Site History
The sites former use as a Gas Works resulted in gross hydrocarbon contamination in soils and LNAPL and dissolved phase in the groundwater. Remediation was required to protect the chalk aquifer beneath the site and adjacent River Anton, an ecologically sensitive chalk bed river. The remediation works were carried out in two stages to fit in with the construction programme to redevelop the site as a supermarket and cinema. The site was located within Andover city centre and as such was limited in space with the gas holder bases and associated contamination extending up to and beyond the site boundaries.
Remediation WorksThe remediation works comprised the following: - Extensive trial pitting of the site to determine the extent of contamination.
- The removal of the gas holder bases and remediation of the associated tars, liquors and contaminated soils.
- Where the excavation of the contaminated soils was prohibited by boundary walls and off site buildings, boundary protection measures were installed to prevent cross boundary migration of contamination,
- The construction of a temporary bund to protect the chalk stream from run off during the excavation works.
- Significant free product was recovered from the excavation areas through the use of skimmer pumps, prior to the contaminated water being pumped through a comprehensive water treatment system.
- The water treatment system comprised large storage tanks (due to sewer restrictions), the water was then pumped through a silt trap and oil water separator. Due to the gross nature of the contamination an air stripper was utilised to strip the volatile organic contaminants from the dissolved phase, the water and air expelled from the stripper was passed through vapour phase and water phase Granular Activated Carbon to remove the remaining contaminants. The treated water was discharged to foul sewer in accordance with a trade effluent discharge.
- Groundwater and surface water monitoring was carried out throughout the remediation works and as part of the validation post remediation.
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