19.2.7 Contamination
An assessment of contaminated land risk is provided in Appendix R (Technical working paper: Contamination) which is summarised in Chapter 16 (Contamination). Areas within the project footprint that may contain contaminated soil and/or groundwater due to past or present land use practices have been investigated. During routine monthly groundwater monitoring as part of the hydrogeological investigation a suite of contaminants was assessed for laboratory analysis including cations and anions, heavy metals and nutrients. Groundwater contamination monitoring was conducted in
September and November 2016 to support the site contamination investigation as summarised in Chapter 16 (Contamination). Key sites investigated are discussed below.
Haberfield and St Peters
Contamination investigations undertaken for the M4 East and New M5 projects have been reviewed to provide an understanding of potential groundwater contamination in the vicinity of the Wattle Street interchange at Haberfield and the St Peters interchange at St Peters, respectively.
Wattle Street interchange
It was determined that the risk of potential groundwater contamination in the vicinity of the Wattle Street interchange at Haberfield is low. Potential contaminating land uses were identified as being located topographically down-gradient of the project and therefore would be unlikely to impact groundwater within the project footprint.
St Peters interchange
The St Peters interchange is to be constructed on a rehabilitated Alexandria Landfill as part of the New M5 project. Leachate is still generated from the former landfill and will continue to be pumped and treated on site before disposal off site. Leachate generation will be reduced by improving internal drainage and capping of the landfill. A cut-off wall is to be constructed along the eastern perimeter of the landfill to reduce groundwater inflow from the Botany Sands aquifer as part of the New M5 project.
The New M5 tunnels and access portals through the former landfill are to be undrained (tanked), preventing the ingress of contaminated groundwater into the tunnel drainage system. The deeper tunnels constructed in the Hawkesbury Sandstone or Ashfield Shale are to be drained, but are unlikely to intersect contaminated groundwater. The risk of contaminated groundwater entering the project tunnels at St Peters from leachate derived from the landfill is low, because leachate will continue to be pumped, collected and treated in a newly constructed water treatment plant as part of the New M5 project, drawing groundwater away from the tunnels. Leachate generation is to be reduced due to the cut-off wall that is to be constructed along the eastern perimeter of the landfill to
reduce groundwater inflow and capping the former landfill to reduce rainfall infiltration.
Hydrocarbon contamination identified within the weathered clay and residual shale is attributed to fuel leaks and spills from the nearby service station.
19.2.8 Existing groundwater users
A review of bores registered with DPI-Water and accessed through the BoM (on 9 May 2016) identified 197 boreholes within a two kilometre radius of the project footprint. There may also be other private bores present within the two kilometre radius that have not been registered with DPI-Water. The distribution of registered boreholes extracted from the database is shown in Annexure B of Appendix T (Technical working paper: Groundwater). In analysing the data, there are two distinct types of bores: bores with recorded hydrogeological data (66), and bores with only the borehole number and coordinates recorded (131).
Typically, boreholes with only coordinates recorded are monitoring wells constructed as part of contamination investigation programs. In most cases these monitoring wells would no longer be monitored, as the site investigation or remediation programs are completed and the sites have been redeveloped. Analysis of the remaining data indicates that the majority of registered wells are constructed for monitoring purposes, with the minority developed for recreation and domestic water supply (see Table 19-6).
Table 19-6 Summary of DPI-Water registered bores within two kilometres of the project footprint
Review of the lithological data indicates that the majority of boreholes are shallow (less than 10 metres below ground surface) and monitor groundwater in the sand, clay, shallow sandstone or shale. The majority of monitoring wells are clustered at various investigation sites within the study area. A 180 metre deep recreation bore is located at Redfern Park within the Hawkesbury Sandstone, and is used to irrigate Redfern Oval. Four domestic bores are located within the study area, ranging in distance between 210 metres and 1,480 metres from the tunnel corridor. It is not known if these bores are still used for domestic use or have been abandoned. A 210 metre deep bore (GW110247) at the University of Sydney at Camperdown extracts groundwater from the Hawkesbury Sandstone and is registered for domestic use.
Even though groundwater quality is generally good within the Hawkesbury Sandstone, groundwater use across most of the study area is low, as bore yields are typically low and the area has access to reticulated water. At Rozelle Rail Yards, there are few registered monitoring wells, suggesting that there have been limited historical groundwater investigations undertaken at this former industrial site (prior to the investigations undertaken for this assessment), or that monitoring wells have not been
registered.
19.2.9 Groundwater dependent ecosystems
A review of the Water Sharing Plan for the Greater Metropolitan Region Groundwater Sources (2011) and the National Atlas of Groundwater Dependent Ecosystems (viewed 22 August 2016) indicated there are no high priority GDEs within the study area (as identified in Chapter 18 (Biodiversity)). The nearest high priority wetlands are the Botany Wetlands and Lachlan Swamps within the Botany Sands, located at Centennial Park, around five kilometres east of the easternmost point of the project footprint, and beyond the range of potential impact.
19.3 Assessment of potential construction impacts
Construction works and operational infrastructure have the potential to change groundwater behaviour and impact on the surrounding environment. An assessment of potential impacts has been undertaken in accordance with the guidelines outlined in Table 19-2.
Groundwater within parts of the study area has the potential to be impacted during the construction phase of the project. The potential impacts that have been identified are:
· Reduced groundwater recharge
· Tunnel inflow
· Groundwater level decline including potential impacts on:
– GDEs
– Surface water and baseflow (the groundwater that discharges to a creek or river)
– Existing groundwater users
· Changes in groundwater quality
· Groundwater drawdown which may result in ground movement (settlement).
A detailed groundwater balance has been calculated for the construction of the project. This is discussed further in section 19.3.9 and in Appendix T (Technical working paper: Groundwater).
19.3.1 Reduced groundwater recharge
Surface disturbance due to the project construction would include paved construction ancillary facilities, acoustic sheds, cut-and-cover sections leading to the tunnel portals, and approach roads. Construction ancillary facilities would create additional temporary impervious surfaces during construction. The impacts of these surfaces, however, are considered minor and would not significantly reduce groundwater recharge during construction. In many instances construction ancillary facilities would be located on existing impervious surfaces and would therefore not impact local groundwater recharge during construction.
The risks during construction would be that access roads, tracks and the bunded isolation areas for stockpiling of construction materials could alter or reduce groundwater recharge. These impacts are considered minimal, as the affected area is small compared to the overall project footprint, and temporary, as the various structures would be removed at the end of the construction phase.
19.3.2 Tunnel inflow
The short term inflow during construction would be dependent upon a number of factors including tunnelling progress, tunnelling construction methodology (including tunnel lining methods and locations and the success of pre-grouting), fractured zones intersected, localised groundwater gradients and storativity (the volume of water released from storage per unit decline in hydraulic head in the aquifer, per unit area of the aquifer). Pre-grouting is the process of pumping grout into the sandstone or shale in pre-determined areas by drilling and injection to reduce the bulk rock permeability before tunnel advancement.
Initial inflows to tunnels can be large, because of the large hydraulic gradients that initially develop near the tunnel walls; however, these gradients would reduce in time as drawdown impacts extend to greater distances from the tunnels and inflows approach steady state conditions. Higher inflow rates are likely from zones of higher permeability, where saturated geological structural features are intersected by the tunnels. During construction these high inflow zones would be grouted to reduce the inflow rate. Groundwater from the Botany sands aquifer is likely to enter the tunnel indirectly
through hydraulic connection with the Hawkesbury Sandstone, however a capture zone analysis undertaken as part of the groundwater modelling confirms the Botany Sands would not be a dominant source of water to the tunnels during construction.
The groundwater modelling has predicted groundwater inflows to the tunnels during construction. Initial groundwater inflows to the tunnels during construction are estimated to range between 0.45 megalitres per day and 2.87 megalitres per day. The maximum inflows are predicted to peak towards the end of construction in 2021 at 2.45 megalitres per day or 0.77 litres per second per kilometre, which remains below the overall WestConnex tunnel inflow criterion of one litre per second per kilometre for any kilometre length of the tunnel.
The predicted water take during construction (year 2023) from each of the Greater Metropolitan Regional resource due to tunnel inflows is compared to the long term average annual extraction limit (LTAAEL) and is summarised in Table 19-7. Comparison of predicted tunnel inflows indicates the reduction in the groundwater availability within the Botany Sands during construction will be reduced by 0.004 per cent of the LTAAEL. Similarly the predicted reduction in the groundwater availability during construction will be reduced by 661 megalitres per year (ML/year) or 1.4 per cent of the
LTAAEL for the Sydney Basin Central groundwater resource. These predicted water ‘take’ represent a small proportion of the available water within the water sharing plan.
Table 19-7 Groundwater extraction from the Metropolitan Regional Groundwater Resources during construction (Year 2023)
During construction, groundwater would be intersected and managed by either capturing the water that enters the tunnels, caverns and portals, or by restricting inflow through temporary dewatering or the installation of cut-off walls (which limit the movement of groundwater) in cut and cover sections. The volume of groundwater and treatment requirements would differ depending on the depth of the tunnel to be constructed, and the geological units through which it passes. It is recognised that high
groundwater inflow during excavation is possible in faulted or fractured zones such as beneath the Hawthorne Canal palaeochannel and in the alluvium. Groundwater intersected during the construction of the tunnels would be the primary source of wastewater. The wastewater management system would be designed to treat and discharge groundwater as well as stormwater and other intersected
water streams.
During construction, long-term water management solutions, such as the installation of water proofing membranes, would also be installed as required. Groundwater inflows would be collected from the low points of tunnel excavations via a temporary drainage system and would be pumped to the surface for treatment and discharge. Water inflows, treatment and discharge would be managed in accordance with a CSWMP that would form part of the Construction Environmental Management Plan (CEMP) for the project.
Construction options at Wattle Street, Haberfield
The modelling has been undertaken for construction Option A at Haberfield, and therefore the modelling results reflect tunnelling from Wattle Street civil and tunnel site (C1a) and Haberfield civil and tunnel site (C2a). Refer to Chapter 6 (Construction work) for further information regarding the construction ancillary facility options at this location.
If Option B for the construction configuration at Haberfield occurs where tunnelling would be undertaken from Parramatta Road West civil and tunnel site (C1b), there would likely be a slight increase in inflow volume due to the increased construction access tunnel length required. It is expected that the change to the rate of inflow (in litres per second per kilometre) would be low, as this additional tunnelling would be through good quality Hawkesbury Sandstone and would not intersect alluvium.
19.3.3 Groundwater level decline
Groundwater modelling has been used to predict groundwater levels at the end of the construction period (2023) within the alluvium, Ashfield Shale and Hawkesbury Sandstone. The degree of drawdown is dependent on a number of factors including the geology intersected, the hydrogeology and the tunnel configuration and depths. Within the alluvium, the groundwater levels are predicted to form a steep elongated cone of depression along the tunnel alignment due to downward leakage to the underlying Hawkesbury Sandstone. However, the depressed groundwater contours are localised,
extending no further than about 500 metres from the tunnels, indicating localised changes to groundwater flow patterns with negligible impacts on the regional groundwater flow.
At the end of construction, steep localised cones of depression are predicted to develop beneath Newtown and St Peters within the Ashfield Shale. Local groundwater sinks are created at these locations due to the low hydraulic conductivity of the shale and the influence of the leachate pumping at the former Alexandria Landfill. In this case the groundwater level decline is due to leachate pumping from the landfill and not the project.
At the end of construction, the maximum drawdown is predicted to be 42 metres centred on the Rozelle interchange. Drawdown within the alluvium is predicted to be up to 10 metres but in some areas it would be limited by the thickness of the alluvium. The groundwater levels within the Hawkesbury Sandstone are predicted to be depressed along the tunnels at the end of the construction period. While the impacts are localised, with two metres or more drawdown extending no further than around 600 metres from the tunnels, the groundwater sink predicted to develop would create a hydraulic barrier along the length of the tunnel alignment, reversing groundwater gradients. Below the base of the tunnel, groundwater flow would cease being drawn upwards into the tunnel and natural groundwater flow within the sandstone would continue uninterrupted below the tunnels.
The predicted groundwater elevations at the end of the construction phase (2023) for the project are presented Figure 19-6. The predicted groundwater elevations presented in Figure 19-6 include the total drawdown for the alluvium, Ashfield Shale and Hawkesbury Sandstone.
Groundwater drawdown
Groundwater drawdown due to construction activities and temporary dewatering would impact the local water table, potentiometric pressures in the deeper Ashfield Shale and the Hawkesbury Sandstone, or surface water features where there is hydraulic connectivity. As the majority of the tunnel lengths are drained structures (ie not tanked), the tunnel inflows could impact the natural groundwater system and potentially alter regional hydrogeological conditions.
During construction, the regional extent of drawdown impacts due to tunnel construction would be minimal, even though groundwater inflows are high. This is due to the generally low hydraulic conductivity of the Ashfield Shale and the Hawkesbury Sandstone restricting the extent of drawdown during the relatively short construction timeframe.
As construction continues, drawdown would decrease as the cone of depression expands
progressively outwards over time. As the depressurisation caused by the tunnel inflows propagates to the surface, causing the water table to decline, inflows would extend outwards to progressively greater distances until steady state conditions are reached, which is expected to be well after the completion of construction.
Groundwater levels would be monitored throughout the construction phase in accordance with a CSWMP. Additional groundwater modelling is proposed to be conducted by the contractors during construction using measured tunnel inflow rates and monitored groundwater drawdown to better calibrate the model and predict impacts.
The project does not propose to extract groundwater during the construction or operational phases for project purposes. Re-use of treated groundwater would be considered in accordance with the DPIWater re-use policy, the National Water Quality Management Strategy (DPI-Water 2006).
Potential impacts on groundwater dependent ecosystems
In accordance with the NSW Aquifer Interference Policy, groundwater drawdown must be within an allowable range of ten percent of baseline levels within 40 metres of a significant GDE. No priority GDEs have been identified within the project footprint. The closest priority GDEs are the Botany Wetlands and Lachlan Swamps within the Botany Sands, located at Centennial Park, around five kilometres east of the project footprint. These wetlands are at a sufficient distance from the project footprint not to be impacted by the project. Potential impacts on these wetlands and GDEs due to the New M5 project were assessed in the New M5 EIS.
There is a manmade wetland constructed at Whites Creek Valley Park at Annandale, immediately west of Whites Creek. This wetland is unlikely to have any groundwater dependence as it continually receives low flows from Whites Creek. Groundwater levels within the Whites Creek alluvium are unlikely to be adversely impacted during construction because the tunnels are below the alluvium. Groundwater levels are predicted to be drawn down in the Hawkesbury Sandstone but are unlikely to
have any groundwater dependence in this area.
Potential impacts on surface water and baseflow
Surface water features within the study area are described in section 19.2.2. Groundwater inflows to the tunnels that would have the potential to impact surface water levels are unlikely for the section of the tunnels that would be constructed through the Whites Creek alluvium beneath the Rozelle Rail Yards. This is because these sections of the tunnels would be undrained (tanked) and the majority of the creeks and canals are concrete lined. Consequently, the risk of surface water from creeks or canals seeping into the tunnels via leakage to the alluvium is considered low. There may be some seepage from the canals through cracks in the aged concrete.
The Sydney Water proposals to naturalise sections of Whites Creek, Johnstons Creek and Dobroyd Canal (Iron Cove Creek) are likely to increase groundwater recharge and may partially increase the baseflow to these creeks through the removal of sections of concrete-lined bases which would allow more groundwater and surface water interaction leading to a higher contribution of baseflow to surface water flow.
Surface water can only flow to the groundwater system when the groundwater levels are lower than the surface water levels, or when the alluvial water table falls below the surface water level in the creeks. In the lower catchment reaches, if brackish water from Whites Creek or Johnstons Creek replaces groundwater lost from the alluvium, the groundwater quality may become degraded. Under conditions where groundwater levels are higher than surface water levels and creeks are not concrete lined, groundwater would naturally discharge into Whites Creek or Johnstons Creek.
Where the channels are concrete lined, groundwater would be expected to flow within the alluvium surrounding the channel, discharging downstream directly into Rozelle Bay or Parramatta River. However, if groundwater levels are lowered due to tunnel inflows, then the direction of groundwater flow could be altered or reversed. Therefore, there is potential for groundwater quality to decline as a result of the groundwater drawdown of the brackish water. The natural groundwater is already known to be brackish in the lower lying reaches of the catchment where there is natural tidal interaction. Higher in the catchments, any groundwater loss from the creeks to groundwater via leakage should not degrade groundwater quality, as the surface water would be of lower salinity.
Predicted impacts of construction on baseflow for major watercourses have been modelled (refer to Appendix T (Technical working paper: Groundwater)). Baseflow is simulated in the model only when groundwater reaches the ground surface and enters the drainage system. It is expected that the majority of river flow would be derived from stormwater runoff rather than baseflow.
Predicted changes in baseflow at the end of construction are summarised in Table 19-8.
During construction, the baseflow to major watercourses is reduced by between five and 75 per cent. These predicted baseflow reductions are not considered likely to impact the local environment, as the majority of baseflow is anticipated to be derived from surface water runoff. Consequently, groundwater is unlikely to sustain ecosystems before discharging into Rozelle Bay or the Parramatta River.
At Whites Creek, there may be some leakage through the aged cracked concrete that could contribute to baseflow, however this leakage would be minor. Although the baseflow component of streamflow in Whites Creek would be substantially reduced, it is expected that the overall contribution to river flow from groundwater input is relatively small due to Whites Creek being lined and tidally influenced and the catchment being heavily urbanised. There is no predicted impact due to project construction activities on other major watercourses near the New M5 project, including Cooks River, Wolli Creek and Bardwell Creek.
Potential impacts on existing groundwater users
A review of current groundwater use has been conducted to identify registered groundwater users within two kilometres of the project footprint (see section 19.2.8).
The groundwater model has been used to assess the potential groundwater level drawdown at sensitive areas and for registered groundwater users. Where the impacts are expected to exceed minimal impact considerations as specified in the NSW Aquifer Interference Policy (NoW 2012), mitigation measures have been recommended (see section 19.5). Potential impacts on existing users during construction include drawdown in registered bores due to the drawdown of groundwater during tunnelling. The groundwater model predicted that no registered bore within two kilometres of the
project footprint would be drawn down more than two metres (the minimum impact criterion under the NSW Aquifer Interference Policy) during the project construction program.
In the event that groundwater users experience a decline in groundwater levels in existing bores in excess of two metres as a result of the project, provisions would be implemented to ‘make good’ the supply by restoring the water supply to pre-development levels. The measures taken would be dependent upon the location of the impacted bore, but could include deepening the bore, providing a new bore, providing an alternative water supply, or alternatively providing appropriate monetary
compensation.
19.3.4 Groundwater quality
Groundwater quality risks from construction activities include potential groundwater contamination from fuel, oil or other chemical spills and from the captured groundwater intersected during tunnelling. There is also potential to intersect acid sulfate soils and contaminated groundwater associated with previous industrial land use. Contaminants within soils at the Rozelle Rail Yards could be mobilised by altered groundwater flow paths. As groundwater drawdown increases due to tunnel inflows, there is the potential for tidal waters to be drawn towards the tunnels, causing saltwater intrusion. Groundwater quality from monitoring wells and groundwater collected during tunnelling would be monitored throughout the construction phase in accordance with a CSWMP. These potential risks to groundwater quality are discussed further in the following sections.
Spills and incidents
There is potential to contaminate groundwater through incidents within the construction ancillary facilities associated with the storage of hazardous materials or refuelling operations. Groundwater could become contaminated via fuel and chemical spills, petrol, diesel, hydraulic fluids and lubricants, particularly if a leak or incident occurs over the alluvium, a palaeochannel or fractured sandstone. Stockpiling of construction materials may also introduce contaminants to the project footprint that could potentially leach into and contaminate local groundwater.
The risks to groundwater as a result of such incidents would be managed through standard construction management procedures in accordance with site specific environmental management plans developed for the project as outlined in Chapter 16 (Contamination) and Chapter 25 (Hazard and risk). Runoff from high rainfall events during construction would be managed in accordance with the measures outlined in Chapter 15 (Soil and water quality). Following high rainfall events, groundwater quality impacts would be minor, as the majority of runoff would discharge to receiving
waters.
Intercepting contaminated groundwater
A number of sites with the potential for groundwater contamination due to various current and historical land uses are located along the project footprint, as outlined in section 19.2.7. A potential contamination risk would be associated with the migration of contaminated groundwater plumes towards the tunnels.
The majority of the tunnels would be constructed within the Hawkesbury Sandstone at depths greater than 20 metres (at the western and eastern ends) and up to 50 metres beneath Newtown and parts of Leichhardt. In general, the risk of intersecting contaminated groundwater decreases the deeper the tunnel depth.
There is potential to intersect contaminated groundwater during construction while excavating the portals and dive structures that are constructed from the top down, although groundwater would typically be isolated from these structures by excavation support options such as diaphragm walls, sheet piled walls or secant piled walls.
Contaminant groundwater investigations have been conducted in the investigation phases of the EIS and have identified some areas where contaminated groundwater may occur, such as the Alexandria Landfill at St Peters, the Rozelle Rail Yards at Rozelle and former industrial sites in areas such as Alexandria and Haberfield. Contaminated groundwater, if intersected, would enter the tunnels and would be treated prior to discharge at one of the water treatment plants.
The primary risk to groundwater quality is the migration of contaminated groundwater along altered groundwater flow paths due to the tunnel construction. At the Rozelle Rail Yards, groundwater beneath the site within the alluvium is shallow and impacted by historical industrial land uses. Potential contaminants of concern include heavy metals (arsenic, cadmium, copper, lead, nickel and zinc) and hydrocarbons. Tunnel sections through the alluvium would be constructed as undrained (tanked), and cut-off walls would be installed to reduce the ingress of groundwater from the palaeochannels, minimising potential contaminated groundwater migration and addressing the
requirements of DPI-Water. However, shallow groundwater is likely to be encountered and would require management during ground excavation works associated with the construction of the tunnel access decline.
Potential contaminated groundwater inflows could be derived from industrial sites that overlie the tunnels at Alexandria and St Peters, where the tunnels are relatively shallow (about 20 metres below ground surface) but constructed within the Ashfield Shale. This area historically contained potentially contaminating operations such as petrol stations, several vehicle service centres, dry cleaners, car manufacturing and mechanical workshops. The risk of intersecting shallow contaminated groundwater is considered low, because the tunnels would be constructed within the Ashfield Shale, where the
hydraulic conductivity and groundwater leakage would be low.
At Hawthorne Canal and around Leichhardt North, the fill from unknown sources flanking Iron Cove deposited during historical land reclamation works is potentially contaminated and may have impacted local groundwater. Similarly, there are other potential soil contamination sources, such as the storage and use of chemicals, pesticides, fuels and oils and hazardous building materials in the former Public Works Depot at Blackmore Park, which may have impacted shallow groundwater quality within the alluvium and palaeochannels. The risk of intersecting shallow contaminated groundwater is considered low, because the tunnels are to be constructed below the potentially contaminated fill and alluvium within the Hawkesbury Sandstone.
Groundwater and surface water captured as a result of tunnelling are likely to be contaminated with suspended solids and increased pH due to tunnel grouting activities. These flows would be captured and treated prior to discharge via water treatment plants located at construction ancillary facilities. Where possible, the treated water would be reused during construction for purposes such as dust suppression, wheel washing and plant washing, rock bolting, earthworks or irrigation before
discharge. Groundwater reuse would be undertaken in accordance with the policies of sustainable water use of DPI-Water. The volume of recycled water required for beneficial use would be variable and dependent on site conditions. The estimated total volume of water required during construction is estimated to be around 900 megalitres (refer to Appendix Q (Technical working paper: Surface water and flooding)). It is expected that there would be a water surplus during construction and recycled water for operational purposes would be used in preference to potable water.
At St Peters interchange there is known groundwater contamination, including elevated ammonia, associated with the former Alexandria Landfill. Geotechnical drilling as part of the project did not identify localised faulting or fracturing, which could provide leachate conduits to the tunnels. Although the tunnel depths are shallow near the portals, the risk of landfill contaminated groundwater being intersected by the tunnels is considered low as a cut-off wall is to be constructed along the eastern perimeter of the landfill to reduce groundwater inflow and continual leachate pumping from the former landfill will maintain internally directed groundwater gradients and pumped groundwater will be treated by the landfill water treatment plant.
Large portions of the Botany Sands are contaminated from a variety of sources, primarily related to previous industrial land use. Groundwater from the Botany Sands aquifer is likely to enter the tunnel indirectly through hydraulic connection with the Hawkesbury Sandstone. However, a capture zone analysis undertaken as part of the groundwater modelling confirms the Botany Sands would not be a primary source of groundwater to the tunnels during construction.
Given the tunnel depth, location of the tunnel in relation to the contaminant sources, and low inflow rates predicted, the risk of intercepting contaminated groundwater is considered to be low. All groundwater captured during construction would be directed to water treatment plants at the following construction ancillary facilities and treated to meet relevant discharge criteria prior to discharge:
· Haberfield civil and tunnel site (C2a)
· Parramatta Road West civil and tunnel site (C1b)
· Darley Road civil and tunnel site (C4)
· Rozelle civil and tunnel site (C5)
· Iron Cove Link civil site (C8)
· Pyrmont Bridge Road tunnel site (C9)
· Campbell Road civil and tunnel site (C10).
Groundwater treatment
The volume and treatment requirements for groundwater would vary for different geological units and tunnel depths. Groundwater and surface water captured as a result of tunnelling are likely to be contaminated with suspended solids and increased pH due to tunnel grouting activities. During construction, the wastewater generated in the tunnel (including collected groundwater) would be captured, tested and treated at a construction water treatment plant (if required) prior to reuse or discharge, or disposal offsite if required.
Based on the knowledge gained from the previous WestConnex projects (M4 East and New M5) it is likely that the water treatment plants would be required to include pH correction as well as the ability to remove iron, manganese, suspended solids and hydrocarbons. The existing groundwater quality within the study area (refer to section 19.2.6) indicates that groundwater in the study area may also be impacted by elevated levels of ammonia, total nitrogen and total phosphorus compared to ANZECC (2000) guideline levels (marine, freshwater and recreational protection levels). Other metals
including copper, chromium, lead, nickel and zinc have been recorded at elevated levels on a limited number of occasions. The type, arrangement and performance of construction water treatment facilities would be developed and finalised during detailed design.
The receiving waterways and ambient water quality are all highly disturbed compared to the water discharge quality. The level of groundwater treatment would consider the characteristics of the discharge and receiving waterbody, any operational constraints or practicalities and associated environmental impacts and be developed in accordance with ANZECC (2000) and with consideration of the relevant NSW Water Quality Objectives. Ultimately the water quality objectives would be set by the catchment manager of the receiving waters in consultation with the NSW EPA.
The assessment of the potential impacts of the quality of water discharged from the water treatment plants during construction is discussed in Chapter 15 (Soil and water quality).
Acid sulfate soils
PASS have been identified within natural alluvium beneath the Rozelle Rail Yards and possibly within the alluvium along Hawthorne Canal. When exposed to air (through actions such as excavation or dewatering), the iron sulphides (commonly pyrite) within acid sulfate soils can oxidise, producing sulphuric acid.
Acid sulfate soils could be disturbed by the project and may cause the generation of acidic runoff and/or the increased acidity of groundwater. At Rozelle Rail Yards, the excavation of low-lying natural soil for tunnel infrastructure may uncover PASS, which will require treatment and removal under the CEMP. The risks associated with PASS would be managed under an ASSMP as discussed in Chapter 15 (Soil and water quality).
Soil salinity
Salts naturally present in soil and rock are mobilised in the subsurface by the movement of groundwater. The concentration of salts within the soil is related to the geological unit from which the soil is derived.
Within the study area, the Ashfield Shale typically has a high salt content due to the presence of marine salts. Salt concentrations within soils derived from the Hawkesbury Sandstone and alluvium are variable, and within the alluvium are impacted by tidal influences. Under shallow groundwater conditions, saline groundwater may be drawn to the ground surface by capillary action or altered recharge/discharge conditions, precipitating the salts as the water evaporates.
‘Urban salinity’ becomes a problem when the natural hydrogeological balance is disturbed by human interaction through the removal of deep rooted trees (causing groundwater levels to rise and potentially dissolve and mobilise salts from the soil profile) or construction of structures that intersect the water table. Since the majority of deep rooted trees were removed from the project footprint over 150 years ago a new equilibrium has been established and the removal of any further remaining trees on the new equilibrium would not be substantial. The development of urban salinity may cause
corrosion of building materials, degrade surface water quality or prevent the growth of all but highly salt-tolerant vegetation.
During construction of the project, there is potential for salts within the alluvium to be mobilised by local dewatering or associated with the tunnel construction program. Tunnels constructed within the alluvium are to be tanked, and consequently could alter local flow paths, creating groundwater mounding and causing the dissolution of soil salts. Beneath the Rozelle Rail Yards, where the undrained (tanked) tunnels are to be constructed in the Whites Creek alluvium, saline groundwater reaching the ground surface would be directed towards the modified drainage system, thereby removing the mobilised salts from the system. It is unlikely the salts within the Ashfield Shale would
become mobilised, as the drained tunnels are expected to draw down the water table, preventing the groundwater reaching the ground surface. The impact of the project on groundwater resources or hydrology, based on the mobilisation of saline soils, is therefore likely to be negligible.
Saltwater intrusion
During construction there are unlikely to be any impacts associated with saline groundwater entering the tunnels. Saltwater intrusion would commence as soon as the hydraulic pressure within the aquifer declines due to groundwater drawdown via the tunnels causing the displacement of fresher water along the shoreline with more saline tidal water. During construction, saline groundwater inflow to the tunnels from tidal areas would be negligible because of the considerable distance of the tidal surface
waterbodies are from the tunnels and the slow calculated groundwater travel times. Close to the shoreline, groundwater quality would become slightly more saline during the construction period due to saltwater intrusion. However, the low salinity increase would be unlikely to impact the environment since the groundwater along the tidal fringe is naturally saline due to tidal mixing. In addition, there are no registered water supply wells or priority groundwater dependent ecosystems along this tidal fringe.
19.3.5 Groundwater monitoring
Groundwater monitoring would be carried out during construction for monitoring wells and groundwater collected during tunnelling. The monitoring program would be designed to monitor:
· Groundwater levels (manual monitoring and automatic monitoring by data loggers)
· Groundwater quality (within key boreholes and tunnel inflows)
· Groundwater inflows to the tunnels.
The monitoring program would identify groundwater monitoring locations, performance criteria in relation to groundwater levels, quality and inflows and potential remedial actions that would be considered to address any non-compliances with performance criteria.
Groundwater levels and quality would be monitored in the alluvium, Hawkesbury Sandstone and Ashfield Shale. The monitoring wells in the monitoring program used to inform this assessment would be used as required for monitoring. It may be necessary to construct additional monitoring wells if some of the existing wells are damaged during construction or other key areas are identified during the detailed design phase where monitoring is required.
It is expected that manual groundwater level monitoring and groundwater quality monitoring would be undertaken monthly. The quality and volume of tunnel inflows are expected to be monitored weekly.
The following analytes are likely to be sampled:
· Field Parameters (pH, electrical conductivity, dissolved oxygen, temperature and redox
conditions)
· Metals (arsenic, cadmium, chromium, copper, iron, lead, manganese, mercury, nickel and zinc)
· Nutrients (nutrients (nitrate, nitrite, Total Kjeldahl Nitrogen (TKN), ammonia and reactive phosphorous)
· Major cations (sodium, potassium, calcium, magnesium) and anions (chloride, sulphate,
carbonate, bi-carbonate).
The analytes to be sampled and the frequency and type of reporting would be confirmed by the construction contractors. The groundwater monitoring program would be developed in consultation with the NSW EPA, DPI-Fisheries, DPI-Water and the Inner West and City of Sydney councils and documented in the CSWMP to satisfy the project conditions of approval.
19.3.6 Ancillary infrastructure
Ancillary infrastructure to be constructed to support the project includes the following:
· Operational facilities for electronic tolling and traffic control
· Fire safety systems and emergency access and evacuation
· Utilities including power supply and water supply
· Buildings such as water treatment facilities and electrical substations
· Ventilation tunnels and systems
· Tunnel portals
· Construction ancillary facilities
· Five motorway operation complexes. The type of facilities constructed at each of these complexes would include substations, water treatment facilities, ventilation facilities, offices, on-site storage and parking for employees.
The majority of these features are above ground and would not impact the hydrogeological regime.
Activities that may impact groundwater during construction include:
· Tunnel portals
· Ventilation tunnels and systems
· Water treatment facilities
· Construction ancillary facilities
· Drainage channels and wetland areas.
During the construction of below ground tunnel ancillary infrastructure such as ventilation shafts or tunnel portals, sheet piling may be installed to assist temporary dewatering. Groundwater levels would be restored after the barriers are removed.
19.3.7 Utility works
The project would involve utility works that would include the protection of existing utilities, construction of new utilities and relocation of existing utilities. The majority of the utility works would occur in new utility service corridors at the Iron Cove Link, parallel to Victoria Road and within and surrounding the Rozelle Rail Yards. The utilities to be impacted include:
· Sewer mains
· Water mains
· Electricity cables
· Telecommunications including fibre optic cables
· Gas mains
· Sydney trains electrical infrastructure.
These works would involve excavating trenches to varying depths and may intersect the water table. At the Iron Cove Link impact on groundwater is expected to be minimal as the groundwater level is typically below the estimated depth of utility trenches. In contrast, at the Rozelle Rail Yards the water table is shallow and within one metre of the ground surface indicating that utility trenches are likely to intersect the groundwater. During trench excavations sheet piling may be required to temporarily provide support in the alluvium and to restrict groundwater inflows to the trench. Once the sheet piling
is removed, groundwater levels would return to pre-excavation levels. The trenches may be encased in concrete or plastic pipes to water proof the utility service corridors. Deeper trenches or excavations may require temporary dewatering during the construction phase.
Where feasible, the new utility corridors are designed to contain multiple utilities to minimise the construction footprint. These works would be undertaken in accordance with the Utilities Management Strategy and the CSWMP.
19.3.8 Ground movement (settlement)
Ground movement (settlement) or subsidence can be caused by volume loss due tunnel excavation or due to the compression of the soil structure due to groundwater drawdown. This discussion relates to groundwater movement due to groundwater drawdown.
When groundwater levels are drawn down, the unconsolidated sediments hosting the groundwater are subjected to an increase in effective stress (the force that keeps soil particles together), and the sediment may experience settlement. If the degree of settlement is sufficient, it can result in damage to structures within the groundwater drawdown zone of influence. Settlement associated with construction tunnelling occurs within a shorter timeframe compared to settlement associated with groundwater drawdown, which occurs over a longer timeframe.
Within the M4-M5 Link project footprint, residual soil profiles developed on the weathered sandstone and shale bedrock are typically relatively thin, stiff and of low compressibility and as such would be less susceptible to ground settlement. Settlement within the alluvium would be dependent on the amount of groundwater drawdown and would be expected to be greater than that within the Hawkesbury Sandstone and Ashfield Shale, due to the competent nature and geotechnical properties these bedrock units. Monitoring of settlement throughout the construction program would be included
as part of the CEMP.
Since ground settlement due to groundwater drawdown would be more likely to occur within the alluvium, the tunnels would be constructed in accordance with design measures to minimise settlement within the alluvium. Design measures include constructing tanked tunnels through the alluvium to minimise groundwater drawdown. Below Hawthorne Canal and Johnstons Creek, the tunnels have been designed to dive beneath the alluvium to reduce groundwater ingress, which would reduce potential settlement. During tunnel construction, the bulk hydraulic conductivity of the
Hawkesbury Sandstone would be decreased by grouting off the tunnel faces, decreasing groundwater inflow and thereby reducing potential settlement.
Small scale dewatering of the alluvium and Hawkesbury Sandstone may be required during construction. This could result in an increase in effective stress, leading to ground settlement. Movement in clay soils between hydrogeological units would cause both consolidation settlement and creep settlement, which may result in settlement continuing over a long period of time.
Although the groundwater model has predicted groundwater drawdown within the alluvium and Botany Sands, it is not considered appropriate to use these regional results to calculate localised ground settlement. The model is a regional groundwater model and is not considered appropriate for use in estimating groundwater induced settlement at a more localised level. A preliminary assessment based on geotechnical conditions has been carried out to assess the potential for ground movement as a result of the project and the results of this assessment are provided in Chapter 12 (Land use and property).
A geotechnical model of representative geological and groundwater conditions would be prepared by the construction contractor prior to excavation and tunnelling for the project. The model would be used to assess predicted settlement impacts and ground movement caused by excavation and
tunnelling on adjacent property and infrastructure. Management measures to control groundwater inflows (which influence groundwater drawdown and therefore ground movement) during construction are outlined in section 19.5.
Pre-construction condition surveys of potentially impacted property and infrastructure would be undertaken before the commencement of construction activities that would pose a settlement risk, to determine appropriate settlement criteria to prevent damage. In the event that the geotechnical model identifies potential exceedances of settlement criteria, management measures such as appropriate support and stabilisation structures would be implemented to minimise settlement impacts on property
and infrastructure.
A settlement monitoring program would be carried out during construction (in accordance with a Settlement Monitoring Plan) and would include a quantitative assessment to develop settlement criteria for tunnel excavation works. In the event that settlement criteria are exceeded during construction for property and infrastructure, measures would be taken to ‘make good’ or to manage the impact.
Further details regarding settlement are provided in Chapter 12 (Land use and property).
19.3.9 Groundwater balance
The groundwater model was used to quantify potential impacts for the project. The simulated groundwater balance computed for the end of the construction phase (2023) is summarised in Table 19-9 and is based on the detailed water balance presented in Appendix T (Technical working paper: Groundwater).
Table 19-9 Simulated water balance – construction (2023)
Additional detail on the water balance is provided in Appendix T (Technical working paper: Groundwater), including a hydrogeological conceptual model which provides further detail on the components of the water balance.
The water balance confirms that the major water inflows during the construction phase would be derived from regional boundary flow and rainfall infiltration. Conversely, major outflows are regional boundary flow and river outflow. The total inputs and outputs indicate that the water components are balanced.
At the completion of construction in 2023 there would be a net loss in storage of 1.67 megalitres per day (3.26 megalitres per day storage input and 1.59 megalitres per day storage discharge), indicating that water is being drained from the system. In the context of the Sydney Basin, 1.67 megalitres per day is negligible (less than 0.3 per cent of the annual recharge rate of 229,223 megalitres per year for the Sydney Basin Central) (NoW 2011).
19.4 Assessment of potential operation impacts
Groundwater within the study area has the potential to be impacted during the operational phase ofthe project. The potential impacts that have been identified are:
· Reduced groundwater recharge
· Tunnel inflow
· Groundwater level decline including impacts on:
– Long term groundwater inflow
– Groundwater drawdown
– GDEs
– Existing groundwater users
– Baseflow
– Ground settlement
· Groundwater quality
· Barriers to groundwater flows from operational infrastructure.
A detailed water balance has been calculated to predict the long-term impacts from operation of the project.
19.4.1 Reduced groundwater recharge
The Rozelle Rail Yards are underlain by alluvium, where groundwater recharge would be expected to be higher than in areas underlain by sandstone and shale. The Rozelle Rail Yards currently behave as a flood storage area where much of the floodwaters would recharge the alluvium. Post construction of the project, the area would be drained by flood channels to minimise flooding, which may result in a reduction of natural groundwater recharge. Parts of the Rozelle Rail Yards not used for road infrastructure would be converted to new open space. These areas would continue to receive rainfall
recharge.
Following the completion of construction, construction ancillary facility sites would be rehabilitated. In the event that sites previously used for construction ancillary facilities are used for open space or project landscaping, rainfall recharge in these areas would increase; however, recharge quantities would be minor. The majority of the project is below ground and is unlikely to directly impact groundwater recharge (see section 19.4.6). Above ground, the surface area of the road network would slightly increase with additions in some key areas such as City West Link, Victoria Road, Anzac Bridge and The Crescent.
Given the limited increase in surface area of the surface road infrastructure including operational infrastructure such as the motorway operations complexes, ventilation infrastructure, substations and water treatment plants, the reduction in rainfall recharge across the project footprint is considered negligible.
19.4.2 Tunnel inflow
Inflow to the drained tunnel is influenced by the construction methods selected, as well as the geology and hydrogeological features of the intersected lithologies such as hydraulic conductivity, storativity and hydraulic connectivity.
The project tunnels are to be constructed predominantly through the Hawkesbury Sandstone and, to a lesser extent, through the Mittagong Formation and Ashfield Shale. To minimise groundwater inflow, the tunnels are designed to avoid the palaeochannels present by diving beneath Hawthorne Canal and tanking (ie lining to prevent groundwater ingress) sections of the tunnel through the Whites Creek alluvium beneath the Rozelle Rail Yards.
Conservative estimates of tunnel inflows can be made by assuming a maximum groundwater inflow rate of one litre per second per kilometre along the whole drained tunnel length during operation of the project, although inflow rates in some sections of the tunnels would be less than the maximum allowed rate. The total combined length of the mainline tunnels, Iron Cove Link and Rozelle interchange tunnels is around 47,940 metres. The total tunnel length of drained tunnel is 44,950 metres.
Assuming a worst case scenario of a uniform groundwater inflow rate of one litre per second per kilometre for any kilometre length of the tunnel along the whole drained tunnel length, a groundwater inflow of around 44.95 litres per second (3.9 megalitres per day) would be expected, although (as explained above) this is an overestimate.
At the Rozelle interchange, groundwater inflows in each tunnel would be further restricted due to the number of tunnels close to each other and the associated interference of available groundwater flowing into these multiple tunnels.
The regional impact on the Sydney Basin Central of long-term groundwater tunnel inflows (or ‘take’) as a result of the project is estimated to vary from 1.74 megalitres per day (635 megalites per year) in 2023 reducing to 0.99 megalitres per day (361 megalitres per year) in 2100. The total regional recharge across the Sydney Basin is 229,223 megalitres per year. Consequently, the groundwater ‘take’ due to long-term groundwater inflow to the tunnels represents 0.27 per cent of the annual recharge across the Sydney Basin in 2023 and 0.15 per cent in 2100.
Groundwater inflow from the Hawkesbury Sandstone is expected to be low due to low bulk hydraulic conductivity values (typically 0.008 metres per day). The Ashfield Shale overlying the Hawkesbury Sandstone typically has an even lower hydraulic conductivity, in the order of 0.001 metres per day (Hewitt 2005), indicating groundwater inflow is expected to be lower in the Ashfield Shale compared to the Hawkesbury Sandstone. The tunnels do not pass through the Botany Sands or Zone 2 of the Botany Sands Source Management Zone, so there would be no direct inflow of groundwater from the
Botany Sands into the drained tunnels.
Alluvium associated with the creeks, canals and edge of the Sydney Harbour and Parramatta River in the study area is partly saturated. Since the alluvium is hydraulically connected to surface waterbodies, water can potentially flow from Rozelle Bay or the Parramatta River via the alluvium and fractured sandstone or shale into the project footprint. Although the majority of the creeks and canals are concrete lined, there remains good hydraulic connection with the groundwater within the alluvium
outside the main channels. There is no direct inflow to the tunnels from the alluvium since the tunnels are designed as undrained (tanked) where the alluvium is intersected.
The overall impact of tunnel inflow on groundwater is considered to be minor.
19.4.3 Groundwater level decline
Long-term groundwater inflow
Previous tunnelling in the Hawkesbury Sandstone in the Sydney region has shown that groundwater inflow is typically highest during construction and then is reduced as the cone of drawdown expands and equilibrium or a steady state condition is reached. This equilibrium is achieved when the tunnel inflow is matched by rainfall recharge via infiltration and/or surface water inflows. Long-term groundwater inflows to the tunnels are influenced by the geology intersected and the tunnel construction methods used to reduce the bulk hydraulic conductivity. Long-term groundwater inflow rates are expected to be lower than construction inflow rates for the project.
The reduction in long-term inflow rates is due to the ‘cone’ of drawdown depression expanding laterally at a rate that is proportional to the log of time. As the cone of depression expands further, the hydraulic gradients towards the tunnels reduce. Drawdown is derived from storage depletion but would be partly offset by recharge, both in the short term and long term.
Based on historical groundwater inflows to other drained Sydney tunnels (section 19.2.5), the longterm inflow rate into the project tunnels is expected to be below the one litre per second per kilometre design criterion for any kilometre tunnel length. Specific zones capable of higher rates of inflow identified during construction would be treated to reduce inflow rates to meet this criterion.
Groundwater modelling has calculated inflows for the construction and operations phases of the project. At project opening (2023), tunnel inflows are estimated to be 441 megalitres per year, declining to 267 megalitres per year at the end of the model simulation in 2100. As observed in other Sydney tunnels, the inflow rate is likely to decrease with time.
Groundwater drawdown
Construction of drained tunnels beneath the water table is expected to cause long-term, ongoing groundwater inflow to the tunnels, inducing groundwater drawdown along the tunnel alignment. Actual groundwater drawdown of the water table would be dependent on a number of factors, including proximity to the tunnel alignment and the specific geological conditions present. Immediately after tunnelling is completed, groundwater inflows would be at their highest, but with time, groundwater inflow to the tunnel would decrease while the water table decline would continue to gradually expand outwards from the tunnels until equilibrium is reached.
In zones where the inflow rates are likely to exceed one litre per second per kilometre for any kilometre length of tunnel, water bearing fractures/rock defects would be pre-grouted during construction to reduce ongoing groundwater inflow. This grouting would also reduce long-term drawdown impacts. Groundwater movement is restricted in Hawkesbury Sandstone because it is interbedded with shale lenses that discourage groundwater movement. Groundwater drawdown within the palaeochannels and river alluvium within the project footprint would be low because the tunnel sections that intersect the alluvium are to be undrained (tanked). In addition, groundwater levels may
be partly maintained by direct hydraulic continuity with surface water.
The predicted drawdown at the various creeks varies depending on local geology, horizontal distance from the tunnel, depth to the tunnel and tunnel design. For some sections, the tunnels have been designed so there would be no direct inflow from the alluvium into the tunnels. This would be achieved by:
· Tanking the tunnels where the alluvium is intersected, such as beneath the Rozelle Rail Yards
· Designing the tunnels to dive beneath the alluvium, such as at Hawthorne Canal
· Constructing cut-off walls where the portals and cut-and-cover sections intersect alluvium, such as at Haberfield.
Drawdown within the alluvium would be variable as it is dependent on a number of factors including leakage to the underlying Hawkesbury Sandstone, rainfall recharge and surface water interaction.
Potential groundwater drawdown due to the project for the long term (2100) has been calculated and is presented in Figure 19-7. The drawdown presented in Figure 19-7 is the total drawdown for the alluvium, Ashfield Shale and Hawkesbury Sandstone.
While the tunnels constructed within the alluvium are proposed to be undrained (tanked), groundwater is predicted to leak from the alluvium into the underlying sandstone, resulting in a decline in the water table within the alluvium. When there is insufficient rainfall recharge or surface water inflow at locations where the alluvium is shallow, the alluvium may be drawn down due to the induced tunnel leakage.
Long-term drawdown (Year 2100) within the Ashfield Shale and Hawkesbury Sandstone extends to the tunnel invert and continues to spread laterally over time. Predicted drawdown in the Hawkesbury Sandstone at Rozelle is a maximum depth of 55 metres, extending laterally 1.4 kilometres either side of the tunnel to the two-metre drawdown contour.
Similarly near St Peters interchange within the Ashfield Shale, groundwater is predicted to be drawn down to the tunnel invert to a depth of 44 metres, with the drawdown extending laterally 0.5 kilometres either side of the tunnel to the two-metre drawdown contour. The reduction in the lateral extent of drawdown within the Ashfield Shale compared to the Hawkesbury Sandstone is due to the sandstone being more permeable than the shale.
Potential impacts on groundwater dependent ecosystems
As identified in section 19.2.9, there are no priority GDEs identified in the Water Sharing Plan for the Greater Metropolitan Region Groundwater Sources within five kilometres of the project footprint. Consequently, no priority GDEs are likely to be impacted by groundwater level decline associated with the long-term operation of the project. The closest priority GDEs are the Botany Wetlands and Lachlan Swamps within the Botany Sands, located at Centennial Park, around five kilometres east of the project footprint. These wetlands are at a sufficient distance from the project footprint not to be impacted by the project. Potential impacts on these wetlands and GDEs due to the New M5 project
were assessed in the New M5 EIS.
Long-term dewatering caused by tunnel drainage could lower the water table and hydraulic heads within the Hawkesbury Sandstone, reducing the amount of groundwater available for non-priority GDE shallow rooted plants. The minimum depth of the water table underlying the majority of the alignment is on average two metres below ground surface. Areas where the water table is shallow, such as at the Rozelle Rail Yards, are typically subjected to periodic flood inundation, which would provide water
for shallow rooted plants that may have some groundwater dependence. Continued flood inundation would recharge to the alluvium, although flows would be reduced due to the installation of flood mitigation measures as part of the project (see Chapter 17 (Flooding and drainage)). At other more elevated topographic areas such as Rozelle, Leichhardt and Newtown, the water table is much deeper below ground surface and consequently flora is unlikely to be dependent on groundwater.
In low-lying areas, such as the Rozelle Rail Yards or close to Rozelle Bay the availability of water for plants is not expected to change, given the high permeability of the sandy soils in combination with frequent rainfall events and higher recharge than elevated sites.
Potential impacts on existing groundwater users
Long-term dewatering caused by tunnel drainage could impact existing groundwater users registered with DPI-Water. A review of the DPI-Water groundwater database indicates that of the registered bores within two kilometres of the proposed project footprint, the majority are registered as monitoring wells. Only five bores are registered for water supply or irrigation. Of these five wells, four are domestic wells and the fifth is registered for irrigation. Two of the domestic wells are located within the Botany Sands and are no longer permitted to be used for domestic purposes due to restrictions
imposed by DPI-Water.
Groundwater modelling has been used to predict drawdown at the location of registered bores across the project footprint. Only one bore (GW110247) located in the University of Sydney grounds at Camperdown is registered for domestic use and is predicted to have a drawdown in excess of two metres that is directly attributable to the project. This bore is predicted to have a drawdown of about 2.4 metres to the hydraulic head in Hawkesbury Sandstone by the end of the long-term simulation in 2100. Given the standing water level is recorded as 31 metres below ground level and the bore is 210 metres deep, the drawdown is likely to have a negligible impact on the bore capacity, however the
drawdown in excess of two metres triggers ‘make good provisions’ in accordance with the Aquifer Interference Policy. The impact on water quality in GW110247 due to saltwater intrusion is also anticipated to be negligible, since the bore is at least two kilometres from the nearest saltwater body at Rozelle Bay and predicted saline water travel times are in excess of 1,000 years.
Potential impacts on surface water baseflow
Within the Hawkesbury Sandstone (and to a lesser extent the Ashfield Shale), saturated secondary structural features can be hydraulically connected to the creeks and canals or their associated alluvium, providing a pathway for surface water to seep into the tunnels.
Losses to stream flows can occur either as a reduction in baseflow, or as streambed leakage from the creeks and canals, and are dependent on the hydraulic connection between the stream channel and alluvium, the underlying sandstone or shale, and the relative water levels of the creek and groundwater. Groundwater contributions to creek baseflow occur only when the water table elevation is above the creek bed, allowing groundwater to flow to the creek. Conversely, stream bed leakage occurs when the water table elevation is below the creek bed level and groundwater seeps into the
underlying lithologies. The concrete lining of creeks would reduce stream bed leakage and baseflow.
Predicted long-term changes to baseflow from the groundwater modelling as a result of the project are summarised in Table 19-10. Although the baseflow component of river flow is significantly reduced in several of the watercourses, it is expected that the overall contribution to flow in these watercourses from groundwater is relatively small, since the watercourses are mostly lined channels. mIt is expected that the majority of flow would be derived from stormwater runoff.
Table 19-10 Predicted long term changes to baseflow
A water quality objective outlined in Chapter 15 (Soil and water quality) is to ‘maintain groundwater within natural levels and variability that are critical to surface flows and ecosystems of the upper estuary’ in the Sydney Harbour and Parramatta River Catchment. Potential groundwater drawdown due to the project for the long-term (2100) has been calculated and is presented in Figure 19-7. These figures show that groundwater drawdown would not extend as far to the north as Rozelle Bay and therefore the natural variability of groundwater levels adjacent to Sydney Harbour and the Parramatta estuary would not be impacted by the project.
Groundwater modelling has predicted the potential for varying decreases in creek base flow during the operation of the project, however under current conditions these creeks are concrete lined, restricting groundwater entering the surface water flow during high flow conditions. It is therefore expected that these reductions in base flow would not substantially impact the ecosystems of the upper estuary catchment. If sections of these creeks are naturalised, groundwater recharge would be enhanced, increasing the groundwater component available to surface water flows.
Long-term, the baseflow to major non-tidal creeks is predicted to be reduced by between
seven per cent and 83 per cent as a result of the project operation. Although the predicted percentage reduction in baseflow in Hawthorne Canal and Whites Creek is substantial, this reduction represents a small reduction in stream flow, since baseflow, as simulated in the model, only represents the occasions when the groundwater reaches ground level and enters the channels. It is expected that the majority of stream flow would be derived from rainfall runoff and tidal inflow.
There is no impact predicted on the baseflow of other major creeks near the New M5 project footprint (including Cooks River, Wolli Creek and Bardwell Creek) due to the M4-M5 Link project. Sydney Water is proposing to naturalise parts of creek channels within the project footprint, including sections of Whites Creek, Johnstons Creek at Annandale and Dobroyd Canal (Iron Cove Creek) in Haberfield. Removal of sections of the concrete-lined base would allow more groundwater and surface water interaction, leading to a higher contribution of baseflow to surface water flow in the creeks. Therefore, the impact of a reduction in surface water flow due to the project in these creeks would be in part balanced by the proposed naturalisation works, resulting in additional surface water recharge via bed leakage when the water table is below the creek bed.
Ground movement (settlement)
Impacts related to settlement during operation would be consistent with the impacts related to settlement outlined in section 19.3.8. Impacts related to settlement during operation would be from groundwater drawdown, which occurs over a longer timeframe as opposed to settlement impacts from tunnel construction.
A geotechnical model of representative geological and groundwater conditions would be prepared by the construction contractor during the detailed design phase prior to and the commencement of tunnelling. The model would be used to assess predicted settlement impacts and ground movement during the operation of the project. Management measures to control groundwater inflows (which influence groundwater drawdown and therefore ground movement) during the operation of the project
are outlined in section 19.5.
A settlement monitoring program would be carried out during operation (in accordance with a Settlement Monitoring Plan) at properties and infrastructure where exceedances of the settlement criteria are identified. In the event that settlement criteria are exceeded during operation for property and infrastructure, measures would be taken to ‘make good’ the impact.
Further details regarding settlement are provided in Chapter 12 (Land use and property).
19.4.4 Groundwater quality
Intercepting contaminated groundwater
There is a risk that contaminated groundwater within the study area (such as a hydrocarbon plume emanating from a former service station or industrial site, for example) could be intercepted during operation of the project, as groundwater is induced to flow towards the tunnel. Altered groundwater flow paths due to the tunnels and hydraulic gradient changes may locally cause existing contaminant plumes (if present) to migrate towards the tunnel alignment. Tunnel inflow quality and quantity would be routinely monitored prior to treatment to detect changes in water quality and treat as needed.
Leachate and elevated concentrations of ammonia are currently generated at the former Alexandria Landfill site. The risk of contaminated groundwater entering the project tunnels from leachate derived from this site is considered low, since the cut-off wall that is to be constructed along the eastern perimeter of the landfill would reduce groundwater inflow cut off walls, the landfill will be capped and ongoing leachate pumping system to be operated as part of the New M5 project will direct mgroundwater flow towards the leachate pumps and away from the project tunnels.
Contamination generated within the tunnels during operation is unlikely to impact the local hydrogeological regime as groundwater gradients are towards the tunnel. The contamination would be captured within the tunnel drainage system and removed during the treatment process prior to discharge.
At the Rozelle Rail Yards, there is a risk that the groundwater within the alluvium is contaminated from a variety of previous industrial activities. The risk of intersecting shallow contaminated groundwater during the operation of the project is considered to be low, because the tunnels intercepting the alluvium in this area would be undrained (tanked). However, there may be hydraulic connection between the Hawkesbury Sandstone and alluvium, through which potentially contaminated groundwater could enter the tunnel. Tunnel inflow quality and quantity would be routinely monitored
prior to treatment to detect changes in water quality, in accordance with an OEMP or Environmental Management System (EMS).
Groundwater from the Botany Sands aquifer is likely to enter the tunnel through hydraulic connection with the Ashfield Shale and Hawkesbury Sandstone at Alexandria. However, analysis undertaken as part of the groundwater modelling indicates the Botany Sands would not be a dominant long-term source of water to the tunnels. Groundwater from the Botany Sands near Alexandria has the potential to be contaminated, but the groundwater entering the tunnel would be treated prior to discharge.
Captured contaminated groundwater through tunnel inflows would be treated in water treatment plants proposed at Rozelle and Darley Road Leichhardt in accordance with the discharge criteria outlined in Chapter 17 (Flooding and drainage).
The quality of tunnel inflows would be monitored throughout the operational phase to allow the operation of the water treatment plants to be modified as required to meet the adopted discharge criteria. The monitoring strategy would be included in the OEMP or EMS. Other risks associated with contamination during the operation of the project would be managed in accordance with the measures outlined in Chapter 16 (Contamination).
Groundwater treatment
Treated flows from the Rozelle water treatment plant would drain via a constructed wetland to Rozelle Bay. Treated flows from the Darley Road water treatment plant would be discharged to Hawthorne Canal. A small portion (around 1.6 kilometres) of M4–M5 Link tunnel would also drain to the New M5 operational water treatment plant at Arncliffe.
The existing groundwater quality within the study area (refer to section 19.2.6) is brackish with elevated metals and nutrients recorded during groundwater sampling. Total metal, nutrient and ammonia loading to Hawthorne Canal and Rozelle Bay would be likely to increase due to the addition of water from treated groundwater discharges. While the total loading of these contaminants would increase for both treated and non-treated groundwater discharge scenarios, the treatment of groundwater for the project would result in comparatively lower impacts due to the reduced concentration of contaminants after treatment. In order to prevent adverse impacts on downstream
water quality within Rozelle Bay and Hawthorne Canal, water treatment facilities would be designed so that the effluent would be of suitable quality for discharge to the receiving environment. By adding additional water to Hawthorne Canal the mass of contaminants would increase (whether treated or not) but the concentration of contaminants in the receiving water would decline if the water is treated, which is beneficial.
The operational water treatment plant at Rozelle and Darley Road would have iron and manganese treatment capabilities. The proposed constructed wetland at Rozelle would remove a proportion of the nutrient and metal load. As no constructed wetland is proposed at Darley Road, opportunities to incorporate other forms of nutrient treatment (for example ion exchange or reverse osmosis) within the plant at Darley Road would be investigated during detailed design with consideration of other factors such as available space, increased power requirements and increased waste production and appropriate discharge criteria.
For groundwater quality, receiving water quality and proposed treatment, the concentration of the key constituents in the treated discharge to Rozelle Bay are unlikely to be significantly higher than the baseline concentration of the constituents in Rozelle Bay. Due to the mixing and dilution affect which would occur at the outlet to the receiving waters, impacts on ambient water quality are likely to be negligible and localised to near the outlet.
The level of groundwater treatment would consider the characteristics of the discharge and receiving waterbody, any operational constraints or practicalities and associated environmental impacts and would be developed in accordance with ANZECC (2000) and with consideration of the relevant NSW Water Quality Objectives. Ultimately, the water quality objectives would be set by the catchment manager of the receiving waters in consultation with the NSW EPA.
Saltwater intrusion
Saltwater intrusion would commence as soon as the hydraulic pressure within the aquifer declines due to groundwater drawdown via the tunnels causing the displacement of fresher water along the shoreline with more saline tidal water.
Over time, saline intrusion is expected to result in saline water reaching the tunnels. The proportion of saline water flowing into the tunnels, however, would be low. A capture zone analysis has been undertaken as part of the groundwater modelling to investigate salt water intrusion within the tunnel catchment areas. From this analysis it is not possible to quantify volumes or concentrations of saline water entering the tunnels and therefore the following discussion is based on a qualitative analysis.
Alexandra Canal and Whites Creek
Travel times for saline water to enter the tunnels within the alluvium have been tabulated for minimum, maximum and average times (refer to Appendix T (Technical working paper: Groundwater)). The minimum travel times for saltwater particles to enter the tunnels from Alexandra Canal and Whites Creek are predicted to be two days and eight days respectively, although these water particles would have a negligible impact on groundwater quality. Initially (minimum travel time), the saline water would be a small fraction of total groundwater entering the tunnel but this is expected to increase over time as water is drawn from further afield. Estimated travel times for saline water to enter the tunnel during operation according to the groundwater model would to be 30 years at Alexandra Canal and 13 years at Whites Creek, although the saline water entering the tunnels would be a minor component of total inflow and changes to groundwater quality are expected to be minimal.
Tidal zones
The capture zone analysis indicates that tidal water from the tidal zones associated with the Parramatta River would enter the project tunnels at the proposed Rozelle interchange. Similarly, groundwater from the alluvium associated with the Cooks River would enter the project tunnels near the St Peters interchange.
As groundwater levels are drawn down below sea level, saline waters from tidal waterbodies would start flowing towards the tunnels and would ultimately enter the tunnels via hydraulic connection with the alluvium. Initially, the saline water would be a small fraction of total groundwater entering the tunnels, but this is expected to increase over time, as groundwater is drawn from further afield. Average times for saline water to enter the tunnels are predicted to be more than 100 years and maximum times are in the order of thousands of years.
As a result, groundwater quality in the tunnel catchment zones would slowly become more saline over thousands of years. Since the operational lifetime for major infrastructure is in the order of 100 years, the slow salinity increase should have minimal impacts on the tunnels and infrastructure in the project’s operational lifetime. Similarly, while there is the potential to increase the salinity in registered water supply bores due to saltwater intrusion, the slow progress is expected to have a minimal impact
on these bores over a period of 100 years.
Under natural conditions within the Hawkesbury Sandstone, a low salinity water layer towards the top of the aquifer is often present. Shallow rooted plants may have a partial dependency on the low salinity groundwater layer; however, it is expected that these plants would be sustained primarily through rainfall recharge and soil moisture.
In accordance with the OEMP or EMS groundwater quality and tunnel inflow would be routinely monitored and treated, as required, prior to discharge (refer below).
19.4.5 Groundwater monitoring
The groundwater monitoring program prepared and implemented during construction would be augmented and continued during the operational phase. Groundwater would be monitored during the operations phase for three years or as otherwise required by the project conditions of approval and would include trigger levels for response or remedial action based on monitoring results and relevant
performance criteria.
At least three monitoring wells and vibrating wire piezometers (VWPs) should be constructed as close as possible to the tunnel centrelines to allow for the comparison of pore pressures and standing water levels. The wells could be constructed about 5-10 metres above the top of the tunnel crown to allow for groundwater drawdown monitoring in the Hawkesbury Sandstone.
The exact nature and frequency of the ongoing groundwater monitoring during operation would be determined by the project operator.
The operational groundwater monitoring program would be developed in consultation with the NSW EPA, DPI-Fisheries, DPI-Water and the Inner West and City of Sydney councils and documented in the OEMP or EMS.
19.4.6 Ancillary infrastructure
The following ancillary infrastructure may impact groundwater during operation of the project:
· Tunnel portals
· Ventilation tunnels and systems
· Water treatment facilities
· Utility works
· Drainage channels and wetland areas.
The tunnel portals and cut-and-cover structures are likely to be constructed in bedrock to prevent the ingress of groundwater into the tunnels. Ventilation tunnels are likely to be constructed as drained tunnels. This infrastructure has been included in the groundwater model, so impacts such as groundwater drawdown or groundwater ingress due to tunnel seepage are discussed in this chapter.
The water treatment facilities would be constructed to enable captured groundwater and surface water that enters the tunnels to be treated and discharged in accordance with NSW Water Quality and River Flow Objectives (NSW Department of Environment, Climate Change and Water 2006) (refer to Chapter 15 (Soil and water quality) for further detail).
The water treatment plants are not expected to impact groundwater, since it would be above ground level and have no interaction with the water table. Utility corridors, drainage channels and wetland areas are likely to impact groundwater at the
Rozelle Rail Yards since groundwater levels are typically less than one metre below ground level. Temporary dewatering or the installation of temporary sheet piling may be required to manage groundwater during construction.
19.4.7 Barriers to groundwater flow from operational infrastructure
Below ground infrastructure, such as a tunnel below the water table, can create physical barriers that cause temporary or permanent interruptions to groundwater flow. Temporary impacts may be seen after heavy rainfall, when infiltration to the water table and lateral flow are slowed by the barrier, creating a build-up of groundwater behind the barrier. Permanent impacts may be caused by the compartmentalisation of an aquifer through the construction of a barrier boundary that alters groundwater flow patterns.
During the operation of the tunnels, physical barriers to groundwater flow are unlikely for a number of reasons. The majority of the tunnels (including ventilation tunnels) are designed to be drained, which would allow groundwater to seep into the tunnel rather than creating a physical barrier to groundwater flow. Only limited sections of the tunnels in the Whites Creek Alluvium beneath the Rozelle Rail Yards would be undrained (tanked) to prevent groundwater ingress. These sections of the tunnels would be
constructed within alluvium and are unlikely to create a physical barrier, as the tunnels would not fully penetrate the alluvium water table, thus allowing groundwater to flow around (above or below) the tunnel.
Although the project tunnels are unlikely to create physical barriers, drained tunnels may create hydraulic barriers impacting local groundwater flow patterns. The hydraulic barrier is formed by lowering groundwater levels centred on the tunnel alignment and, in some cases, locally reversing the groundwater flow direction. Permanent drawdown around the drained tunnels is likely to occur as discussed in the sections above. The creation of this groundwater ‘sink’ would occur along the alignment and extend to a level beneath the tunnel invert. Below this level, there would be no discernible lowering of groundwater pressures, and the groundwater flow pattern would remain unchanged.
At tunnel portals or cut-and-cover sections, the potential interruption of groundwater and possible groundwater mounding caused by the installation of cut-off walls would be avoided by the inclusion of drainage blankets or drains in the detailed design.
19.4.8 Groundwater management
Where higher long-term groundwater inflows into the proposed tunnels are identified during construction, these could be reduced using methods such as pre-grouting and the installation of waterproofing. However, because the proposed tunnels are designed as drained tunnels, with groundwater being captured, treated and discharged at the surface, the need for this measure is likely to be minimal. Strip drains or similar would be installed behind wall panels to assist in dissipating groundwater.
Tunnel drainage and treatment infrastructure would be designed to accommodate groundwater ingress. Separate sumps would be provided at tunnel low points to collect tunnel drainage from separately from groundwater ingress.
Groundwater would be pumped from the sumps to a water treatment plant at the Darley Road motorway operations complex (MOC1) at Leichhardt, with treated flows ultimately discharged to Hawthorne Canal or to the sewer and at the Rozelle East motorway operations complex (MOC3) with treated flows discharged via a constructed wetland within the Rozelle Rail Yards to Rozelle Bay. Further information regarding tunnel drainage and treatment infrastructure is provided in Chapter 5 (Project description).
The beneficial reuse of the treated water would also be considered, the most likely reuse option being the irrigation of parks and playing fields, for example at the proposed Rozelle interchange. Groundwater reuse would be in accordance with DPI-Water policies for sustainable water use.
19.4.9 Groundwater balance
A groundwater balance has been prepared for the transient simulation (see section 19.1.5) and was run to predict the long-term operations impacts. The estimated water balance is summarised in
Table 19-11 and is based on the detailed water balance presented in Appendix T (Technical workingpaper: Groundwater).
Table 19-11 Estimated water balance – project operation (year 2100)
Additional detail on the water balance is provided in Appendix T (Technical working paper: Groundwater), including a hydrogeological conceptual model which provides further detail on the components of the water balance.
The transient water balance confirms that the regional boundary flows and rainfall infiltration are the primary recharge parameters, and the primary discharge parameters are river outflow and regional outflow. The total recharge and discharge components match within an acceptable margin of error, indicating the water components of the model balance.
19.5 Environmental management measures
Mitigation and management measures would be implemented during construction and operation of the project to reduce or eliminate the risks to the existing groundwater regime. These environmental mitigation measures, including management, engineering solutions and monitoring, are summarised in Table 19-12.
Table 19-12 Environmental management measures – groundwater
High groundwater inflows in excess of the one litre per second per kilometre design criterion, which would cause significant groundwater inflows and groundwater drawdown
GW1 Groundwater inflows within the tunnels will be minimised by designing the final tunnel alignment to minimise intersections with known palaeochannels and alluvium present in the project footprint.
Construction
GW2 Appropriate waterproofing measures will be identified and included in the detailed design to permanently reduce the inflow into the tunnels to below one litre per second per kilometre for any kilometre length of the tunnel.
Construction
GW3 Appropriate measures will be investigated and implemented at dive structures and shafts and for cut-and-cover sections of the tunnel to minimise groundwater inflow.
Construction
Corrosion of building materials by sulfate reducing bacteria
GW4 Further assessment of the risk posed by the presence of sulfate reducing bacteria and groundwater aggressivity will be undertaken prior to construction. A corrosion assessment will be undertaken by the construction contractor to assess the impact on building materials that may be used in the tunnel infrastructure such as concrete, steel, aluminium, stainless steel, galvanised steel and polyester resin anchors. The outcomes of the corrosion assessment will be considered when selecting building materials likely to encounter groundwater.
Construction
Groundwater drawdown impacting a water supply well water level by more than two metres
GW5 In accordance with the Aquifer Interference Policy, measures will be taken to ‘make good’ the impact on an impacted water supply bore by restoring the water supply to pre-development levels. The measures taken will be dependent upon the location of the impacted bore but could include, for example, deepening the bore, providing a new bore or providing an alternative water supply.
Construction
Alteration of groundwater flows and levels due to the installation of subsurface project components
GW6 Potential impacts associated with subsurface components of the project intercepting and altering groundwater flows and levels will be considered during detailed design. Measures to reduce potential impacts will be identified and
included in the detailed construction methodology and the detailed design as relevant.
Construction
Actual groundwater inflows and drawdown in adjacent areas exceed expectations
GW7 A detailed groundwater model will be developed by the construction contractor. The model will be used to predict groundwater inflow rates and volumes within the tunnels and groundwater levels (including drawdown) in adjacent areas during construction and operation of the project.
Construction
GW8 Groundwater inflow within and groundwater levels in the vicinity of the tunnels will be monitored during construction and compared to model predictions and groundwater performance criteria applied to the project. The groundwater model will
be updated based on the results of the monitoring mas required and proposed management measures to minimise potential groundwater impacts adjusted accordingly to ensure that groundwater inflow performance criteria are met.
Operation
Impacts on groundwater quality or groundwater levels
OGW9 A groundwater monitoring program will be prepared and implemented to monitor groundwater inflows in the tunnels and groundwater levels as well as groundwater quality in the three main aquifers and inflows during construction.
The program will identify groundwater monitoringlocations, performance criteria in relation to groundwater inflow and levels and potential remedial actions that will be considered to address any non-compliances with performance criteria. As a minimum, the program will include manual groundwater level and quality monitoring monthly and inflow volumes and quality weekly.
The monitoring program will be developed in
consultation with the NSW EPA, DPI-Fisheries, DPI-Water, City of Sydney Council and Inner West Council.
Operation
OGW10 The groundwater monitoring program prepared and implemented during construction will be augmented and continued during the operational phase. Groundwater will be monitored during the operations phase for three years or as otherwise required by the project conditions of approval and will include trigger levels for response or remedial action based on monitoring results and relevant performance criteria.At least three monitoring wells and vibrating wire piezometers (VWPs) should be constructed as close as possible to the tunnel centrelines to allow for the comparison of pore pressures and standing water levels. The wells could be constructed about 5-10 metres above the top of the tunnel crown to allow for groundwater drawdown monitoring in the Hawkesbury Sandstone.
The operational groundwater monitoring program will be developed in consultation with the NSW EPA, DPI-Fisheries, DPI-Water and the Inner West and City of Sydney councils and documented in the OEMP or EMS.
Operation
Corrosive groundwater could adversely impact the tunnel and associated infrastructure
OGW11 Where the corrosion assessment that will be carried out prior to construction indicates potential issues, corrosion and other associated impacts of highly aggressive groundwater on the tunnel infrastructure will be monitored during operations. The monitoring program will be documented in the OEMP or EMS. Corroded or otherwise impacted infrastructure will be repaired orreplaced as required to maintain operational
integrity of the road infrastructure.
Operation
Groundwater drawdown due to the project may exceed two metres in registered bores or at other receptors
OGW12 In accordance with the Aquifer Interference Policy, measures will be taken to ‘make good’ the impact on an impacted water supply bore by restoring the water supply to pre-development levels. The measures taken will be dependent upon the location of the impacted bore but could include, for example, deepening the bore, providing a new bore or providing an alternative water supply.
Operation
Based on the above mitigation and management measures it is considered that potential groundwater impacts that may arise as a result of the construction and operation of the project can be effectively managed
The People's M4/M5 EIS 