Louise

Get the developers/consults to provide a detailed conceptual model before you start.

In Gloucester there are rarely groundwater issues (Lias Clay) so any risk assessment and remediation invariably focuses of human health. The main potential pathways are vapour phase exposures (mainly indoor, but potentially outdoor) and drinking water services infiltration. Generally redevelopment proposals have not included gardens or soft landscaping, but if they did then there would be other possible linkages as well. Its also important to consider possible off-site impacts.

We also ask for a degree of risk assessment - but do balance off the level of detail required against remedial proposals. If the developer is intending to use suspended slabs, ventilated voidspace and a hydrocarbon resistant barrier membrane then generally I'd accept more contamination or 'uncertainty' remaining in the ground.

In general:
I'd always expect speciated hydrocarbon analysis - to include BTEX and usually MTBE (though this has never been a problem).

I always request justification for whatever clean-up levels are proposed.
Usually I'd expect soils removal and validation sampling to be carried out concurrently with any UST removal.
Usually I'd want removal of any gross free-phase product.
I'd typically expect vapour protection measures (as outlined above) to be incorporated into the foundations.
I'd require copies of the necessary documentation from the Petroleum Officer and Water Services Provider.

The Water Services Provider should be provided with copies of all relevant SI reports and will typically specify the use of barrier pipe on former service stations. Where conditions are really poor they may require over excavated trenches backfilled with clean material, or even lined. Clay 'stanks' can be used to prevent lateral migration of contaminated groundwater along service trenches. They often use an assessment system known as CLIPS - details of which are on the WRAS website.

http://www.wras.co.uk/publications/default.htm

Regards




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