Thanks for the responses...

Firstly, from a technical perspective, the identified risks are from access to the soils - gardens/vegetable consumption etc - hence the proposal to cover with concrete - as well as from the ground-gases.  I appreciate the interesting comment about possible changes to the under-concrete gas regime - anaerobic and off-site flow issues- which we will have to look into.  Any thoughts on how the proponent can risk model and manage those future changes? 

Secondly the institutional management of the site... on discussions with our caravan sites man the site will have to be managed under a caravan site license.  Apparently any caravan site (single or group of caravans) must be licensed whether for residential or holiday let purposes.  Although the license cannot dictate the design/construction of the caravan itself, it does provide a regulatory mechanism for enforcing conditions over the site, including requiring periodic inspections (by LA and/or by a “competent person”), making good any damage to cover system, clearing under-van spaces or vents and for the provision of an annual inspection and maintenance report at the license holders cost, or indeed any other such H&S measures as appropriate.  License fees apply to holiday lets and Council Tax to residential lets which helps off-set the cost of regulation.  Failure to comply with conditions triggers enforcement by the LA-EHO.  There is a little uncertainty as to who the license-holder is but consensus is that it is the person with control over the “site” under the particular commercial lease or license.  This may be a site owner or a individual caravan lot leasee.  On the face of it, it is a pretty powerful piece of preventative regulation. 

The suggestion of Restrictive Covenants was less well received by my colleagues mainly because they are essentially advisory in nature and as we all known often people dont take kindly to being told what to do - something about being the nanny state!

So armed with my site license conditions it got me thinking... why aren’t all risk management schemes (i.e. cover systems, gas protection membranes and venting systems, MNA) subject to a similar licensing system to monitor and manage their effectiveness in perpetuity?    Why does the cover system or gas protection strategy at a caravan site require long term enforceable regulatory oversight, but an identical system at a bricks and mortar development does not. Surely cover systems degrade over time, occupiers grow vegetables and block up gas vents at both caravan parks AND housing estates.   Why do caravan occupiers deserve more protection than house owners?

I have recently been looking at a 1970s housing estate on a former industrial site.  The risk based solution at the time was to cover the gardens with 300mm of topsoil to minimise exposure to contaminated soils. Unfortunately I (nor the current occupiers) have any idea whether that 300mm cover system has been maintained, or whether occupiers have planted fruit trees through the cover, or whether garden ponds, children’s sand pits or other domestic excavations have exposed contaminated subsoils?  In contrast we have a brand new commercial development on an area of made ground found to be producing ground-gases (CS2). Gas protection membranes and underfloor venting were designed, installed and certified by the building inspector, but how can I be sure that these will be effective (or still in place) in 5years from now.  

Do I have to with for an “incident”?

It seems that we go to extra-ordinary lengths to characterise and mitigate risk for today, but give scant regard to how to manage that risk for tomorrow. 

As ever, your thoughts are welcomed?
David E Jackson
Sometime pessimist.