Coates keeps former wetlands dry to construct critical wastewater infrastructure

Find out how Coates' solution facilitated construction of a new high-capacity wastewater pump station in WA

 

The project

Significant work is underway across Western Australia to upgrade the state’s wastewater infrastructure. This includes the construction of a new high-capacity below ground pump station in Baldivis, 46km south of Perth, to meet the current and future needs of this community.

“Baldivis is a large and rapidly developing suburb and the wastewater pump station that currently services this area can’t keep up with growing demand,” says 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.”

Coates was engaged by lead contractor BMD to design and deliver a comprehensive water management solution for 6 major excavations on site. Work began in March 2023 and is due for completion in late 2024.

The challenge

Keeping the site dry

The new Baldivis pump station is being constructed on the site of a former wetland, making it prone to flooding in winter. Keeping the site dry was further challenged by the need to excavate to depths of 8m-16m, across spans up to 34m, 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,” says Jack Mears, Senior Project Engineer for BMD.

“These site conditions created a critical reliance on dewatering systems being operational,” Jack continues. “If dewatering fails it would lead to flooding or an imposed buoyancy force with risk of damage to the project structures, making Coates’ solution paramount to the success of this project.”

The pump station sits on the site of a former wetland which presented challenges for excavation

Ground conditions

During excavation BMD encountered peat, clay and fine silt in the soils.

“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,” says Paul. “With acid sulphate contamination present in the soils, all extracted water must also be treated before discharge.”

Water discharge

After treatment, all water must be discharged into a pressurised sewer main that is also utilised by the existing pump station. “To prevent exceeding the capacity of this line there are restrictions on the amount of water that can be discharged over a set time period,” says Paul. “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.”

Environmental impact

With residential areas and an abundance of 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.

The solution

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.

To ensure there is always redundancy in the discharge system a standby pump remains on site, activated by water levels in a control tank if the duty pump fails. This system is telemetry enabled, so if a fault occurs and the standby pump comes online, Coates is notified to attend site and investigate.

To implement this solution, Coates supplied:

• 10 submersible pumps for water extraction (including 4 on standby)

• 4 sediment tanks for water filtration

• An on-site chemical treatment plant to balance pH

• Two high pressure pumps and control tank for automating water discharge into the sewer main

• The construction of 3 new bores for daily groundwater monitoring

Coates' solution allowed water to be removed, treated on-site and then discharged into the sewer main

The impact

Coates’ dewatering system has successfully operated 24/7 since March 2023. To support this solution, specialists from the Water Management team attend site daily to measure groundwater levels; perform water testing; monitor and deliver equipment; and check on 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,” says Paul. “This on-site monitoring and reporting allows BMD to confidently plan and execute construction activity around the amount of water that each excavation is producing. It also helps BMD to deliver on the project’s environmental and documentation requirements.”

Coates’ comprehensive solution is backed by quality customer service, deep industry expertise, innovation and accountability, providing additional assurance to BMD.

“We have found Coates to be approachable, quick to respond and transparent about the service they provide,” says Jack. “With a large equipment requirement, having a Coates branch nearby and support available at short notice has also helped to keep work moving. In particular, as project manager Paul has committed a lot of his own time and made himself available to assist with problem solving and brainstorming, which our team has valued.”

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