FORMER COLONIAL ARMS COMPANY DUMP SITE

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During the works to build the Hamilton Ring Road at the Cobham Drive interchange, the construction team discovered small arms ammunition mixed with highly contaminated soil. 4Sight were required to provide technical contaminated land advice and support, and designed and led the investigation and remedial process from 2018 to 2020.

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Initial site investigations were conducted to support the resource consent process for the earthworks. These identified the potential for a range of contaminants to be present, including small arms ammunition associated with a former armoury, with all work proceeding under a Certified Security Management Professional.

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During the earthworks, a small arms ammunition dump was identified. On investigation, soils and fill material at this location also contained highly elevated levels of asbestos and heavy metals which had the potential to present a risk to human health and/or environmental receptors.

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The project involved addressing multiple issues associated with the soil contamination identified, including ordinance, asbestos and the treatment of heavy metal impacted soils prior to disposal, as well as ensuring a safe approach to both investigation work and remedial activities. This required close liaison with a range of specialists and stakeholders, including ordinance specialists and the NZ Police, local and regional Council, and contractors.

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The remedial approach involved the consideration of sustainability alongside practical considerations. The majority of contaminated soil and ordinance was removed under the direction of both ordinance specialists and Class A asbestos removalists, and this was followed by the implementation of long-term controls to manage contaminants remaining at depth (placement of geosynthetic clay liner and geofabric warning layer, prior to placement of clean cover). Remediation was conducted safety and successfully, with no health and safety incidents, and the remaining soils were considered highly unlikely to present a risk to human health or the environment following the remediation.