Separating Launceston’s combined sewerage network at a ‘cost of hundreds of millions of dollars’ is not likely to significantly improve the health of the Tamar River, a TasWater senior engineer believes.
The river is subject to about 1000 sewerage outflows each year thanks to the city’s unique combined sewer system – the second oldest in Australia to Sydney.
Consisting of one pipe for sewerage and stormwater, some of Launceston’s brick-barrelled network dates back to the 1870s.
It works by catching stormwater and sewerage in one pipe before pumping it to a treatment plant.
In heavy rainfall the pipe can overflow, discharging raw sewage and stormwater into the river to prevent localised flooding.
Separating the system has long been mooted as a fix to faeces flowing into the river.
But TasWater treatment asset performance senior engineer Cameron Jessup said the entity’s modelling showed splitting the network might not provide a value for money.
“Work done to date doesn’t suggest separation will give the best environmental outcomes,” he said.
“The issues with separation was it was going to be very costly compared to the other upgrade options.”
TasWater studies found the combined system contributed about 5 per cent of sediment load in the river, about 1 per cent of its nutrient load and 30 per cent of its pathogen.
“The work we’ve done to date doesn’t suggest a separated system is going to be a silver bullet,” Mr Jessup said.
“You weren't going to see a marked reduction in solids load, you will see some reduction in that pathogen load – it's not going to be as significant as people expect.”
The catchment area of the Tamar’s tributary, South Esk, makes up about one-sixth of Tasmania’s land mass.
Forestry, farms and industrial pollution contributes to the quality of flow into the river.
“It's very difficult to put our hopes on one activity to significantly alter what's going on in the receiving environment,” Mr Jessup said.
“Spending hundreds of millions of dollars on separation doesn’t seem to represent great value to our customers.”
Mr Jessup said Launceston’s combined system was able to capture and treat the first rainfall flush, which pushes road contaminants and sediment into drains.
Under a separated system the stormwater would flow untreated into the river.