The site posed a number of challenges including disused underground storage tanks and hotspots of soil contaminated with TPH, PAH and heavy metals which exceed site specific re-use limits.
The site was adjacent to a main river and a potential risk to human health and groundwater had been identified by the completion of a risk assessment. In addition to the soil contamination, GEMCO removed all buried obstructions to enable piling and the resulting materials were re-processed on site for re-use in the permanent works.
450 cubic metres of contaminated soils were treated by ex-situ bioremediation to remove the organic contamination. The resulting materials were subsequently graded to provide suitable engineering fill for use in the backfilling operations.
During treatment, soil samples from the treated materials were collected and sent to an independent lab for testing. The testing requirements were tailored to the identified contaminants of concern, namely TPH and Speciated PAH. The results of the testing confirmed the success of the treatment methodology and the soils were deemed suitable for use within the development.
GEMCO completed 12 months of post remedial gas groundwater monitoring to confirm the success of the remediation works. The monitoring confirmed there was no requirement for gas protection measures and this presented significant costs savings for the client. Foundations were constructed on Vibro stone columns a technique that was inappropriate prior to remediation, again providing cost saving over use of CFA techniques.
The site obtained regulatory sign-off and discharge of relevant land quality conditions with insurers such as the NHBC. GEMCO successfully validated all private gardens and areas of public open space.
GEMCO saved the developer both time and money and ensured all planning and land quality conditions were satisfied in time for completion and occupation.