Big dig inches closer to softer water

Exploratory drilling has raised hopes that significant supplies of better ? and softer ? water for Wanganui city are on the city's doorstep.
And if initial samples are a reasonable guide, delivery and treatment of the water will not be significant budget issues for the Wanganui District Council.
Julian Rewiti, council's infrastructure manager, said the drilling just completed next to the Westmere reservoir has indicated softer water in the aquifer the drilling was targeting.
Mr Rewiti said the water samples carried about 100 parts per million of calcium ? about half the reading which is common to the bulk of the city's current supply from the Kai Iwi bores further inland. It's calcium that creates one of Wanganui's bugbears ? liming of appliances, especially water heaters ? and hardness.
He said the drilling was showing that the further away from Kai Iwi that they tap into the aquifer, the better the supply. The downside is it's at greater depths.
But given the find next to the reservoir on Great North Rd, the drilling programme has shifted to a site at the Springvale end of Tayforth Rd. Drilling is under way and is expected to take about eight weeks to complete.
Mr Rewiti said seismic surveys over half a kilometre established that the aquifer being drilled into now was the same one that Kai Iwi draws from as well as Aramoho and Lenihan St.
"We'll have to drill down to about 700 metres but we're sure that the water we'll find there will be of similar quality to what we've got at Aramoho," Mr Rewiti said.
"We've got to balance the treatment costs and where the existing reticulation is and we believe where we're looking now we'll find it."
The Aramoho bore, tapped into about three years ago, is supplying parts of that suburb and some users across the Whanganui River in Wanganui East. It delivers potable water of 50 parts per million of calcium and is much softer than what the rest of city residents have to put up with.
Mr Rewiti said some treatment is required of the Aramoho water because of its ammonia content. But mixed with the city supply it provides good, drinkable water and even mixed with the city supply, it is still much softer.
The Lenihan St bore in Wanganui East is soft but hot, shows "lots of colour" and needs treatment. "It can be treated but it would cost a lot of money and then only be helpful to part of our water supply system anyway," Mr Rewiti said.
Drilling to date has followed a line that runs from Kai Iwi bores to Lenihan St but they made a decision to branch off at Westmere.
"We found the water getting softer as it moved toward the river and assumed the same would apply toward the coast. So that's why we went at right angles and went to the Westmere reservoir site," he said.
It's not just the hunt for soft water either. The council is anxious to find other sources as its three ageing Kai Iwi bores are nearing their "use by" date. The No 1 bore is "in a really poor condition."
They were commissioned in 1960 and while treatment of that supply is minimal, the problem is "it's so far away" from the city. In recent years pipeline failure and repairs have been costly.
Those hoped for new "finds" may not be able to supply all that the city needs, but Mr Rewiti said it is possible to "blend" water from different sources, to at least take the hard edge off it.
And blending would require a much smaller ? and cheaper ? treatment plant.
In terms of volume, the aquifer will provide plenty. Ultimately council may be looking at three or four bores through the area its researching now, put down of a period of 10 to 15 years. The water can be blended with the existing supply and may eventually stand alone as the city's main supply source.
"We definitely know that we don't need a full scale treatment plant in terms of a full scale water softening, because that's what the treatment plant would have been for. "What we can do here is kill two birds with one stone. It's about securing our source and minimising costs involved in softening the water."
+ Wanganui Mayor Michael Laws said "hard" (limey) water cost Wanganui residents and businesses over $3 million a year. A supply of soft water could cost urban households a surcharge of $70 a year and save them an average of $150 a year on replacing hot water cylinders and using less energy, soap and detergent. Residents voted to research soft water options in the 2006 council referendum. The options would be presented to the public at the 2007 referendum, so that they could make final choices.