Toxic Truth: Cap on contaminated soil too shallow for trees

2013: Remediation of the old Pasminco lead works site at Boolaroo.  Robert Simmons who works for Pasminco, and a weather station on a hill next to the  containment cell under construction. Picture: Max Mason-Hubers
2013: Remediation of the old Pasminco lead works site at Boolaroo. Robert Simmons who works for Pasminco, and a weather station on a hill next to the containment cell under construction. Picture: Max Mason-Hubers

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TREES are banned from Pasminco smelter’s contaminated soil hill because a reduced soil and membrane ‘‘cap’’ is so shallow that roots could breach it.

Lake Macquarie Council has raised concerns about how goal posts, lights and amenities buildings will be established on the 6.5 hectare hilltop that’s earmarked for playing fields and open space, when the ‘‘cap’’ is less than one metre below the surface in places.

The council has also raised concerns about long term management of the 1.9 million cubic metres of contaminated material in the hill after reports a revised ‘‘cap’’ ‘‘will require additional quality control during installation and may have long term maintenance issues’’.

The ‘‘cap’’ comprises 150 mm of topsoil, 600 mm of subsoil, a 10 mm gravel drain and 1 mm linear low density polyethylene liner, 100 mm of clay with a metre of sub-base below it.

An earlier plan for a 600mm clay layer was reduced to 100 mm of clay, along with the polyethylene liner, because Pasminco administrator Ferrier Hodgson was unable to source enough clay.

The reduced ‘‘cap’’ was approved by the Department of Planning under delegation in August 2012. In February that year the council did not object to the proposed change, but questioned the visual impact of a prominent hill with only low shrubs.

‘‘It is council’s understanding that trees will be precluded due to the potential for their root systems to breach the capping layer and infiltrate the encapsulated contaminants,’’ the council said.

In December 2012 the department approved a 450,000 cubic metre increase in the amount of contaminated soil in the hill, after Pasminco and Incitec Pivot agreed to undertake a consolidated remediation of the entire former Pasminco lead smelter site.

Incitec Pivot manufactured superphosphates from a site within the Pasminco site.

One year later, in December 2013, the department approved another 250,000 cubic metre expansion of the containment cell within the contaminated soil hill, after surveys found former dams on the site had been backfilled with contaminated soil.

As the amount of contaminated material within the containment cell increased from an approved 1.1 million cubic metres in 2007, to 1.59 million cubic metres in 2012, and 1.9 million cubic metres in 2013, the height of the hill increased from 34 metres to 42.15 metres, and the size of the open space on top of the hill reduced from 11.9 hectares to 6.5 hectares.

In a letter to the department in February 2012 accredited site auditor Graeme Nyland said he expected his role would include ‘‘monitoring of potential leaking from the containment cell as part of the overall site groundwater monitoring’’.

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