New dust suppression method

Oil will no longer be used by the Central Otago District Council to suppress dust from gravel roads.

An international method of sealing will instead be implemented throughout the district over the next three years.

Central Otago residents have previously raised concerns about the safety, cost and effectiveness of oiling.

A resolution to implement Otta sealing to replace oiling was passed at a CODC roading subcommittee meeting in Alexandra this week.

The CODC resolved to phase out oiling of gravel roads over three years, and instead use the Otta method, which originated in Norway after it was first used on gravel roads in the Otta Valley. Otta sealing is a 16-30mm-thick mixture of bitumen and crushed rock.

In a report to the group, CODC roading manager Julie Muir recommended Otta sealing be funded as part of the council's New Zealand Transport Agency-subsidised district roading programme, with the local share of funding being provided from an existing unsubsidised seal extension budget.

Otta sealing would cost an estimated $3500 per 100m of road, although costs varied depending on the amount done at once, she said.

Otta was deemed safer, more environmentally acceptable, and of better long-term quality than oiling.

In 2008, the council received 41 requests to oil roads and four requests to seal short sections of road.

Just over 20 complaints resulting from oiling were received by the council and Fulton Hogan Central during the year.

Trials throughout Central Otago proved Otta seal lasted five years, making it more cost-effective than oil in the long term.

In her report, Ms Muir said Otta seal would have to be replaced after less than three years to make it more expensive than oiling, which was a worst-case scenario.

This week's meeting adjourned for a site visit to roads on which Otta seal could be used, and had been trialled, throughout the district. Ms Muir showed subcommittee members gravel roads around Galloway and the Ida Valley, where issues of dust suppression were apparent, and trial Otta-sealed roads of the area in comparison.

When the meeting resumed, subcommittee members approved Ms Muir's recommendations to phase out oiling in favour of Otta sealing.

Otta sealing will be undertaken when it can coincide with metalling programmes and other roading upgrades in the area.