Remediation of the Villawood site includes site establishment, soil treatment operations, validation, auditing, final site reinstatement and decommissioning.
Key project milestones
|Project Plans, Design and Documentation
||April 2013 - March 2014
|Commissioning and Performance Testing
||April 2014 - December 2014
|Soil Treatment Operations
||January 2015 - August 2015
|Equipment Demobilisation and Backfilling
||September 2015 - December 2015
What Was Remediated?
The site contained waste by-products from industrial activities which occurred between 1941 and 2000. The main contaminants were dichlorodiphenyltrichloroethane (DDT), an organochlorine pesticide, and its degradation products dichlorodiphenyldichloroethane (DDD) and dichlorodiphenyldichloroethylene (DDE). Manufacture of DDT ceased in 1961.
The volumes requiring remediation were approximately:
- 13,000 m3 of in-situ soil
- 10,000 m3 of soil excavated from the western part of the property in 2003 and 2004
- 2,000 m3 of contaminated material brought from the former Orica Chester Hill facility in 2008
Excavation and treatment of contaminated soil during site remediation work has effectively removed a significant source of groundwater contamination.
What's the Soil Contaminated With?
The main contaminants of concern were:
- DDT (and its degradation products DDD and DDE)
- total petroleum hydrocarbons (TPHs)
- 1,2-dichloroethane (1,2-DCA also known as EDC)
- trichloroethene (TCE)
- chlorobenzene (MCB)
- hexachlorobenzene (HCB)
- polycyclic aromatic hydrocarbons (PAHs), including benzo(a)pyrene.
Orica remediated the contaminated soil on the Villawood site using a treatment method known as directly-heated thermal desorption (DTD).
The DTD technology involves:
- Desorption, or vaporisation, of contaminants in the soil at temperatures typically in the range of 300ºC to 450ºC in a rotary dryer
- Discharge of the soil from the rotary dryer, cooling it with water. Than stockpiling and testing it for re-use
- Destruction of the off-gas from the rotary dryer in a thermal oxidiser at around 1,000ºC
- Rapid cooling of the gas stream for further treatment and also to avoid dioxin formation
- A 'baghouse' to remove fine dust particles
- A 'scrubber' with a large flow of circulating water and the addition of caustic soda to remove and neutralise hydrochloric acid produced during the combustion of the contaminants
- A 30 metre high chimney stack through which the treated gas is emitted.
The DTD process (click for full-size image)
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The DTD Process
DTD technology has been successfully used for many remediation projects worldwide since the 1980s, including two projects at Rhodes, NSW, and at Orica's Car Park Waste Encapsulation Remediation Project at Botany Industrial Park, NSW.
The main infrastructure comprises:
Feed Soil Building (FSB)
- This was an extension of the existing SSF
- An emission control system (ECS) extracted and treated contaminated air using carbon filtering
- Soil was sampled and blended for feeding to the DTD
- Sealed trucks transported the excavated contaminated soil to the FSB before it was fed into the DTD plant.
- Built adjacent to the FSB
- Treated the contaminated material
- Operated 24 hrs a day in 1-2 week campaigns between routine maintenance shutdowns, for approximately 9-10 months.
Water Treatment Plant
- Treated contaminated storm water recovered from excavations or generated from truck wheel washing or decontamination units for workers
- One sealed holding pond for feed water and three sealed holding ponds for storage and testing before discharge to sewer.
Internal roads, site offices, stores, work sheds, lunchrooms, changing areas, ablution blocks and decontamination units for workers were constructed for the project.
Commissioning and Performance Testing
Before the DTD Plant went into full operation a rigorous commissioning and performance testing process took place, consisting of;
Project Environmental Monitoring
In accordance with the environmental assessment (EA) requirements issued under Part 3A of the Environmental Planning and Assessment Act 1979, a statement of commitments (SoC) is provided in Section 10 of the EA. The SoC states Orica's environmental commitments and provides details on the environmental management and monitoring for the project during its construction and operational activities.
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