Hornsby Quarry spoil upgrade commences

The plan to fill Sydney’s disused quarry with stone and spoil from the nearby NorthConnex motorway tunnel project was meant to take place more than a year ago.

However, despite these delays, up to one million cubic metres of spoil will fill the quarry between now and 2018, with 35 trucks scheduled to bring up to 700 m3 of materials per hour, starting from middle to late May. {{image2-a:r-w:300}}

Hornsby state MP Matt Kean told The Daily Telegraph the delivery of the conveyor belt, worth $9 million, is one of the final milestones before the quarry site starts being filled in. The conveyor belt, which was delivered in 40 pieces from Queensland, will be able to carry and unload up to 2000 tonnes of spoil per hour.

Paul Fletcher MP, the federal minister for urban infrastructure, added that once the conveyor is assembled, the “first stage of transforming the site into public parkland” can begin.

“Up to one million m3 of spoil will be used to help fill the quarry, so it can be transformed into a new public parkland for the community,” a NSW Roads and Maritime Services spokesperson also informed The Daily Telegraph. 

Site significance

As previously reported by Quarry, the Geological Society of Australia (GSA) had raised a number of concerns about plans to fill Hornsby Quarry from NorthConnex back in 2015.{{image3-a:r-w:300}}

According to Dr Ian Percival, co-convenor of the GSA’s NSW geoheritage sub-committee, excavation at the quarry in the 1960s and 1970s revealed a geological phenomenon known as a diatreme. This feature, which is believed to date back to the Early Jurassic period about 200 million years ago, formed from an unusual type of volcano known as a maar-diatreme.

The quarry site occupies an area of 23ha and has been in disuse since the late 1990s. According to the Hornsby Quarry land filling preliminary impact assessment, it is ‘well known’ as the largest volcanic diatreme in the Sydney area.

However, the impact of filling the quarry on the diatreme was assessed during the environmental impact statement (EIS) as not ‘significant’, despite the EIS also stating the “environmental, social and economic assessment undertaken identified that the proposed works result in several significant risks, even after the implementation of appropriate mitigation measures”.

The GSA disagreed with the EIS, arguing in a submission that the report was ‘inadequate, incorrect’ and “undertaken by consultants with limited geological knowledge”.

Sydney geologist Dr John Byrnes recently told The Daily Telegraph that the plan to fill the quarry will “largely obliterate this feature of state, national and arguably global significance”.

As part of the project, photos of the diatreme will be taken after the dewatering of the quarry and given to Hornsby Shire Council. In accordance with the EIS, the spoil fill will cover “sections of the geology” but not “physically damage the diatreme”.

NorthConnex is responsible for the construction works, and Hornsby Shire Council has allocated approximately $52 million for the project. To date, approximately 700,000m3 of an expected 2.25 million m3 of spoil has been excavated from the NorthConnex tunnel.

More reading
Spoil management project set to begin at Hornsby Quarry
Quarry rehab gets environmental green light
Spoil to fill quarry void from October
Geologists lobby to preserve quarry rock formation
EIS released for quarry spoil management project
Spoil deal to transform quarry in six years

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