Underground pipes Christchurch suburbs leaching asbestos, although no immediate concerns for public health — CHRIS LYNCH NEWS

The University of Otago, in collaboration with ENGEO Consulting Ltd, sent samples from all 35 citywide locations to an international specialist laboratory in the United States for analysis.

Study co-author Michael Knopick, who undertook the study for his University of Otago Masters of Science thesis, said asbestos cement pipelines are known to be the most vulnerable in earthquakes as they are brittle and subject to damage and breakdown.

“Ground acceleration, shaking or vibration can cause them to shear, meaning they can degrade both inside and out.”

“Christchurch has a moderate to highly aggressive water supply as it’s low in dissolved calcium and magnesium, and that aggressiveness has enhanced internal pipe corrosion. The outer surface of the pipes is also vulnerable to decay, especially in conditions where there are high groundwater tables, which is what happens with prolonged liquefaction.”

Asbestos cement was commonly used for water pipes worldwide in the 20th century due to its strength, thermal and chemical resistance, plus technical superiority to other materials. However, by the 1970s it became clear of these pipes, when damaged, could release asbestos fibers into water supplies, prompting global restrictions on their use. In New Zealand, asbestos cement pipes in water mains were widely used up until the 1980s.

Of Christchurch’s 1814-kilometer total underground water mains network, 789 kilometers is laid in asbestos cement piping. The oldest pipes pre-date 1950 and are laid underneath small pockets of New Brighton, Hei Hei, Mt Pleasant and Halswell. More were laid during the 1950s in Hei Hei, Riccarton and Aranui; in the 1960s around Wider Halswell, Ilam, Riccarton, Burnside, Bishopdale, Redwood, Hornby, Parklands and Lyttleton; and in the 1970s in Philipstown, Parklands, Somerfield, Woolston and Bishopdale. Much of the piped network adjacent to the Ōtākaro Avon river was replaced due to liquefaction post-2011.

“The lifespan of asbestos cement piping in New Zealand is between 40 to 60 years, depending on the environment in which its laid.”

“We know asbestos piping that’s been in the ground longer than 50 years can degrade and release fibers from its walls. It’s been described at this point as having the characteristics of wet cardboard.”

The authors say it’s now crucial that councils across New Zealand establish which pipes in their networks are subject to deterioration and plan for targeted replacement roll-outs as soon as possible.

Dr Mager said many of these pipes have reached the end of their life.

“Some are up to 80 years old and therefore 20 to 30 years overdue for replacement. We believe authorities should prioritize replacing pipes over 50 years old to reduce the risk of water-carried asbestos release, and to mitigate any potential risk of asbestos from ingested, contaminated water sources.”

The study points out New Zealand currently has 9000 kilometers of asbestos piping requiring replacement, at an estimated total cost of NZ$2.2 billion.

Christchurch City Council responds

Christchurch City Council’s Acting Head of Three Waters Tim Drennan said the data collected through the Otago University study builds on the Council’s knowledge of the impact of having asbestos cement pipes in the water supply network.

“We carried out our own small study, sampling water from 17 hydrants, in 2017 and found asbestos fibers in only one sample.”

“This Otago University study though was much more comprehensive and used a different, more precise methodology. As a consequence we now have a better picture of the amount of asbestos fibers in our water.”

“It is very important to reiterate that the asbestos cement pipes in our water supply network are not causing any immediate health concerns.”

Mr Drennan said “internationally there is no consistent evidence to suggest that ingested asbestos is hazardous – a fact the authors of the study acknowledge.”

Mr Drennan said “the Otago University study only sampled water in Christchurch, however, it is likely that asbestos fibers would be detected in most water supplies as asbestos cement pipes were widely used up until about 40 years ago.”

Christchurch’s underground infrastructure is subject to an ongoing renewal program to maintain and improve our water supply network. Pipe renewals have been increasing since the 1990s and now only 21 per cent of the water supply pipes in Christchurch are asbestos cement pipes.

“Some of those asbestos cement pipes have reached the end of their life and will be replaced through our renewal programme, but others still have life left in them.”

“We run a risk-based prioritization process for pipe renewals. We look at not only how likely a pipe is to fail, but how bad the consequences may be to the community as a whole. We prioritize renewing pipes feeding hospitals, pipes where failure would close a main road, and pipes where failure could lead to contamination of the water supply.”

“We don’t prioritize based solely on the type of material a pipe is made out of. If we did that, we would end up renewing pipes that were functioning without issue before other pipes that were causing numerous and frequent water supply shutdowns to residents and businesses.”

“Having said that the majority of our planned water main renewals over the coming 27 years will be asbestos cement pipes.”