I think words are as important as pictures. A model isn't just a diagram, a
diagram is useless without explanation. A model is a concept, a linking of
processes that must be coordinated to reflect particular philosophies that
are enveloped by specified parameters and variables. This cannot be shown by
diagram alone. It is imperative that the transparency of such parameters is
exhibited in order to determine potential flaws in any model. Every model
has flaws, that's why it is only a model. Dismissing 3 pages of words is
surely not good practice. Would you look at a geological sheet without
reading the memoir or explanation? If so you are ignoring very important
information and this is surely not good scientific practice.
-----Original Message-----
From: Contaminated Land Management Discussion List
[mailto:[log in to unmask]] On Behalf Of steve
wilson
Sent: 21 May 2009 19:06
To: [log in to unmask]
Subject: Re: Landfill Gas
It is quite common to find high levels of methane and carbon dioxide in
inert material. We once found elevated levels in an engineered earthworks.
It does not necessarily mean there are large volumes of other non inert
material in there.
The opposite is also true as other people have pointed out. However the
risk of significant gas generation is much lower if the pit was filled
before the late 1960's, because of the type of waste materials and also the
way they operated landfills before this time. As is usual with gas there
will always be exceptions to this. The highest risk is if it was filled in
the 1970's and 1980's when waste had an increasing degradable content and
there was very little engineering or control of landfills.
The most important thing is to construct a conceptual model (and by this I
mean a scale drawing of a cross section through the site and the landfill -
not three pages of words and tables which are of use to no one). Quite
often inspection of this will show whether gas migration is a credible
hazard.
Also remember - just because there are high concentrations in a borehole, it
does not mean there is a risk of significant migration. Volumes of gas being
generated are the most important factor. Even for diffusive flow to be
maintained at any significant rate the source has to generate the gas at a
sufficient rate to maintain the migration.
As I said before however it is down to the consultant to justify whatever
they are proposing in a clear and rational way.
I would also second the comments made about dry waste becoming wet. This is
a real issue, I have seen several sites with dry waste and no gas - dry
sawdust seems to a problem waiting to happen.
Steve Wilson, Technical Director
EPG Limited
Tel 07971 277869
www.epg-ltd.co.uk
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-----Original Message-----
From: Contaminated Land Management Discussion List
[mailto:[log in to unmask]] On Behalf Of Robin
MacKenzie
Sent: 20 May 2009 11:51
To: [log in to unmask]
Subject: Re: Landfill Gas
Kevin,
In my experience, where cuts have been infilled there is usually gas. We
have investigated many inert fills and while there is very little methane, 0
to <1% where there is very little or no visible organic material CO2 can be
1 to 15%. This is usually when the material is unconsolidated and there is
varying degrees of void space in the fill. Flows vary from hole to hole as
does the concentrations accross sites. Needless to say there are exeptions
when there is no visible organic material identified and thre are high
levels of methane 1 to as much as 10%. As Judith pointed out, what is shown
on a map is not always acurate and the extent of the area can be 2 to 4
times the area of the former surveyed area, meaning it was mapped, extended
and then filled. The one question I would as is would gas reach the receptor
in concentrations that is likely to cause risk? These are observations I
have made but there are a few experts who can hopefuly shed some light on
the great gas conundrum within the group.
Regards,
Robin Mackenzie
Contaminated Land Co-ordinator
Perth and Kinross Council
Tel 01738 476443
Mob: 07810057566
[log in to unmask]
----- Original Message -----
From: Contaminated Land Management Discussion List
<[log in to unmask]>
To: [log in to unmask]
<[log in to unmask]>
Sent: Wed May 20 10:52:36 2009
Subject: Re: Landfill Gas
Dear Kevin
I can't comment on the landfill gas, but I can tell you that the extent of
the chalk pit shown on the map may not be correct.
A while ago, I investigated an infilled chalk pit expected to be a certain
size and likely to be investigateable with a JCB (so maximum 3-4m deep).
Trenching to locate the edges of the pit, revealed an old topsoil and a much
larger pit which had been infilled at intervals with a variety of rubbish.
I can't remember how far the actual edges of the pit were compared to what
was shown on the map but it could have been 50m or more.
In the end we had to get a Himac in - the pit ended up being 7m+ deep and we
unearthed a car.
So whatever they "officially" filled the pit with, there could have been
some unofficial filling prior to that.
Judith
________________________________
From: Contaminated Land Management Discussion List
[mailto:[log in to unmask]] On Behalf Of L.Warhurst
Sent: 20 May 2009 10:21
To: [log in to unmask]
Subject: Re: Landfill Gas
Hi Kevin,
We have an infilled railway cutting (in limestone, probably fissured)
where a Waste Disposal Licence was granted to the site operators in 1977
giving permission to deposit building rubble and excavation material not
containing any combustible or putrescible material or any other waste
likely to cause a nuisance or pollution.
However, intrusive investigations carried out during the past 5 years
have revealed areas containing ash, clinker, plastic, wood, paper,
clothing and other non-inert waste. Gas monitoring has recorded
localised pockets of methane over 50% and carbon dioxide up to 20%.
Regards,
Leigh Warhurst
Environmental Protection Technician - Land
Ashfield District Council
Urban Road
Kirkby in Ashfield
NG17 8DA
Direct line 01623 457477
-----Original Message-----
From: Contaminated Land Management Discussion List
[mailto:[log in to unmask]] On Behalf Of Kevin
Beer
Sent: 18 May 2009 14:30
To: [log in to unmask]
Subject: Landfill Gas
Hi all,
I have a site that has come through the planning process where the
applicant wants to build a new property approx 100m from an infilled
chalk pit. The applicant states the pit was infilled with inert clay
material, however we have no way of knowing this for sure.
In order to give us more weight in our argument I was just wondering if
anyone has any examples of where someone has said a pit or quarry has
been infilled with apparently inert material only for a site
investigation to show that it is giving off elevated gas concentrations?
I have a feeling there was a part IIA site from a couple of years ago
where there was a similar situation??
Many thanks
Kevin
Kevin Beer
Contaminated Land Officer
Community Protection
Basingstoke & Deane Borough Council
Civic Offices, London Road, Basingstoke, Hants, RG21 4AH
Tel: 01256 845520
Fax: 01256 845200
email: [log in to unmask]
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