Soil and Water Solutions were commissioned by GO Homes Ltd to implement the remediation of the workshops at the listed former coachworks and showrooms of Henry McMullen, Herford.
A previously completed DQRA process established that the identified contamination on site was localised to the proximity of the former waste oil underground storage tank (UST) and so posed no significant risk to the greater water environment including the highly sensitive Principle Aquifer residing within the chalk beneath the site.
A residual potential risk to future site users may have existed if the soil and groundwater was left untreated via ground gas intrusion from volatilisation of hydrocarbons directly surrounding the former waste oil tank. Localised contamination of the near surface water was present within the confines of the site in the form of free phase hydrocarbons floating within/on top of the shallow groundwater as well as some dissolved phase.
To remedy this potential risk, Soil and Water Solutions implemented a remediation strategy which included:
- Removal of the 8(No.) decommissioned (foam filled) UST associated with the former coachworks.
- Excavation of the soil surrounding the UST within a sheet piled box and removal of the impacted soils to a suitably licenced waste disposal/off-site treatment facility.
- Remediation of a hotspot centred around the position of the former waste oil storage tank (previously removed) with the impacted soils being excavated progressively to allow on-site segregation of the soils to enable ex-situ remediation and reuse or declassification and off-site disposal.
- Validation samples were taken of the base and sides of the excavation to confirm that the soil remediation had achieved the site-specific target.
- Skimming of the Separate Phase Hydrocarbons (SPH) LNAPL hydrocarbons from the surface of the shallow groundwater within the excavation with subsequent off-site disposal to suitably licenced facility.
- Pump-and-treat of the dissolved phase hydrocarbons from the excavation at a maximum rate of 24m3 per day to avoid drawing down the groundwater within the surrounding gravels. The water was pumped from the excavation and processed through an oil water separator and an activated carbon filter prior to discharge to foul sewer under an appropriate discharge consent.
- The treatment system was run continually until the sampling of the water recharging into the excavation validated that it no longer contained contaminants above the remedial targets before the plant was decommissioned.