Geotech Report - Acid Sulfate Soil Assessment - Appendix A

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PARTNERS

Residential Development

215-219 David Low Way, Peregian Beach

Draft Acid Sulfate Soil Management Plan (ASSMP)

 

 

 

 

 

Element Acid Sulfate Soil Management Plan

Objective/Target The objective of the ASSMP is to control net acidity levels within soils disturbed during
site development works, and to restrict to an acceptable level any potential on-site and
off-site environmental impacts during site redevelopment.

ASS Management To mitigate and manage potential environmental impacts associated with ASS during the

Strategy redevelopment works. This will be achieved by having a materials handling and
management strategy in place, as well as procedures for either on-site lime treatment of
soils or, the appropriate off-site treatment of soils (if a suitably sized and appropriately
located space is not available for on-site treatment).

Tasks/Actions An ASS investigation has been carried out to assess the soils within the redevelopment

 

site, to a maximum depth of 2.5m below the existing surface level. Fill materials, sands
and silty sands have been shown to contain negligible levels of net acidity and do not
require treatment for ASS. However, the natural dark grey-brown, silty clays encountered
in Bores 1 and 2 have been shown (in Bore 2) to contain levels of net acidity that exceed
the State Planning Policy 2/02 Action, Criteria of 0.03 %S. The natural silty clays will
therefore require treatment as follows:

© |fon-site treatment is undertaken then lime treatment of the soils will be undertaken

as described below.

e Where on-site treatment is not possible the silty clays will be excavated, then
transported in a sealed truck to an appropriately designed off-site treatment area for
neutralisation.

ASS Treatment On-Site

e Any silty clays exposed in the base of the basement excavation will require an
application of ag-lime at a rate of 5 kg/square metre.

e Where excavated silty clay soils are to be treated on-site, a suitably sized dedicated
treatment area will be created. Soils to be treated shall be placed on the treatment
area in layers not thicker than 0.3m.

e Bunding will be constructed around the perimeter of the designated treatment area
to intercept and contain run-off from the area during the soil treatment operations.

e The base of the treatment area is to be lime treated prior to placement of each layer
of excavated material. Re-treatment with ag-lime is required prior to placement of
each new layer of excavated material to be treated, and at the conclusion of all
treatment. The base of the treatment pad shall have a minimum ag-lime application
of 5 kg/square metre.

e Ag-lime will be applied evenly over the surface of the treatment area and thoroughly
blended into the ASS at a rate of 3 kg of ag-lime/tonne of dry silty clay soil. This
liming rate is based on a factor of safety of 1.5 and the use of good quality fine ag-
lime with a neutralising value of not less than 80 %.

e When incorporation of the lime is complete, chromium suite validation testing of the
treated spoil will be carried out to establish that sufficient ag-lime has been added to
neutralise the acid generation potential of the spoil. Where validation testing fails to
meet performance indicators, application of additional ag-lime will be required until a
satisfactory net acidity validation result has been achieved.

e Once ag-lime treatment is complete, the treated spoil may then be stockpiled for
later use or off-site disposal (as appropriate).

© Should the proposed depth of disturbance extend below 2.5m in depth from surface
level, then additional ASS testing will be required.

e Lime-treated, stockpiled soil shall have sediment fences and/or hay bales placed
downslope to intercept any eroded material. Earthen bunds shall be constructed
downslope of stockpile areas to divert run-offfdrainage to a collection sump. The
water quality of the sump is to be monitored against the water quality objective

 

 

 

Residential Development

Appendix C

215-219 David Low Way, Peregian Beach Page 1 of 3

Project No. 07160

18 June 2007