Before the Tasman District Council (TDC) put out its tender for the Richmond Water Treatment Plant (RWTP) build, there was a lot that needed considering. PATRICK WATSON explains.
NOT ONLY WOULD the plant need to have a 50-year lifespan that would meet the drinking-water demands (and regulations) of one of the country’s fastest growing areas, but its build would have to incorporate a new water filtration technique.
The existing water supply system, which required considerable altering, would also have to continue to function for industrial and residential users as the construction went on. To top it all off, the build site for RWTP was a sprayed out boysenberry field with no direct road access.
Hawkins Infrastructure was eventually awarded the tender, but only after negotiating the total cost in partnership with the Council. The negotiation, which was necessary because Hawkins’ initial price exceeded available funds, saw TDC select a more cost-effective glass-fused steel balance tank, instead of a more traditional concrete tank as it originally wanted.
As a major player in the civil engineering space, Hawkins’ ability to overcome significant design changes and budget constraints put it in good favour with the Council. Hawkins currently has a reported annual turnover of around $500 to $600 million and a water project portfolio that includes, among others, the Greymouth Waste and Patea Water Treatment Plants, as well as the Riverhead Reservoir and Domain Watermain Project.
The other core member in the RWTP build is MWH Global, which designed the plant and helped supervise its construction. The total estimated project cost for RWTP now sits at $10.5 million, $7.5 million of which is construction related.
Ground first broke on the project in May 2014. Just over nine months later, the commissioning of the RWTP is underway and a seven-metre high, 18-metre diameter tank (capable of holding 1.5 million litres of treated water) is connected to three kilometres of pipework.
The full project should be complete at the end of July, after a three-month trial operation. In all, it will include a treatment plant building, reservoir tank and changes to the pipe network between the Waimea Bores and the new treatment plant.
Getting it to this point, however, has seen Hawkins work across three core sites and make use of seven subcontracting companies to deal with, among other tasks, earthworks, pipe laying, building, mechanical, electrical and tank work.
In its most basic form, the RWTP will allow the council to maximise how it manages its water supply, which will help accommodate Richmond’s population growth and provide greater security of supply in periods of drought.
The plant itself is designed to keep any operational noise within acceptable levels. The walls of the building have a textured surface to provide aesthetic interest and are screened by bunds approximately 1.5-2 metres high, to keep with the Lower Queen Street environment where it is located.
The Council’s project manager for Engineering Services, Chris Blythe, says Richmond has been supplied by two main bore fields and the supplies have been distributed separately, with one chlorinated and the other untreated. The RWTP will blend the two sources and treat them with UV light instead of chlorine.
“A key challenge was bringing two quite different water supplies into one treatment plant, owing to the chemical composition being different. Complex controls are needed to manage the flows from the different sources – pump speeds, blend ratios, etc,” says Chris.
The other challenge was the significant change to the reticulation network from two supplies to one.
“A large portion of the work was installing pipelines, large scale valve installations and deep trenching. The building and balance tank were the other main elements. The building contains high lift pumps, UV units, caustic soda treatment, emergency chlorine treatment, surge vessels, mixing units, and electrical-mechanical controls.”
Hawkins’ senior project engineer Thomas Maw says the three kilometres of pipework involved pipes of various sizes and types, with piping work beginning as far from the plant as possible, so as to tie in with the works at the plant site once ready.
“After the earthworks had been constructed, the slab, building foundation and building was erected. This is a tilt panel building that has considerable portal frame and bracing steelwork to meet level one earthquake asset specifications. The balance tank foundation was also completed at this point,” he says.
“The tank slab was constructed with no construction joints and in one pour to eliminate potential leak points.”
Another major phase was getting the process pipework right.
“[This] had been designed with no flexible couplings, dissembling joints or gibaults. Therefore the whole plant was hard piped and had to be perfect to ensure fit.”
For his part, the most challenging part of the project was integrating the existing infrastructure, which required proving the build approach in 12 carefully-considered and strategic stages. This approach was necessary to ensure Council buy-in and stop risk, as well as to enable minimal interruption to existing water supply or outages.
“Once commissioned, to start sending water to supply it had to be integrated, which significantly increased the risk and challenge of the task, but saved the client a significant portion of capital because we re-used infrastructure assets that were capable and would have otherwise become redundant and abandoned,” Thomas says.
The Hawkins team also had to take an innovative approach to research and development, in particular with how they achieved the exposed aggregate pattern on the pre-cast panels.
“As the exposed aggregate faces were on the face down site for the casting bed it meant that there was the need to develop an innovative approach to achieving a sharp edge to the exposed area and not having the retardant run or travel past this edge.
“We had to achieve this without reducing the cover to the steel reinforcing. The approach was to weld R6 steel rod to the bed to create the negative detail and an edge to the exposed area while stopping the retardant from running and affecting outside of this area.”
Thomas credits subcontractors Gibbons Construction with going the extra mile to ensure quality and testing out the different ideas around how to achieve the pattern.
The next phase of work is the commissioning and trial operation of the plant. Commissioning will take place between January and April and trial operations will start once the plant is successfully commissioned.
The project is on track for completion by the end of July.