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Preliminary vs Detailed Site Investigations: Understanding Environmental Site Assessments

Do you think you might have contaminated land and now you are wondering if you need an investigation? When it comes to land contamination investigations, there are two primary types typically completed by environment consultants in Australia — Preliminary Site Investigations (PSI) and Detailed Site Investigations (DSI). You’re probably wondering what’s the difference between the two and when you would need one or the other. The Queensland Guidelines for Contaminated Land Professionals relate to the local market. For perspective on the PSI and DSI processes throughout Australia the National Environmental Protection Measure Volume B2 is extensive, or read on and discover a potted summary from ENVENGEO Environmental Consultants.

Phase 1 Environmental Site Assessments and Preliminary Site Investigations

The terminology used in this sector often creates confusion and misunderstandings. The confusion exists because of similar terminology meaning different things. A Phase 1 Environmental Site Assessment (ESA) applies globally (typically a site is assessed in accordance with the ASTM Standard ASTM E1527-21), however the term is commonly used interchangeably with Preliminary Site Investigation in Australia, but they actually mean different things. A Preliminary Site Investigation may cover some of the “Recognized Environmental Conditions” identified in a Phase 1 ESA but not others (such as dangerous goods on site, as these do not necessarily indicate land contamination) and a PSI may identify factors that are not required of a Phase 1 ESA. Establishing the scope of the investigation is key to timely delivery of an assessment report and presentation that exceeds expectations.

A Phase 1 ESA or Preliminary Site Investigation may be requested by bank-appointed valuers or for acquisition (buyer) or vendor (seller) due diligence purposes, while planning authorities such as Council, the Department of Environment and Science (or other State Authority) will typically refer to a Preliminary Site Investigation. Before you can do any sort of construction or development on the land, a thorough investigation and assessment may be needed. A PSI is the first stage of assessing whether the property is safe to work on and occupy.

An extensive research investigation is initiated to assess whether there is any possibility of contamination or if, in the past, there was anything that could have potentially contaminated the land. Reviewing the history of the site is important to make sure that the ground is free from any contamination. To do this, contaminated land consultants access materials that will help them in their investigation, including a variety of important documents like:

- Site Historical or Operational Records (commercial site) e.g. historical photographs

- Environmental, Safety and Management System records (if available)

- Site Safety Data Sheet (SDS) records

- Acid Sulfate Soil maps

- Fire and Flood Risk Maps

- Current and Historical Title Information

- Development Application and Planning Records

- Topographical and Geological Maps

- Contaminated Land Record

- Environmental Management Register

All these sources are pertinent to the investigation and are just a few of the things that consultants look at to assess the state of the land. The surrounding land and properties are also investigated as it’s possible for contaminants to have seeped into the assessed site throughout the surrounding land.

Detailed Site Investigations

If the details of the PSI report reveal any evidence of potential contamination in the past or present, or if there is a proposed change of use, then a phase II assessment may be requested to conclusively establish if there’s contamination or not. A phase II assessment is also known as a Detailed Site Investigation (DSI), which involves, as the name suggests, a more detailed and in-depth assessment. The goal of a DSI is to further investigate any signs of contamination that may have presented themselves during the Phase I investigation. If required for a bank valuation, the DSI may not be mandatory, however it may be recommended based on the initial findings of a PSI. If the preliminary site investigation was required by Council, DES or another authority, a detailed site investigation may also be mandatory as a result of earlier findings.

Using the data from the PSI report, the consultant can target specific contaminants or substances that may have become of interest during the earlier assessment. For example, if a structure was built and demolished on site before 1983, soils may contain asbestos fragments, which could pose a risk to workers or future occupants. Environment consultants will then tailor the assessment for the site. If there are any findings of contamination, a remediation plan may be required.

PSI vs. DSI - What’s the Difference?

A PSI focuses more on preliminary and desktop type research and investigation, with a site inspection, while a DSI is a much more complete and thorough form of investigation involving soil testing and may also involve groundwater, surface water, ground gas or indoor air sampling and testing for retained structures. The PSI merely ‘scratches the surface’ of whether there’s contamination or not, and the DSI is more intrusive and time-consuming. However, both of them are crucial stages in environmental site assessments to ensure that any piece of land is safe to occupy or redevelop.


Performing the needed environmental site assessment to a particular property that you or your client own or are planning to acquire is important. Both PSI and DSI effectively assess the possibility of contamination on the land and should be taken into account before any form of construction work is undertaken.

ENVENGEO is composed of a group of specialists providing environmental compliance services to meet your needs. We perform site assessments, environmental planning, and remediation to clients in Brisbane, Queensland. Contact our environment consultants today to request a service.

For further reading, the Queensland Guidelines for Contaminated Land Professionals referenced earlier provides a good starting point, or talk to one of our experienced and qualified consultants on 1300 ENV NOW, which is 1300 368 669.

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