Contaminated Land Part 2A Support Chicken Road Closed Landfill

DBS Environmental Phase 2 Ground Investigation

Contaminated Land Part 2A Support – Chicken Road Closed Landfill

DBS was appointed by North Tyneside Council to support them in the investigation and long term management of a closed historical landfill site in North Tyneside.

  • Client: North Tyneside Council
  • Date: January 11, 2016

Summary

DBS was appointed by North Tyneside Council to support them in the investigation and long term management of a closed historical landfill site in North Tyneside.

Like most areas of the UK, there is a historical legacy of closed landfill sites in North Tyneside that were operated before the Control of Pollution Act 1974, as such they were operated without containment and waste inputs were not recorded. Landfills without containment require long term management to ensure that risks to public health and the environment do not occur, due to migration of landfill gas from the site (explosive and asphyxiating), and through leachate release to the local hydrogeological regime.

Landfill gas typically comprises methane and carbon dioxide in an approximate 60:40 ratio, along with other trace gases. It can migrate in the subsurface and impact sensitive receptors. The Chicken Road landfill site comprises a natural valley that was infilled with wastes post the 1940s up to the early 1970s.

Due to concerns about contamination, the landfill was capped by NTC in the 1990s to remove exposure pathways to wastes, and a granular gas vent trench was constructed around the landfill perimeter to prevent subsurface gas migration from migrating out of the site and reaching residential housing in the vicinity of the site. Long term perimeter landfill gas and groundwater monitoring wells were also installed at this time, the wells are regularly monitored for landfill gas to confirm that subsurface migration of gases is not occurring.
DBS was appointed by NTC to assist them with the continued management and risk assessment of the landfill site, and to determine the potential for off site risks from the landfill to the local area.

The work consisted of four main elements:
1. Undertake remedial earthworks to the perimeter granular vent trench.
2. Undertake a 6 month programme of monitoring for gas and groundwater, including a borehole survey with replacement where not functional.
3. Undertake an intrusive investigation and risk assessment of superficial deposits in the local area.
4. Prepare a factual and interpretative report of the work, including ground gas risk assessments and human health risk assessments to update the sites Conceptual Model.

The remedial earthworks comprised the removal of the upper 0.5m of the granular vent trench along its entire length with an excavator, screening of the material with a rotating bucket screen to remove fines and other deleterious material, with replacement of processed aggregate back into the trench. Landfill gas and groundwater monitoring was undertaken monthly, and boreholes found not to be working were replaced using cable percussion methods. Upon completion of the monitoring a ground gas risk assessment was undertaken in accordance with CIRIA C665 and other relevant guidance.

An intrusive investigation was undertaken of the superficial deposits in the vicinity of the site, the investigation was undertaken using a terrier rig, with samples taken for laboratory analysis. The laboratory analysis results were used to undertake a generic quantitative risk assessment (GQRA) for human health.

The work resulted in the revising of the sites Conceptual Model, and the gas risk assessment undertaken by DBS identified that landfill gas risks previously identified as significant were not present at the site.  DBS also undertook an extensive desk based assessment of the landfilling from the 1940s to identify potential areas where waste was not previously understood to be present, the council will be targeting future resources at these areas as the long term management of the site continues.

The findings were reported in one factual and interpretative report for the council, and the work undertaken by DBS is allowing the council to target resources for future work effectively, to continue the long-term management of the site.

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