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Gareth I disagree that there is insufficient geological data in most of the country to allow a quick rough and ready assessment to be made. I also stated topography and likely gas generation rates are important, so it is not just a matter of looking at geology. I agree entirely with your sentiments regarding clay. As I said it is up to the consultants to justify their conclusions. I am sure that if there is a real risk of gas migration people will want to know that. Equally it is important not to cause blight to areas and not to spend money on a pointless exercise. Steve Wilson, Technical Director EPG Limited Tel 07971 277869 www.epg-ltd.co.uk -----( Disclaimer )----- > > 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 Gareth Rees Sent: 14 August 2007 14:26 To: [log in to unmask] Subject: Re: Extensions within 250m of landfill..... The statement on the risk of gas migration being negligible within 250m and this being capable of being shown by a desk study relies on geological, and hydrological data for the area being accurate which for may closed landfill sites could be argued is a big assumption. Most consultants I have dealt with look at 1:50k or 1:25k geological maps with drift data as this is the most widely available data, which for fluid migration is largely useless, generating a decent model for where gas is likely to travel requires much more detail and a good idea of the tectonic setting of the site (i.e. faults, jointing, intrusions etc. Overall geological data on the scale to perform a worthwhile desk study to predict the movement of gas and fluids is largely unavailable for most of the country. Also I find that as soon as someone sees they word clay on a lithostratic section they assume that means impermeable which for an unfractured section may be an appropriate assumption however it does not take into account fractures and joints caused by may mechanisms that modify the permeability of clays and in some cases make them better modes of transfers than some high porosity sandstones, merely saying the site is on clay does not mean there is a low risk of gas migration. In my opinion if you don't know if the landfill is producing gas then you have no insite into potential gas pressure underground and where it is likely to migrate. If however the site is known to be either not producing or producing an insignificant amount of gas then the assumption that there will be no build up of gas pressure therefore no mode of lateral migration can be made And if I was the owner of an unprotected property close to a landfill site I wouldn't mind spending a bit of money to know if there is a risk of ground gas building up in my house and causing asphyxiation / an explosion. Gareth Rees Contaminated Land Officer, Harborough District Council, Tel: 01858 821174 -----Original Message----- From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of steve wilson Sent: 14 August 2007 13:11 To: [log in to unmask] Subject: Re: Extensions within 250m of landfill..... Mark My view is that on many sites within 250m of a landfill monitoring and investigation may not be required because the risk of gas migration can shown to be negligible just from simple desk study information. Equally I have seen landfill gas migrate 400m and enter a building! Personally I would take a staged approach and first insist on a desk study. If the consultant cannot justify a negligible risk of gas migration, a site investigation and monitoring can be asked for. The three critical aspects are likely gas generation rates in the landfill, geology and topography. Is there a credible potential pollutant linkage? If not then monitoring is not required. This approach does assume that there is no on site source of gas, which is rare these days. Steve Wilson, Technical Director EPG Limited Tel 07971 277869 www.epg-ltd.co.uk -----( Disclaimer )----- > > 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. Steve Wilson, Technical Director EPG Limited Tel 07971 277869 www.epg-ltd.co.uk -----( Disclaimer )----- > > 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 Mark Newman Sent: 14 August 2007 10:50 To: [log in to unmask] Subject: Extensions within 250m of landfill..... Hello All, I asked a similar question a while back, but didn't get much of a response. I am getting a lot of planning applciations for extensions/conservatories within 250m of closed landfill sites. I have recently started using the condition: "Prior to commencement of development, a site investigation shall be carried out to include monitoring for methane gas. Monitoring should include sampling for methane, oxygen and carbon dioxide and should be carried out over a period of at least 2 months with a minimum of 8 readings taken - spike testing will not be accepted. The report, together with any recommendations for remedial works, must be submitted to and agreed in writing by the local planning authority. Such remedial works must be carried out prior to commencement of construction works. Prior to the discharge of this condition, details of any remedial measures used shall be submitted to the Local Planning Authority." Am i justified in asking for this, or would the condition below be suitable for these types of applcation: "A gas impermeable membrane should be incorporated within the structure. Any services entering/leaving the structure should be located above the gas impermeable membrane or adequate seals will have to be provided if the membrane has to be breached. Prior to the works commencing, details of the gas impermeable membrane should be submitted to and approved by the LPA." We have very little information regarding gas monitoring in the past, and what we do have is about 15 years old. So i cannot make a reliable judgement about whether or not the site is gassing. It is this uncertainty that makes me want to request gas monitoring each time.... Any input on this would be very gratefully appreciated. Many thanks, Mark (Dover DC) <HTML> ** The contents of this message do not necessarily represent the opinions, views, policy or procedures of Harborough District Council. http://www.harborough.gov.uk - Council Website http://www.harboroughonline.co.uk - Community Portal http://www.lutterworthonline.co.uk - Community Portal ** </HTML>