Reference Document - Acid Sulfate Soil Report 11_2023- OPW23_0189 · OPW26/0094

                                                                                                                   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




Document Set ID: 22828362
Version: 1, Version Date: 26/02/2024