Crays Hill

Crays Hill


Amber Valley Borough Council


Site investigation and gas mitigation on a former landfill

GeoDyne Role:

Design and implementation of gas investigation and monitoring works

Supervising and validation of a gas mitigation system

Work Undertaken:

  • Site Investigation
  • Risk Assessment
  • Public consultation and stakeholder liaison
  • Mitigation works specification
  • Regulatory sign-off for all completed works
  • Produced savings of 90% for the Client

Due to our proven track record and experience, Amber Valley Borough Council (AVBC) instructed GeoDyne to investigate the source of methane, which had been identified at the former Crays Hill Recreation Ground in Swanwick, Derbyshire. Our task was to establish the generic gas migration pathways and identify the site-specific source-pathway-receptor plausible pollutant linkages. Utilising this captured data we were able to design a robust but cost effective remedial strategy.

AVBC established a public liaison group at the start of the project, which convened at regular intervals at the Council Chambers and were attended by representatives of the Councils Executive. We made several presentations to residents and local councillors at these meetings to keep all parties informed of our progress.

Following an extensive programme of intrusive works and monitoring, we confirmed that the principal source of methane were the existing landfill materials rather than other potential sources. The landfill represented the key potential gas migration pathway and nearby houses were identified as the critical receptor. After producing a Detailed Quantitative Risk Assessment report, AVBC instructed GeoDyne to recommend potential mitigation solutions for the site and assist in the tendering process.

Following completion of a value engineering exercise we recommended a bespoke virtual curtain system, which would offer more effective control of the landfill gasses than the gravel vent trench solution originally proposed by an earlier consultant. Our recommendation was approved by the Environment Agency. Installation was completed in less than four months, validated and the site was returned to the community.


A virtual curtain is a passive system designed to intercept and dilute migrating gases and provides an effective dispersal of gas to the atmosphere.

The system consists of a series of permeable vent nodes connected to an upper horizontal gas collection and dilution duct, which then connects to either a proprietary vent bollard or vent stack.

The system exploits differences in pressure to draw gasses out of the ground and disperse them safely.