If your asking for 1m cap I assume there is significant contamination so
a capillary break layer should be incorporated as well
For a 1m cap I would go with 200-300mm capillary break layer (hardcore)
400-500mm of sub-soil and the rest as topsoil.
Your topsoil wants to be between 200-400mm for a decent growing medium
Remember that all imported material needs to be 'clean' i.e. below the
GAC's or similar lots of places require the imported material to be 1/2
the sgv for a clean cap in order to allow for mixing.
This is also why lots of councils require caps to be a minimum of 600mm
which is approximately 2 spade depths. The reason for this is people
growing vegetables may undertake 'double digging' in order to improve
the soil, dig in manure/fertiliser etc.
Thanks
Gareth Rees
Contaminated Land Officer,
Harborough District Council,
Tel: 01858 821174
Email: [log in to unmask]
Web:
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http://www.marketharboroughonline.co.uk/
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http://www.lutterworth-online.co.uk/
-----Original Message-----
From: Contaminated Land Management Discussion List
[mailto:[log in to unmask]] On Behalf Of Clare
Horton
Sent: 29 July 2008 09:58
To: [log in to unmask]
Subject: 'Clean Cover'
Dear all,
I appreciate this is a very old chestnut, but I'm looking for a
consensus:
What would you say the proportion of topsoil to subsoil should be for
1000mm clean cover and 500mm clean cover:
Scenarios are 1) garden, 2) landscaped areas. AND the CoC's would be HC'
S and metals and PAH's.
The reason I ask is that the choice of material for subsoil is obviously
much less stringent.
We also ask for validation testing os 1 sample per 100m3 for all clean
cover. Is this appropriate?
Thanks,
Clare
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