Royal Far West Manly Dewatering

NPE was awarded a dewatering and water treatment project to facilitate construction activities. To manage this project effectively, the temporary groundwater level beneath the basement has been set to 1.0 m below the proposed bulk excavation level, resulting in a level of 3.0 m during the excavation and dewatering processes.

Maintaining this lowered groundwater level will yield a maximum inflow of 71 L/sec. Over the first year of construction, the total predicted inflow is estimated to be around 1699 ML.

The dewatering strategy being implemented is Deep Well Dewatering, preceded by a preliminary assessment of water quality and accompanied by a treatment system before discharge into the stormwater system.

Deep Well Dewatering involves the excavation of deep wells in soil or rock, particularly when significant volumes of groundwater need to be pumped from considerable depths. The configuration of the deep wells—number, depth, and spacing—along with pump capacity, will depend on specific site conditions. This method is recognised as a cost-effective and efficient solution for dewatering larger projects with excavations exceeding 4 meters, compared to a wellpoint system.

As part of the project, NPE will focus on treating for pH, turbidity, heavy metals, and contaminants.

NPE will establish one large upfront holding tank, chemical dosing pods and secondary holding tank. NPE will also establish a multimedia filter, continue to a subsequent holding tank, and specialised in-house designed and manufactured Multi-Media Filtration Units (MMFU’S). The treated water will be collected in one last holding tank for testing prior to discharge, with all equipment outfitted with appropriate PVC piping and fittings, as well as a discharge flow meter.

Our proposed setup aims to effectively manage heavy metals, with a primary focus on pH, turbidity, and contaminant levels.

Groundwater quality assessment and water treatment setup for holding tank discharge, involved a trial run where water samples are taken for NATA lab analysis, alongside continuous online monitoring of pH and turbidity.

Our scope includes Weekly testing to sample post-treatment water and assess water quality through laboratory analysis. Regular daily site monitoring which includes checking the pumping installation, adjusting pump timers based on water table levels, refilling chemicals, and making necessary adjustments. Additionally, sludge build-up in decantation tanks will be monitored, and sludge will be transferred to a designated sludge tank. Sludge will be removed off-site through decanting using specialised vehicles.

Due to the strict timelines and dynamic site environment, NPE has worked in partnership with the client across all aspects of the project from project management, commercial and contract management, to technical design, and made necessary adjustments to our scope to date, with the project expected to complete on schedule in December 2025.