Introduction
Buying development land without knowing what sits beneath it is one of the costliest risks in property. Contamination, uncontrolled fill, soft clay and shallow groundwater rarely appear on a title search or a site inspection. Yet each can change a project’s price, design and programme.
An environmental and geotechnical due diligence checklist gives developers a structured way to test those unknowns before committing capital. This article sets out the investigations to commission before acquisition and development application (DA) lodgement. It also explains how environmental and geotechnical findings interact, how one site visit can serve both disciplines, and which red flags justify pausing or repricing a deal.
Examples draw mainly on NSW. Other states apply their own frameworks, although the logic carries across. Readers who meet unfamiliar terms can check the environmental and geotechnical glossary.
What Does an Environmental and Geotechnical Due Diligence Checklist Include?
A complete checklist covers site history, contamination, hazardous materials, ground conditions, groundwater and the regulatory record. Environmental work shows whether the land suits its intended use. Geotechnical work, in contrast, shows whether the ground can carry the proposed buildings and what it will cost to excavate and found them. Together, these investigations form the core of environmental due diligence for a development site.
Which environmental investigations should developers commission?
Start with a Preliminary Site Investigation (PSI), a desktop review of site history combined with a walkover to identify potential contamination. A PSI costs far less than intrusive sampling, so it usually comes first and tells the consultant where to sample next. A Detailed Site Investigation (DSI) follows when the PSI finds a credible risk. Both stages sit within the scope of preliminary and detailed site investigations.
The core environmental items are:
- A PSI covering historical titles, aerial photographs, EPA and council records, and a site walkover
- A DSI with soil, groundwater and, where relevant, soil gas sampling assessed against the National Environment Protection (Assessment of Site Contamination) Measure 1999, as amended in 2013 (the NEPM)
- A hazardous materials survey of existing structures, because the Work Health and Safety Regulation 2017 (NSW) sets duties to identify asbestos before demolition or refurbishment
- An asbestos in soil assessment wherever fill or demolition history suggests fragments
- A preliminary soil and waste classification under the NSW EPA Waste Classification Guidelines (2014) for any soil that will leave the site
Which geotechnical investigations should developers commission?
A geotechnical investigation measures what the ground contains and how it behaves under load. AS 1726-2017 Geotechnical site investigations provides the framework for boreholes, test pits and in-situ testing. Engineers then use the results to recommend footings, excavation methods and earthworks. Geotechnical engineering services typically deliver this as a single factual and interpretive report.
The core geotechnical items are:
- Boreholes, test pits or cone penetration tests, with laboratory testing of samples
- Site classification under AS 2870-2011 Residential slabs and footings for low-rise housing, which addresses reactive clay
- Groundwater level and permeability measurements that feed dewatering design
- Acid sulfate soils screening in low-lying or coastal areas, guided by the NSW Acid Sulfate Soils Manual (1998) and the acid sulfate soils clause that many local environmental plans carry
- Slope stability and retaining advice aligned with AS 4678-2002 Earth-retaining structures
- Earthworks and fill assessment against AS 3798-2007 Guidelines on earthworks for commercial and residential developments
- Foundation advice, including piling to AS 2159-2009 where shallow footings will not perform
When Should Developers Commission Due Diligence?
Developers should commission due diligence before a contract becomes unconditional, or at least within a negotiated due diligence period. After settlement, the buyer loses the leverage to renegotiate price or walk away.
Access is the practical hurdle. Intrusive drilling needs the vendor’s permission, so access rights belong in the contract or option agreement, and a solicitor should handle that drafting. Staging also helps. A desktop review finishes quickly, while field work and laboratory analysis take longer, and timing varies with access, weather and groundwater monitoring.
The planning pathway adds a second deadline. Under clause 4.6 of Chapter 4 of the State Environmental Planning Policy (Resilience and Hazards) 2021, a consent authority must consider whether land is contaminated before granting consent. If contamination exists, the authority must be satisfied that the land suits the proposed use, either as it stands or after remediation. A DA lodged without adequate contamination information therefore risks requests for further information and delay. Councils also commonly ask for geotechnical advice where a project involves basements, deep excavation or sloping land.
How Do Environmental and Geotechnical Findings Interact?
Environmental and geotechnical findings interact because the same fill, soil and groundwater control both contamination risk and engineering performance. A result in one discipline often changes the cost of the other. The main links are:
- Fill: Uncontrolled fill can settle unevenly, which concerns the engineer. The same fill may also hold asbestos, hydrocarbons or metals, which concerns the environmental scientist.
- Groundwater: Shallow groundwater complicates basement construction and may carry contaminants. Dewatered water then needs treatment or approved discharge, as the article on dewatering obligations in NSW explains.
- Acid sulfate soils: Disturbed acid sulfate soils generate acid that attacks concrete and steel, so the finding affects both pile specification and environmental management.
- Excavation volume: The geotechnical design sets how much soil leaves the site, while the waste classification sets what each tonne costs to dispose of.
- Remediation: Capping, removal or containment changes earthworks levels and foundation options, so remediation and structural design need coordination.
Reading the two reports together, rather than in isolation, prevents surprises late in design.
Can Both Investigations Share a Single Site Visit?
Yes. In most cases, environmental and geotechnical fieldwork can share one mobilisation, which saves cost and reduces disruption to the vendor and neighbours. A coordinated program uses the same drilling rig and test pits, with an environmental scientist sampling while an engineer logs the profile. Groundwater wells can serve both purposes if the installer designs them for both. Environmental and geotechnical drilling services often combine the work for this reason.
Three conditions make a combined visit succeed. First, the PSI should come first, because it tells the team where environmental sampling matters most. Second, sampling methods differ. Contamination sampling needs clean handling, appropriate containers and chain of custody, while geotechnical sampling preserves soil structure and strength. Staff therefore need competence in both. Third, if the PSI suggests serious contamination or asbestos in fill, the team should plan controls for drill spoil before any boreholes go down, because drilling through contaminated material can spread it or generate waste.
What Red Flags Should Pause or Reprice a Property Transaction?
A red flag is a finding that exposes unquantified cost or approval risk. As a rule, pause the transaction when the extent of a problem is unknown, and reprice it once the problem has a measured scope and cost. A solicitor should advise on the contract mechanics for either path.
Which findings justify pausing a deal?
- A history of service station, dry cleaning, foundry, tannery or gasworks use, because the NSW planning guidelines list these activities as likely sources of contamination. Former fuel sites may also hold underground petroleum storage systems.
- Fill containing visible asbestos-containing material or demolition waste
- Past use of firefighting foams or other PFAS sources, which the PFAS National Environmental Management Plan addresses
- A neighbouring or underlying landfill, where leachate and gas monitoring may be necessary
- A section 10.7 planning certificate under the Environmental Planning and Assessment Act 1979 showing the land is declared significantly contaminated under the Contaminated Land Management Act 1997
- Location inside a mine subsidence district under the Mine Subsidence Compensation Act 2017 (NSW)
Which findings justify repricing a deal?
- Deep fill or soft clay that forces piled foundations under AS 2159-2009
- Shallow groundwater that demands dewatering for basements
- Soil that classifies as restricted solid waste or hazardous waste, which raises disposal costs and levies
- Acid sulfate soils needing a management plan and neutralisation
- Highly reactive clay, steep slopes or deep cuts that need engineered retaining
- Contamination that requires a Remediation Action Plan, remediation, validation and, where councils require it, a Site Audit Statement from an accredited auditor
Ask the consultant for indicative volumes and cost ranges. Those figures give the developer evidence for negotiation instead of a guess.
Conclusion
A rigorous environmental and geotechnical due diligence checklist protects a development from risks that stay invisible until excavation starts. It combines a Preliminary Site Investigation, targeted sampling, geotechnical testing, groundwater and acid sulfate soils checks, and early waste classification. Commissioning these investigations before acquisition and DA lodgement lets a developer price accurately, design with confidence and approach councils with evidence. A pre-purchase site assessment developers can rely on also turns red flags into negotiating points instead of post-settlement liabilities.
At Nova Group Pacific, we coordinate environmental and geotechnical investigations into one site visit, so developers get clear answers before they commit. Contact us to scope the investigations your site needs, or take our free compliance check to see which reports apply at your project stage.
