ADG Dewatering Management Plan · OPW21/0315

                                                                                        ADG Consulting Pty Ltd



     1.    A groundwater pH buffering treatment system (primary treatment)
     2.    A sedimentation tank to provide additional residence time and sedimentation (secondary
           treatment).
     3.    Installation of fine media filtration to retain suspended sediments and/or heavy metals (tertiary
           treatment), if required.

     Details of the treatment systems and methodologies are provided in Section 6 of this report.

     Note: Consideration should be taken, regarding placement of treatment gear on site to enable easy
     cleaning and maintenance throughout the dewatering phase for the project. Consider the potential
     requirement for regular de-sludging of sedimentation tank/s to suitable area onsite, if available (cost
     minimisation).

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, this system will provide approximately seven minutes contact
     time during the initial chemical dosing, prior to secondary treatment using a sedimentation tank.
     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 43,200 L/hr (equivalent 720 L/min) from section 5.3.3 of
     this report, one sedimentation tank will provide approximately thirty-two minutes retention time
     following primary treatment of the extracted groundwater.


ADG1290.21 Dewatering Management Plan_Rev0_12.10.21                                                       Page 11