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The works primarily included the desludging of existing pond sludges, driving of piles and the installation of baffle curtain walls within the ponds, 17,000m3 of earthworks construction, and the construction of numerous pump stations, inlet screen structures and drainage lines.

A combined total of 27,000m3 of waste sludge was removed from the two ponds using our dredge and flocculation plant. Different dewatering methods were used at each of the sites. At Ngaruawahia, a temporary drying pond was constructed and the flocculated sludge was pumped into this temporary pond and allowed to dry through drainage and evaporation of the liquid. At Huntly, the sludge was pumped into geobags where it was dewatered for removal at a later date.

Collaborative Arrangement:

The project was constructed under an NEC3: Engineering and Construction Contract, cost reimbursable with a target outturn cost arrangement. Under these Conditions of Contract, the actual costs incurred to construct the works are paid to the contractor with a fixed margin. If the final contract value is less than the predetermined target outturn cost the difference is split 50:50 between the Principal and the Contractor. Similarly, if the contract value overruns the target outturn cost the overruns are split 50:50. This form of contract allowed scope for innovative ideas and methods to save cost, considered all stakeholder outcomes in an open forum and promoted a collaborative working arrangement.


  • Numerous changes to pipework details, and materials allowing simpler, more cost-effective construction.

  • Use of rock rip rap as wavebands on the pond walls in lieu of concrete.

  • Designed and built our own piling barge to drive the timber piles in the existing ponds.

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