ADG1290.21 Dewatering Management Plan_Rev1_02.02.22 · OPW21/0315

                                                                                        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 3 and Table 4 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. The proposed secant pile shoring wall and
     location of proposed dewatering treatment equipment contemplated under this DMP is provided in
     Appendix C.
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 3 to 5 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 sixteen to twenty‐seven
     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 3 to 5 L/sec (or 180 to 300 L/min or 10,800 to 18,000 L/hr)
     from Section 5.3.1 of this report, one sedimentation tank will provide between approximately seventy‐
     six and one‐hundred‐and‐twenty‐seven 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.


ADG1290.21 Dewatering Management Plan_Rev1_02.02.22                                                       Page 13