When Does a Site Require a Detailed Site Investigation in NSW?

A Straightforward Guide for Developers, Planners, and Consultants Navigating Site Contamination Risk

If you're preparing a development application (DA) or planning a land use change in New South Wales, you may be required to assess whether the site is contaminated — and if so, how to manage that risk.

A common question we hear is: do I need a Detailed Site Investigation (DSI), or is a Preliminary Site Investigation (PSI) enough?

At Confluence Environmental, we specialise in contaminated land assessments for planning approvals and project delivery. This article explains when a DSI is required in NSW, how it's triggered under legislation, and what you should expect.

What Is a Detailed Site Investigation (DSI)?

A Detailed Site Investigation is a formal assessment that:

• Confirms the presence, nature, and extent of contamination

• Evaluates potential risks to human health and the environment

• Supports decisions around remediation, land use suitability, and development consent

It involves targeted sampling (soil, groundwater, vapour), laboratory analysis, and interpretation in accordance with the National Environment Protection (Assessment of Site Contamination) Measure (NEPM 1999 as amended 2013).

What Triggers the Need for a DSI in NSW?

In most cases, a DSI is only required after a Preliminary Site Investigation (PSI) has been completed and indicates the potential for contamination.

Common DSI triggers include:

Planning pathways under SEPP 2021

If you're changing the land use to a more sensitive one (for example, from industrial to residential or childcare), the NSW EPA and planning legislation require you to assess contamination risk under the Contaminated Land Planning Guidelines and the State Environmental Planning Policy (Resilience and Hazards) 2021.

If the PSI finds evidence of past uses that could have caused contamination (e.g. fuel storage, workshops, illegal dumping), a DSI is usually required.

Findings from a PSI

• Known or suspected fill material

• Visual signs of contamination (e.g. staining, odours, debris)

• Anecdotal or historical records suggesting pollutant storage or use

Council or EPA direction

Sometimes, your local council or a referral authority (such as the NSW EPA) will require a DSI as part of a DA condition or voluntary management proposal.

Unexpected finds or site disturbance

During earthworks or excavation, discovery of buried waste, asbestos, or stained soils may trigger the need for a retrospective DSI and Remediation Action Plan (RAP).

Common Scenarios That Require a DSI

• Redevelopment of a former service station or mechanics yard into housing

• Conversion of agricultural land with historical pesticide use to a school or childcare centre

• Large-scale subdivisions involving imported fill material

• Infill development on legacy industrial or commercial land

• Development approvals requiring EPA sign-off or ongoing site management

What’s Involved in a DSI?

A Detailed Site Investigation typically includes:

• Development of a Sampling and Analysis Quality Plan (SAQP)

• Soil sampling and laboratory testing

• Groundwater monitoring, if required

• Assessment of health and ecological risks

• Recommendations for remediation or ongoing management

The investigation must be completed in accordance with the NEPM and relevant NSW EPA guidelines.

What Happens After a DSI?

Depending on the results, the site may be:

• Declared suitable for the proposed use, with or without conditions

• Subject to a Remediation Action Plan (RAP)

• Included in a Site Audit if required by Council or the EPA

At Confluence Environmental, we work with your planner, certifier, or council contact to ensure all documentation supports your development pathway — without delay or confusion.

Don’t Assume You Don’t Need One

We often see DAs delayed because:

• Contamination wasn't flagged early

• An insufficient PSI was submitted

• A DSI was avoided, but later required by Council

Bringing in a qualified contaminated land consultant early in the planning stage can save months of rework and avoid costly hold-ups.

Need Help Determining if You Need a DSI?

Confluence Environmental provides clear, responsive advice for developers, planners, and consultants across NSW — including Newcastle, the Central Coast, Sydney, and regional areas.

We deliver Preliminary and Detailed Site Investigations aligned with Council and EPA expectations, ensuring your project stays compliant and moves forward.

Call 0493 042 642 or Request a Quote