Pipe dream takes shape

THE numbers are big, very big. The project requires 10,000 cubic metres of concrete, 2500 tonnes of steel and 20 kilometres of pipe. It’s costing some $200 million and will deliver 160 million litres – that’s 64 Olympic pools – of water per day.

The new Bryn Estyn plant is the largest single project ever undertaken by the state’s primary water utility, TasWater, and will supply more than 200,000 people. It nears completion as pressure mounts on its source in the Derwent River, the state’s main drinking water supply. Upstream from the plant, towards the river’s origins in Lake St Clair and the rivers that feed it, claims are being made by agriculture and aquaculture, forestry and hydroelectric power.

Just to the south, demand for water has swelled as a housing boom has added thousands of new customers from New Norfolk, Brighton and Sorell, to Hobart and the Kingston area in the south. The river’s water itself is under pressure, including increased incidence of algal blooms, along with compositional changes brought by changing seasons.

According to TasWater, the existing plant at Bryn Estyn was originally designed to deliver 160 million litres per day, but “aging infrastructure and changing environmental conditions have restricted its ability to keep up with that The plant sends water down the West Derwent pipeline that gravity-feeds Hobart from the hills above.

On the other side of the river, the Southern Regional Pipeline takes water south and east. Massive storage tanks hold a reserve in such places as Tolosa in Glenorchy and in Claremont. Well aware that its output is constantly being tested and critiqued by customers just kilometres away, TasWater’s new plant includes three new water clarifiers, an ozone contact tank and eight new filtration units.

Ultra violet light, ozone gas and a carbon treatment system are part of a process that takes out solids and the brown tannins common to the Derwent. An interim pump station, a new power switchyard and roughly 20,000 metres of new pipework – much of it a massive 1400mm in diameter – are being added to the site. Linking and governing the entire operation is a battery of mechanical and electrical systems, not the least of which is a high voltage electric fence that surrounds the plant. TasWater says the project is on track to be tested and commissioned about mid-next year. Fun fact: Bryn Estyn is the original Derwent Valley farm on which TasWater’s treatment plant is built. It was settled by a Welshman, Lieutenant Henry Lloyd, and the homestead built in the 1840s. Bryn Estyn translates from the Welsh as ‘long hill.’ flow rate.”

The upgrade will help ensure that TasWater can reliably supply that amount well into the future in all river water conditions. “We’ll be able to add components to extend the capability of the facility, as we need to,” says Anthony Willmott. On site, Mr Willmott – TasWater’s General Manager, Project Delivery – first pays tribute to the specialist trades and contractors who’ve managed to work safely in and around the multiplicity of hazards presented by such massive construction project. Between a cram of excavators and concrete trucks, stacks of reinforcing steel and piles of stored gravels, a forest of containers and temporary pipeworks, as many as eight large construction cranes are at work at any one time. They include the largest crawler crane in the state, weighing in at 180 tonnes.

The 10,000 cubic metres of ready-mix concrete is being brought onto the site to encase 2500 tonnes of reinforcing steel bars that sit inside the 600mm thick walls of the new water treatment tanks. There are four of them, ranging in height up to 10 metres. While Melbourne-based Ausform – a specialist in large reinforced concrete structures – is supervising the work, the majority of the hundred of so pairs of boots here are worn by Tasmanians. That includes the Hazell Bros crew down at the concrete batching plant at Boyer.

This new treatment plant is built in a large U-shape around the brick and concrete structures of the original Bryn Estyn facility. Sitting in the hillside behind the new works is a million-litre silt retention pond, where solids captured during treatment are pumped to dry out before disposal.