expect, full traceability and for results to be accompanied by uncertainty analysis and discussion as part of appropriate use/re-use risk assessment.
Kind regards
Ruth
Ruth Willcox
Planning Officer
Strategic Planning and Infrastructure
T +441752304154
E <mailto:[log in to unmask]> [log in to unmask]
www.plymouth.gov.uk <http://www.plymouth.gov.uk/>
From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of Peter Fleming
Sent: 26 June 2018 14:02
To: [log in to unmask] <mailto:[log in to unmask]>
Subject: Re: Composite sampling
Rowan
As Robert suggests, taking a number of samples over an area and at various depths will give you an idea of the spread of concentrations as well as the average. Hotspots may not be obvious so even mixing a number of samples may not be representative. What is your definition of “surface”? some roots may penetrate a great depth whilst others may not. I seem to remember that Dave Jackson did some work on this when at Wakefield so I have copied him in.
Regards
Peter Fleming
07958 205920
Skype: petermfleming
From: Contaminated Land Management Discussion List <[log in to unmask] <mailto:[log in to unmask]> > On Behalf Of Robert Tyler
Sent: Tuesday, 26 June 2018 11:55
To: [log in to unmask] <mailto:[log in to unmask]>
Subject: Re: Composite sampling
It gives a good average but a poor range. You would probably be best taking a phased approach to identify chemicals of concern through low density investigation and then investing resources in sampling and analysing for the key chemicals of concern, which often works out significant cheaper and provides better coverage. Depending on determinants could look in to XRF or other similar analyses which can work out cheaper for larger sample batches. Of course what is appropriate will depend on exact details.
Hope that helps.
Robert
Robert Tyler
Principal Pollution Control Officer - Land, Air & Water
London Borough of Hackney
Public Realm
Neighbourhoods & Housing Directorate
PO Box 70210
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On Tue, 26 Jun 2018 at 11:42, Rowan Devlin <[log in to unmask] <mailto:[log in to unmask]> > wrote:
Guidance says that composite sampling (taking a sample from bulk material collected from a number of sample locations) isn't usually suitable for contaminated land investigations. However, do you think it would be appropriate for sampling surface soils on individual allotment plots, which are all located on a former tip? (i.e. no obvious hotspots for targeted sampling). It seems like a sensible way to assess the mean quality of soil within each plot.
Any thoughts?
Regards
Rowan Devlin
Environmental Control Officer
Tel: (01482) 396206
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