Construction of the Water Treatment Plant
A Water Treatment Plant (WTP) was constructed to remove contaminants from water during the remediation. After treatment, the water was discharged to the sewer under a trade waste agreement with Sydney Water.
Contaminated water sources
Excavation activities intercepted contaminated groundwater and decontamination activities such as the washing of plant also generated water that required treatment. Contaminated water was pumped to holding tanks before passing through the water treatment plant.
Groundwater is encountered during the remediation works. As such, water is pumped out of the excavation areas to allow the excavation of contaminated material to continue.
Decontamination of plant and equipment
All plant, equipment and vehicles required decontamination before they were removed from the Environmental Control Enclosure (ECE) where the main remediation works took place. Contaminated water was generated when high pressure water was used to remove soil from plant and equipment, including washing the wheels of trucks.
Decontamination of project personnel
All project personnel involved in contaminated works followed a decontamination procedure before entering a non-contaminated area. Contaminated water was generated from decontamination activities such as showering, washing clothes and personal protective equipment, and from cleaning the decontamination unit.
The water treatment plant
All contaminated water was stored in tanks before being pumped to the onsite Water Treatment Plant (WTP) where a combination of processes took place: coagulation, flocculation, sedimentation and Granular Activated Carbon (GAC) adsorption.
The first treatment process in the WTP was coagulation. A chemical was added to the water to make suspended fine particles clump together so they could be more easily settled out of the water at a later stage. Solids, including particulate-bound contaminants, were also removed from the water by flocculation and sedimentation.
The water containing the coagulated solids was then flocculated, which involved gentle mixing of the water, causing the suspended particles to further clump together, or form a floc.
The flocculated water flowed into a tank known as a clarifier where the particles settled. The settling occurred due to gravity and contact with the surfaces of the clarifier.
Granular activated carbon adsorption
After the solids had been removed from the water, dissolved contaminants were removed by passing the water through granular activated carbon (GAC) filters in a process known as adsorption.
Offsite disposal of treated water
Following the GAC treatment, the water was pumped to a clean water tank before being pumped to the Sydney Water sewer under a trade waste agreement. The agreement required monitoring of flow rates, volumes and the residual contaminants.
As a result of the treatment activities, solids removed from the contaminated water during the treatment process were thickened and dewatered. The resulting cake was discharged into a bin and remediated along with the other material from the site.