Too much wastewater?

Sinclair Knight Merz (SKM), has helped a rural council in Queensland solve the problem of having too much water. SKM played a key role in the planning, design and construction management of a wastewater recycling scheme for Stanthorpe Shire Council (SSC). This project enabled treated wastewater to be pumped to local irrigators, providing significant benefits to the local environment.

Located near the NSW border, to the south of Toowoomba, the Stanthorpe township currently has a population of about 5500 residents, of which the homes for approximately 4500 are connected to the sewerage system.

Until recently, about 90% of the treated effluent from the town's sewage treatment plant (430 ML/year) was discharged to a local waterway, Quart Pot Creek. Faced with more stringent environmental legislation, SSC was going to need a major upgrade to this existing plant. However, the expensive upgrade (AU$4.75m) would have provided no guarantee of constant compliance with the required standards.

Fortunately, recent years have also seen a growth in horticulture around the township. A lack of regular rainfall meant that these producers were highly interested in finding a cheap and reliable source of water for irrigation.

With that, the Stanthorpe Water Reuse Scheme was born. Besides being value for money, the solution needed to be environmentally sustainable, legally sound and had to address the needs and concerns of community.

A plan was developed to pipe treated wastewater to 10 commercial horticultural customers after expressions of interest had been received from 17 parties. The selected customers were allocated quality quota based on investigations carried out by consultants from SKM.

On average, the volume of allocated wastewater accounts for about 93% of that produced by the township. In most years, 100% of the wastewater will be used.

A key aspect of the project was that while SSC would build the pipeline and pumping infrastructure to carry the treated water to the growers, these customers had to provide on-farm storage capacity equivalent to their entire annual quota.

This solved the problem experienced by similar schemes whereby customers only accept water according to their immediate needs.

This puts the onus of excess storage back on the treatment plant and increases both costs and the risk of overflow discharge during wet periods.

SKM's design allowed the bulk of the construction work to be carried out by the council's day labour force, providing further savings while capitalising on local knowledge and building a pool of skills.

Project manager Ralph Burch said the Stanthorpe Water Reuse Scheme shows what can be done by a committed Council taking an open-minded approach to design.

"The Scheme has remove the bulk of Stanthorpe's wastewater problem, whilst helping local businesses obtain an affordable irrigation solution," Mr Burch said.