Contaminated Land

How What it affects your build (and budget).

It’s not uncommon to walk onto a site that looks perfectly clean, only to find out later that waste was buried there decades ago, or that the land was previously used for timber treatment, fuel storage or heavy vehicle servicing.

If that discovery happens after you’ve purchased the property, the financial impact on your project can be jaw dropping.

Land contamination isn’t always obvious, and it’s not always a deal breaker. However, it can affect construction costs, building design, stormwater management, earthworks, and project staging. In most cases, the biggest risk isn’t the contamination itself. The real risk is when your earthworks design requires contaminated soil to be excavated and removed from site. That’s when costs can escalate quickly.

Understanding how to identify contamination early, what contamination means in the New Zealand regulatory context, and how to design around it can protect your budget and programme. Let’s take a look at where contamination risk comes from, when councils get involved, and how smart design decisions can minimise risk before you commit to buying or building.

Where contamination risk actually comes from in NZ

In New Zealand, contamination risk is closely linked to historic land use. One of the most important tools is the Hazardous Activities and Industries List (HAIL). Councils use the HAIL register to identify land that has been used for activities likely to generate contaminants.

Common HAIL activities include:

Being listed on HAIL does not mean the land is unusable. It simply means the site needs proper investigation. Many HAIL-listed properties are low risk or only partially affected. Likewise, a site that is not on HAIL is not guaranteed to be contamination-free. The HAIL register is best used as an early screening tool.

How to check if a site is on the HAIL register

It’s also worth noting that “greenfield” does not always mean “clean.” Rural land can still contain buried rubbish, fuel pits, orchard residues, or historic farm chemicals. It’s uncommon but contamination can exist even on sites that appear untouched.

What land contamination really means for construction projects

For industrial and commercial developments, contamination is less about immediate health risk and more about earthworks and cost exposure. Councils are primarily concerned with two questions:

If the answer to both is yes, regulatory requirements and disposal costs increase rapidly.

The cost difference between a manageable site and an expensive one usually comes down to the volume of soil excavated and where it goes. Contaminated soil must be disposed of at approved facilities, with strict classification and high landfill fees. Deep excavation, large building cuts, or major retaining structures can quickly turn a minor contamination issue into a major cost problem.

There are sites that appeared greenfield but were historically used for timber processing. While contamination levels were low, the required building platform cut resulted in large volumes of soil needing disposal, driving costs far beyond expectations. The contamination wasn’t the core issue – the earthworks strategy was.

Conversely, we’ve heard of sites where contamination was isolated and easily managed through capping or minor layout changes. In some cases, contamination has even supported rezoning from productive rural land to industrial use, as the soil was no longer viable for horticulture. In these cases, contamination informed the design rather than derailing the project.

How to manage contaminated land without blowing the budget

Most contamination issues can be managed cost-effectively with the right strategy. The key is avoiding unnecessary soil removal, which requires early collaboration between geotechnical engineers, contamination consultants, designers, and contractors.

Common and accepted approaches include:

Councils are generally focused on containment rather than removal. As long as contamination is not being spread and the site condition is not made worse, keeping material on site under controlled conditions is often the most practical and cost-effective solution.

This is where experience matters. Consultants are excellent at identifying risk, but real value comes from translating those risks into workable construction solutions. Small design changes – such as a slightly higher floor level or adjusted yard gradients – can dramatically reduce excavation volumes and eliminate the need for soil export. These decisions can remove millions from a project’s risk profile without compromising functionality.

How do you know if a site is actually contaminated?

A HAIL listing is only one indicator. Geotechnical investigations often provide the first practical insight into contamination. Geotech testing examines soil layers, groundwater, compaction, and unexpected fill materials. If something unusual is present, it typically shows up during this process.

While it’s possible to find isolated contamination on sites with no recorded history, these cases are rare and usually limited in scale. When identified early, they are typically manageable through targeted remediation or capping.

In practical terms, contamination risk is very low if:

Where contamination becomes a real financial risk

The biggest risk is not contamination itself, but the interaction between contamination and design.

Deep excavations, major earthworks and retaining structures increase the likelihood of encountering contaminated soil. The most expensive scenario occurs when contamination is discovered after construction has started and the design requires that material to be removed from site. Disposal costs, additional testing, consent changes, and programme delays can impact the entire project.

The solution is simple:

How to approach a potentially contaminated site

These three steps remove most uncertainty:

With this approach, most contamination risks become predictable, manageable and can be budgeted for.