Reference Document - OPW23 0189

                                                                                             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 7 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, a 5 kL system will provide approximately eleven 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 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 25,200 L/hr (equivalent 420 L/min) from section
         1.1 of this report, a 23 kL sedimentation tank will provide approximately fifty‐four 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


    ADG1580.23 Dewatering Management Plan_Rev0_28.09.23                                                       Page 12