What are the Rhodes Remediation Projects? The Projects are a clean up, or remediation, of two neighbouring industrial sites at Rhodes: the former Allied Feeds site and the former Lednez/Union Carbide site. Both sites need chemical contamination in the soil to be substantially reduced. As part of the Lednez/Union Carbide project, the most contaminated areas of sediment in Homebush Bay will also be remediated.
What dangerous chemicals are being cleaned up? The main contaminant of concern found within the soil and bay sediment is dioxin. Other chemicals of concern also being cleaned up include volatile organic compounds (VOCs) such as benzene, toluene, ethylbenzene and xylene; and semi-volatile organic compounds (SVOCs) such as organochlorine pesticides, phenols, chlorophenols, polycyclic aromatic hydrocarbons, chlorinated hydrocarbons and chlorobenzenes.
Sometimes I can smell odour from the project sites, does this mean I am being exposed to dangerous chemicals? The most odorous chemicals found on the project sites are volatile organic compounds (VOCs), not dioxins, which have no smell. When soil or sediment containing VOCs is excavated, the chemical compounds “volatilise,” or become vapour, causing odour to be emitted to the atmosphere. Hours after excavation activities have finished, volatilisation may still be occurring, although at a reduced rate. The human nose can usually smell chemical odours at concentration levels well below those that may cause health problems. Since the Rhodes Remediation Projects commenced, Thiess Services has monitored VOC levels in the air as part of its Air Quality Management Plan. Special monitoring “response levels” have been set to keep VOC emissions below levels that may cause irritation or adverse health impacts.
Where do dioxins come from? Dioxins are not manufactured intentionally. Generally, they are by-products of chemical manufacturing or combustion. In nature, dioxins will be created during bushfires. The dioxins found at the Rhodes sites were produced over many decades during chemical manufacturing on the Lednez/Union Carbide site.
Why are dioxins a human health risk? Dioxins accumulate in the human body through two main exposure pathways: inhalation and ingestion. Inhalation is a minor pathway, accounting for up to 5% of a person’s lifetime exposure, whilst ingestion of food is the major pathway, accounting for over 95% of exposure. Foods from animals - such as fish, pork, beef and dairy - contain the highest dioxin concentrations because levels tend to increase up the food chain. There are more than 200 chemical compounds classed as dioxins and of these, 10% have sufficient toxicity values to be of concern. These more toxic dioxins are not easy for the human body to metabolise or excrete. They have been linked to increased cancer rates in animal studies and in studies of people exposed to high levels eg. levels 100 to 1000 times higher than average exposure levels in developed countries.
If ingestion of food is the main pathway for dioxin exposure, why do the sites at Rhodes need to be cleaned up? The NSW Department of Environment and Climate Change (NSW DECC) has determined that the sites pose risks for human health and the environment based on:
- the potential for direct contact with contaminated soil and bay sediment; and
- evidence that dioxins have entered the food chain and could be consumed by humans and wildlife eg. elevated dioxin levels have been found in fish from Homebush Bay and the Parramatta River.
Without remediation, the land based sites could not be residentially developed or used for public purposes because they do not meet the required standards. Remediation is also essential to prevent the ongoing movement of chemicals from the land into Homebush Bay.
What is the significance of the Stockholm Convention? Article 5 of the Stockholm Convention on Persistent Organic Pollutants (POPs), to which Australia is a signatory, requires that parties to the Convention take measures to minimise or eliminate certain POPs in the environment, including dioxins.
How is the work done? Soil and bay sediment is dug up. It is then tested to determine what contaminants it contains and at what levels. On the Allied Feeds project, all of the contaminated soil is being treated. After treatment, the soil can be safely backfilled on site or transported to landfill. On the much larger Lednez/Union Carbide project, soil and sediment with the greatest degree of contamination is being treated, whilst material with lesser concentrations is being contained deep underground, where it cannot be accessed. The material “reuse criteria” for untreated soil and sediment was approved by the NSW Department of Environment and Climate Change (NSW DECC).
How are the contaminants removed from the soil and bay sediment? The material is treated in a directly heated thermal desorption (DTD) plant. DTD is a complex process but put simply:
- the soil or sediment is heated up in a rotary drum to between 450 and 550 degrees Celsius by natural gas;
- the heating process removes the contaminants from the soil or sediment and turns them into a gas;
- the gas is then further heated to 920 – 980 degrees Celsius to combust the gas, eliminating the contaminants and turning the gas into carbon dioxide and water;
- the gas stream of carbon dioxide and water is cooled down within seconds to prevent the contaminants from reforming. Acids form in small amounts during this cool down;
- almost all of the dust and acids are removed by various processes before the gas stream is released to the atmosphere;
- gas discharge quality is monitored to ensure compliance with stack emission criteria set by the NSW DECC.
(For further information about the DTD process, see the fact sheets in the website’s “Media Centre.”)
After directly heated thermal desorption (DTD) treatment, how much dioxin remains in the soil or sediment? On the Allied Feeds project, soil dioxin levels are reduced to less than one part per billion (1 ppb) after treatment, which is at least ten times less than what is allowed at most commercial or council landfills. On the Lednez/Union Carbide project, the soil and bay sediment is treated so that dioxin is reduced to a number of different concentration levels. The dioxin concentrations which have been approved by government authorities depend on where the soil is going to be reused on site. For example, if soil is being placed in an area that maintenance workers may access in the future, dioxin levels must be 0.16 ppb or less; however, if soil is being placed in an area of open space and more than 5 metres below the surface, dioxin levels must be 85 ppb or less. On both project sites the top 1 metre of soil will be clean material known as VENM or "virgin excavated natural material."
What is in the smoke that is coming out of the emission stacks? The emission stacks for the DTD plants emit steam, not smoke. Emissions are monitored for particulates, fluoride, sulphuric acid, volatile organic compounds, nitrogen dioxide, carbon dioxide, hazardous substances such as lead, hydrogen chloride, chlorine and dioxins. So long as the DTD plants operate at optimal temperatures, emissions should remain below set limits. If pressures, temperatures or flows fall outside a predetermined range, an alarm will be activated. Corrective action must be taken or the soil feed will be stopped automatically.
Is there any monitoring of human health while the remediation is ongoing? Due to community concerns about living in the vicinity of a contaminated area and the affects of remediation, the NSW Department of Health is undertaking the Rhodes Serum Dioxin Study over the life of the Rhodes Remediation Projects. Phase 2 of the study found no increase in levels of blood (serum) dioxin in residents since remediation began. Levels of dioxins in local residents remain well below the levels known to be associated with adverse health effects. Information on the study can be found at:
http://www.health.nsw.gov.au/PublicHealth/environment/hazards/env_rhodes.asp
In addition, Thiess Services has a health monitoring program in place for personnel working on the project sites. It includes periodic blood testing for a range of contaminants including dioxin.
What sort of environmental monitoring is undertaken on and off site? As well as monitoring stack emissions from the treatment plants and volatile organic compound levels (VOCs) in air during excavations, Thiess Services monitors many other environmental factors. Importantly, both on and off site, very fine dust known as PM10 is monitored. Elevated PM10 in the atmosphere can sometimes cause people to experience nose and throat irritation. When communities are exposed to elevated PM10 levels over long periods of time, some individuals may develop more serious health problems such as respiratory or cardiovascular disease.
Who guarantees the sites will be safe after the clean up? Standards of remediation are in accordance with modern international and Australian “best practice.” Site auditors accredited by the Environmental Protection Authority, part of the NSW DECC, provide the rigour of expert independent review. They have a legal liability under the NSW Contaminated Land Management Act 1997 to ensure that once the Rhodes Remediation Projects are complete, the sites will be suitable for residential occupation.
What credentials and expertise does Thiess Services have to guarantee the successful undertaking of such large scale clean up projects? Thiess Services has more than 30 years’ experience in managing remediation projects. The company successfully undertook the remediation of several Olympics sites within the local region of Rhodes and Homebush Bay. Thiess Services has also completed large, high profile projects across Australia, including the clean up of the former nuclear site at Maralinga in South Australia.
Will the remediation of Homebush Bay mean that the fishing ban can be removed? Ongoing monitoring of fish contamination levels in Homebush Bay will be required after remediation to make a case for the removal of the fishing ban in the region.
What hours do you work? Regular working hours are 7:00am – 5:00pm Monday to Friday and 8:00am – 1:00pm on Saturday; however, the Directly Heated Thermal Desorption (DTD) plants are designed to operate 24 hours a day, seven days a week, so there are always teams of DTD plant operators on each site.