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Thanks to Steve for the good advice and BS 8485 overview. Ruth Ruth Willcox Planning Officer Strategic Planning and Infrastructure Ballard House West Hoe Road Plymouth Devon PL1 3BJ T +441752304154 E [log in to unmask]<mailto:[log in to unmask]> www.plymouth.gov.uk<http://www.plymouth.gov.uk/> From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of Steve Wilson Sent: 09 March 2017 16:29 To: [log in to unmask] Subject: Re: Recycled DPM installed as GAS Protection prior to discharged of conditions [Scanned] Lisa This question and the replies have highlighted a number of issues with ground gas assessment and risk assessment. 1. The first question is what is the CSM for the site and is the CS2 designation realistic and valid? Quite often gas monitoring data is incorrectly interpreted to over estimate the risk. 2. Any one giving truly impartial advice on gas membranes would not state that recycled material is no good for gas membranes (although someone whose business is selling gas membranes made from virgin materials might tell you that). A 2mm thick membrane made from recycled materials may be OK. BS8485 does not preclude the use of recycled materials – it warns about their use and states that if membranes are made from recycled materials they must meet all the requirements stated earlier in the standard. The same applies to any type of membrane (even if it has a BBA certificate) - designers should consider all the factors identified in BS8485 that affect membrane choice and then choose the appropriate membrane. This should be done by consultants not suppliers. If you are using the standard please read ALL OF IT. 3. In recent years the plastics industry has made massive advances in being able to supply higher quality recycled materials and they are used in load bearing drainage applications. It does all depend on QA/QC though and the manufacturing process makes things harder with membranes. 4. The GSV approach to gas assessment is an extremely conservative method that works most of the time. It can be over ridden by DQRA – this is explained in BS8485. It is quite likely that Clive W is correct about a membrane not being required, but the route to that conclusion is not to randomly assign scores to the floor slab and membrane. The construction of the slab needs to be looked at and site specific gas flow modelling and risk assessment completed. DQRA involves a lot more that adjusting the GSVs and scores. As Mike says there may be areas that are less well ventilated for example that need to be considered. 5. It is also questionable whether BS8485 is valid once construction of the floor slab has been completed and the risk is being reassessed. It is not intended to be applied to existing buildings! This is because it is so conservative. Steve Steve Wilson, Technical Director The Environmental Protection Group Ltd Tel 07971 277869 www.epg-ltd.co.uk<http://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, 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 know viruses, the Company cannot accept responsibility for any which may have been transmitted. From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of Lisa Maxwell Sent: 09 March 2017 12:38 To: [log in to unmask]<mailto:[log in to unmask]> Subject: Recycled DPM installed as GAS Protection prior to discharged of conditions [Scanned] Dear All I remember on a ground gas training course (I think it was run by PAG at the Vermont Hotel in Newcastle upon Tyne) but there was definitely a gentleman there speaking who did design membranes. He advised that recycled membranes were of no use as a gas protection membrane as they act like sieves (I may be paraphrasing slightly). Can anyone point me in the right direction please as I need literature to back theses comments up. The reason being and please keep in mind I am not discharging this condition. We have a commercial development (supermarket) that has been identified as characteristic site 2. The developer has started building without the conditions being discharged and has installed the Visqueen Eco membrane. The Data Sheet for Visqueen Ecomembrane, shows that this is a Damp Proof Membrane not a gas protection membrane. I have reviewed the Data Sheet that has been submitted to discharge the condition; it states: IMPORTANT Based on BBA, BRE and CIRIA guidelines, Visqueen Building Products recommend the use of special gas protection membranes (rather than traditional polythene DPMs) as suitable protection against ground gases. On brownfield sites or where there is ground contamination please seek further advice from Visqueen Building Products . I have advised that at this stage it would to their benefit to obtain the additional advice as indicated by Visqueen within the data sheet prior to any further discussions. Kindest Regards Lisa Mrs. Lisa Maxwell Contaminated Land Officer [NTP Logo Process RGB (Email).jpg] Quadrant, The Silverlink North, Cobalt Business Park, North Tyneside, NE27 0BY Tel: 0191 643 6642 Email: [log in to unmask]<mailto:[log in to unmask]> This email and any attachment are intended solely for the addressee. It may contain information or opinion which is strictly confidential or is legally privileged. If you are not the intended recipient you should not use, disclose, copy, print, distribute or otherwise rely upon the contents of this email. If you have received this email in error please notify the sender immediately by email and then permanently delete this email. This email has been scanned for viruses and inappropriate content by Mimecast Unified Email Management Services. North Tyneside Council does not guarantee this email to be free of any viruses. It is the responsibility of the recipient to ensure that this message and any attachments are virus free. 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