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prevent further damage. “Nature is amazing in its ability to adapt to massive, one-off upheavals,” notes Maucor. “The earthquake dumped huge amounts of silt and millions of tonnes of raw sewage into the rivers and yet – apart from a few critical areas where intervention was necessary – the ecology has stabilised itself to deal with this new situation.” A far graver threat to the environment comes from the reconstruction, he explains: “A massive project like this could mean chronic pollution over many years – the discharge of chemicals, contaminants and cement slurry; the creation of waste and its subsequent disposal; the control of sediment. That long-term assault is far harder on the environment than a single catastrophe, so we have to manage all of those factors very carefully.” In Christchurch, sediment is truly the enemy: the city has a very high water table – which explains the extent of liquefaction caused by the quake – so any work that requires digging more than a metre down (which means all of Downer’s pipe-work projects) makes de-watering of the ground a necessity. And that means pumping silt and any existing contaminants along with the water. “Once that goes into the storm-water system, it is in the river – there’s no going back,” says Maucor. “So we have had to devise very efficient and cost-effective filtration systems at every site. First, we have physical barriers, such as tanks with baffles that will encourage sediment to settle, and ‘socks’ with very small pores. Where that isn’t enough, we add treatments to ionise the particles, causing them to bind and settle.” Controlling run-off from concrete work is equally critical as the highly alkaline slurry will change the pH of the rivers. “Normal is pH7 and water becomes toxic at about pH9, which will kill the fish. It happens very fast.” So, too, is the need for military-style precision in managing the replacement of waste water pipes: “It’s a live system; we cannot interrupt the service. But if we get it wrong we risk having millions of litres of waste discharging into the eco-system.” Testing for sediment content, alkalinity and contaminants such as e-coli is constant and rigorous. But the challenge goes beyond what gets pumped into the rivers, to work that takes place right in the rivers – such as the Heathcote Opawa Bridge reconstruction. On the main route from the city to Lyttleton, its piles and abutments have all had to be renewed, in order to raise the road bed back to its correct level. “The impact on the river would be immediate and real because we would be disturbing both the bank and the riverbed,” says Maucor. “The traditional solution – sandbags – are cumbersome 48 / DOWNER / IN BLACK & WHITE


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