003 ECM_22828362_v1_Reference Document - OPW23 0189 · OPW26/0094

                                                                                                                 ADG Consulting Pty Ltd


                      3.2     Groundwater quality
                              In the absence of any localised monitoring well data, and based on numerous groundwater investigations
                              and dewatering monitoring projects that have been undertaken by ADG throughout the Noosa Coast
                              Region and immediate locality in recent years, our understanding of the groundwater quality in the region
                              is provided below:
                                  Groundwater is generally mildly acidic to neutral, with pH levels ranging from approximately 5.5 to
                                   6.5 and electrical conductivity ranging from brackish to saline between 2,000 µS/cm to
                                   48,000 µS/cm. Groundwater pH has the potential to reduce (become more acidic) following
                                   oxidisation of PASS as dewatering progresses, particularly if re‐wetting of the soils occurs.
                                  Dissolved oxygen levels in static groundwater typically range from approximately 35 – 40 %
                                   saturation.
                                  The groundwater associated with indurated sand strata is moderately to highly turbid as a result of
                                   staining and organic content.
                                  Concentrations of dissolved metals are typically below the available marine water trigger values
                                   (MWTV’s) provided in ANZECC/ARMCANZ (2000) for the receiving waters, however elevated levels
                                   of aluminium and particularly iron are expected in the untreated groundwater and have the
                                   potential to increase following oxidisation of PASS as dewatering progresses or as a result of existing
                                   acidic groundwater conditions.
                                  Given the location and previous use of the site, groundwater impacts resulting from site
                                   contamination are not anticipated.
                              A groundwater investigation will be undertaken at the commencement of dewatering as described in
                              Section 6.5.2 of this report. This assessment will be representative of the groundwater being extracted
                              and treated from the entire site, as opposed to localised monitoring well data which is often misleading.
                              Based on previous experience with dewatering in the area, ADG expects the groundwater to require
                              treatment to increase pH and dissolved oxygen levels, as well as reduce turbidity, suspended sediments
                              and dissolved metal concentrations prior to being discharged to the Noosa River.




                        ADG1580.23 Dewatering Management Plan_Rev0_28.09.23                                                         Page 5




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