Gas risk assessment, Southampton
Client: Barratt
Barratt is developing residential properties on a site close to a landfill. To comply with Local Authority planning conditions, we were commissioned to establish in detail the prevailing gas regime, provide a risk assessment and design gas protection measures.
Gas was confined within the underlying sand by a clay mantle, and migration was primarily through the sand. However, the local geology resulted in the gas being ‘funnelled’ under pressure to an area where extremely high gas flows were recorded when the clay mantle was pierced.
To provide protection against the possibility of the clay mantle being punctured during the development robust gas protection measures were provided. The houses were given confirmation of a minimum thickness of clay mantle between the base of the foundations and the underlying sand, gas proof membranes and passively vented underfloor voids.
