Down in the dumps: Why this Pasadena home is slowly sinking
A home in the Mitcham Council area is sinking because it was built on top of a dump at the centre of a contamination probe. Now a report reveals what went wrong.
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A couple have had to repeatedly jack up part of their southern suburbs house which has sunk after it was built on top of a dump at the centre of a contamination probe.
But Mitcham Council denied responsibility for the dumping of rubbish at the property before the Pasadena house was built, according to a report.
The council is investigating potential gas and groundwater contamination from the former dump which received council-collected waste between 1959 and 1962 and was used as a private dump until the late 1960s.
The couple’s Quinton Court house was built in the late 1980s on top of domestic waste up to 12m deep, according to a preliminary site investigation by environmental consultants LBWCo for the council.
On April 30, LBWCo measured that the ground level below the house had dropped by 700-800mm below “the ground level present at the time the building slab was poured in the mid-1980s”.
“The (occupants) stated that significant subsidence has occurred beneath their property, due to settlement of uncontrolled fill and waste,” said the May 28 LBWCo report produced for the council.
“The eastern side of the dwelling has subsided due to the sinking of piers and has required the (owners) to engage engineers on multiple occasions to raise the dwelling to level, and pack the gap between the footing beams and top of piers.
“Sinking of piers suggested that the affected piers were not actually founded in rock and may have been (founded) on uncontrolled fill or waste.”
The report said 27 piers were to be installed into natural rock under the property at the time of construction due to the presence of “deep uncontrolled fill”, but that some piers may not have been drilled into rock.
“The (couple) stated that council at the time did not accept that domestic waste had been placed at the property on the instruction of council,” the report said.
The owners had claimed damages for the condition of the land but the Sunday Mail understands the council avoided liability.
No landfill gas assessment has been undertaken at the property, the LBWCo report said.
The majority of the former dump and quarry site is under land owned by developer Warren Masters. The couple’s Quinton Court home is also wholly within the former dump footprint.
Mr Masters paid $2.3m for his 1.4ha block at Port Lincoln Boulevard in 2008.
In April, The Advertiser reported Mr Masters’ claim that it would cost him at least $12m to rehabilitate his land.
Through Freedom of Information laws he had obtained an independent report from April 2020, sent to the Environment Protection Authority, which said there was potential risk to human health and groundwater from a range of chemicals.
Mr Masters wants the council to buy the site and turn it into a park, claiming it should “clean up the mess”. But the council had voted in confidence in March against such a move.
LBWCo undertook testing on Mr Masters’ property on May 22, with results showing elevated levels of carbon dioxide and methane in several wells in and outside of the landfill boundary – above EPA guidelines.
Mr Masters has been advised extra holes for environmental testing will be drilled into his property this month.
In a community notice issued this month, the council said sampling of new and existing groundwater wells and landfill gas bores had been completed.
“In the case of the Pasadena historic landfill, there is no evidence to date of landfill gas reaching the soil surface or impacting people’s homes,” the bulletin said.
“Additional indoor testing at some properties was recently undertaken … and once again, methane and carbon dioxide were not detected above background levels.”
Testing is expected to be completed by the end of the year.
The couple, who were approached through Mr Masters, declined to comment.