ADG Dewatering Management Plan · OPW21/0315

                                                                                         ADG Consulting Pty Ltd



       Laboratory analysis of samples recovered from     Initially, then as                       Environmental
                                                                              ADG Consulting
       extracted groundwater (pre-treated)                    required                              Consultant

6.6 Maintenance
     The groundwater treatment systems must be regularly maintained. Maintenance must include:


          −    Regular cleaning and or replacement of the filters within the filtration unit, where required to
               be installed.
          −    Regular removal of sediment from the sedimentation tank. The sediment must be either
               returned to the excavation pit for dewatering and bulking out with excavated material, or
               removed from the site by a licensed liquid waste contractor.
          −    Regular check of the dosing system and top-up of buffering solutions and flocculants.
6.7 Reporting
     Dewatering management procedures and monitoring results will be reviewed by ADG Consulting weekly
     to ensure that the treatment procedures are effective, and that the receiving waters are not being
     impacted by the extracted groundwater being discharged.

     The following reporting procedures will be adopted:


          −    A summary report will be prepared upon completion of the initial pre-discharge monitoring. The
               report will be submitted to the Site Manager, Dewatering Contractor, and NSC upon request.
          −    Weekly interim reports will be prepared upon receipt of laboratory data for each round of
               ongoing compliance monitoring. The interim reports will display all data obtained during the
               previous monitoring event, and provide comments and recommendations based on the results.
          −    A dewatering compliance report will be prepared on completion of the project (upon request).
     The above reports will be prepared by ADG Consulting and provided to the Site Manager and Dewatering
     Contractor as they become available. The reports will include all water quality results and comparison to
     the WQOs, corrective actions and recommendations made to the Site Manager and Dewatering
     Contractor during the monitoring period.

     The Site Manager must keep records of complaints, volumes of chemicals used and treatment methods
     employed. These records must be available on-site at all times and submitted to NSC by the Site Manager
     upon request.
6.8 Contingencies
     If water quality monitoring indicates ongoing exceedances of the performance criteria, and the water
     quality objectives for the receiving waters cannot be met, then corrective actions will be adopted as
     necessary. Possible contingencies may include one or more of the following:


          −    Installation of additional sedimentation tanks to provide increased residence time and assist
               with the retention of precipitated iron hydroxides, other heavy metals and/or suspended
               sediments.
          −    Installation of additional flocculant and/or coagulant dosing systems to assist in precipitation of
               suspended sediments and/or heavy metals.
          −    Installation of activated carbon filtration or other fine media filtration to retain suspended
               sediments and/or heavy metals.




ADG1290.21 Dewatering Management Plan_Rev0_12.10.21                                                        Page 14