3.0 Investigations

Step 1: Soil sampling supported by desktop assessment and site investigation; and
Step 2: Sample selection and laboratory analysis (supported by Step 1).

3.1 Step 1: Desktop assessment and site investigation

3.1.1 Desktop assessment

The desktop assessment is a preliminary appraisal of ASS risk within the property/landholding. This involves gathering information from ASS risk maps, generic soil maps, geological maps, topographic maps, aerial photographs and other local investigations or environmental impact reports, to assess the possibility of ASS occurrence.

Appendix 1 provides a draft ASS risk map based on existing geomorphological and hydrological properties of the relevant soil formation. The ASS risk map is a broad scale assessment for planning purposes. The ASS risk map provides an indication where acid sulfate soils may exist. Local variance in soil conditions will greatly influence the on-ground validation of key map units. The ASS risk map will not replace the need to undertake a detailed soil identification and on-ground assessment. Whilst information from this map should form part of the information presented in an investigation report, it cannot be used alone at the property scale to confirm absence of ASS, or define the amount of existing or potential acidity for a disturbance.

The following geomorphic or site description criteria should be used to determine if ASS are likely to be present:

• land with elevation less than 5 metres AHD;
• soil and sediment of recent geological age (Holocene);
• marine or estuarine sediments and tidal lakes;
• low-lying coastal wetlands or back swamp areas, waterlogged or scalded areas, stranded beach ridges and adjacent swales, interdune swales or coastal sand dunes;
• coastal alluvial valleys;
• areas where the dominant vegetation is tolerant of salt, acid and/or waterlogging conditions e.g. mangroves, saltcouch, swamp-tolerant reeds, rushes, paperbarks (Melaleuca spp.) and swamp oak (Casuarina spp.); and
• areas identified in geological descriptions or in maps as:
  • bearing sulfide minerals;
  • coal deposits or marine shales/sediments (geological maps and accompanying descriptions may need to be checked); and
  • deep older estuarine sediments below ground surface of either Holocene or pre-Holocene age.

3.1.2 Site investigation

Soil sampling locations should be guided by the desktop assessment and site characteristics. Relevant characteristics to consider include:

• nature of the disturbance (excavation, filling or groundwater extraction);
• specific location or locations of disturbance;
• total area of the site (in m² or hectares) to be disturbed;
• volume of material to be disturbed; and maximum depth of disturbance with reference to metres AHD (including any underground service pipes such as sewerage or drains).

Care should be taken to ensure representative samples are collected especially on sites with more than one type of geomorphological unit, or clearly different land surface elevations, so that sampling is representative of the area.

Appendix 2 provides a list of soil and water indicators that can be used (as a result of either site investigation or field soil tests) to identify if ASS are present. The site inspection should investigate for the presence of actual and potential ASS. Also note that it is common to have an actual ASS that also contains some un-oxidised iron sulfides or potential acidity.

3.1.3 Soil sampling

Soil sampling involves drilling or augering investigative boreholes to at least 3 metres depth, or at least 1 metre below the maximum depth of disturbance (whichever is the greater), describing and undertaking field soil tests on the soil profiles retrieved and collecting and storing samples for laboratory analysis. The information gathered from this step will be required to assist in selecting appropriate samples for laboratory analysis and enable both the proponent and the Department of Environment, Water and Catchment Protection (DEWCP) to review and assess the results. The following information should be provided as part of the soil sampling procedure:

• the full grid reference of each borehole using Australian Metric Grid ;
• the exact location of each borehole shown on an appropriately scaled map;
• an exact description of the vertical dimensions of the borehole relative to existing surface height AHD;
• a brief description of the equipment and/or methods used to retrieve the samples;
• a field description for each soil profile including soil texture, colour, mottling and other diagnostic features (e.g. jarosite, shell); and
• results from field soil tests (field pH (pH_F), pH after oxidation with hydrogen peroxide (pH_FOX) and reaction with peroxide) at 0.25 metre vertical intervals to the base of the soil profile (see Appendix 3 for notes on how to interpret these tests).

The number of boreholes required is dependant on the volume of ASS disturbance, or for disturbances greater than 1000 m³, the area (m² or hectares) to be disturbed. Table 1 summarises the minimum number of boreholes to be drilled, described, field tested and sampled for non-linear and linear disturbances.

Table 1 - Minimum number of boreholes required for ASS investigation

Extent of site project		Number of boreholes
1. Area project	< 1 ha	4
	1 - 2 ha	6
	2 - 3 ha	8
	3 - 4 ha	10
	> 4 ha	2 for every hectare
2. Volume of disturbance (m3)	≤ 250	2
	251 - 1000	3
	> 1000	1 for every 500m3
3. Linear project	Minor width and volume and low S(%)	@ 100 m intervals
	Major width and volume	@ 50 m intervals

Note: The borehole density relates to the pre-development stage, as opposed to sampling requirements after disturbance - adapted from Queensland State Planning Policy 2/02 Guidelines .

Once boreholes have been dug, the profiles described and soil field tests conducted, soil samples must be collected from each profile at a vertical maximum of 0.5 metre intervals. In deciding the appropriate sampling intervals, the field operator should refer to the field description notes and identify any significant changes with depth down the profile in field description properties (such as a change in pH, colour, texture etc.). Samples with clearly different physical, visual or chemical properties should not be 'bulked' together, as this will reduce the precision of future laboratory results.

When collecting samples in the field it is important to prevent oxidation of the soil as much as possible. This can be achieved by immediately placing the sample in plastic bags or other suitable containers, excluding air, then placing in a field freezer or with ice in an esky. Samples should be kept out of direct sunlight even on ice. The samples should be carefully marked (using a waterproof pen) for easy identification, and be frozen or specially dried within 24 hours of collection.

All samples should be retained in storage (frozen or specially dried) until the field investigation report and any related ASS management strategy has been assessed for the purposes of the development, i.e. approval given. Further laboratory analysis may be required to clarify results, or provide a more accurate understanding of the soil for management purposes. Re-drilling is expensive.

Further information on how to conduct ASS sampling can be found in the Guidelines for Sampling and Analysis of Lowland Acid Sulfate Soils (ASS) in Queensland 1998 on the website www.environ.wa.gov.au

It is important to note that there are occupational health and safety issues related to soil collection and field-testing, particularly in regard to handling hydrogen peroxide, digging soil inspection pits and dangers associated with hydrogen sulfide gas poisoning. A Health and Safety Plan should be prepared and communicate to all field staff prior to site investigation.

3.1.4 Using information gathered in step 1 to make a decision

Appendix 3 outlines how to interpret field pH (pH_F) and field peroxide pH (pH_FOX) results. These tests are essential for indicating whether ASS are likely to be present or absent. If the proponent concludes that the desktop assessment, site and field indicators and pH test results all show that ASS are absent then this should be clearly stated.

Irrespective of the field test results, Step 2 (confirmatory laboratory analysis) is required in the majority of situations. The exception is when a non-linear disturbance up to 1000 m³ which does not involve activities that may alter groundwater, is planned in one of the following situations:

• the area is mapped as low risk of ASS on a draft ASS Risk Map and the conclusions of Step 1 show that ASS are absent. The applicant may submit the results of Step 1 to the Land and Water Quality Branch, DEWCP for assessment without undertaking Step 2; and/or
  
  
• compelling geomorphic and geologic evidence (e.g. soils developed on basalt) supported by field pH tests on the soil provides strong evidence that ASS are absent from the areas to be disturbed. The proponent may submit this evidence (i.e. photographs, soil description and results from Step 1) to support non-completion of Step 2.

NB: All soil samples should be retained until the application is approved. The DEWCP may call upon one or more of the samples to be confirmed by laboratory analysis.

3.2 Step 2: Sample selection and laboratory analysis

NB: The DEWCP will likely compare the laboratory results with the field results and if dissatisfied with the sample selection, may request that additional samples be analysed.

3.2.1 Sample selection for non-linear disturbance up to 1000 m³

The sampling protocol outlined below, together with Table 3, should be used as a guide to selecting samples for laboratory analysis where a non-linear disturbance up to 1000 m³ is proposed. Use of this protocol assumes that high quality field investigations have been undertaken as outlined in Step 1.

1. Use Table 1 to determine the minimum number of boreholes required (based on the maximum volume of disturbance).
   
   
2. Collect samples at the required interval and collate field information (see Step 1).
   
   
3. Using the field results from Step 1, select the soil profile most likely to contain ASS.
   
   
4. From this soil profile, and using the field results as a guide, select one sample that is most likely to contain ASS from each metre interval.
   
   
5. Using the field results, select a single (one) sample most likely to contain ASS from each additional soil profile.
   
   
6. Submit the selected samples for laboratory analysis, and store the remaining samples frozen or specially dried for possible future use.

3.2.2 All other disturbances

For disturbances that are greater than 1000 m³, linear disturbances and activities involving alteration to groundwater, consult the Land and Water Quality Branch, DEWCP for advice.

Table 2 shows the minimum soil samples to be initially selected for laboratory analysis for non linear disturbances less than 1000 m³

	Maximum disturbance depth
	<1 m	1 - 2 m	2 - 3 m	3 - 4 m
	Borehole depth 2m	Borehole depth 3m	Borehole depth 4m	Borehole depth 5m
Volume of disturbed soils 251 - 1000m3	3	4	5	6
Volume of disturbed soils ≤ 250 m3	4	5	6	7

Number of samples to be analysed per total volume of soil to be disturbed, not per borehole.
Depth of disturbance from ground surface. Borehole depth must be 1m maximum of disturbance

3.2.3 Laboratory analysis selection

Once the appropriate samples have been selected, the samples should be submitted to an approved accredited laboratory for analysis. The existing acidity and potential acidity of the soil should be analysed. Potential acidity can be determined by Chromium Reducible Sulfur (S_CR), Peroxide Oxidation Combined Acidity and Sulfate (POCAS) and Total Oxidisable Sulfur (TOS). For samples with pH_F <5.0, the existing acidity must also be determined by appropriate laboratory analysis e.g. Titratable Actual Acidity (TAA) if S_CR and TOS analyses are to be conducted. Soils with jarosite or other similar insoluble compounds have a less available existing acidity and will require more detailed analysis. Refer to the Guidelines for Sampling and Analysis of Lowland Acid Sulfate Soils (ASS) in Queensland 1998.

Different laboratory analyses provide different types and levels of information on the chemistry of the soil e.g. Titratable Potential Acidity (TPA) and the full Suspension Peroxide Oxidation Combined Acidity and Sulfur (SPOCAS) methods have been developed by the Queensland Department of Natural Resources and Mines for ASS investigation. A combination of analyses may be required if a more detailed knowledge of the soil chemistry is necessary e.g. to determine the most appropriate neutralising agent or management technique, or if the proponent wants to minimise the amount of neutralising agent used (often economical for larger scale disturbances). Advice from the Land and Water Quality Branch, DEWCP on an appropriate laboratory can be sought before analysis commences.