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Contamination outside project boundaries

In advance of physical works commencing, additional testing was carried out (in the first part of 2016) to confirm existing data on dioxin levels through sediments in the Canal and its tributaries just outside the project area and on canal stopbanks.

These test results indicate that contamination levels west of SH30 are higher than previous test results taken around ten years ago, with the highest result being 150 picograms per gram (toxic equivalents per gram of sediment). Some higher readings were also found within sediments located adjacent to the eastern end of the Canal in an adjoining wetland area.

The map below illustrates the location of the samples taken to the West of the project boundaries and the level of dioxin found at those sites. (click to see larger image)

comtamination outside boundaries - West

The map below illustrates the location of the samples taken in the Eastern part of the Canal and the level of dioxin found at those sites. (click to see larger image)

Contamination outside boundaries - east

The project team is investigating options on how to best address these newly identified areas and the first step is to carry out further testing and analysis to understand the extent of the issue. The Project is also discussing the results with the remediation contractors to ensure that the project area is kept clean before an appropriate solution is implemented in the extended area.

The area affected is outside the current resource consent boundaries and the deed of funding from the Ministry for the Environment. This means the new areas cannot be ‘added on’ to the current Kopeopeo Canal Remediation Project. The Project will continue within the original boundaries while further investigations and remediation or management options are considered.

It is important to note that while the results are higher than the in-canal remediation target (60 picograms per gram) they are not at the levels seen inside the project boundaries. Contamination levels in the project area range from 60 to 2300 picograms per gram. Recent analysis indicates that 86% of contaminant mass is located within the current project area so the existing project will get the bulk of the dioxins out of the canal and safely stored to be treated.

Kope Bulk Of Dioxin graph

(click to see larger image)

Why are the results higher?

The area west of State Highway 30 is a significant distance upstream of the historic sawmill’s stormwater outfall pipe, the known source of the dioxin contamination in the Canal. There are a few possible reasons why these new readings are showing higher contamination levels, but we can’t be absolutely sure.

  • Current sampling and testing methods are much better than they were 10 years ago
  • The cost of testing has also come down in recent years therefore more samples are taken even in locations not considered likely to be impacted. (This has proved to be true in most instances, with only two of twenty areas tested returning elevated results above the remediation target).
  • Tests in different locations to previous samples. Contaminant concentrations in the canal aren’t spread evenly and although we generally see diminishing concentrations further away from the original discharge point, there are also some ‘hot spots’. 
  • Salt water tidal flow up the canal may have moved some of the contaminated sediment further upstream, creating the higher results (the gates are currently being kept closed until we understand the situation better).

Elevated levels to the west of SH 30 could be due to any one of these factors or a combination of them.

These results have been added to the GIS information and maps which are updated on (you can find the GIS information under the Quick Links  menu on the right hand side of the Kopeopeo Canal pages).