Coates Engineering Solutions has designed and delivered a comprehensive water management solution in Baldivis, 46 kilometres south of Perth. This enabled lead contractor BMD Group to construct a new high-capacity wastewater pump station to service the growing community.
“Baldivis is a large and rapidly developing suburb. The wastewater pump station that currently services this area can’t keep up with growing demand,” said Coates Project Manager Paul Scott. “By constructing a new Type 350 station – to accommodate flows of up to 350 litres per second – Baldivis is upgrading this infrastructure to the largest capacity facility currently available in WA.”
The new pump station is being constructed on the site of a former wetland, which makes it prone to flooding in winter. Keeping the site dry was further challenged by excavating to depths of 8 to 16 metres across spans up to 34 metres, with the water table sitting just half a meter below the surface.
“Baldivis has a reputation as quite a swampy area, but as these stations rely on gravity to feed the pump, we need to dig quite deep in these adverse conditions,” said Jack Mears, Senior Project Engineer for BMD.
“These site conditions created a critical reliance on operational dewatering systems,” Jack continues. “If dewatering fails, it will lead to flooding or an imposed buoyancy force with the risk of damage to the project structures, making Coates’ solution paramount to the success of this project.”
During excavation, BMD encountered peat, clay, and fine silt in the soil.
“The ground conditions on site add another layer of complexity to excavation and water management and require additional measures to minimise sand ingress into the pumps,” said Scott. “With acid sulphate contamination present in the soils, all extracted water must also be treated before discharge.”
After treatment, all water must be discharged into a pressurised sewer main that the existing pump station also utilises. “To prevent exceeding the capacity of this line, there are restrictions on the amount of water that can be discharged over a set period,” said Scott. “This means adhering to strict water pressure parameters of 540 kPa and a flow limit of 26 litres per second, which required some innovative thinking and problem solving to achieve.”
With residential areas and abundant flora and fauna surrounding the new pump station, the project team must adhere to environmental standards and ensure that excessive water is not removed through dewatering.
Coates’ water management solution includes a system of continuous pumps to remove groundwater, an on-site water treatment system to meet the necessary environmental standards, and an automated pumping system to pump treated water back into the sewer main within the required parameters.
A standby pump remains on site to ensure redundancy in the discharge system. If the duty pump fails, water levels in a control tank activate the standby. This system is telemetry enabled, so Coates is notified to attend the site and investigate if a fault occurs and the standby pump comes online.
The dewatering system has successfully operated 24/7 since March 2023, and construction work is due to be completed in late 2024.
Specialists from Coates’ Water Management team attend the site daily to measure groundwater levels, perform water testing, monitor and deliver equipment, and check excavation abstraction flow rates across the site.
“BMD receives daily reports created by Coates in Procore, communicating all recent activity, including man hours, equipment utilisation, water test results and more,” said Scott. “This onsite monitoring and reporting allows BMD to confidently plan and execute construction activity around the amount of water each excavation produces. It also helps BMD to deliver on the project’s environmental and documentation requirements.”
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