Mardi Water Treatment Plant upgrade

Project overview 

Central Coast Council’s Water and Sewer team are working with our contractors to deliver an $82.5M upgrade to Mardi Water Treatment Plant.

The NSW Government provided $6.85M through the Safe and Secure Water Program along with over $75M from Central Coast Council.

The Mardi Water Treatment Plant typically provides around half of all drinking water to the Central Coast, future proofing this asset and ensuring it can continue to deliver safe and secure water to our customers is a key priority.

Once finished, Mardi Water Treatment Plant will be able to treat up to the equivalent of 64 Olympic-sized swimming pools, providing drinking water for over 210,000 homes and businesses across the Central Coast region and the lower Hunter.

Project snapshot

• The upgrade will establish the facility as the principal drinking water supply for the Central Coast, meeting demands of a growing population and increasing water security
• Mardi WTP currently treats raw water via direct filtration. Advanced clarification technologies including dissolved air filtration (DAF) will improve the plant’s capabilities
• Mardi WTP was built in 1982, with the last major upgrade in 1992 to increase capacity
• Major works are scheduled for completion by the end of 2026
• Central Coast Council has invested over $75M towards the project, with $6.85M from the NSW Government’s Safe and Secure Water Program
• Design and construction of the project is being delivered by Abergeldie Contractors Pty Ltd.
   

Project details

Why is this project happening?

Mardi Water Treatment Plant currently treats water via direct filtration, meaning water from our catchments is fed directly to the filters following coagulation and flocculation. The latter processes create flocs, which are later removed in the filters. If the level of suspended solids in the raw water is high, the flocs can block the filters, reducing filter runtime and the plant’s overall capacity to produce water. In this way, the treatment process is affected by environmental factors such as storm events and algal blooms which can lead to the deterioration of raw water quality entering the plant, putting pressure on the filtration system.

As certain water quality risks and regional demands increase, and to optimise the efficiency of water storages for the future, Mardi Water Treatment Plant requires upgrades to ensure it can still produce up to 160 million litres of water per day into the future under all projected raw water quality conditions.

Project scope – what are we doing?

The Mardi Water Treatment Plant upgrade includes targeted improvements to core treatment processes and supporting infrastructure to:

• introduce Dissolved Air Flotation (DAF) clarification to improve turbidity and algae removal during poor raw water conditions
• upgrade coagulation and polymer dosing systems to enhance particle removal and overall treatment efficiency
• expand the use of powdered activated carbon (PAC) to improve removal of taste and odour compounds
• strengthen treated water disinfection through improved chlorine contact time and dosing control
• improve operational reliability and flexibility during algal bloom events and variable raw water quality
• construct a new access road, electrical switch rooms, sludge lagoon outlet and upgrade of existing treatment plant facilities.

The existing water treatment plant will continue operating safely while construction is underway.

What is the current status?

• DAF concrete structure complete; mechanical and electrical installations are underway
• New chemical dosing systems will be completed in mid-2026
• Baffle installation and existing asset refurbishments are complete 

Completion of the Mardi WTP upgrade project is expected by the end of 2026.

Water supply impacts?

Most of the time, the existing water treatment plant will continue operating safely while construction is underway.

Earlier in the project, four extended plant shutdowns were completed successfully with no impact on customers due to alternative sources of drinking water.

In this final year of the project, minor plant shutdowns presenting lower risks of water supply interruptions will still be required. Should there be an interruption of water services, we will ensure customers are informed in a timely manner.

Key upgrade details 

The key component of the upgrade is the addition of a Dissolved Air Flotation (DAF) clarifier along with new flocculation tanks. The DAF process uses a saturated air stream to generate bubbles which attach to flocs and bring them to the surface. The flocs are then skimmed off the surface using a mechanical scraper system.

The DAF clarification system will improve the plant’s performance in poor raw water conditions by removing suspended particles significantly reducing the turbidity of the raw water. The DAF is also the most robust system for algae removal, allowing Mardi Water Treatment Plant to continue treating water from Mardi Dam during algal blooms, rather than sourcing water from the region’s drought contingency storage.

Works will also include the conversion of the coagulant used to create flocs from Aluminium Sulphate to Ferric Chloride. This includes upgrades to the storage, delivery, and dosing system. Using Ferric Chloride will decrease the levels of Total Organic Carbon (TOC) in the water, improving flexibility to manage disinfection residuals in the network, reducing the risk of bacterial contamination and the need to re-chlorinate. A new Cationic Polymer dosing system will work in conjunction with the coagulant to maximise efficiency.

A new PAC storage and dosing facility will also be constructed, and the existing flocculation tanks will be repurposed as Powdered Activated Carbon (PAC) contact tanks. This will improve the plant’s ability to remove taste and odour compounds that can occur in the raw water.

Baffles and a trim chlorine dosing system are being added to the existing clearwater tank, which stores treated water before being distributed to the water supply network. The addition of baffles will increase chlorine contact time, allowing for more effective disinfection of water and increasing the safety of drinking water distributed to customers.

The upgrade will also involve a new access road, electrical switch rooms, sludge lagoon outlet structure and the refurbishment and upgrade of existing facilities at the treatment plant.

Project timelapse video