ADG1290.21 Dewatering Management Plan_Rev1_02.02.22 · OPW21/0315

                                                                                          ADG Consulting Pty Ltd


     As part of the Additional Geotechnical Investigation, DP installed a PVC standpipe in BH3, and undertook
     sampling and analysis of groundwater on 18 January 2022 generally consistent with the National Acid
     Sulfate Soil guidance documents. Sample analysis was performed by ALS Environmental laboratory, with
     a summary of the analytical data provided below.

   Table 2 Summary of key analytical groundwater data (sourced from DP 2022)
       Parameter/Analyte                                                       BH3/MW3
       Physico‐chemical
       pH (pH units)                                                              7.76
       Electrical conductivity (µS/cm)                                           1,200
       Total alkalinity (mg/L)                                                    89
       Dissolved metals (µg/L)
       Aluminium                                                                  20
       Arsenic                                                                    <1
       Cadmium                                                                    <0.1
       Chromium                                                                   <1
       Copper                                                                      2
       Iron                                                                       <50
       Lead                                                                       <1
       Nickel                                                                      1
       Zinc                                                                        8
       Total metals (µg/L)
       Aluminium                                                                128,000
       Iron                                                                     75,100
       Other (mg/L)
       Calcium                                                                    127
       Magnesium                                                                  19
       Sodium                                                                     106
       Potassium                                                                   7
       Chloride                                                                   93
       Sulfate                                                                    355
       Chloride: Sulfate ratio                                                    0.26
     Table notes:
     <LOR = less than the limit of reporting

     In summary, groundwater beneath the site is considered to be brackish and slightly basic pH, with low
     alkalinity and buffering capacity. The soluble chloride to sulfate ratio is less than 4, which indicates that
     where ASS are present underlying the site, they have been previously oxidised and sulfate released. No
     exceedances of the relevant groundwater investigation levels (GILs; NEMP (2013)) or Noosa River
     environmental values and water quality objectives (DERM 2010) were reported for any dissolved metals.
     High levels of total iron and total aluminium were reported however there is currently no relevant
     criterion for total iron or aluminium in marine waters. The high total iron and total aluminium
     concentrations, along with low to non‐detectable concentrations of dissolved aluminium and iron,



ADG1290.21 Dewatering Management Plan_Rev1_02.02.22                                                         Page 5