Beneficial Moderate risk of Construction Testing of rock to uses of impact on assess site specific risk of Precinct 1 - groundwater Beneficial Uses potential acid sulfate soil. Tunnels at party of groundwater Prevent acidification of CBD North properties within predicted groundwater by minimizing station to CBD degraded by area of impact drawdown in the area: South station groundwater Use of injection or acidification Precinct 3 - Arden discharge bores to from potential station prevent drawdown and acid sulfate contaminant migration soil activation Minimisation of drawdown through construction techniques such as construction using a TBM or grouting of the tunnels Reduced Some drawdown Construction Mitigation measures would groundwater predicted at include grouting, and Precinct 1 - levels at CityLink temporary injection bores Tunnels CityLink recharge bores located in the Yarra River CBD South recharge palaeovalley station to Domain bores station - Linlithgow shaft construction Precinct 6 - CBD South station Drawdown has been assessed individually for each precinct and each tunnel section, but in practice, drawdown would occur at the same time for adjacent precincts as construction progresses. Where significant drawdown occurs, the drawdown cone from one precinct (or tunnel section) may intersect with the drawdown cone from a neighbouring precinct. The cumulative effect where drawdown cones overlap is a greater total drawdown, which may increase impacts on groundwater dependent values in the areas of overlap. In the areas of the alignment where cumulative impacts would be most significant (such as the mined tunnels and CBD North and CBD South stations), mitigation measures, such as those described in Table would be employed to manage drawdown. This mitigated drawdown even allowing for cumulative – impacts is expected to be significantly less than the unmitigated drawdown (not – allowing for cumulative impacts) on which this assessment is based. Prediction of cumulative drawdown is therefore not critical for identifying risks in this assessment, but would be analysed further as part of the detailed design phase of the project. Operation Groundwater dependent assets not be susceptible to impacts during operation due to the sealing of tunnels and sub-surface structures that would result in negligible groundwater seepage into tunnels or structures.
Beneficial uses of groundwater at party properties degraded by groundwater acidification from potential acid sulfate soil activation Moderate risk of impact on Beneficial Uses of groundwater within predicted area of impact Construction Precinct 1 - Tunnels CBD North station to CBD South station Precinct 3 - Arden station Testing of rock to assess site specific risk of potential acid sulfate soil. Prevent acidification of groundwater by minimizing drawdown in the area: Use of injection or discharge bores to prevent drawdown and contaminant migration Minimisation of drawdown through construction techniques such as construction using a TBM or grouting of the tunnels Reduced groundwater levels at CityLink recharge bores Some drawdown predicted at CityLink recharge bores Construction Precinct 1 - Tunnels CBD South station to Domain station - Linlithgow shaft construction Precinct 6 - CBD South station Mitigation measures would include grouting, and temporary injection bores located in the Yarra River palaeovalley Drawdown has been assessed individually for each precinct and each tunnel section, but in practice, drawdown would occur at the same time for adjacent precincts as construction progresses. Where significant drawdown occurs, the drawdown cone from one precinct (or tunnel section) may intersect with the drawdown cone from a neighbouring precinct. The cumulative effect where drawdown cones overlap is a greater total drawdown, which may increase impacts on groundwater dependent values in the areas of overlap. In the areas of the alignment where cumulative impacts would be most significant (such as the mined tunnels and CBD North and CBD South stations), mitigation measures, such as those described in Table would be employed to manage drawdown. This mitigated drawdown – even allowing for cumulative impacts – is expected to be significantly less than the unmitigated drawdown (not allowing for cumulative impacts) on which this assessment is based. Prediction of cumulative drawdown is therefore not critical for identifying risks in this assessment, but would be analysed further as part of the detailed design phase of the project. Operation Groundwater dependent assets not be susceptible to impacts during operation due to the sealing of tunnels and sub-surface structures that would result in negligible groundwater seepage into tunnels or structures.