Waikato Regional Council is expecting preliminary results in the next 24 hours from sampling of sediment that turned the Ohinemuri River bright orange on Friday afternoon.

The council’s incident response team were on site on Friday afternoon and Saturday, taking water and solid samples upstream and downstream of where a load of bright orange sediment was discharged from a historic mine shaft and entered the Ohinemuri River.

Regional Compliance Manager Patrick Lynch said it was appropriate to urge people to treat the discoloration as contaminated until sample results had been obtained.

“We only know what could be lingering inside a mine and that could include residual arsenic and heavy metals, so people need to be cautious and not touch any of the orange sediment that still may be lingering in the environment.”

The Department of Conservation has put up signs near the site, warning track users of potential contamination.

On Saturday morning council staff confirmed the discharge point of the sediment as an old mining asset above a stream opposite the Karangahake Gorge car park.

Council investigators and scientists were returning to the mine entrance again today.

Water flowing from the mine on Saturday was running relatively clear. There is still sediment that has settled in the stream and in the river in quiet locations or around rocks.

There is heavy rain forecast this week and a lot of water does come down the hills into the Ohinemuri River, so that may trigger more flushing of the settled sediment down the stream, into the river.  People can expect to see more discolouration until all the sediment has been flushed out of the stream.

Mr Lynch said council staff would now complete a thorough scene examination, including how the event occurred and what a “normal” discharge from the mine should look like.

The council will update information as it becomes available.

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