Ōhinemuri River: Preliminary results from orange sediment sampling expected in next 24 hours

Waikato Regional Council is still urging people to treat the Ōhinemuri River as contaminated. Photo / Davidda Hikatangata

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

The council’s incident response team was 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 historical mine shaft and entered the Ōhinemuri River.

The old mining shaft has been confirmed as the cause of the Ōhinemuri River turning bright orange.

Council 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 (DoC) had erected 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 carpark.

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

Water flowing from the mine on Saturday was running relatively clear, while there was still visible sediment which had settled in the stream and river in quiet locations or around rocks.

The council said there was heavy rain forecast this week and a lot of water was expected to flow from the surrounding hills into the Ōhinemuri River, which might trigger more flushing of the settled sediment down the stream and into the river.

People could expect to see more discolouration until all the sediment had been flushed out of the stream.

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.