Detailed Site Investigations (DSI) — Expert Phase 2 Contamination Assessments Across NSW

At Confluence Environmental, we deliver authoritative, regulator-ready Detailed Site Investigations (DSIs), also known as Phase 2 Environmental Site Assessments, for clients navigating complex planning, environmental, and remediation requirements. Whether required for DA approval, site remediation, or due diligence, our DSIs provide the data-driven clarity needed to move forward with confidence.

What Is a Detailed Site Investigation (DSI)?

A DSI is an intrusive environmental assessment conducted when a Preliminary Site Investigation (PSI) identifies potential contamination. It involves soil, groundwater, surface water, vapour, and material sampling to:

• Confirm the presence, extent, and severity of contamination

• Define the nature and behaviour of contaminants

• Assess risks to human health, ecosystems, and sensitive receptors

• Determine site suitability for proposed land use

• Support the preparation of Remediation Action Plans (RAPs) or Validation Reports

All DSIs are conducted in accordance with the NEPM (Assessment of Site Contamination) 2013, the NSW EPA Guidelines for Consultants Reporting on Contaminated Sites, and relevant planning legislation.

Why Is a DSI Required?

A Detailed Site Investigation is often triggered by:

• Contamination identified or suspected during a Preliminary Site Investigation

• DA conditions from councils requiring intrusive testing

• Change to a more sensitive land use (e.g. residential, childcare, schools)

• Known environmental incidents or historical contamination

• Compliance with the Contaminated Land Management Act 1997 (NSW)

• Landowner or purchaser due diligence prior to acquisition or development

Failure to undertake a required DSI can lead to DA refusal, planning delays, legal liability, or project redesign.

Our Detailed Site Investigation Process

At Confluence Environmental, we tailor every DSI to the site history, proposed land use, and regulatory context. Our structured process includes:

1. Sampling Design and DSI Plan

We begin with a site-specific DSI Sampling and Analysis Quality Plan (SAQP) outlining:

• Investigation objectives and scope

• Sampling density and location rationale

• Laboratory analytes, QA/QC procedures

• Justification in accordance with NEPM 2013 Schedule B2

2. Field Sampling and On-Site Assessment

Our experienced team undertakes targeted sampling, including:

• Soil sampling (surface and subsurface, via test pits, augers, or drill rigs)

• Groundwater monitoring well installation and purging

• Groundwater, surface water, and sediment sampling

• Soil vapour sampling and sub-slab gas testing

• ACM and hazardous materials screening

Fieldwork is completed in line with relevant health, safety, and environmental protocols. Chain of custody is maintained throughout.

3. Laboratory Analysis

All samples are analysed by NATA-accredited laboratories for contaminants such as:

• Heavy metals, TPH, PAHs, BTEX, pesticides, herbicides

• Asbestos in soil, PFAS, phenols, solvents

• Groundwater indicators: pH, EC, major ions, nutrients

• Vapour-phase VOCs and methane

4. Data Evaluation and Risk Assessment

We interpret results against:

• NEPM HILs, EILs, GILs, and health-based criteria

• ANZECC guidelines for water quality

• Site-specific exposure pathways and receptors

A Conceptual Site Model (CSM) is updated and used to conduct a risk-based assessment of land use suitability.

5. DSI Reporting

Every DSI report includes:

• Executive summary and compliance overview

• Detailed methodology, maps, borelogs, and analytical tables

• Contaminant delineation and visual site models

• Assessment of potential exposure risks and land use constraints

• Recommendations for remediation (if required)

Our reports are regulator-ready and suitable for submission to councils, planning authorities, and the NSW EPA.

Who We Support

We work with:

• Developers preparing sites for residential, commercial, and mixed-use development

• Planners, certifiers, and councils requiring assessment for DA and rezoning

• Government agencies and infrastructure providers

• Industrial operators with legacy contamination

• Landowners and solicitors seeking due diligence or transaction support

Where We Operate

We conduct Detailed Site Investigations across New South Wales, including:

• Sydney and Greater Sydney

• Central Coast, Newcastle, and Lake Macquarie

• Illawarra and South Coast

• Mid North Coast and Northern Rivers

• Hunter and Tablelands regions

• Regional and remote NSW by arrangement

Why Choose Confluence Environmental?

• Deep technical expertise and NEPM-aligned methodology

• Clear, risk-based conclusions and practical next steps

• Fast mobilisation and responsive project delivery

• Trusted by developers, councils, and government bodies

• Transparent communication and stakeholder engagement