Hydrocarbon and knotweed remediation of a former industrial site, West Lothian

Challenge

The intention was to redevelop a derelict former industrial site to allow the construction of a new prison.  ERS were appointed to address areas of hydrocarbon contamination and to treat soil infested with Japanese knotweed.

A site investigation revealed that approximately 1,000 m3 of soil was affected by hydrocarbon contamination, comprising mainly diesel range hydrocarbons (DROs) and mineral range hydrocarbons (MROs) with concentrations of up to 10,000 mg/kg.

Parts of the site were also affected by Japanese knotweed, which co-occurred with hydrocarbon contamination in some areas.

Solution

The most cost-effective treatment option for Japanese knotweed was selected as on-site treatment, involving excavation of affected areas, with relocation at depth and installation of phytotoxic barriers to prevent the possibility of re-emergence.

ERS undertook a hydrogeological investigation and identified a suitable area for the treatment of knotweed, to provide eventual cover of 5m below proposed finished levels.  The excavated treatment area was first lined with a phytotoxic geomembrane and biomass, with affected soil, was placed on the membrane to a maximum depth of 3m.  A further phytotoxic membrane was then placed over to encase the material. The encasement cell was covered with a layer of protective sand, followed by 2m of clean soil, to finished site level.

The knotweed contaminated material was transported to the treatment area using covered tippers. Tippers were wheel washed and brushed down when leaving both the contaminated and treatment zones to prevent the possibility of secondary infection of other areas.

Hydrocarbon remediation was undertaken using on-site static biopiles.  The excavated soil was first screened to remove oversize and inert material for later reuse on site and to minimise volumes for biological remediation. 

Soils from areas where knotweed coincided with hydrocarbon contamination entered a separate treatment stream.  Material was first biopiled within the knotweed treatment zone to reduce hydrocarbons to acceptable screening levels and then encased in the treatment cell, as described above.

Outcome

• Screened soils were successfully remediated on site using static biopiles.
• On achieving the required target concentrations of DROs and MROs, ERS was able to return all treated soil for reuse on site.
• Successful on-site Japanese knotweed treatment avoided the need for costly off-site transport and disposal.
• Targets were achieved on time and within budget.
• The site is now ready for redevelopment.