The UK Chemical Industry has, for many years, appreciated the strategic use of Hazard and Operability (HAZOP) assessments in reducing the risks posed by their activities and sites. But what other industries can benefit from this approach? The landfill sector has just begun to demonstrate how the innovative use of the HAZOP assessment methodology can help underpin significant decisions on site operations as exemplified by the Mont Cuet landfill site on the Channel Island of Guernsey.
Subsurface Landfill Fires
Signs of a subsurface landfill fire were noted on the only operational landfill site on the island in 2005—the indicators being steam and smoke issuing from boreholes and an area of collapse along one of the site boundaries. The operator and island government employed specialist consultants to investigate the potential causes and location of the fire and extinguish it as soon as possible to avoid any harm to site workers, residents, the environment and the island’s tourist industry. The fire was deep (more than 10m below the waste) and could not be dug out which is the traditional approach to quelling landfill fires. Measures to reduce the temperatures and engulf the oxygen around the fire (using surface water and nitrogen injection) were successful in the short-term (a few hours and days at most) but could not be sustained. The site is coastal and due to the groundwater hydraulics and sea water levels, the only option left was to attempt to extinguish the fire by turning off the leachate pumps, and allowing leachate and the ingress of sea water levels within the waste to rise, whilst at the same time as injecting fresh water into the waste at depth and at high volumes.
The natural sulphate content of the seawater meant that there was a high likelihood of hydrogen sulphide emissions from the site during the procedure. Additional risks of chronic or acute structural failure from flooding a previously “dry” waste mass and the potential for pollution from discharging the resultant leachate were also of serious concern to the project team. Should there have been negative impacts on the surrounding seawater colouration, beaches and odours, the tourist impact would have been fundamentally damaging to the island’s economy.
The obvious risks associated with these activities were high and the potential for disruption to the island’s waste management activities during this period would have been considerable, should the site have to close. As such it was decided to bring in HAZOP specialists to help plan the project in detail.