Project: Former Ipswich Gasworks
Client: Major House Builder
Contract Value: £1,500,000

Knight Environmental Limited provided remediation services for the redevelopment of part of the former Ipswich Gasworks site, located adjacent to Ipswich Wet Dock. The proposed end-use was residential with a high rise apartment complex on the waterfront, amenity space and houses with private gardens.

Gas production at the site ceased in 1971. It was then used as a concrete batching depot and a timber treatment facility. Although site buildings had been demolished, hardstanding, foundations and the below ground infrastructure were still present.

Site investigations identified 'typical' gasworks residues, which had impacted both the soil and groundwater. A remediation strategy was developed in conjunction with the Client’s representative and target levels agreed with the Regulatory Authorities.

Clearance works commenced in the summer of 2002 with completion of the soil remediation in the autumn of 2003. The most suitable groundwater treatment was decided upon following on-site trials and tests. The treatment works commenced in the winter of 2003 and continued until the summer of 2004. The remediation techniques used included:-

Pre-screening of granular materials resulting in the reduction of volumes of materials requiring off-site disposal.

Biopiles developed with a nutrient enrichment process to accelerate microbial breakdown of the hydrocarbon contamination.

A groundwater pump and treat system installed during foundation development with pipelines laid concurrently with drainage and  service systems.

The soil treatment comprised the ex-situ bio-remediation of over 10,000 cubic metres of contaminated soil. Approximately 50% of excavated material was suitable for re-use at the site.

The excavations were backfilled with remediated soils with a ‘marker’ geotextile membrane laid beneath a capillary break comprising crushed concrete placed at finished remediation levels. A capping layer of topsoil overlying subsoil was placed in the in garden areas.

A fully operational treatment system comprising three oil/water separation vessels, two sediment settling vessels, two vapour stripping systems and two granular activated carbon vessels converted contaminated water to effluent acceptable as a licensed discharge to foul sewer. The primary oil/water separation vessel was significantly affected by floating tarry hydrocarbons resulting in a continuously operating oil skimmer being installed to prevent contaminant re-solution.

The volume of water pumped and treated was recorded with maximum rates of throughput reaching around 14 cubic metres per hour and was only limited by the water yield available from the pumping wells. Carbon efficacy was monitored with exchanges completed with minimal system interruption. Fortnightly groundwater monitoring occurred which showed an improvement in groundwater quality which gained the approval of the local Environment Agency.