Acid Sulfate Soil Assessment & Management Plans

Confluence Environmental provides acid sulfate soil assessment, testing and management planning for development, infrastructure and construction projects across NSW.

Acid sulfate soils (ASS) are naturally occurring soils and sediments containing sulfide minerals that can generate acidity when disturbed and exposed to oxygen. Excavation, drainage and groundwater lowering can therefore create environmental and construction risks where ASS is present.

Effective assessment is not simply about determining whether a property falls within a mapped acid sulfate soil area. It requires understanding whether the proposed works will encounter or disturb ASS, the characteristics of the material, and what management measures are required for the project to proceed.

Our capability extends from preliminary risk assessment and field investigation through to laboratory characterisation, Acid Sulfate Soil Management Plans (ASSMPs), groundwater and dewatering assessment, construction support and verification.

Acid Sulfate Soil Assessment and Investigation

ASS investigations are developed around the proposed works, environmental setting and likely depth and extent of disturbance.

Depending on the project, our assessments can include:

• review of Acid Sulfate Soil mapping and applicable planning controls;

• assessment of geology, geomorphology and groundwater conditions;

• review of proposed excavation, earthworks, drainage and dewatering;

• targeted soil investigation and profile logging;

• field screening and identification of potential ASS materials;

• laboratory characterisation;

• assessment of potential acid generation and neutralisation requirements; and

• recommendations for avoidance, management or further assessment.

Investigation depth, sampling density and analytical requirements are selected to address the actual zone of disturbance and project decision, rather than applying a standard investigation program to every site.

This is particularly important where ASS occurs at depth or where groundwater lowering may expose sulfide-bearing materials beyond the immediate excavation footprint.

Acid Sulfate Soil Testing and Characterisation

Field observations alone are not sufficient to characterise acid sulfate soil risk.

Where laboratory assessment is required, samples are analysed using recognised acid sulfate soil methods to determine the presence and significance of existing and potential acidity.

Depending on the investigation objectives, analytical assessment can include parameters associated with:

• existing acidity;

• reduced inorganic sulfur;

• potential sulfidic acidity;

• acid neutralising capacity; and

• net acidity.

Laboratory results are interpreted together with the soil profile, proposed disturbance and groundwater conditions to determine whether management action is required and, where relevant, the treatment or neutralisation requirements for excavated material.

The objective is not simply to identify ASS. It is to provide the information required to determine how the material can be safely disturbed and managed.

Acid Sulfate Soil Management Plans

Where acid sulfate soils will be disturbed, Confluence Environmental prepares Acid Sulfate Soil Management Plans (ASSMPs) that translate the investigation findings into practical construction controls.

Depending on the project, an ASSMP can address:

• excavation sequencing and management;

• segregation of ASS materials;

• temporary stockpiling and containment;

• neutralisation and treatment requirements;

• treatment rates and application methodology;

• verification of treated material;

• soil reuse and off-site management;

• groundwater and dewatering controls;

• runoff and surface-water management;

• environmental monitoring;

• inspection and hold points;

• contingency and unexpected finds procedures; and

• project records and completion documentation.

The management strategy is developed around the proposed construction methodology and site constraints.

An ASSMP should therefore function as a working project document, providing clear requirements for contractors, environmental personnel and project managers during delivery.

Dewatering and Groundwater Management

Groundwater management can be a critical component of ASS projects.

Lowering the groundwater table can expose previously saturated sulfide-bearing soils to oxygen, while extracted groundwater may also require assessment and management before discharge, treatment or reuse.

Where relevant, Confluence Environmental can integrate ASS assessment with:

• groundwater level assessment;

• dewatering risk assessment;

• groundwater quality monitoring;

• water treatment requirements;

• discharge monitoring;

• drawdown considerations; and

• surface-water protection measures.

This allows the soil and groundwater components of the ASS risk to be considered together rather than as separate project issues.

Construction Support and Verification

ASS management does not necessarily end when the management plan is issued.

For projects involving active soil treatment or complex earthworks, Confluence Environmental can provide construction-phase environmental support including:

• contractor pre-start advice;

• inspection of excavated materials;

• field screening;

• verification sampling;

• assessment of treatment effectiveness;

• groundwater and surface-water monitoring;

• review of treatment and material records;

• unexpected finds advice; and

• completion or verification reporting.

This provides continuity between the investigation findings, management strategy and implementation of the works.

Integrated Soil, Waste and Environmental Management

Acid sulfate soil management frequently overlaps with other environmental requirements.

Excavated material may also require assessment for waste classification, VENM or ENM, while deeper excavation or dewatering may interact with groundwater, contaminated land or broader environmental management requirements.

Our capability across contaminated land, groundwater, waste classification and environmental monitoring allows these related issues to be considered within a coordinated investigation and management strategy.

This can reduce duplicated investigation, simplify project interfaces and provide a clearer soil and environmental management pathway through construction.

Integrated with Planning and Construction

ASS investigations are designed with consideration of the broader project.

We consider matters such as:

• proposed excavation levels;

• cut and fill requirements;

• service alignments;

• basements and foundations;

• drainage works;

• dewatering;

• construction sequencing;

• temporary treatment areas;

• material reuse;

• off-site disposal; and

• project staging.

This allows ASS risks to be identified and addressed at the appropriate project stage and provides a sound technical basis for Development Applications, infrastructure approvals and construction environmental management.

Technical and Planning Framework

Acid sulfate soil assessment and management in NSW is undertaken with reference to the applicable planning controls, ASS risk mapping and recognised technical guidance.

Relevant guidance includes the NSW Acid Sulfate Soil Manual together with current national guidance for sampling and identification, laboratory characterisation and groundwater dewatering.

The appropriate investigation and management approach depends on the site, proposed disturbance and applicable planning requirements.

A mapped ASS risk does not, by itself, establish the actual conditions that will be encountered during construction. Site-specific assessment is used to determine whether ASS is present within the proposed zone of disturbance and what management measures are required.

Acid Sulfate Soil Consulting Across NSW

Confluence Environmental undertakes acid sulfate soil assessments, testing and Acid Sulfate Soil Management Plans across Newcastle and the Hunter, Lake Macquarie, Maitland, the Central Coast, Sydney and Greater Sydney, the Mid Coast, Mid North Coast and regional NSW.