Millions set aside to deal with underground toxic waste in Dunedin

The former Dunedin Gasworks underground tar well containing an estimated one million litres of tar and about 200,000 litres of contaminated water. Photo / ODT

More than $2 million has been set aside to deal with a potentially significant toxic problem held underground in South Dunedin.

But what the money might be used to do remains unclear while the toxic legacy of the Dunedin Gasworks remains in place.

The Dunedin City Council said it had no immediate plans to deal with the potentially cancer-causing chemicals, or other toxic waste, contained in up to 1,000,000 litres of tar below ground in Hillside Rd.

The tar well is a leftover from the former city-owned Dunedin Gasworks, which operated from 1863 to 1987.

The history of the former gasworks is preserved through a nearby museum about 150m from the contaminated well.

At present, the old tar well was well managed and the hazard contained, a DCC spokesman said.

The council had $2.64 million in its 10-year plan for any future remediation of the site, he said.

The bulk of the money was due to be spent in 2023-24 ($2.1 million) with the remainder to be spent the following year ($540,000), he said.

''There are a range of potential remediation options available, including removing the contaminants or treating them in situ,'' he said.

''The site remains well managed, monitored and contained, and we continue to work with the Otago Regional Council to assess the best remediation option and to ensure whatever decision we make has the lowest possible impact on the South Dunedin community and businesses.''

Gas purifying machinery at the Dunedin Gasworks Museum site in South Dunedin is a reminder of the many toxic by-products of gas production. Photo / ODT

About seven years ago, engineering consultants MWH told the council the cost of remediation and disposal for the site could be significant.

This week, the council spokesman confirmed the DCC received about $20,000 from the Ministry for the Environment's contaminated sites remediation fund for a feasibility study in 2017 looking at options for the site.

The council was unable to release a copy of the associated report at present because staff needed more time to review its contents and ensure it could be made public, the spokesman said.

A confidential report to the council in 2013, released to the Otago Daily Times the following year, revealed council staff had initially been pumping about 30,000litres of toxic rainwater from the tar well into the foul sewer every three months to prevent the tar well from overflowing.

Testing found the water was too toxic for the practice to continue and it was suspended, the report said.

Subsequently, in 2014, the council started to make payments of $10,000 for a 20,000-litre tanker load of contaminated water to be disposed of in Christchurch.

That practice continued today and contaminated water was sent north to Christchurch once every 10 to 12 months, the spokesman said.

Old reports detail some of the remediation already done at the site.

An investigation ahead of the development of Andersons Bay Rd Countdown, now covering much of the old site, noted sealing the site would mitigate the risk from direct exposure to related contaminants in the soil.

But it said contaminated groundwater could move laterally and potentially posed a risk to Otago Harbour.

A report from 2012 said maintaining the status quo could work for the site, but would prevent the land from being used for anything productive.

The city council now owns only two properties on the site: 45 Hillside Rd, which includes the underground tar well, and 20 Braemar St, home to the Dunedin Gasworks Museum.