Draft DEWCP and EPA guidance on managing acid sulfate soils




Referral to EPA

Source of Information


App. 1: Checklist


Draft DEWCP and EPA guidance on managing acid sulfate soils

2 DEWCP and EPA position and guidelines

2.1 Management objective for acid sulfate soils

The DEWCP and EPA management objective for acid sulfate soils is that development that may potentially disturb acid sulfate soils is planned and managed to avoid adverse effects on the natural and built environment and human health and activities.

2.2 Key management principles

The DEWCP and EPA position is consistent with the aims of the National Strategy for the Management of Coastal Acid Sulfate Soils (NWPASS 2000). In broad terms the principles supported by DEWCP and the EPA are as follows:

  • The preferred approach is to avoid disturbing soils and sediments exhibiting acid sulfate soil characteristics where possible.

  • All projects should consider acid sulphate soils if they involve earth works, excavation works; lowering of the groundwater table by dewatering or drainage works; and, in some cases, filling (see Section 1.4);

  • All decision-making authorities, agencies, infrastructure providers and individuals involved with earthworks that may disturb acid sulfate soils, are aware of the risks associated with such disturbances, and will have set procedures to complement the broader State-wide guidelines (as recommended in this guidance).

  • No impacts on key elements of the biophysical environment eg conservation areas and public drinking water supplies, are acceptable;

  • Where a project or proposal that has the potential to disturb acid sulfate soils, a preliminary site assessment such as using onsite indicators, field pH tests and chemical analysis, will need to be carried out. This process will ensure that acid sulfate soils issues are considered at the early planning phase of the project; (see Section 2.3 and Appendix 2).

  • Where the disturbance of acid sulfate soils is unavoidable after the preliminary investigation and soil sampling have been conducted, it is expected that the general procedures outlined in the flowchart in Appendix 1 will be followed. Key steps include;
    • Consideration of a range of mitigation and management strategies, and demonstration that every reasonable step has been taken to minimise and avoid the disturbance of acid sulfate soils and adverse environmental and community impacts;
    • Demonstration that there will be no unacceptable risks to the natural or the built environment or human health;
    • Preparation of an appropriately detailed Acid Sulfate Soil Management Plan (see Section 2.4 and Appendices 3 and 4); and
    • Implementation of the Acid Sulfate Soil Management Plan;

  • Where there are development pressures in acid sulfate soil risk areas, the local authority is urged to ensure that the community are aware of the acid sulfate soil issue, to complement any actions being taken at other government levels e.g. DEWCP and Department of Planning and Infrastructure (DPI);

  • Where damage to the environment has occurred as a result of previous inappropriate disturbance of acid sulfate soils, works to rehabilitate the environment and to mitigate any on-going adverse affects should be implemented as soon as practicable; and

  • At this stage the extent and the variability of acid sulfate soils in Western Australia are not well documented, a precautionary approach is urged.

DEWCP is currently developing a series of guidelines to assist with the management of acid sulfate soils. In the absence of local acid sulphate soils guidelines, the investigation, assessment and management procedures developed by other States, particularly Queensland and New South Wales, may be used as an interim guide (see sources of information in Section 4). However, it should be noted that some procedures and management techniques are not applicable for Western Australian conditions. It is therefore recommended that methodologies for detailed site assessments and management plans are developed in consultation with DEWCP and other relevant authorities.

Should a proposal need to be referred to the EPA (see Section 3), the EPA may have additional specific requirements either at the referral stage, or during any formal assessment.

2.3 Site investigations for acid sulfate soils

Adequate information on the extent and nature of acid sulfate soils is clearly crucial to ensuring that development does not result in adverse impacts on the environment and on human health and amenity. Investigations may be carried out in a hierarchical way to establish whether particular land contains or is near acid sulfate soils, and if so, the extent and severity of acid sulfate soils.

The first step is to establish whether or not a proposed development site is in an area where there could be a risk of disturbing acid sulfate soils. It involves a desktop assessment and a site visit to identify indicators of acid sulfate soils, followed by soil sampling. The desktop assessment includes copies of site maps, aerial photos, and description of the site works. Groundwater issues should be considered at this early stage.

The desktop assessment should check the location of the proposed development against suitable ASS maps. In the absence of a comprehensive acid sulfate soils map in Western Australia, DEWCP with assistance from the DPI has developed a draft ASS map for the Swan Coastal plain areas. The categories include high to moderate risk, moderate to low risk and low to nil risk of acid sulfate soils presence. The map units have been classified on the basis of the geomorphological and hydrological properties of the relevance formation, including depth to groundwater and height above sea level in AHD.

ASS maps are broad scale assessment (1:25,000) of the presence of acid sulfate soils to assist for planning purposes. The reliability of the ASS map is dependent on the correspondence between the properties of the map units and the occurrence of acid sulfate soils on-ground. Local variance in soil conditions will greatly influence the onground validation of key map units. Rapid field appraisal of these units will verify the classification scheme based on "best-guessed" of the chances of acid sulfate soils occurring in different surface geological units.

Where a preliminary site assessment has established that acid sulfate soils are likely to be disturbed by a proposed development, further investigations and analyses should be carried out at an appropriate time, to determine the extent of potential impacts, and how manageable these are.

A more detailed site assessment may be carried out in a hierarchical way. The level of detail of site survey work and analyses may reflect the stage of planning, the extent of ground disturbance proposed, the potential impacts on the environment and human health and amenity, and the severity of the acid sulfate soil.

Until comprehensive site assessment procedures are developed for Western Australia, the investigative and assessment procedures adopted by the Queensland or the New South Wales Governments may be useful as a guide (see Ahern 1998, Stone 1998, and the websites for the Queensland Department of Natural Resources and the NSW Department of Agriculture).

2.4 Management

Management of acid sulfate soils presents difficulties and some risk. If development has to occur on acid sulfate soils, it should be carried out in a manner that ensures that there is no resultant acid water discharge that may adversely affect the biophysical environment and human health and amenity.

In each case, it is recommended that alternatives are considered with a view to favouring an alternative that minimises disturbance of acid sulfate soils.

In the event that disturbance is considered acceptable in particular circumstances, it is generally expected that an Acid Sulfate Soil Management Plan will be prepared and implemented. The detail will be dependent on the scale and characteristics of the particular development, the potential on-site and off-site environmental impacts and sensitivity of the environment likely to be affected, and the level of certainty associated with the proposed mitigation strategy.

Guidelines for the preparation of an Acid Sulfate Soil Management Plan area in Appendix 3.

Techniques for the management of acid sulfate soils are referred to in the references in Section 4. However, these are for other States and may not in all instances be directly applicable to Western Australian circumstances, or meet the objectives of the EPA.

2.5 Consideration of acid sulfate soils during the land use planning process

The WAPC is currently developing a policy response to deal with the issue of acid sulfate soils. That response, however, will require completion of acid sulfate soil risk mapping. In the meantime, the WAPC has published Planning Bulleting No. X: Acid Sulfate Soils which contains a set of general guidelines that should be sued in the assessment of town planning scheme amendments, subdivision and strata applications and applications for planning approval where there is evidence of a significant risk of disturbing acid sulfate soils.

A copy of the Bulletin is available at http://www.planning.wa.gov.au.

2.6 Works that do not require planning or external approval

A range of excavation, drainage and dewatering works currently may not always be subject to an external assessment and approval process. It is nonetheless very important that these works are well managed to avoid inadvertent disturbance of acid sulfate soils in areas at risk.

Works in this category may, depending on the circumstances, include:

  • Local authority road and drainage works, and works in public open space;

  • Works by public authorities in regional reserves;

  • Works for main roads and railways;

  • Works for sub-surface infrastructure eg for gas, water, effluent disposal, oil, power and telecommunication services;

  • Agricultural works eg drainage works;

  • Bore water extraction in areas that do not require a licence; and

  • Ground disturbing works associated with any other land use or development.

To avoid unanticipated impacts on the environment, human health, infrastructure, buildings and a range of water uses, it is strongly urged that:

  • Authorities, infrastructure providers and individual operators that carry out subsurface works:
    • Check with the draft acid sulfate soils risk map where applicable and home in on likely areas of acid sulfate soils in the localities in which they work; and
    • Take on board the following general procedures and considerations:
      • Check whether a site is in an area where there is a risk of disturbance of acid sulfate soils (see Section 2.3 and Appendix 1);
      • If the works are to be carried out in an area of risk, engage qualified people to carry out investigations and analyses using an acceptable methodology, generally as recommended in Section 2.3 and Appendix 2;
      • If disturbance of acid sulfate soils is proposed, the authority, infrastructure provider or operator, should generally follow the steps in the flowchart in Appendix 1, and, as appropriate prepare and implement an acid sulfate soil management plan following consultation with relevant agencies such as DEWCP;

  • Local authorities and other responsible agencies with advisory and regulatory functions become aware of likely areas of acid sulfate soils in development areas and ensure that the community are aware of the issue, and complement any actions by authorities such as DEWCP and DPI.

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