Stevensons Road (Cranbourne) Closed Landfill gas migration

Current Update

What's happening at the Stevensons Road Closed Landfill in Cranbourne?

When the landfill was closed, a gas and leachate (contaminated water) extraction system was installed on the landfill. This leachate removal system has not worked effectively and therefore the landfill is flooded.

As a result of the high water levels, the gas extraction system is also partly flooded, and therefore not effective. Because the gas extraction system is not working effectively, landfill gas is migrating from the sides of the landfill.

These diagrams are a simplified representation of the situation at the landfill. They are not to scale.

The figure below represents how a closed landfill should operate if an effective leachate extraction system is in place. As the amount of leachate is reduced, the gas extraction bores are not flooded and are able to effectively remove landfill gas that is generated from the decomposition of waste.

This picture shows how the landfill gas is thought to be moving through the estate.

There are now a range of measures being undertaken to help protect the safety of residents, to reduce the level of gas moving from the closed landfill and to determine where the gas is moving.

These measures include two key elements:

1. Increased monitoring of landfill gas.
2. Work to reduce gas movement.

1. Increased monitoring of landfill gas
More methane monitors are being installed in homes so that residents can be aware of methane entering their home. Monitoring has also been rapidly increasing throughout the estate, both underground and in services, to help understand where the gas is moving.

2. Work to reduce gas movement
Work is being undertaken to reduce the level of gas moving from the closed landfill. This work involves:
Gravel trench with gas extraction – as gas tries to move out of the landfill through the gravel, the pipes will suck the gas out into the flares and prevent it moving into the estate.

Underground gas extraction pipes – as gas at deeper levels tries to move out of the landfill, the pipes will suck the gas out into the flares and prevent it moving into the estate.

Soil ventilation – vents are being drilled into the ground across the estate to pump the gas out of the soil into the atmosphere.

Increased ventilation and sealing gas entry points in resident’s homes – vents are being drilled under homes to ventilate any captured methane. Potential entry points, for example around kitchen pipes, are being sealed.

 

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Current Actions:

On Thursday 18 September 2008, EPA issued a Clean Up Notice to the City of Casey requiring works to reduce the level of landfill gas moving from the closed landfill site and to assess the extent of gas moving from the site. These actions will help protect the safety of residents. They are designed to reduce the rate of gas moving from the landfill.

Action 1:  Passively vent landfill gas hotspots and potential migration pathways including service conduits within the residential area adjacent to Stevensons Road closed landfill.

Action 2:  Installing a cut-off trench along the western and northern landfill boundary.

Action 3:  Installing horizontal wells or closely spaced vertical wells venting along the northern and western boundaries of the landfill to intercept landfill gas migration at depth.

Council is required to have monitoring in place to assess the effectiveness of these actions in slowing the gas moving from the closed landfill.

EPA’s International Expert Group has reviewed these measures, and the group is supportive of these measures.

The notice also requires Council to determine the full extent of landfill gas moving from the landfill.  Works to drill additional bores and test for landfill gas commenced this week.

The notice requires weekly reporting from Council regarding their progress in implementing these actions.

Download a copy of the clean-up notice ( Adobe PDF, 247KB)

Expanding Monitoring Networks:

In-home monitoring

By the end of Friday 19 September it is expected that more than 187 in-home monitors will be in place.

City of Casey and their contractors anticipate that 318 monitors will be in place by Friday 26 September 2008.

Bore Network

City of Casey and its contractors have been extending the bore network to test for landfill gas.

EPA’s Clean Up Notice requires the City of Casey to determine the full extent of the landfill gas migration throughout the estate.

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Summary

Since 10 September the issues from landfill gas escaping from the Stevensons Road (Cranbourne) closed landfill  continue to be  managed through state emergency management services and EPA is supporting that process.
Communications and support to residents being affected by this problem are being managed by Casey Council who own the closed landfill.  Casey Council will provide up to date information on their website: www.casey.vic.gov.au/stevensonsroad.
If you have questions about:

• organising in-home monitoring;
• health and safety of residents; or
• support for or information about relocation

Casey Council will be able to assist you.  Please call their 24 hour number: 9705 5200.
The following key messages that have been provided by the Country Fire Authority (CFA):

• There is a very real risk within the Brookland Greens Estate of gas concentration sufficient to cause an explosion;
• This is being mitigated through a variety of methods including monitoring of levels, venting of confined spaces and storm water drains, and long term actions to decrease the overall below ground levels of gas;
• The only sure way to eliminate this risk for residents is for them to relocate from their homes. On expert advice including from the EPA, CFA recommends this approach as the safest option;
• The State’s emergency management protocols will oversee any relocation and ensure that affected residents are supported in every possible way;
• Should you choose not to relocate, then there is a range of actions that you can take on your property to increase your safety. These include ensuring all confined spaces are adequately ventilated, being vigilant and reporting any gas build up detected and by avoiding using ignition sources in confined spaces. Residents should also avoid environments where gas has become concentrated as it can cause adverse affects;
• The City of Casey will play a key role in the response and recovery actions for affected residents;
• Our main concern is for the safety of residents in the Brookland Greens Estate and we want to ensure the appropriate measures are taken to protect them from any potential danger.

To know more:

Casey Council are establishing a permanent information centre to support residents.  This centre will provide coordinated information about in-home monitoring, health and safety, and relocation support from the different emergency support agencies involved, such as CFA and Department of Human Services.  Please refer to the Casey Council website for further information: www.casey.vic.gov.au/stevensonsroad.

What can I do if I stay?

Some residents homes are not currently affected by the gas, however gas movement is hard to predict, which means more houses may be found as more monitoring is undertaken.
In order to take part in the monitoring, you can make a request with the City of Casey by calling 9705 5200.

Residents can also help prevent gas entering their homes. “What should I do?”  ( Adobe PDF, 65KB) explains what you can do around your home.

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Background

Landfill gas produced from the closed Stevensons Road landfill, Cranbourne is affecting a neighbouring residential estate. The gas from the closed landfill is travelling through the air and through the soil and has spread under some houses in the residential area adjacent to the closed landfill.

The landfill gas consists predominately of methane and carbon dioxide, which is produced when household and garden waste break down over time within the landfill. 

Landfill gas may have serious associated safety risks including  -

• Methane is a flammable gas and is known to become explosive between 5% - 15% methane volume for air.
• Asphyxiation due to the displacement of oxygen within enclosed spaces.
  

In-house and services methane monitoring received by EPA in June made it important that the issue was elevated.

Further readings in late August 2008 increased our understanding of the level of risk even further.

Methane levels detected particularly in some service pits are in the range known to be explosive.

There are potentially explosive levels of methane evident from the monitoring undertaken and residents need to be aware of what they should do in certain circumstances.

Landfill gas extraction systems have been implemented by the council to extract and safely dispose of the gases at the landfill site, but this has not been as effective as hoped and increased monitoring is an important way to provide the community information on levels of safety.

EPA is supporting Council to increase in-house monitoring, improve their emergency response and evacuation plans and increase the management of methane in the landfill.

Landfill gas is usually diluted to safe concentrations in the outdoor environment.  The risks of asphyxiation and explosion are more possible when landfill gas builds up within an enclosed, poorly ventilated space, for example within service conduits, basements and cavities.

This is a highly important safety issue, but there are some things that residents can do to mitigate the risk. For more information, refer to the document What Should I Do?

Download the What Should I do? document ( Adobe PDF, 65KB)

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About landfill gas

As the waste in landfills decay, gases are generated. These gases are mostly methane and carbon dioxide, but also contain a small percentage of hydrogen sulfide and other organic gases that give landfill gas its distinctive odour –similar to a rotten rubbish smell.

Closed landfills are known to produce gas for over 20 years once the landfill is closed.

The closed Stevensons Road Landfill is currently producing large amounts of landfill gas, with much of the gas being extracted from the site and burnt in flares.

The remainder of the landfill gas is moving off-site either through cracks in the landfill surface or underground through the sides of the landfill and into the surrounding soil.  Once the landfill gas is in the soil, it can travel through spaces within the soil structure for some distance away from the landfill.

Monitoring of landfill gas within the Brookland Greens Estate has been conducted by the City of Casey.  The data collected has indicated that landfill gas appears to be travelling through the soil in a northwest direction.  This gas has been detected on properties, in electrical pits and in the stormwater system at concentrations that pose a safety risk in areas of the estate.

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Managing landfill gas

Casey City Council owns and manages the closed Stevensons Road Landfill site. In 2006 Council installed a gas extraction system at the landfill to capture landfill gas.   The aim of the extraction system is to extract the gas before it moves off-site. 

High water levels at the landfill site are hampering the success of the gas extraction system due to flooding of the gas extraction bores.  In an effort to lower water levels on site, Council is installing additional bores.  This has been partially successful, however there continues to be a number of blocked wells at the landfill.

Landfill gas is further monitored in the Brookland Greens Estate in boreholes, stormwater drains and electrical pits where landfill gas may collect.

Council has conducted periods of limited in-house air quality monitoring using methane detectors.. These devices help understand where the gas is travelling to and how great the risk is. The monitoring program will be increased, as recent readings in some houses give rise to concern and require a cautious approach.

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History of the site

Landfills in the area have accepted waste since the early 80s. The now closed Stevensons Road Landfill operated between June 1996 and June 2005 as a municipal tip for the Casey and Frankston Councils under an EPA licence.

Approximately 1.1 million tonnes of waste was disposed of at the landfill over the operational period. The landfill is an old sand quarry hole, and was not lined, so there is no impermeable barrier between the waste and surrounding soil.

In 2007, EPA issued a Pollution Abatement Notice to the Casey City Council to require improved monitoring and control of landfill gas and leachate (rubbish-contaminated water) from the landfill. The notice further requires Council to commission an environmental audit to assess the risk.

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Air quality at and near the landfill

Council commissioned an Environmental Audit Report ( Adobe PDF, 4.7 MB) into air quality at the landfill and its surrounds. This report details the current risks to air quality posed by the closed landfill, including the risk of escape of landfill gas to the environment and possible effects to uses of land surrounding the landfill.

The report confirmed the results of earlier monitoring that found:

• the Victorian standards for air quality objectives are not being met at the landfill boundary and in some areas outside of the landfill; and
• additional measures are required to control landfill gas from the landfill.

EPA has requested the Council to immediately increase in-house monitoring, improve their emergency response and evacuation plans and increase the management of methane in the landfill.

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For more information

If local residents have any questions about:

• organising in-home monitoring;
• health and safety of residents; or
• support for or information about relocation

Casey Council will be able to assist you.  Please call their 24 hour number: 9705 5200.
Some answers to common questions may be found in Cranbourne Landfill Gas Migration Questions and Answers ( Adobe PDF, 78KB)
More general information on Landfill Gas is located on the United Kingdom Environment Agency’s website.

If you have any technical enquires you can also email EPA on stevensonsroad.closed.landfill@epa.vic.gov.au

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