RFI - Attachment E - Acid Sulfate Soil Management Plan · MCU25/0053

In accordance with the ‘Queensland Acid Sulfate Soil Technical Manual – Soil Management Guidelines Version 5.1’ (Qld
Government, 2024), a “Very High Level of Treatment” is required at this site based on:

»      Approximately 800 tonnes of soil to be disturbed below RL 5 m AHD; and
»      Highest recorded net acidity value of 90 mol H+/t in the ground surface to 3.5 m depth range.

As a “Very High Level of Treatment” is required, an Environmental Management Plan and closure report are also required in
accordance with the information presented in the ‘Queensland Acid Sulfate Soil Technical Manual – Soil Management
Guidelines Version 5.1’.

An experienced, competent and suitably qualified soil scientist or engineer must be present onsite to ensure that the lime
treatment activities including validation testing, and groundwater monitoring (where required), described in this ASSMP are
followed onsite.

5.3.1 Background
It should be noted that Acid Sulfate Soils are typically observed in the field as a grey, or dark grey brown to black soil in colour,
sometimes with a yellow mottle. Acid Sulfate Soils may also emit a hydrogen sulfide (‘rotten egg smell’) gas/odour, especially
when the soil is disturbed such as during earthworks and excavation operations.

The aims of the ASSMP are as follows:

»      Analysis of the data from the investigation and assess the severity of Acid Sulfate Soil within the project area and formulate
       a suitable lime treatment regime for the soils to be disturbed by earthworks, and reduce the potential for acid generation
       due to the site earthworks; and
»      Monitor groundwater (where encountered) during earthworks.

In order to reduce the potential for acid generation due to the proposed earthworks, soil treatment and groundwater
monitoring (where required) should be carried out in accordance with the information presented in Section 5.3.2 of this
ASSMP as follows.

5.3.2 Recommended Management of Acid Sulfate Soils & Groundwater
The proposal to manage Acid Sulfate Soil and groundwater (as required) as part of the planned site earthworks below
RL 5 m AHD covers the following issues, which are detailed further in Table 1.

Table 1: Acid Sulfate Soil Management for Proposed Site Earthworks
    Issue:                 Acid Sulfate Management and Treatment, Groundwater Monitoring and Potential Treatment

    Operational Policy:    To effectively manage the Acid Sulfate Soils and groundwater at the site and avoid any adverse
                           environmental impacts before, during and after site earthworks.
    Performance            »    Validation sampling indicates that the appropriate treatment procedures have been employed
    Criteria:                   such that results of these tests do not exceed the Action Criteria levels of 18 mol H+/tonne,
                                assuming that more than 1000 tonnes of soils are disturbed below RL 5 m AHD.
                           »    Groundwater should be monitored for depth/level, pH, Electrical Conductivity, aluminium
                                content and iron content, before, during and after the earthworks period. On site performance
                                criteria for water monitoring should be based on the Queensland Water Quality Guidelines 2009
                                (revised in 2013), herein referred to as the ‘QLD DEHP Guidelines’ (DEHP, 2013). For any
                                parameter values not covered in the QLD DEHP Guidelines, refer to the Australian and New
                                Zealand Guidelines for Fresh and Marine Water Quality (ANZECC and ARMCANZ, 2000).
    Soils:                 Based on the soil test results, it is recommended that:

                           »    The earthworks are managed by a reputable and suitably qualified consultant experienced in the
                                field of Acid Sulfate Soils and treatment.
                           »    Soils excavated below RL 5 m AHD in the existing fill profile will require lime treatment. The lime
                                treatment rate for soils excavated in the existing fill profile is 4 kg/tonne (6.8 kg/m3). The values
                                presented as kg/m3 assume a bulk density conversion factor 1.7 t/m3.
                           »    A bulk density factor will be required to convert from kg/tonne to kg/m3. A bulk density
                                conversion factor of 1.7t/m3 has been used in the absence of soil test results, however it is

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