The County Council proposes a membrane under the road as its principle means of containing contamination. But any seepage through a standard tarmacadam road surface is fairly negligible anyway.   The vehicle oil that is regularly spilt on the roads floats on the tarmac surface.  WCC's membrane notion is an irrelevance, or a distraction.  It is unlikely to make any real difference.  Ordinary oil leaks onto the road surface would eventually go down the storm-water drains, which have low-volume surface-oil interception as standard.  Wiltshire County Council is basically allowing for every-day minor spillage, in a minimal manner.

One basic contradiction in Wiltshire CC's minimalist approach is that the manufacturers of the membrane, which would be laid under the road, warrant it for twenty years.  So what would happen after that?

There is also a serious risk of a bulk tanker coming off the proposed embankment within the Wellhead Valley and causing catastrophic contamination of the water-bearing ground on either side.

The Environmental Statement produced by Wiltshire County Council’s consultants suggests that the design would prevent this happening.   But their plans are inadequate.

Earth side walls to the embanked road through the Wellhead water source area are to be only 1m high.

However, the underneath of the bulk liquid tank of a fuel transporter is typically 1.5m above road level.

If there was a serious accident, a toxic liquid load could be projected off the road and spilt over the side.

Walls are anyway proposed for only a short length just in the immediate vicinity of the abstraction borehole.

According to the bypass design drawings, there is to be nothing at all to stop vehicles coming off the road in the area of the old Bere’s Mere Farm, which is just a field away uphill from the Wellhead water borehole.

This exposure is proved by section G, referenced from layout sheet 2, of the RPS JR4515 project drawings.

Bere's Mere Farm is shown on the previous map on this web-site; it is on the edge of the inner water zone.

The inner ground-water zone does not have an impervious edge.   Geology maps show porous chalk layers, both within and without.  A toxic spillage near the edge would penetrate to the inner water protection zone.

There may be a crass argument that the chance of a catastrophic event is too remote to have to consider.

If built, this eastern bypass would be in use for a long period, with plenty of opportunity for an accident.

The consequences of a bulk toxic liquid spillover would be completely disastrous for the water source.