How end-to-end consenting can turn suitable surplus soil from a project liability into a reusable resource
What happens when good productive soil cannot meet a clean fill definition, but still has clear value for growers?
Across the Bay of Plenty, GWE Consulting Engineers has been working with orchard clients to find a practical, evidence-based answer.
Orchard redevelopment, replanting and earthworks can generate surplus soil containing lowlevel residues associated with historic horticultural land use. These can include arsenic, copper and chromium associated with treated timber posts, together with trace DDT-related pesticide residues.
The presence of these contaminants does not necessarily mean the soil presents an unacceptable risk as concentrations may sit above local background levels while remaining below relevant human-health or ecological guideline values. But that creates a practical problem as the soil may not meet the requirements for clean fill, despite potentially remaining suitable for productive use.
Historically, that can leave landowners with limited options; either retain the soil on site or incur the cost of transporting and disposing of it elsewhere.
GWE is helping develop another option – responsible, consented reuse in order to keep suitable soil in productive use.
GWE has been working with Bay of Plenty orchard clients to establish a pathway through which suitable surplus orchard soil can be characterised, assessed and reused on compatible receiving orchard land.
Working with Bay of Plenty Regional Council, GWE has established that end-to-end consenting is possible, including an approved pathway where both the source and receiving orchards hold consents for their respective works. GWE has also established a pathway where soil from a consented source orchard may be received by suitable orchard sites without those receiving orchards holding separate consents, subject to appropriate requirements.
The principle is straightforward; soil should be managed according to the risk it presents and its suitability for its proposed use, rather than being treated as waste simply because a contaminant has been detected or the material cannot meet a clean fill definition.
That requires robust science.
Before soil can be considered for reuse, GWE needs to understand its source, its contaminant profile and the characteristics of the proposed receiving site. This can involve representative sampling and laboratory analysis, comparison against appropriate background concentrations and guideline values, development of a conceptual site model and assessment of potential risks to people and the environment.
The objective isn’t to lower environmental standards, it’s to provide the evidence needed to make better decisions about soil.
An end-to-end consenting pathway.
The critical difference is looking at the entire soil movement rather than treating the source and destination as disconnected activities.
GWE’s end-to-end approach considers:
- where the soil is coming from
- its previous land use and potential contaminant sources
- how the soil has been sampled and characterised
- what contaminants are present and at what concentrations
- whether those concentrations are appropriate for the proposed reuse
- where the soil is going
- the characteristics and existing land use of the receiving site
- how transport, placement and earthworks will be managed
- the regulatory approvals and consent conditions that apply
- how compliance will be documented through to final completion reporting.
Depending on the circumstances, this may involve consents at both the source and receiving sites, or a pathway where the source site is consented and suitable receiving sites can accept the soil without obtaining separate consents.
In either case the objective is to creates a documented chain from source → assessment → movement → receiving site → verification, giving landowners, contractors and regulators confidence that the soil has been appropriately assessed and managed.
Why risk matters more than simply detecting contaminants.
One of the challenges with surplus soil is that the presence of a contaminant and the risk posed by that contaminant are not the same thing. Environmental risk depends on factors including contaminant concentration, exposure pathways, the receiving environment and the proposed land use.
That distinction is particularly relevant to former horticultural land.
Historic orchard activities may have resulted in diffuse pesticide residues or localised impacts around treated timber posts. Finding those compounds in soil does not, by itself, determine whether the material is unsuitable for reuse.
The technical question is more specific; what is in the soil, at what concentration, what risk does it present, and is it suitable for its intended receiving environment?
Answering this question properly creates opportunities for better environmental and commercial outcomes while maintaining appropriate safeguards.
Changing the economics of surplus soil.
For growers and developers, the implications can be significant. Soil disposal isn’t simply the cost of tipping material. Excavation, loading, transport, disposal charges and replacement with imported material can all contribute to project costs.
If suitable surplus soil can instead be responsibly reused, some of those costs may be avoided and the receiving site may also gain access to suitable soil at a lower cost than sourcing virgin material. That has the potential to fundamentally change the economics of surplus soil. Material that would otherwise represent a disposal liability may instead have beneficial value to another site.
The environmental benefits are equally important. Beneficial reuse can reduce material sent to disposal facilities, reduce demand for virgin soil resources and avoid unnecessary transport and handling. It’s a more circular approach to soil management by keeping suitable material in productive use where the evidence demonstrates that it can be done safely.
Starting with orchards, but not ending there.
The work underway in the Bay of Plenty provides a practical application of this approach, but the opportunity is potentially much larger. The same risk-based principles could potentially be applied to surplus soils generated from former agricultural land, residential redevelopment, brownfield sites and commercial or industrial projects.
GWE is actively engaging with councils to investigate how these principles could be applied more broadly, including the potential for responsible soil movement and reuse between brownfield sites. For developers, that raises an important question early in a project; before paying to dispose of surplus soil, has anyone established whether that soil has a suitable beneficial reuse pathway?
That question needs to be asked before excavation begins, not once trucks are already moving.
LIFT in Action
This work reflects GWE’s LIFT values in practice.
Listen
We work with growers, developers, planners, contractors and regulators to understand both the technical requirements and what actually needs to happen on site.
Innovate
We apply environmental science and risk-based assessment to challenge the assumption that surplus soil which doesn’t meet a clean fill definition must automatically become waste.
Follow Through
We connect site investigation and soil characterisation with the consenting process, soil movement, compliance requirements and final completion reporting.
Team Up
We work across landowners, receiving-site owners, laboratories, planners, contractors and Council officers to create a pathway that is technically robust, practical to implement and clearly understood.
A smarter approach to soil reuse.
The opportunity isn’t about finding ways around contaminated-land requirements, it’s about using those requirements, together with sound environmental science, to distinguish between soil that genuinely requires disposal and soil that can be responsibly reused.
The Bay of Plenty orchard work is demonstrating the potential. GWE is now actively working with councils to explore how the same evidence-based principles could support a much broader range of development projects and help change the way suitable surplus soils are managed.
If you’re planning earthworks on an orchard, former agricultural property, brownfield site or development project, talk to GWE before surplus soil is classified for disposal. There may be another pathway.