Articles & Case Studies

Fire in the hole

Posted: Wednesday 20th July 2011

When Mont Cuet Landfill Site in Guernsey caught fire multiple attempts were made to extinguish the burning beneath the surface of the site, before an innovative solution which included use of equipment from Flygt Rental worked.

The Mont Cuet landfill on Guernsey is the island’s only refuse site. In April 2005 a subterranean fire was discovered smouldering deep within the site after abnormally high temperatures were recorded inside the waste.

Fire is a serious risk with landfill sites because of the combination of combustible gases and high underground temperatures. “During the waste decomposition process, a range of substances are released from the waste matter, and become concentrated as water percolates through the waste, into leachate. Methane gas and other Volatile Organic Compounds are also released.” says Mark Warren, Flygt Rental Manager. “With decomposition there is also a temperature build up below ground which means the waste gases have to be vented out. These temperatures are continually monitored in order to provide early identification of any hot spots so early intervention can take place. The presence of these fires below ground, if left unchecked, might lead to the formation of underground caverns which could make the waste unstable at surface level, especially when heavy plant is driven above it”. The States of Guernsey, the island’s government, reviewed numerous proposals to put out the fire, including the use of seawater pumped into the site.

“We had discussions two years earlier, when they were considering pumping seawater up the beach and into the landfill site to flood it and extinguish the burn,” says Mark. “There were concerns that the naturally occurring sulphates in seawater would dramatically increase the anaerobic activity which in turn would generate unacceptably high levels of hydrogen sulphide, making the situation worse.”

However, leaving the fire burning was not an option. “Although there was no immediate danger there was always the possibility that the fire could create large voids and destroy the underground gas extraction duct work,” says Mark.

It was clear that a freshwater solution was going to be the only way to douse the fire, but that posed huge logistical problems, both in terms of moving equipment into the right place and moving huge volumes to Mont Cuet.

A scheme was devised by Nick Nicolle, the Senior Technical Manager of The States Works Division, and ITT Water & Wastewater’s distributer on the Island. Nick was part of the project team assigned to produce practical recommendations to deal with this problem. The plan was to use the disused Torrey Canyon quarry as a reservoir. However, there was not enough water in the quarry, which has no water source of its own, so alternative sources of water were required.”

He continued: “The project team had estimated that they needed approximately thirty litres of water per second to feed the landfill site. The proposal was to use clean water from a pond and a watercourse, but both of these were 2.5km away.”

The two alternative sources were Vale Pond and Vale Marais. “The plan was to utilise Vale Pond as the primary source,” says Mark. “My role was to specify the pumps, controls and pipe sizes, and supply the equipment to make the plan work.”

At Vale Pond two Flygt NS3202HT pumps were used to deliver a maximum flow of 55 l/sec at 46.5m total generated head with the water pumped to Torrey Canyon via 2,000m of pipe.

At Vale Marais a single NS3153HT pump was used to deliver a maximum flow of 11 l/sec, at 20m total generated head, via 1,500m of pipe. Both of these pump discharges were then combined into a single main pipeline for the final 500m.

“When moving such large volumes of water with such long pipe runs, there is a huge amount of momentum contained within the fluid with the biggest problems occurring when the pumps stop,” says Mark. “For this reason, all three of the pumps were controlled using variable speed drives, which allowed us to slowly reduce the speed of the pump to a stop.”

Beyond the Torrey Canyon Quarry, the water was pumped across fields to the Mont Cuet Landfill Site. At the site, the water was pumped around the hot spot and injected underground at various points. Back at the holding quarry, Flygt Rental provided two further Flygt BS2151LT Pumps fitted onto Flygt Flotation Modules. Each pump was capable of delivering 30 l/sec at 24m total generated head into the landfill site.

Once there was sufficient water in the landfill site, two Flygt BS2201HT EX Pumps were used in a duty and standby mode to pump the contaminated water out to an adjacent holding lagoon prior to treatment using the sites existing plant. The duty pump was capable of draining 14 litres per second at 87 metres total generated head, matching the treatment capacity of the existing facility.

In total, water was pumped into Mont Cuet landfill for approximately four weeks, with the fire being totally extinguished by the time the project ended.

“This was a very demanding set of circumstances to work in,” says Mark. “The distance of the water sources from the landfill made the movement of water extremely difficult whilst the conditions in the landfill itself meant that explosion proof pumps were necessary. The fact that we achieved a successful outcome was down to a well planned team effort by all those concerned.”

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