Innovative Solutions to Multiple Project Challenges - Connecting a Satellite Wastewater System

Currently, wastewater from Ashhurst is treated at the Ashhurst wastewater treatment plant and then discharged into the Manawatu River. With the discharge consent of this plant expiring shortly, Palmerston North City Council identified efficiencies in diverting the Ashhurst wastewater system to the Palmerston North wastewater treatment plant. An additional advantage to this connection is that it will pass through and could provide service to the Whakarongo residential growth area, located 8 km from Ashhurst.

This paper looks at the challenges faced in designing the connection between the two systems and the innovative design implemented to overcome these challenges. By making use of existing Ashhurst oxidation pond infrastructure, risks associated with multiple design issues were mitigated.

In undertaking the design, three key variables were identified, each having multiple options. The variables were the route of the proposed rising main, the Ashhurst pumping regime and how the system incorporates the Whakarongo growth area. This resulted in a total of 18 combined options which were assessed using the Net Present Value method. Considering the existing ponds at Ashhurst, the new pump station and also the delivery pipeline as a single system instead of individual components allowed the team to select a design that best suited the community’s needs at the lowest whole of life cost.