Soil Contamination

How does soil become contaminated?

Common causes of soil contamination in New Zealand residential properties, associated areas you might consider testing and the contaminants you are most likely to find in your soil as a result are displayed in the table below.


Source of Soil Contamination Likely Soil Contaminants
Houses, garages & sheds painted with lead-based paint that is flaking or previously sanded, or built with material containing asbestos (eg; baseboards, soffits, garage walls & gable ends) in poor or broken condition Lead & asbestos
Garden surrounds, houses, decks, garages & sheds built using treated timber Copper, chromium, arsenic & boron
Historic property use (eg; horticulture, agriculture, industrial/commercial) Full range of contaminants that may include heavy metals, pesticides, herbicides, asbestos & hydrocarbons
Roof runoff (from eg; galvanized steel, lead headed nails and flashings and lead-based paint) Zinc & lead
Wastewater disposal field Heavy metals, pathogens & hydrocarbons
Fill soils Full range of contaminants that may include heavy metals, pesticides, herbicides, asbestos hydrocarbons
Backyard fire pits where rubbish or treated timber may have been burned Full range of contaminants that may include heavy metals, pesticides, herbicides, asbestos hydrocarbons
Runoff or overspray from neighbouring properties Pesticides, heavy metals & herbicides
Previous renovations or alterations Heavy metals & asbestos
Previous buildings that have been removed Heavy metals & asbestos


Sources of soil contamination in a residential houseCommon Sources of Soil Contamination from a typical New Zealand house built in the 1970's (Source: EWB Consultants)

Why should I test my soil?

Soil contamination can be a health hazard to adults, children and pets and most soil contamination isn't visible. Test your soil to find out if any contamination is present so you can take action if needed.

When should I test my soil?

The most common reasons people want to test their soil include:

  • Buying a house or empty section
  • Unsure of the history of your property
  • Starting a new garden
  • Adults, children or pets in the household are sick and the cause is unknown
  • Older house, garage or shed may have been painted with lead-based paint
  • Raised garden bed surrounds have been made with treated timber
  • There is a suspicion that soil may have been brought in from a different property
  • Plants or vegetables aren't growing well or are dying
  • Vet has advised a pet has lead poisoning
  • Suspicion that a neighbour has sprayed your plants
  • Rubbish or old building materials have been found buried in the soil or lying under the house
Raised garden beds made with treated timber and galvanized steel
Raised garden beds made with treated timber & galvanized steel

    What should I test my soil for?

    This depends largely on the history of your property - The table at the top of the page gives you some ideas of what to look for.

    If you're not sure where to start, the Common Contaminants Soil Test Kit covers the contaminants that are most commonly found at dangerous levels in New Zealand residential soils.

    Where should I take my soil samples?

    You want to take your soil samples from the areas that you are concerned about. eg; if you are concerned about contaminants in your vege garden then that's where you want to sample. If you are looking at buying a house or are unfamiliar with the history of your property then you might like to check multiple areas of the property such as:

    • Front & back yard
    • Vege garden
    • Areas where your children or pets spend time
    • Around the curtilage of the house where lead-based paint flakes, treated timber, broken asbestos and roof runoff could contaminate the soil
    • Areas where grass or vegetation isn't growing as well or the soil looks discoloured
    • Beneath or surrounding back yard fire pits

    How many samples should I take?

    This is entirely up to you, however we recommend you take at least one sample from each area that you want to represent. A general rule of thumb is to take at least one sample per 100m2 of land.

    If you are sampling so you can dispose of your soil, then you will need to take at least one sample per 500m3 of soil.

    You can take multiple individual samples to pinpoint any areas that are problematic, or you can mix multiple samples together (composite sample) to give you an average level. The larger the number of samples taken in a composite, the better average result you will get, however conversely, the higher the likelihood of any high or low levels being diluted by the other samples.

    How does contaminated soil make people or animals sick?

    There are three main exposure pathways for contaminated soil: inhalation (breathing it in), dermal absorption (direct contact with the skin) and ingestion (eating it, hand to mouth, soil on vegetables, vegetable uptake of contaminants during growth). Children and pets are particularly susceptible as they have lower body weights and are more likely to ingest soil, but even adults, over time, can ingest enough contaminants through gardening or eating produce grown in contaminated soil to make them sick.

    Soil Contamination Pathways
    Soil Contamination Sources, Pathways & Receptors (Source: MfE)

    Where can I buy a soil testing kit?

    We offer Soil DIY Test Kits. All Lab Analysis test kits come with:

    • Sampling Instructions
    • Sample bag/s
    • Gloves
    • Sample Submission Form
    • Pre-Paid Sample Return Courier Bag
    • IANZ accredited laboratory analysis of your sample/s
    • Professional assessment of your results from a qualified and experienced contaminated land specialist.

    How long will it take until I get my results?

    Each test has a different turnaround time so check each product for details.

    What reporting do I get?

    There are several key benefits to using an EWB Soil DIY Test Kit.

    Firstly, we send you a sampling kit including detailed instructions so you can take your own soil sample/s.

    Second, we send you a pre-paid courier bag for quick and easy sample return.

    And most importantly, we take the IANZ accredited laboratory results and one of our specialists will interpret the results for you. We assess your results against the relevant New Zealand Guidelines & Standards, and tell you what your results actually mean.

    Laboratories are able to give you analytical results, but only a Suitably Qualified & Experienced Practitioner (SQEP) such as the specially trained staff at EWB Consultants are able to provide a professional assessment of what your soil contamination test results mean.

    How will you send me the report?

    Your lab report and accompanying assessment will be delivered to you via the email address you used when you purchased the DIY Test Kit/s.

    Is the report suitable for Council?

    In short, no. Council require independent specialist testing, investigation and reporting following specific New Zealand guidelines and standards. Council will not accept results from DIY sampling. If you are planning to subdivide or develop property, and Council has advised that you need to check for contaminants in the soil before they will approve your application, contact the specialist team at EWB Consultants for more information.

    What if I want to test for other contaminants?

    If you need to test for a wider range of contaminants that aren’t included in the Shop, please contact us as we may be able to provide you with a personalised DIY Soil Test Kit.