What Happens After a Detailed Site Investigation (DSI)? A Practical Guide for Developers

Prepared by Confluence Environmental - environmental and contaminated land consultants supporting development, remediation and validation projects across NSW.

Once a Detailed Site Investigation (DSI) has been completed, many project teams are left asking: what happens next? Understanding the post-DSI pathway from risk assessment through to remediation, regulatory engagement and eventual site validation is critical to managing project timelines, costs and compliance outcomes.

In this article, we break down the stages that typically follow a DSI, how they support planning and approval processes, and what developers and project managers should expect in practice when progressing through the contaminated land assessment and remediation {link: /contaminated-land-and-remediation} framework in NSW.

1. Interpreting DSI Results: What They Tell You

A DSI produces a detailed dataset of chemical, physical and geological information about site conditions. These results are interpreted against relevant assessment criteria based on the proposed land use, commonly considering both human health and ecological receptors.

Key outcomes may include contaminant concentrations relative to criteria, the spatial distribution of impacts, identification of exposure pathways and receptors, and the presence of contingent risks or uncertainty zones. Rather than being an endpoint in itself, the DSI functions as a decision-making foundation that informs the next steps in contaminated land risk assessment.

Many councils and regulators rely on the interpretation of DSI results to determine whether further action is required before development can proceed.

2. Updating the Conceptual Site Model (CSM)

Following a DSI, the Conceptual Site Model (CSM) is refined to reflect investigation findings. The CSM provides a narrative and diagrammatic representation of contaminant sources, exposure pathways and receptors, aligned with the proposed land use.

A robust and well-documented CSM helps planners, councils and regulators understand why certain risks are relevant or not for a given development scenario. It also provides transparency in decision-making and underpins subsequent risk assessment and remediation planning.

3. Risk Assessment and Prioritisation

Once contaminants of concern and exposure pathways are clearly defined, a risk assessment is undertaken. This assessment evaluates potential impacts to human health, potential impacts to groundwater and surface water, and longer-term risks associated with construction activities and site occupation.

In some cases, the risk assessment may confirm that no further action is required beyond routine management or monitoring. In others, it will identify the need for remediation or mitigation measures to reduce risk to acceptable levels, consistent with NSW contaminated land guidelines.

4. Remediation or Management Planning

Where the risk assessment identifies unacceptable risk, remediation or management strategies are developed. This typically involves preparation of a Remediation Action Plan (RAP), which defines remediation objectives, methodologies and validation criteria.

Remediation strategies may include excavation and off-site disposal, on-site treatment, containment measures or management-based approaches for lower-risk scenarios. Remediation planning is designed to be proportionate to risk and aligned with the intended land use and regulatory expectations.

5. Regulatory Engagement and Approvals

In NSW, councils and regulators assess post-DSI documentation including the updated CSM, risk assessment and proposed remediation approach — against planning and environmental protection frameworks. This review may result in additional approval conditions, requests for supplementary information or defined remediation requirements prior to construction or occupation.

Clear, defensible reporting at this stage supports efficient regulatory review and reduces the likelihood of delays during the development application assessment process.

6. Implementation of Remediation Works

Where remediation is required, works are implemented in accordance with the approved RAP. This stage commonly involves controlled excavation, treatment or disposal of contaminated material, and on-site management measures to protect groundwater, surface water and other sensitive receptors.

Remediation activities are typically coordinated with construction and earthworks programs to minimise disruption and maintain project momentum, often alongside waste classification and material management requirements.

7. Validation and Reporting

Following remediation, validation sampling and reporting are undertaken to confirm that remediation objectives have been achieved. A validation report demonstrates that residual contamination is below relevant criteria and that the site is suitable for its intended use.

Successful validation is commonly required prior to occupation, construction sign-off or final regulatory approval.

8. Ongoing Monitoring and Management

In some cases, residual contamination may remain in a form that can be safely managed through monitoring or institutional controls. This may include groundwater monitoring programs, environmental management plans or long-term maintenance obligations.

These measures provide ongoing assurance that risks remain controlled over time and are an accepted part of many long-term contaminated land management frameworks.

Conclusion

A Detailed Site Investigation is a major milestone but it is not the end of the contaminated land pathway. What comes after a DSI is often where projects succeed or stall. By clearly interpreting results, updating the CSM, undertaking risk assessment, planning proportionate remediation and aligning with regulatory expectations, developers can maintain project momentum while managing environmental risk.

Confluence Environmental supports project teams through every stage of the post-DSI process, from interpretation and planning through to remediation and validation, providing clarity, compliance and confidence across complex contaminated land projects.