After years of lobbying from local water experts and concerned residents over the significant quantities of extra water that have been entering Mullumbimby’s gravity sewerage system Byron Shire Council is taking action.
According to Alan Dickens, who previously worked for the council in their water and sewerage department, the clay pipes laid in the 1960s have been cracked and in poor condition since at least the 1980s, allowing both water into the system and sewage to leak out into the water table beneath Mullumbimby.
Local hydrologist Duncan Dey explained that the problem stems in part from the fact that the deeper sewer pipes that were laid in the 1960s sit below the water table and some even below sea level. Reports at the time of construction pointed out defects that were never addressed.
‘In the wet season the water table can be three or four metres above some of the pipes’ said Mr Dey.
‘Leaky pipes create inflow (of storm and ground water) into the pipes and that water is then pumped along with the actual sewage to the sewage treatment plant (STP). That extra load is known as Inflow and Infiltration (I&I).
In the Mullumbimby system, there can be up to twenty times as much I&I as there is sewage, for which the system was built. This unwanted load can trigger the need for upgrading or replacing an STP. The current Brunswick Valley STP was commissioned in about 2010 at a then cost in the order of $40million.
‘The issue of surface inflow compounds the problem’, said Mr Dey.
On 1 February 2018 Byron Shire Council ‘adopted the recommendation of the Water, Waste and Sewer Advisory Committee to commence a Mullumbimby Sewerage System Inflow and Infiltration Programme as a part of the sewer fund capital program.’
Since that point they have had the gravity mains pressure cleaned and they ‘conducted CCTV inspections of Council’s stormwater and sewer assets in the main town area of Mullumbimby during May–June this year.’
This was followed by smoke testing and bucket testing inspections that were carried out last week.
Waste of money?
Mr Dickens believes that Council is wasting ratepayers money on repeating smoke tests and taking more CCTV footage as he believes this will not show anything new.
However, Council has said, ‘The reduction of inflow and infiltration into Mullumbimby’s sewerage network is a priority for Council’ and they are attempting ‘to develop the most economical solutions to reduce inflow and infiltration’.
Long time coming
‘We applaud Council’s recent admission that all is not well under the streets of Mullumbimby. We have been waiting for decades to get Council on side on this,’ says Mr Dey.
However, with the increasing pressure for more urban development in the valley, he says the issue needs to be resolved quickly. Failure to correct matters could even lead to a sewage moratorium on the Brunswick Valley’s urban sewerage system.
‘If this leakage is not overcome we will certainly need a new STP sooner than would otherwise be the case,’ he told The Echo.
‘In the world of asset management, later expenditure equals cost savings. Money spent now to reduce I&I will reap savings by pushing back the date of the next STP upgrade.’