Water Main Installation in the Town of Bassendean

DM Civil engaged NPE for the installation of approximately 90 meters of new water main in the Town of Bassendean, a project that required extensive dewatering, water treatment, and environmental management. The work involved tunnelling a sleeve from Ashfield Reserve under an existing rail line and two busy main roads, ultimately emerging at Railway Parade. To facilitate this, three drill/receival and connection pits underwent dewatering, utilising wellpoint spearing methods to achieve an aquifer drawdown of 3 meters at each location. This ensured a continuously dry invert work area throughout the project duration.

The management of dewatering effluent was critical, necessitating adherence to strict water quality criteria. Initially, water extracted from dewatering underwent pH adjustment through a Caustic Dosing Unit, raising its pH from 5.6 to a range of 7.2 to 7.8 to precipitate dissolved metals like iron and aluminium. The treated water was processed through a Lamella Clarifier, where insoluble metals settled and were collected. Thickened sludge from the clarifier was subsequently drained into Intermediate Bulk Containers (IBCs) and transferred to a secondary clarifier, with an automatic submersible pump facilitating the process. This included the injection of Polyacrylamide 910 solution, which enhanced sludge density and allowed for the effective separation of supernatant for recycling.

Additionally, the Metal Removal Module (MRM) played a crucial role in ensuring that water quality met environmental standards. Water was pumped through the MRM, where liquid chlorine was injected to facilitate the oxidation and precipitation of metals. Target levels for iron and aluminium were achieved before the safe discharge of treated water into the storm drainage system. The MRM underwent hourly backwashing to clear out residues, which were collected for additional sludge thickening, reinforcing a comprehensive approach to waste management.

Overall, the successful execution of this project not only improved the local water infrastructure but also demonstrated a commitment to sustainable environmental practices.