07/1586 - Response to Information Request [As Published] · 132007.1586

* Project No. 307-2624 Page 7
August, 2007

 

Given the limited extent of the proposed excavation works, it is recommended that the
application of aglime be carried out using the simple surface treatment method. This
method involves applying the aglime to the ground surface in the area of the excavation,
prior to its commencement. The amount of lime applied on the surface in this manner
should be appropriate for the depth of the excavation. That is, if excavation to 1.5m
depth was required and using the rate of 5kg/m®, then a surface layer of 1.5m x 5kg/m? =
7.5 kg/m? should be applied. The mixing of lime with the excavated soil would then be
achieved during the excavation, handling and transport processes. It is also noted that if
the excavation is to be staged, then the amount of lime spread over the surface may
need to be adjusted accordingly, or be reapplied over a lower benched level.

By adopting the recommended surface treatment of aglime, the management of the acid
sulfate sulfate soil occurring at this site can be effectively finalised within the single
activity. Other ASS management issues such as site runoff, catchponds, groundwater
monitoring, staging of excavation works and ASS treatment, stockpiles of untreated
ASS, and the sampling and monitoring of treated ASS, are all either inapplicable or are
simplified to the extent where they are resolved and finalised within the single ASS
treatment/verification site activity.

6.2 Site Monitoring

A simple monitoring program should be conducted to verify the effectiveness of the
management strategy.

Considering the relatively low required application rate of lime, and the limited extent of
the affected soil, it is recommended that the ASS monitoring simply consist of
verification testing using the acid neutralising capacity (ANC) test procedure, of the
treated soil at the rate of 1 test per 500m°.

It is also recommended that in the event that extraction of groundwater is required
during the basement construction, the acidity and turbidity of the groundwater should be
checked, and these water quality criteria must be at acceptable levels prior to discharge.
We note that the results of a pre-construction groundwater monitoring program should
also be considered when establishing water quality criteria in relation to discharge of
extracted groundwater.

 

ZB SOIL SURVEYS ENGINEERING