Dewatering Management Plan · OPW24/0032

                                                                                        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
     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, a 5 kL system will provide approximately seven minutes contact
     time during the initial chemical dosing, prior to secondary treatment using a sedimentation tank.
     Secondary treatment
     A sufficiently sized 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 43,200 L/hr (equivalent 720 L/min) from section
     5.3.3 of this report, a 23 kL sedimentation tank will provide approximately thirty‐two minutes retention
     time following primary treatment of the extracted groundwater.
     Tertiary treatment – may be required following initial testing of extracted groundwater.
     A filtration treatment system with specialised fine filtration media and chlorine dosing will be utilised to
     provide the required heavy metal removal (specifically for total and dissolved iron) where not
     precipitated and retained within the sedimentation tank/s (secondary treatment). This treatment system
     will provide tertiary treatment of the groundwater prior to offsite discharge.

     Tertiary treatment will only be required if the required water quality is unable to be achieved following
     primary and secondary stages of treatment. Subject to the results of field and laboratory testing during
     the pre‐discharge monitoring event.




ADG1304.21 Dewatering Management Plan_Rev0_08.10.21                                                       Page 12