Project Description: Monitoring of surface gas emissions using the flux box method.

Client: Potters Waste

Introduction

Following the completion of a landfill operation, finished cells are covered with an engineered cap to ensure that no rainwater can percolate in and no gas or odour can escape from the landfill.

The effectiveness of the cap depends both on the properties and application of the capping materials and on the gas emission potential. The Environment Agency Guidance on Monitoring Landfill Gas Surface Emissions LFTGN07 requires that gas surface emissions are monitored to assess the integrity of the cap and the efficiency of the gas management system.

The recommended method of monitoring is the Flux-Box method, in conjunction with a portable Flame Ionising Detector (FID). This allows gas fluxes to be measured within a known enclosed volume at soil-air boundary.
FIDs measure the concentration of flammable gases such as volatile hydrocarbons, odorous VOCs and the like and are calibrated to CH4 with a detection range between 1 ppm and 1% CH4 (14,000 ppm).

Following monitoring, emission rates are calculated using the Guidance LFTGN07 calculation methodology. The results are then assessed against PPC Compliance to compile site-specific Pollution Inventories.

Project Brief

Egniol were commissioned by Potters Waste to carry out flux box monitoring on older parts of their landfill. This involved:

• Walkover monitoring survey of aerial emissions of methane over the surface of the cap, using a Flame Ionising Detector (FID)
• Surface emission monitoring of methane over an area of cap using a Flux Box/FID methodology
• Assessment of surface gas emissions and identification of problem areas, which required further remediation measures
• Design of a cap remediation plan and liaison with the Regulator.

Project Delivery

Flux box monitoring showed clearly where gas was escaping from the landfill from fractured areas of landfill cell cap.

Moreover, the survey indicated those areas of the landfill where the gas field would need balancing to achieve higher abstraction rates.

Overall the results of this accurate, yet simple monitoring exercise backed up the operator's remediation proposal and helped prevent unnecessary regulatory intervention.