As a result of the Canterbury 2010 and 2011 earthquakes, many areas of Christchurch experienced a phenomenon called ‘liquefaction’, which resulted in many streets and houses becoming flooded with watery grey silt, in some cases contaminated with sewage and other products.

Removing large quantities of silt from in and around homes has become a significant activity in helping return residents’ lives to normal.
Intergroup is helping in earthquake recovery through applying it’s innovative ‘dry process’ high-velocity extraction method to remove silt from under house foundations, making them drier, warmer and reducing associated health risks from living in a cold and damp home.

To date, Intergroup has removed silt from beneath more than 400 homes in the Christchurch area. With multiple teams working on silt removal, more and more homes are cleared every week.

Persistent dampness from liquefaction residue

While much of the silt was removed through the concerted efforts of homeowners, family and volunteers from the surrounding districts, much of the material, lying under pile foundation houses, remained. This residue has been termed a ‘ticking time bomb’ for its potential adverse health effects and impact on buildings.

The silt can cause harm by trapping moisture and reducing airflow, contributing to ongoing damp indoor conditions and potentially creating:

  • Unhealthy living environments from mould and fungus growth, as well as possible toxic dust
  • Structurally unsound dwellings

As well as visible liquefaction in the subfloor crawl space, other indicators that a home may have a residual liquefaction silt problem include:

  • Increased dampness inside the home
  • Distinctive musty smell when entering an area
  • Noticeable mould or fungal growth inside the home

Delivering an effective way to dry out homes

Recognising residual liquefaction silt as a significant health and safety issue for Christchurch residents, Intergroup is using its proven ‘Dry Process’ high-velocity extraction to address the problem.

All extraction is carried out under high-velocity vacuum, using specialist staff trained in working in confined space entry in earthquake affected structures. The process does not introduce any additional moisture into the subfloor for the purposes of removal, meaning no additional time is required to dry the house out after the process has been carried out.

‘Dry Process’ high-velocity extraction is the only accepted method for removal (other than manual removal) of liquefaction silt in the Canterbury Residential Rebuild project.

As the process avoids introducing excessive amounts of additional water and is relatively unintrusive, house occupants do not need to move out during the removal activities, an important consideration for residents already stressed and disrupted as a result of the earthquakes and their aftermath.

Market Leaders

As an accredited specialised contractor and preferred liquefaction removal contractor to many of the recovery agents, insurance companies and other contractors in Canterbury, Intergroup is recognised as the market leader in this area of service to local residents.

Intergroup has multiple teams working in Christchurch clearing homes every day, with a total of 400 houses cleared to date.

Health and Safety to the fore

Importantly, as an established contractor in commercial waste removal, Intergroup’s operations are all carried out within a comprehensive health and safety infrastructure that protects personnel as well as residents. This means that personnel wear full personal protective gear, are trained in safe work practices and use equipment that is mechanically and electrically safe.


1. Check with EQC before removal

Any cost for liquefaction removal needs to be approved prior to work being undertaken to be sure that the homeowner will get their money back.

If you have a fire insurance policy covering your home, which was in force at the time of the earthquakes, you should be covered for the cost of getting the liquefaction cleared and taken away from your home and your insured land.
Contact EQC on 0800 DAMAGE for more information on cover.

2. Use an ACCREDITED remover

Intergroup is an accredited contractor with specialised ability to do this work properly. We have invested in safety procedures, fit-for-purpose, well-maintained equipment and operator training so that the job is done properly and safely.
When Intergroup carries out liquefaction removal for you, we will provide you with a tax invoice and related receipts such as tip receipts so that you can claim back costs from the EQC.

3. Get a free inspection and quote

Intergroup can provide a free inspection and quotation for EQC or insurance purposes and will bring to your attention any other obvious related issues at the time of inspection. You can then provide this, to your insurance company or
EQC to assist in speeding up your remediation process.

4. Don’t worry about moving out

With our approach in most cases, we are able to work around your daily life. We’ll arrange a suitable time to carry out the removal and in all likelihood, you won’t have to move out.

5. Click for more information

For more information, download the attached Liquefaction Removal brochure, here.

Liquefaction causes long-term problems
‘Liquefaction’ results when significant earth movement occurs during an earthquake. With severe shaking unconsolidated, water-logged ground loosens and transforms into a silty, fluid-like, material.
The Christchurch earthquakes produced over 400,000 tonnes of this material which spread in a thick layer across whole areas of the city.
Thousands of dwellings were affected. While many support teams mobilised to remove the silt manually, tonnes remain in amongst house foundations.
Affected homeowners report bronchiolitus, unshakeable coughs, asthma and other health problems.
Many tonnes of silt can be contained in amongst a house’s foundations.