Compiled Reference Document - MCU25/0020 (As Published)

ADG Consulting Pty Ltd

 

6 Water quality management
6.1 Responsibility

The Site Manager is ultimately responsible for implementing the water quality management procedures
described in this DMP.

6.2 Operational policy

To prevent impacts on the receiving waters by effectively treating all extracted groundwater prior to
discharge from the site.

6.3 Performance criteria

The performance criteria for the discharge of extracted groundwater are the water quality objectives
provided in Table 2 and Table 3 in Section 4 of this report. Both the discharge and receiving waters (within
a 20 m radius of the stormwater discharge point) will be assessed against the WQOs to ensure that the
environmental values of the waterway are maintained. Receiving waters data will also be assessed
against background monitoring data if non-compliant results are obtained at the receiving waters
monitoring location.

6.4 Implementation strategy

All extracted groundwater will be treated on-site using available technologies prior to discharge to the
stormwater network. The treatment system described in Section 6.4.1 will be adopted, installed and
operational prior to the commencement of dewatering.

6.4.1 Groundwater treatment systems

Subject to final appointment of shoring and dewatering contractors (who all generally have different
treatment systems), the following treatment systems are generally proposed for dewatered groundwater
treatment prior to discharge. Regardless of the contractor employed, groundwater treatment systems
should be installed with capability for treating flow rates of up to 10 to 12 L/sec, as a contingency against
higher than anticipated flow rates exceeding the estimated 9 L/sec as a result of varying ground conditions
across the extent of excavation or construction during wet weather.

Primary treatment
A groundwater treatment system will be installed to provide primary treatment of the extracted
groundwater. The system will provide the following capabilities:

A baffled treatment tank with 5 kL minimum capacity

Automated in-line chemical dosing systems for the addition of buffering solutions and coagulants
A filtration system to reduce fine particulates (if required)

Emergency response alarms for non-routine situations.

FWnNr

Based on the estimated extraction rate, this system will provide approximately nine minutes contact time
during the initial chemical dosing, prior to secondary treatment using a sedimentation tank. Primary
treatment tank will be vertically stacked on the secondary treatment tank wherever practicable to
minimise site area required for groundwater treatment equipment.

Secondary treatment

A 23 kL sedimentation tank will be utilised to provide the necessary residence time for secondary
treatment of the groundwater prior to discharge to the stormwater system. Based on the estimated
groundwater extraction rate of approximately 32,400 L/hr (equivalent 540 L/min) from Section 5.3.1 of
this Report, one sedimentation tank will provide approximately fourty-two minutes retention time
following primary treatment of the extracted groundwater. This is considered to be sufficient secondary
settling / retention time based on extensive prior experience on other sites in similar ground conditions.

 

ADG1786.25 Dewatering Management Plan_Rev1_07.10.25 Page 13