Acid Sulfate Soils Management Plan · OPW19/0205

PROCEDURE B
Treatment and Verification of Excavated ASS


Figure B4-1: Schematic cross-section of a treatment pad, including a compacted clay layer, guard
layer, leachate collection system and containment with bund




B4 (c) ASS Treatment
Excavated ASS materials shall be placed into identified treatment lots (not more than 250 m3) within the
treatment area where the material shall be spread in layers and allowed to dry (if required). The overall layer
thickness shall be a maximum 300 mm loose thickness.
Where required, drying shall be enhanced by mechanical methods (rotary hoe, disc plough, etc) to create a
relatively homogenous, friable material prior to addition of lime for neutralisation.

Maintain soil moisture through the following methods: controlled irrigation; covering with plastic to reduce
evaporation; or application of lime soon after excavation of moist soils. These measures will improve the
dispersion of lime throughout the soil profile.

Liming rates have been calculated in kg CaCO3/m³, using a factor of safety (fineness factor) of 1.5 and an
assumed bulk density of 1.8 tonne/m3. Calculation of liming rates required for full neutralisation of combined
actual and potential acidity are presented in Table B1.
Table B1: Liming rates
 Material Type                           Depth                         Treatment Rate
                                         0 m – 1 m BGL                 5 kg CaCO3/m³
 Natural Sands
                                         Below 1 m BGL                 15 kg CaCO3/m³
Note:   * Below Ground Level
        ** Liming rate based on maximum values.

These liming rates can be immediately adopted for lime neutralisation treatment.
In-situ treatment may also be carried out. This would involve the application of lime to the surface of the soil
at a rate sufficient to treat a soil thickness of 300 mm. The lime should then be mixed through the soil profile
(to a maximum depth of 300 mm) with an excavator, and validation samples collected. Once the 300 mm
layer has been treated and removed the process can start again and continue until the depth of excavation is
reached.

It should be noted that should this process be adopted then the offsite disposal location would be required to
have a bunded area for stockpiling of the treated soil until verification results have confirmed appropriate
lime treatment.

The following management measures should be followed at the offsite disposal location:

    Stockpiles are to be contained by bunds with stormwater runoff directed to a collection sump. Bunds are
     to be constructed from low permeability materials.

    The surface area of the stockpile is to be minimised by shaping and possibly capping or covering to
     prevent moisture loss and rainfall entry.

    Each stockpile will require tracking to allow for future lime treatment should it be required.




April 2019
J000799-003-R-Rev0 – Procedure B                       2/3