A 70-acre site off the M20 earmarked for a huge lorry park to cope with Operation Stack has poor foundations and could be vulnerable to flooding, a previously confidential county council report has revealed.

It also reveals that KCC may have to relocate protected wildlife if it chooses to press ahead with its plan.

The report was provided to the Kent Messenger Group under the Freedom of Information Act, following a successful appeal made after KCC initially refused to release it.

Audio: KM Group political editor Paul Francis talks to kmfm's Adam Williams about the report >>>

However, large sections of the report relating to other locations considered by the county council, as well as separate financial details, have been blacked out.

The authority has maintained its decision to veto disclosure of these details, citing commercial interests and the fact that much of the detail will eventually be published when a formal planning application is made.

However, the 22-page report does shed a little more light on aspects of the proposed site, which is off the M20 at Aldington, near Ashford, and which could hold up to 3,000 lorries.

It describes the site as potentially exposed to the risk of flooding, stating: "The geology of the area...suggests poor foundations and there are large areas of water adjacent to the site, with a high-potential for Great-crested newts. There are no significant planning constraints except for a potential risk of flood risk designation."

Although the issues would not necessarily prevent the lorry park - which could cost up to £40million - being built, any potential for flooding is likely to be seen by opponents of the scheme as a reason why it should be dropped. It might also lead to concerns from the Environment Agency, which has been given greater powers to oppose development in high risk area.

The re-location of protected wildlife could prove to be an additional complication, potentially requiring KCC to spend thousands of pounds moving species to new sites. Great-crested newts are a legally-protected species.

Dr Hilary Newport, director of the Kent Campaign for The Protection of Rural England: "The challenge of parking hundreds of 34-tonne lorries on a site such as this and the possibility of what might happen should not be under-estimated.

"The site is very close to the area which are currently maintained as flood defences for Ashford. One of our major worries has always been the knock-on impact a lorry park might have."

Cllr Richard Honey (Con), who represents the area, said: "The work done by KCC investigating sites is extremely superficial and confirms our worst fears about the suitability of this site in terms of its ecology and geography."

However, KCC cabinet member for highways Cllr Keith Ferrin (Con) said: "We are fully aware that the site has potential flood risk and the possibility of great crested newts. We have known about this for a long time. It’s not a sudden discovery. It has already been taken into account in all our costings."

The report, which was written in May 2007 by council officials, also sets out how access to the site is "more complex" than alternatives.

One controversial option floated is for Church Road to be used to give two-way access to the park, with what is described as a "buffer zone" on the north side of the M20 to store lorries and phase their departure from the park when Operation Stack is lifted.

• Read more about the report and reaction to it in next week’s Kentish Express.