Waiouru water clear of ash probiems

Ruapehu Bulletin, Volume 13, Issue 609, 24 October 1995, Page 5

Waiouru water clear of ash probiems

By

Michele

Monaghan

Ash fall in the Waiouru area hasn't had a great effect on the Waiouru water supply according to water technician Terry Gray. "Ash fall in the Home Valley catchment area has been minimal," Mr Gray told the Bulletin. "It hasn't become necessary to alter the chemical dose rates. The ash is not very toxic at all. It acts as a pH depressant." He said the ash is basically acidic with a pH of about 4. The human stomach has a pH of 4.3, while Waiouru drinking water has a pH of between 8 and 8.5. Heavy ash falls in the Waiouru area recently blan-

keted the military camp and surrounding businesses, but the water treatment plant escaped most of it, probably because of its protected location. 'The turbidity test on the water has been pretty good lately, well within the New Zealand drinking water standard," Mr Gray explained. A turbidity test measures the passage of light through the water as it reflects off possible contaminants. "We could have one kilogram of ash per cubic metre of water and still be well within the New Zealand drinking water standards," Mr Gray said. Catchment water is tested once a

day, although when Mount Ruapehu first erupted in September, checks on the Home Valley stream were carried out every two hours. "We do a daily test any way, so the daily regimejustcontinues," MrGray said. Waiouru water is treated with aluminium sulphate and polymers that form a floc blanket to filter out impurities. In addition the water is put through a sand filter. Fluoride is added as is caustic soda when pH correction is necessary. When it turns up in your taps it contains a chlorine residual that keeps the purification process going, Mr Gray said.