Whangaehu naturally acid

Waimarino Bulletin, Volume 6, Issue 251, 19 July 1988, Page 2

Whangaehu naturally acid

Water in the Whangaehu River is more acidic than the Karioi Pulp mill effluent that pours into it.

The Central Districts Catchment Board monitor the river and have found the river water has a pH level of 3-4 both above and below the effluent outfall. Effluent from the mill has been tested and found to be neutral. The findings follow complaints from a party of canoeists who ran a camp at Crozier's Bridge earlier this year. Two of the canoeists fell ill after being on and in the river and complained to the catchment board about

the mill discharge, believing it to be the cause of their illness. "Swallowing water of three to four pH acidity would not do you any good," said Catchment board officer Morrie Holland. He said swimrning pool water has a recommended minimum pH of 6.4. The more acidic a substance is the lower the pH number. Pure water is pH 7. The acid content of the river comes from the Ruapehu Crater Lake outfall.

"There is a terrific variation in the lake's acidity which is tied to volcanic activity," said Mr Holland. High rainfall down river of the lake would dilute the acid and thus also vary the river's acidity. Asked about claims by Karioi staff that the mill effluent was cleaner than the river, Mr Holland said:"I don't know about that but the acidity levels are definitely better. The effluent is fairly inert but we are monitoring it and we've asked them to improve their effluent." "They've spent large amounts of money to improve the effluent," he said. Before it reaches the

river the effluent passes though a settling pond to remove the solid material and then an aeration pond to oxygenate the water. Pulp Mill staff have said this oxygenation of the effluent actually improves the river. Mr Holland said Winstones are working on finding the cause of the bright o r a n g e colour of the effluent.

He said while it seems to be harmless the board has asked them to investigate the cause. Neither the board nor the mill know what the cause might be. The colour only affects the river down stream to the road bridge and is then dis.sipated into the milky coloured river water.