Ferry Lane, Rainham – Case Study

Reuse and Treatment

Soil and groundwater contamination was identified to be affecting localised areas across the Site during previous site investigations. Contaminants included:

Hydrocarbons, ammonia, cyanide and Light NonAqueous Phase Liquid (LNAPL, .i.e. oil/hydrocarbons floating on water).

The known contaminants can be associated with the offsite former chemical works and landfill sites to the northwest, and in the wider area, respectively. It is believed that the contaminant source originates off-site from these through the migration of the groundwater.

The localised exceedances formed the basis for 12no. hotspot excavations (undertaken on a 10mx10m grid) to remove / treat the contamination to the Site’s Remediation Strategy target criteria for reuse.

To reduce the environmental impact, JFHR processed, screened, and bioremediated the Made Ground under an Environment Agency issued Mobile Plant Permit (SR2008 No.27). This permitted JFHR to condition the soil for reuse in compliance with the Remediation Strategy.

This method prevented 1236m³ of hazardous material from being removed from site and suitable doner material having to be re-imported.

~2,500m³ of bulk concrete arising from the breakout of surface slab and buried infrastructure was also broken down and processed to a Type 1 recycled aggregate.

This was to supply the temporary works platforms for the development‘s construction phase. The reduction in transport and production of a recycled aggregate saved ~ 1,300 tonnes of CO₂ emissions.

Regulator Liaison

Prior to works fully commencing, the Environment Agency (EA) queried the Remediation and Verification Strategy, specifically the re-use criteria for Total Petroleum Hydrocarbons (TPH).

Following meetings and correspondence, the Client sought the advice of JFHR to assist with the consultation with the EA. JFHR provided a detailed proposal on the application of biostimulant and bacteria to excavated material from hotspots, and to the bases and excavation faces of the hotspot excavations that exceeded the target criteria limit for reuse. This was to expedite the breakdown of hydrocarbons over time and provide a significant betterment approach to continual soil condition improvement post completion +of the works.

This proposal was accepted by the EA, allowing the works to continue.

Low Permeability Barrier

Following the remediation undertaken by JFHR, previous site investigations identified that the source of the contamination will have originated off-site in relation to the historic chemical works to the northwest of the site boundary.

The client was concerned about the potential for the recently remediated ground to be later contaminated through the natural migration of groundwater ingress from the off-site source, which would later affect the value and resale price of the land.

As a betterment approach, JFHR designed and installed a 100m low permeability barrier along the affected boundary to reduce the migration of hydrocarbon product and contaminated water, to alleviate the principal risks to future site users and the SSSI downgradient of the site. The barrier consisted of a bentonite/cement pellet mix with existing site soil instead of a more traditional barrier to reduce off-site disposal of excess material.