INVASIVE: Major root intrusion in council pipelines in Mullumbimby.
INVASIVE: Major root intrusion in council pipelines in Mullumbimby.

‘Very high’ chance sewer, stormwater systems could fail

AN ASSESSMENT report that will go before a Byron Shire Council committee this week has revealed a high risk of sewer and stormwater systems in Mullumbimby failing.

The report will go before the council's Water, Waste and Sewer Advisory Committee when it meets on Thursday.

After a review of the 30-year capital works plan, the condition assessments of the town's gravity sewer and stormwater assets were conducted, to establish whether they should be renewed.

This process found 41 per cent of the sewer network and 69 per cent of the stormwater system has "either a high or very high risk of failure", the report said.

 

Heavy infiltration in a council pipeline in Mullumbimby.
Heavy infiltration in a council pipeline in Mullumbimby.

The findings "identified that various assets are presenting a high risk to council that should be remedied in a risk-based manner".

An initial assessment was focused on a small catchment of the sewer network upstream of Mullumbimby's sewer pump station, which found evidence of inflow and infiltration issues.

The report said this section of the system "consists largely of Vitrified Clay pipe which is prone to brittle failure (cracking) and is therefore subject to high rates of inflow and infiltration".

More detailed assessments of both the sewage and stormwater network involved CCTV of the sewer mains and stormwater culverts, visual inspections and smoke testing.

"In total there were 109 sewer mains and 107 stormwater culverts that were assessed including the associated maintenance holes," the report said.

 

Major root intrusion in council pipelines in Mullumbimby.
Major root intrusion in council pipelines in Mullumbimby.

 

"It was apparent through the development of the condition assessment reports that the stormwater culverts and sewer mains that were initially constructed in the 1940s and 1960s respectively were subject to significant deterioration and had not been sufficiently maintained."

According to the report, the findings mean the council faces the risk of pipe collapse that would lead to expensive emergency rectification works, stormwater movements that could lead to flooding and property damage and extensive infiltration that could result in pavements being undermined and collapsing.

 

Major displacement at a pipeline replacement in Mullumbimby.
Major displacement at a pipeline replacement in Mullumbimby.

 

The renewal, rectification and maintenance works have been slated to cost $1.095 million.

But the council could be facing $2.17 million over five years to resolve similar issues in other parts of the shire.

"As the assessment of the Mullumbimby sewer and stormwater catchment has revealed the poor condition of a large portion of the catchment … it is evident that other portions of the BSC network may be in particularly poor condition as well," the report said.

"This presents various previously noted risks … all of which have the potential to adversely impact on the public perception of (the council)."

The report said it was "strongly recommended" ongoing condition assessments be undertaken for the remainder of the sewer and stormwater systems in the Mullumbimby township.