Kopeopeo Canal, located near Whakatane in the Bay of Plenty region of New Zealand, was constructed to convey drainage and floodwaters from low-lying farmlands in the Rangitāiki Plains into the Whakatane Estuary.
Between 1950 and 1989, Kopeopeo Canal received discharges of surface run-off and stormwater from a sawmill operation. The discharge contained timber-treatment chemicals primarily comprising pentachlorophenol (PCP), which contained a small percentage of impurities including dioxins and furans, although this was unknown at the time. These discharges into the canal led to contamination of the canal sediments with dioxins.
Kopeopeo Canal supports a population of eel that is harvested by the local community for human consumption, and the presence of dioxins in the canal sediments represented a risk to human health and recreational use.
Bay of Plenty Regional Council undertook remediation of 5.1 km of Kopeopeo Canal, including dredging dioxin-contaminated sediments from the canal and containing the dredged sediment in Geotube® bags at two purpose-built containment sites. The containment sites were designed to provide for long-term containment and bioremediation of the dredged sediment.
Investigations between 2005 and 2015 estimated that between 30,000 m3 and 41,000 m3 of dioxin contaminated sediments would need to be remediated. The adopted remedial approach was selected following a consultation process with local stakeholders including Bay of Plenty Regional Council, iwi (Ngāti Awa), community organisations and government agencies.
A program of excavation, containment and treatment (bioremediation) was identified during the consultation as it addressed the human health risks, dealt with the issue locally and minimised the risk of transferring the problem to future generations. Dredging of the canal was also required for the operation of the Rangitāiki Drainage Scheme, which supports agricultural and horticultural production across the Rangitāiki Plains.
Golder supported the project with baseline environmental investigations for the containment site locations; geotechnical investigation, design, and construction phase services for the containment sites; and environmental monitoring and validation during the sediment dredging works.
Supporting the remedial contractor, our team prepared environmental and dredging management plans required as conditions of the resource consent. We also undertook environmental monitoring during placement of sediment in the containment cells, completed the sediment validation and prepared the final validation report for the sediment dredging remedial works.
At the completion of the remedial dredging and containment, approximately 37 000 m3 of dioxin-contaminated sediment had been removed from the canal and contained within the containment sites. We documented that the remediation project was successful in achieving the key project objectives for this phase of the remedial project established through the resource consent and in agreement with the wider project stakeholders, including the local community.
The remediated canal is now safe for recreational purposes. Eels (along with other fish species) were removed from Kopeopeo Canal prior to the remedial dredging works. As eel repopulate the canal and given residual dioxin contaminated sediment (below the remedial criteria) remains, further monitoring will be undertaken as part of confirming eel tissue is safe for consumption.
Golder is proud to have supported this project, which is one of the largest decontamination projects in New Zealand and will help to ensure a safer and healthier environment for the enjoyment of future generations.
The project won Best Regional Remediation Project in the 2019 Australasian Land and Groundwater Association awards.