Following the identification of pollutant linkages on a site, a remediation strategy needs to be agreed with the appropriate Regulatory Bodies (e.g. Local Authority, Environment Agency, National House-Building Council) prior to its implication. This is achieved by the development of a Remediation Method Statement (RMS) in conjunction with the client and the site restraints. On relatively simple sites this is undertaken by Applied Geology in conjunction with the groundworks contractor. On more complex sites, a RMS is commonly developed in conjunction with a specialist remediation contractor to ensure that the best solution is adopted for the problems identified.
Case Study 1
Applied Geology was employed to assist with remediation on a site that comprised an old garage with a number of underground and above ground fuel tanks. The geology of the site comprised River Terrace Deposits (minor aquifer) overlying the London Clay (non aquifer). A surface water receptor was identified with 50m of the site boundary and this was considered the most sensitive receptor. Several phases of ground investigation were undertaken on the site and the materials surrounding the underground tanks were found to be severely impacted with hydrocarbons. Due to time constraints it was decided by the client to excavate and remove impacted soils form site. Applied Geology therefore produced a Remediation Method Statement to allow safe development of the site. This method statement included a P20 Risk Assessment for groundwater. The RMS was agreed with the Local Authority and the Environment Agency.
Following removal of the tanks a contractor excavated any soils which were visually and olfactoily impacted with hydrocarbons and Applied Geology was then contacted to visit the site and obtain soil samples for validation testing . A Photo Ionisation Detector (PID) was also used on site to screen samples.
Hydrocarbon impaction was noted on the wall of an excavation. Further excavation into the bank could not be undertaken without undermining the road and a low permeability plastic membrane was therefore placed along the site boundaries affected.
Along the west of the site was a high pressure water main at around 2.5m bgl, the backfill around which appeared to be a conduit for hydrocarbons from an above ground fuel tank to leach along. For safety reasons it was not possible to excavate closer than 1m to remove the soils. It was agreed with the Environment Agency that the volume of impact soil was not significant and that as long as soils up to 1m around and above the tank were remediated the hydrocarbons could remain in the ground. This was also agreed with the Environment Agency.
Following the main part of the remediation (removal of impacted soils), a validation report was produced which was agreed with the Local Authority and the Environment Agency.
Case Study 2
Applied Geology was commissioned to carry out a Phase I Desk Study by a client, who was carrying out a design and build contract to redevelop a former hospital site as sheltered housing.
Demolition of the former hospital was completed which essentially left the site vacant for a Phase II Investigation to proceed. Initial liaison was carried out with both the Environment Agency and Local Authority regarding the scope of work, with some adjustment being requested by the Environment Agency, comprising additional borehole monitoring points within the northern portion of the site. This confirms how important such early contact with the Regulatory Bodies can be on projects.
The final Phase II report included a detailed groundwater risk assessment the results of which were agreed in advance with the Environment Agency.
Subsequently a Remediation Method Statement was formulated, again with the agreement of the Environment Agency and Local Authority. Essentially the main portion of the site was underlain by natural river gravels and apart from one small area of Made Ground which required a simple cover system no other remediation was deemed necessary, there being no pollutant linkages. A smaller former car park area of the hospital separated by a road was however proved to comprise a former infill Gravel Pit and hence a piled foundation solution had to be agreed, together with the groundwater risk assessment and a more robust cover system. Applied Geology has completed validation of the cover systems.
Applied Geology attended the grand opening of the scheme and as indicated in his presentation the Chairman of the Housing Association noted that the project was ambitious, costing around £18m in its concept, but has been successful in providing a sustainable housing solution to their clients.