Neil,
My only experience of dealing with TPO'd trees on a contaminated site
resulted in them being cut down anyway (in consultation with the Tree
Officer) and replaced with young trees. Would your Council's tree person go
with that sort of solution? Can you not use some risk assessment to show
that the small area around the trees doesn't pose a risk when averaged out
across the whole site area?
I think digging out round the roots will be difficult to achieve
effectively, as a lot of the roots will be very shallow and spread along way
from the trunk (varies species to species). You may also find that the roots
predominately sit above the contaminated layer (trees are pretty good at
avoiding contaminated soils - on one site in my borough some pretty large
trees have restricted root growth to the top 200-300mm avoiding the alkali
waste below) making it even harder to get to dig out the ash. And yes,
piling soil up against the trunk can kill a tree. Hmmm, I think I should
stop now too much tree-based information.
Just a few thoughts,
Will
Will Watson
Contaminated Land Officer
Halton Borough Council
Rutland House
Halton Lea
Runcorn
WA7 2GW
Tel - 0151 906 4833
Fax - 0151 471 7612
Email - [log in to unmask]
www.halton.gov.uk
-----Original Message-----
From: Neil Brown [mailto:[log in to unmask]]
Sent: 19 December 2005 09:25
To: [log in to unmask]
Subject: Remediation around protected trees
I've just joined this forum, so many apologies if this isn't the type of
query which should be sent to the list.
We have a development site which is historically contaminated with a
discrete ash layer about 300mm below the surface. The area is to be cleared
by removing the topsoil and ash layer and replacing with 'clean' sub and
topsoil. However, there are trees on the site protected by a tree
preservation order. The idea is that the ash layer will be hand dug out
around the trees and then topsoil added above the contamination to provide
a barrier. The area will be used as public open space within a housing
development.
What I'm looking for is guidance on what depth of soil layer should be used
to cover the ash layer to make it suitable for use as public open space.
I've seen many values quoted ranging from 30cm-120cm. There's also the
issue of covering the trunk base of a tree in soil, which I'm sure can't be
good for them.
Does anyone have any experience of remediating around trees? Any help would
be greatly appreciated.
Neil Brown
West Lothian Council
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