Confidential reports on the contaminated former gasworks site in South Dunedin have called it a serious health and safety issue and a significant financial and environmental risk. Is Dunedin about to discover it is yet another community bearing the brunt of previous generations' ignorance and inaction? Bruce Munro takes a look.
The two reports lie deep in a thick wad of laboratory results, tank-level data and consultants' reports recently obtained from the Dunedin City Council by the Otago Daily Times under the Official Information Act.
The first is dated April 30, 2013, the second, June 11, 2013. Both are headed ''Confidential Report'' and are addressed to the city council's Executive Management Team.
''A serious Health and Safety issue has been identified at the Council-owned property located at 45 Hillside Rd, South Dunedin,'' the first report states.
''It has been identified that the tar pit [containing an estimated 1,000,000 litres of coal tar and water] is filling with water and requires regular removal.
''The water in the pit is contaminated with hydrocarbons, volatile and semi-volatile organic compounds as well as unacceptable levels of Polycyclic Aromatic Hydrocarbons [PAHs].''
By the time the second report is being typed six weeks later, the situation is being called ''a significant risk to Dunedin City Council in terms of the financial implications and the potential hazard to the environment''.
The tar pit, or well, is among the remnants of the first and last commercial coal gas operation in New Zealand.
Dunedin Gasworks began production in 1863 on a large site bounded, on its northern edge, by Andersons Bay and Hillside Rds, South Dunedin. Set up to provide gas street lighting, the gasworks expanded to supply reticulated domestic and commercial gas throughout much of the city.
It was a busy, hot, odorous and often dusty place where coal, coke and oil were used to produce gas that was purified and then stored for reticulation.
Dwindling gas demand and increasing production costs saw the city-owned works closed in 1987. Much of the machinery was removed. The foundations of the original gasometer on Hillside Rd were turned into a crude storage tank for 1000cu m of leftover tar.
In the decade to 2005, most of the land around it was sold for a variety of commercial uses. 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.
The potency of the many by-products of gas production have long been known, to a certain extent.
Willis Bagley worked as a maintenance fitter at the gasworks for 22 years until it closed. He says there was good awareness of obvious risks such as gas leaks.
But staff working in the coke dust, the gas fumes, and with the tar did so without face masks or other safety equipment, Mr Bagley said.
''There was a lot of tar ... and tar sludge,'' he recalls.
''And a lot of ground that was contaminated, that looked a greeny-blue sort of colour. That's all your arsenics and other stuff in there.''
Accidents did happen.
''I got tar in my eyes once and ended up in hospital,'' he says.
''We were pumping straight into a line in the tar well ... and the damn thing spun around and I got it in the eye.
''They whipped me down to outpatients and I caused quite a stir there.
''Coal tar does burn you because it is full of that creosote distillate, and it's got all the properties of benzene. It's got the whole damn lot in it.''
Understanding of health and environmental risks posed by gasworks sites has grown with time.
Gasworks wastes are a complex mix of cancer-causing hydrocarbons and other compounds, many linked to various health risks.
How long, how often and how much a person is exposed to these chemicals are important factors in determining their risk, a spokesman at the Dunedin-based National Poisons Centre says.
That said, polycyclic aromatic hydrocarbon (PAH) benzo(a)pyrene is highly carcinogenic; volatile organic compound (VOC) benzene is considered to be one cause of leukaemia; and non-carcinogenic PAH naphthalene can cause blood conditions. Gasworks sites are also associated with other known nasties such as arsenic and cyanide.
City council-commissioned reports on the contamination were compiled in the years after the plant closed in the late 1980s. Around the new millennium, more work was done on management and possible remediation of the site. But that came to an end in 2004.
The next year, the Government amended the Resource Management Act. The change made territorial authorities responsible for ''the prevention or mitigation of any adverse effects of the development, subdivision or use of contaminated land''.
Two years later, when the Ministry for the Environment looked at local government implementation of the new requirements it concluded most were not doing a good job.
As a result, in January 2012, the National Environmental Standard for Assessing and Managing Contaminants to Protect Human Health (NES) came into force. The NES specifically identifies former gasworks sites as contaminated sites that must be dealt with.
Perhaps not surprisingly, within a few months the city council contracted consultants MWH, which reported back by the end of the year. The report summarised the history of the tar well and relevant legislation and finished with some recommendations.
''A key issue, possibly the most significant of all, would be the cost of a remediation and disposal exercise,'' the report stated.
''The DCC may simply not wish to contemplate this option because of these costs.''
Four months later, the first confidential report goes to the executive team. It states that a manager within the council's water and waste services has become aware his staff have been removing about 30,000 litres of toxic rainwater from the tar well every three months to prevent it overflowing.
The practice has been to pump the water into the foul sewer. But Citilab tests have shown the concentrations of PAHs, volatile and semi-volatile organic compounds and other health and environment-damaging contaminants in the water are too high for that to continue, the report, written by Tim Buchanan, the council's property management project co-ordinator, says.
By now a flurry of new investigations are under way.
June's confidential report says the tar well water, which has also been found to have an unacceptable level of cyanide, poses an environmental risk if it overflows and runs into neighbouring properties or on to Hillside Rd. Tar has also been found in the nearby stormwater pipe.
It is not clear whether the tar is coming from the contaminated ground or from a potential leak in the tar-well wall. The contamination is likely to have human, aquatic and environmental health implications, the report says.
It is 1989 revisited. Testing commissioned by the city council when the gasworks closed showed soil samples from the site were contaminated with tar, cyanide, phenols and sulphur ''above unacceptable levels''.
Not that this is the first time industrial pollution has been left for others to clean up.
Two of New Zealand's worst examples are the Tui copper and lead mine, in the Waikato, and the Fruitgrowers' Chemical Company (FCC), at Mapua, near Nelson.
The FCC closed in 1988 after 56 years producing pesticides on a strip of land sandwiched between a residential area and a sensitive marine ecosystem. In 2004, the Government stepped in, coughing up most of the $12 million required to remediate the site.
In the Waikato, almost $22 million was invested by government departments, regional and territorial authorities and local iwi to clean up the abandoned Tui Mine. In May last year, two years and 10,000 tonnes of cement later, the remediation was complete.
And Dunedin is not alone in having had gasworks. Ministry for the Environment guidelines on managing gasworks sites, published in 1997, said there were about 54 sites in New Zealand. Many of them, when they were closed, still had underground structures containing contaminants, the guidelines said.
Sixteen years later, in the council's second confidential report, a four-part action plan was outlined: a preliminary site investigation (already covered by the MWH report), an investigation of the health and environmental risks, identifying remediation options and then either managing or remediating the site.
The health and environmental risk assessment, conducted by environmental and engineering consultants Taylor and Tonkin at a cost of $48,100, was delivered to the council in February.
The report concludes contamination is widespread in soils and groundwater across the former gasworks site. This could potentially pose an unacceptable risk to health if VOCs escape into the air and became trapped in occupied buildings, the report says.
Groundwater contaminants could get into the environment beyond the site through leaky service pipes. Skin contact or accidental ingestion of contaminated soils is a risk for people in unsealed areas onsite and for construction workers digging onsite or in the road reserve.
What the council will choose to do, or be able to afford, remains to be seen.
Graeme Proffitt, an environmental consultant with Wellington-based Pattle Delamore Partners, has not been involved with the Dunedin site. He has, however, investigated several other former gasworks throughout New Zealand.
One of the key challenges in remediating sites is finding safe and affordable ways of disposing of the contaminated material, Mr Proffitt says.
''What you might have been able to get away with a few years ago is much harder now,'' he says.
Remediation, as opposed to management, tends to be an expensive option.
''You can spend millions on fixing up a gasworks, or you can spend relatively modest amounts to just build over the top of it, depending on what structure you want to put over the top of it.''
The key issue is putting a suitable barrier between the contaminant and people or the surrounding environment, he says.
In Dunedin, the council is doing more groundwater, surface water and soil monitoring. Staff have also begun indoor air monitoring to check for a build-up of VOCs.
A patch of unsealed and possibly contaminated soil on the museum site will be fenced off.
There is a plan to put a waterproof covering over the tar well to stop more rainwater getting in. Citilab staff are investigating a filter that would enable the water to once again be pumped into sewer pipes. In the meantime, the council will shortly make another payment of $10,000 for a second 20,000-litre tanker load of contaminated water to be disposed of in Christchurch.
The council, staff who formerly did the pumping, and their union, are discussing whether staff health checks are needed.
The search for funds to remediate the site, however, has been put on hold. Preliminary discussions had been held with Otago Regional Council staff, through whom an application to the Government's Contaminated Sites Remediation Fund would have been lodged.
But ''no funding is being sought at this time'', a council spokesman told the ODT.
The council has its collective fingers crossed that the monitoring will show expensive steps are unnecessary. The hope is that a lucky escape does not mean the opportunity for salutary lessons about ''not putting off until tomorrow'' are lost today.
