Disaster Recovery - Advice for Working with Sewage-Contaminated Silt and soil
The Canterbury earthquakes caused widespread deposits of liquefacted silt over a wide area.
It is quite likely that soil, silt or liquefied material in some areas has been contaminated with sewage and/or stormwater, because of the rupture of underground services. It is not easy to determine if such contamination has occurred.
Any silt in earthquake-affected residential areas should be considered as potentially contaminated. Silt may still remain under or around dwellings and other buildings.
Health risks
Bacteria, viruses and parasites
There is the potential for ill health from bacteria, viruses and parasites from sewage. It is thought that these can live in wet silt or wet environments for many months. The main health risks when working with contaminated silt are gastro-intestinal illnesses, including E.Coli, Salmonella and Campylobacter. Other potential health hazards include skin infections, leptospirosis and viral illnesses such as hepatitis.
Workers will be most at risk of coming into contact with bacteria through oral ingestion or from direct contact with skin (e.g. facial splashes). Broken skin is also another avenue for bacterial infection.
Moulds and fungi
Moulds, fungi and some bacteria favour musty and wet conditions, and can be found where water has leaked into houses from:
- damaged roofs, windows, roof tiles and gutters;
- places where wet silt has been in contact with house structures such as wooden floors or piles;
- places where dampness has entered wall cavities.
Moulds and fungi produce tiny particles called spores. These can easily become airborne and be inhaled, especially when mouldy material is disturbed (for example, when pulling gib from walls or digging around wooden piles), or in dusty, windy environments. Some moulds produce toxins that can be a danger to health.
Moulds and fungi can cause a hacking cough, respiratory problems (e.g. shortness of breath or wheezing), nose or throat irritation, nasal and sinus congestion, eye irritation, allergic reactions, skin rashes/irritation and worsen pre-existing asthma.
How to minimise contact with bacteria, viruses, moulds and fungi:
- Minimise time spent in damp attics, cellars, sheds or inside/under houses where silt, moulds or fungi may be present.
- Always avoid direct contact with silt, especially if it is wet, and avoid areas contaminated with mould or fungi.
- Do not splash in pools of water, even if it looks clean.
- Use appropriate personal protective equipment (PPE), including full-covering disposable overalls, waterproof gloves, gumboots and a respirator. A P2 or P3 particulate disposable face mask suitable for biological aerosols should be used.
- Never eat, drink, smoke or bite your nails while carrying out any work where it is likely that contact with silt, moulds or fungi will occur.
- During work breaks, remove PPE, wash hands and/or use hand sanitiser before eating, drinking or smoking.
- When working inside buildings, ensure adequate ventilation by opening windows and doors.
- Consider using a fresh air blower and trunking (ducts/hoses connected to the blower) if working in poorly ventilated spaces both inside and outside, or under, buildings.
- After work is completed, always take a shower, place dirty overalls carefully in a separate bag to avoid cross-contamination and if re-usable, wash them separately from other clothes in hot water and detergent.
- If a worker comes into contact with silt, moulds or fungi and feels unwell, that person should seek medical advice and tell the General Practitioner (GP) about where they were working and what they were doing.
Liquefaction dust
Liquefaction dust can occur when silt dries out and is subject to movement, for example from demolition or clean-up. It contains very small particles which are capable of entering the lungs and causing respiratory and cardiovascular problems. These dust particles are likely to be encountered in dry and windy weather, and when handling dry silt, especially with machinery.
Liquefaction dust also contains silica. If one is exposed to silica for prolonged periods of time over many months to years without respiratory protection, this compound is known to cause a serious respiratory condition called silicosis. However, health issues of this nature are not anticipated in the Canterbury region, as worker exposure to the dust is not expected to be high enough.
Brief exposures to dust clouds or handling small quantities of dust are unlikely to result in significant health problems, but is likely to cause eyes, nose and throat irritation.
In dry, windy conditions, or where work generates dust clouds, dust suppression techniques should be used and PPE should be worn.
Contaminated silt disposal
Contact the local authority (council) in advance about where, and how, to dispose of contaminated silt.
Further advice is available from:
- Community and Public Health Service: phone 03 379 9480
- Department of Labour Health and Safety: phone 0800 20 90 20.
