Dear all

Having spent a lot of time thinking about what should go in a conceptual model whilst LQM and Keynetix were developing software to create conceptual models (www.KeyCSM.com) I have come to the conclusion that most conceptual models need:

(1) graphical representations to show the 3D relationships of the various features on site (2) a diagram/table identifying the pollutant linkages; and (3) text to explain what's going on

The graphical representation should definately include a cross section - as Steve says - wherever sub surface migration issues are involved, eg groundwater pollution or ground gas migration.  Working out the likely sub-surface configuration is hugely important both to identify the likely linkages and to pick appropriate risk assessment tools.  I am open as to whether the cross section needs to be to scale - A scale can only be beneficial, especially on more complex sites, but might not be necessary on all sites.  I think a CSM should also include a plan showing the locations of the various sources and surface receptors on the site and its vicinity.

There also needs to be some way of identifying what the linkages are - it's not always obvious from arrows on the cross section.  But a table or network diagram (in addition to the graphics not instead of) will make the pollutant linkages clear.

Text can amplify what is shown on the pictures.  In particular text is required to (1) justify why a particular pollutant linkage is present/absent     (2) identify the uncertainties in the CSM

KeyCSM was created to make creating and updating the pictures and diagrams for CSMs quicker and easier; it also ensures consistency between the different views. Anyone can download a trial version of KeyCSM from keycsm.com.

kind regards


Judith Nathanail


-----Original Message-----
From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of steve wilson
Sent: 22 May 2009 09:17
To: [log in to unmask]
Subject: Re: Landfill Gas

If words are necessary all well and good - annotate the diagram and if it is needed, then write an explanation.  A picture is worth a thousand words!
Unfortunately I see far too many "conceptual models" that are just tables and words that do not show any understanding of a site.  This is usually because there is no geological cross section onto which potential pathways have been marked and assessed.

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 Russell Corbyn
Sent: 22 May 2009 08:52
To: [log in to unmask]
Subject: Re: Landfill Gas

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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Information contained in this e-mail is intended for the use of the addressee only, and is confidential and may contain commercially sensitive material. Any dissemination, distribution, copying or other use of this communication, other than for which it is explicitly intended, without the permission of the sender is strictly prohibited. If you have received this e-mail in error, please advise the sender immediately and delete it from your system. Whilst all e-mails are screened for known viruses, the company cannot accept responsibility for any which have been transmitted.


-----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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