Nelson City Council is urgently investigating the extent of contaminated material found after routine testing of sawdust at the Tāhunanui Back Beach area.
In the 1960s, sawdust material from a local timber mill was used in this area as fill for the raised carpark. Over time, erosion has left this material exposed.
Group Manager Community Services Andrew White says last July, a decision was made not to remove the material.
“We understood it was not considered a pollutant to the beach and inlet and would break down over time. We were also concerned that removing the sawdust would hasten the erosion occurring in the area. However, we took the prudent approach to continue to monitor the erosion of the material and regularly test for contaminants.
“Our monitoring recently discovered that there were offcuts of sawn timber in the mix of eroded material. We tested the sawdust, and this testing has confirmed that some of the sawdust originated from pieces of timber that had been chemically treated with a preservative to prevent them from rotting.”
The contaminant concentrations are on average below the applicable human health protection standards for recreation land use, meaning it is considered unlikely that the exposed material will pose a risk to human health. However, the concentrations of arsenic, chromium and copper exceed the ANZECC sediment quality guidelines that assess potential risk caused by the erosion of the material into the marine environment. This means the material may represent a risk to the environment.
“We are now going to excavate pits across the area to determine how widespread the chemically-treated offcuts are throughout the filled area, and this will determine our next steps. Depending on the results of this investigation, it is quite possible that we will need to remove some or all of the filled area,” says White.
While excavations take place, the raised carpark at the Back Beach will be closed from Wednesday 14 June until Friday 16 June. We recommend that you use other carparks such as those near the Skating Rink if you are heading to the Back Beach while this work is underway.
The front face of the carpark is already taped off because of the risk of collapse due to erosion, but please keep away from the area. We know the Back Beach is a popular dog walking area and we ask that you please keep your dog away from the area as well.