ADG1673.24 Dewatering Management Plan_Rev0_12.07.24

                                                                                        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 8 to 10 L/sec, as a contingency against
     higher than anticipated flow rates exceeding the estimated 6 L/sec as a result of varying ground conditions
     across the extent of excavation.

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

     1.    A baffled treatment tank with 5 kL minimum capacity
     2.    Automated in‐line chemical dosing systems for the addition of buffering solutions and coagulants
     3.    A filtration system to reduce fine particulates (if required)
     4.    Emergency response alarms for non‐routine situations.

     Based on the estimated extraction rate, this system will provide approximately thirteen 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 21,600 L/hr (equivalent 360 L/min) from Section 5.3.1 of
     this Report, one sedimentation tank will provide approximately sixty‐three 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.




ADG1673.24 Dewatering Management Plan_Rev0_12.07.24                                                       Page 13