Wastewater project will be the biggest ever undertaken

At a cost of more than $21 million, the massive upgrade of the urban wastewater treatment plant stands as the biggest project in Masterton District Council's history. But how will it be done? JAMIE MORTON talks to the man behind the plan - assets and operations manager David Hopman. 
 
t some point in the near future, in a paddock about 5km east of Masterton, a crater will appear.
Beavering away in this crater will be three or four huge dam-building trucks, digging out one of seven large oxidation and maturation ponds to treat and store the millions of litres of wastewater that arrives daily to the town's urban wastewater treatment plant.
Standing in what will be the centre of this vast pit, David Hopman could already visualise the works happening around him.
"I can see people sitting up on top of Lees-Pakaraka Road and looking down into this big Legoland."
It was a little under a year ago that Mr Hopman took over the project from former council assets and operations manager Kevin Montgomery, who had helped shape the project over the past decade.
"Kevin left me quite a few memos about it," Mr Hopman, who fortunately has had plenty of experience in the design and project management of wastewater plants both in New Zealand and the UK, said.
The Homebush site, which is locked to the public and lies on about 42ha of flat land, has housed some form of wastewater facility since the turn of last century.
Masterton's first municipal septic tanks were constructed in 1900, and then an oxidation pond system originally comprising two primary ponds and one secondary pond was constructed and commissioned between 1970 and 1971.
The latest upgrade was in 2003, when the council was granted interim resource consents to undertake an initial upgrade of its system.
The year after, the council bought 91ha of land to create the space to upgrade the oxidation ponds and develop a border-dyke irrigation land treatment scheme.
Then in 2007, another 107ha chunk of land adjacent to the site was bought for the future disposal of wastewater to land, but since the council at that stage did not know how much of it would be used, the land was leased back until 2010.
Later that year, councillors approved the current proposal, which will see the construction of seven ponds on the 91ha site, the emptying and land filling of the existing sludge-bottomed ponds and developing a land treatment system on part of the 107ha site.
The land not used will be available for further treatment if it's needed, Mr Hopman said.
The design and clay lining of the new ponds meant they would not have the same leakage problems as the old ponds, which need special protection against erosion and flooding.
Today, each time a Masterton resident uses their toilet, their waste travels a few kilometres to the plant's step screen, which on average filters around 16 million litres of effluent each day before it reaches the ponds.
The first step of the upgrade will be to replace the screen with one slightly bigger, and then move it and a nearby building along about 100 metres to make way for one of the large primary ponds.
The council expects that once the upgrade is finished, 40 percent less treated effluent will reach the Ruamahanga River, which today has treated wastewater discharged into it via the Makoura Stream at rates generally proportional to the inlet flows.
In scientific terms, the 40 percent reduction will slash the total phosphorus load on the river from the plant to less than 5 percent, down from a maximum of 8 percent.
More significantly, the upgrade will reduce the peak phosphorus load on the river during periods of low flow from 43 percent to less than 3 percent, meaning less potential for algae growth.
Under the upgraded system, summer discharges would happen only during freshes - or when there are "sustained flows" above median flow - while discharges in winter would happen only when flows are above half median.
And when discharge does occur, it will be at a controlled 30-fold dilution rate through a rock diffuser lying on the bed of the Ruamahanga.
When it's not possible to discharge the wastewater, it will be either stored in one of the large maturation ponds or treated on land.
Grass grown on that land - which would be levelled and formed into strips, with water flowing down the lengths - is planned to be harvested five times a year and sold as baleage.
More recently, the council has been looking at other ways to both make money from the wastewater and divert it from the river.
Neighbouring farmer David Holmes has proposed the building of a reservoir to store the wastewater before piping it to farmers, vineyards and other users.
Mr Hopman said while there had been plenty of interest from farmers keen to use the effluent to irrigate their properties, the big question remained unanswered - who would pay for it?
"Will the ratepayers pay for it, or will the farmers? That's what we're looking at the moment."
A few rivers stand in the way between the plant and farms in Taratahi - and then there were other problems around the route it would take to get there.
"On paper it might only look like it would take 2.5km to get to a farm, but if it can't go straight to it and has to follow along the route of a road, it ends up being 3.5km and then 4km. At the end of the day it's going to be pretty expensive. So it all comes back to the question, who will pay?"
In the mean time, the council is preparing to argue its case against several appellants, some who have specific technical issues with the proposal and some who are against any discharge to the river and oppose it outright.
The council has made its own appeals on the decision, mainly relating to some imposed monitoring conditions it doesn't believe are necessary.
Depending on when those issues can be resolved - it's hoped that will be done in mediation next month and not through a costly Environment Court battle - the upgrade will be carried out over what Mr Hopman calls a "series of summer campaigns".
The cost of the loan-funded project will be paid off over its 25-year resource consent period, but will still hit rates hard over the next three years.
Rates hikes of 9.6 and 10.1 for 2010-2011 and 2011-2012 respectively have been projected.
"All in all, it's going to be the biggest project in terms of cost we've worked on. I've been told it will be about four times the size of the rec-centre project."
But with all the work and money that will go into it, the plant upgrade will patch up only half Masterton's urban sewer woes - another costly and ongoing battle is how to solve the headache of widespread infiltration and inflow into the town's sewer system.
Infiltration into the system, which is at its worst when rainfall and groundwater levels are high, means the average flow into the plant is much higher than one would expect from a township with a population of nearly 18,000 people.
Like the treatment plant, the history of Masterton's sewer network goes back a century, and much of the old pipes will need repairing or replacing.
The total cost of fixing the public part of the network is expected to cost four times the amount of the plant upgrade at $80 million, while the private sections of laterals are estimated to cost a further $35 million.
To complete enough repairs in the network to stop all discharges into the river, it would cost about $50 million.
"Accordingly, replacement of the sewer network is not affordable for the community," Mr Hopman said.
"However the council is committed as part of its ongoing asset management strategy to progressively upgrade areas of the reticulation system that are significantly under-performing in terms of infiltration and inflow."
At the moment the council has locked in about $15 million in its just-finished 10-year plan towards investigations, renewals, maintenance and capital works on the network over the next decade.
"Extensive work has already been undertaken by the council to identify the area of the network that require upgrading or repair. These areas have been categorised in terms of severity and are being scheduled into the ongoing programme of works."