Passive vents at the Tucker Beach landfill could cost the Queenstown Lakes District Council a further $44,000 if gases exceed the allowed level.
The Otago Regional Council requires the QLDC to monitor the landfill, which has been out of action since 1999, once a month for the next six months.
At the infrastructure committee meeting in Queenstown yesterday, QLDC solid waste manager Stefan Borowy told the committee if results during that time showed concentrations of gas exceeded the levels in its resource consent, up to $44,750 would have to be spent installing four extra passive vents.
The 6.05ha Tucker Beach landfill was closed in 1999 after 37 years of operation, and Ministry for the Environment guidelines required the owner - the council - to maintain and monitor it for a minimum of 30 years.
Landfill gas is about 40%-60% methane and the remainder carbon dioxide, and the rate of the gas generated depends on the type of waste, its density, moisture content and temperature.
The gas develops naturally and "generally" declines in time, Mr Borowy's report said.
The risks associated with the gas were flammability, asphyxiation, odour and the greenhouse gas effect.
An investigation at the landfill in April 2010 showed a subsurface bore had elevated levels of methane above the limited 0.5% by volume.
The following June, August and December, monitoring levels demonstrated elevated levels of 11%-34%, in breach of the allowed 0.5%, and three more bores were installed for a cost of about $30,000.
In June this year, a further three bores were installed as required, which meant the total number of landfill bores at Tucker Beach was eight.
Results of two of the bores have shown an excess of the allowed gas so far.
