Cromwell Geobag Removal and Pond Desludging

The Central Otago District Council is inviting proposals from experienced and qualified contractors for desludging two oxidation ponds at the Cromwell Wastewater Treatment Plant (WWTP). The scope of work covers: • Removal of the existing sludge stored in Geotextile bags (Optional Separable Portion) • Design of a sludge removal methodology, dewatering basin and monitoring programme • Desludging of the two oxidation ponds • Dewatering of the dredged sludge using suitable technology This procurement specifically covers the desludging and dewatering components. Disposal of the dewatered sludge and the new geotextile bag are excluded from the contract works. Desludging is a routine but infrequent maintenance activity essential for maintaining the treatment. The Cromwell ponds have been desludged previously in 2017. Further sludge surveys were conducted in 2026 and confirmed the need for intervention. For more info, see RFP document