Epping to Thornleigh Third Track Environmental Impact Statement

Epping to Thornleigh Third Track Environmental Impact Statement 14. Surface and groundwater This chapter considers the potential impacts of the ETTT proposal on surface and groundwater including water quality. 14.1 Existing conditions 14.1.1 Surface water and drainage The proposal site is located predominantly within the upstream areas of the Byles and Zig Zag Creek catchments, and downstream of the Upper Devlins Creek catchment. Surface waterways within the vicinity of the proposal site include Devlins Creek, Byles Creek, Zig Zag Creek and a number of smaller unnamed overland flow paths. These creeks are shown on Figure 14.1 except Zig Zag Creek which is located just to the north of the figure extent. The external catchments between Epping Station and Pennant Hills Road generally drain from the western side of the corridor to the eastern side, towards Devlins Creek and Byles Creek. These creeks discharge to the Lane Cove River. North of Pennant Hills Station, the catchment falls from the eastern to the western side towards Zig Zag Creek, which discharges into Berowra Creek. The ETTT proposal would pass through undulating terrain, with Devlins Creek the only major watercourse crossing the corridor. Flooding of the creek is unlikely to impact the existing rail corridor, as the creek is located more than 20 metres below the corridor level. No works are proposed in Devlins Creek. There are currently 19 drainage culverts which convey surface water across the railway corridor. Due to the construction of the third track, 14 of these culverts would be required to be extended. 14.1.2 Surface water quality Water quality monitoring is undertaken at a number of locations within the Hornsby LGA, and the results are provided in Council’s Annual Water Quality Report. These sites may provide valuable baseline data at downstream locations. 14.1.3 Groundwater The main aquifer in the vicinity of the proposal site is the Hawkesbury Sandstone that underlies a portion of the site. The Hawkesbury Sandstone is partially confined by the overlying Ashfield Shale. Water quality in the Ashfield Shale is likely to be poor with high salinity. Groundwater is assumed to flow in a southerly direction. Groundwater monitoring was undertaken as part of the initial geotechnical investigations for the proposal (Golder Associates 2011b). On average, groundwater levels varied between 3.3 and 9.8 metres below ground level. However two monitoring locations indicated that groundwater was located at 16 metres below ground level. Groundwater in all wells was found to be brown in colour with low to medium turbidity and no odour, with the exception of one location where a slight hydrogen sulphide odour was detected. PR_5709 Rev0 Page 259 Epping to Thornleigh Third Track Environmental Impact Statement Concentrations of heavy metals which exceed the Australian and New Zealand Environment Conservation Council (ANZECC) 2000 freshwater trigger values were detected at ten locations. A toluene exceedance was also detected. The source of these contaminants is unknown and would require further investigation to determine if they are representative of regional groundwater quality. A search of the NSW Office of Water register of groundwater bores identified 13 registered bores within a two kilometre radius of the proposal site. The nearest bore is located within the Beecroft Village Green on the western side of the corridor. Based on the depth and location of these bores, the majority extract water from the Hawkesbury Sandstone aquifer. Groundwater in the Hawkesbury Sandstone underlying the study area is likely to be connected with Devlins Creek, Byles Creek, Terrys Creek (located to the east of Epping), Scout Creek and Camp Creek. The shallow water levels suggest groundwater may be providing baseflow to these streams. Page 260 PR_5709 Rev0 Thornleigh Station Pennant Hills Station Beecroft Station Cheltenham Station Epping Station N 0 600m Existing track Drainage line Figure 14.1 Overview of drainage lines Proposed third track Lane Cove National Park Note: Indicative only, subject to detailed design. Track refurbishment Culvert Epping to Thornleigh Third Track Environmental Impact Statement 14.2 Potential impacts 14.2.1 Construction Surface water quality Construction activities have the potential to expose large areas of soil and rock that may be eroded by wind and water. Erosion may lead to sedimentation of surrounding drainage lines (refer Figure 14.1). Some fill and sandy residual soils have been identified as having a high or extremely high risk of erosion (refer section 15.1). Where larger cuts are required, excavation works have the potential to destabilise landforms, particularly on cutting faces. Earthworks would also require stockpiling of material prior to removal off site or re-use as fill. There is potential for stockpiles to be eroded, resulting in the sedimentation of nearby waterways during periods of high rainfall or during windy conditions. Other aspects of the proposal which have the potential to expose soils and lead to sedimentation include: construction of a temporary earth embankment to the south of the M2 Motorway in the vicinity of Devlins Creek widening of cuttings station construction vegetation removal not associated with earthworks works within drainage lines such as removal/extension of culverts and construction of access tracks vehicle movements construction compound and stockpile establishment landscaping. Potential impacts associated with increased sediment loading include increased turbidity and an increased potential for the transport of contaminated sediment. Water quality impacts associated with erosion and sedimentation would be greatest where construction works are undertaken adjacent to the existing drainage network, or where there is a potential for sediments to wash into stormwater drains e.g. on sealed areas and roads adjacent to the construction zone. Accidental spills and leaks associated with the transport, use and storage of chemicals and hazardous substances could contaminate stormwater run-off from construction areas. Water quality outside of the proposal site could also be affected by accidental spills during the transport of chemicals and hazardous substances or spoil to and from construction sites. Water quality impacts would be minimised during construction by the implementation of soil and water management measures through the CEMP. A summary of the measures to be incorporated into the CEMP are included in sections 14.3 and 15.5. Page 262 PR_5709 Rev0 Epping to Thornleigh Third Track Environmental Impact Statement Drainage There could be temporary impacts to the local drainage system during construction. These impacts could include temporary loss of capacity and temporary redistribution of flows as a result of material stockpiles and works within flowpaths and at culvert crossings. These impacts would be localised and temporary and would depend on the occurrence and intensity of any storm events that occur during construction. To reduce the potential impacts to surface water systems, stockpiles would be located away from overland flow paths and not located adjacent to existing culverts or waterways. Localised flooding could occur at various culverts during a storm event if these are not maintained clear of debris and water is inhibited from draining freely. The potential for flooding of construction work sites would be addressed by the contractor during construction planning. Contingency plans relating to flooding would be incorporated into the construction environmental management plan. Groundwater Construction of the ETTT proposal would involve some excavation activities, which have the potential to intercept groundwater. The following activities and potential impacts are expected during construction: Widening of cuttings has the potential to impact on groundwater seepage. However, as the depth of cuttings would not be increased, no additional groundwater interception is expected to occur. Piling works have the potential to intercept groundwater. Dewatering at these locations has the potential to reduce base flows to surrounding creeks and locally reduce access to groundwater for bore users. Due to the distance of the nearest registered bores and the density of development, the likelihood of impacts is considered to be very low. The compaction of land during construction has the potential to reduce storage and recharge of the shallow groundwater systems, which could result in decreased base flow to surrounding creeks and the associated ecosystems. The proposal would likely result in some compaction of land, however overall the likelihood of impacts to groundwater systems is considered low. Accidental spills and sedimentation have the potential to impact the quality of groundwater. This could potentially result in impacts on groundwater users and the creeks to which the groundwater discharges. Potential impacts would be reduced by implementation of the mitigation measures listed in Section 14.3.2. Two existing bores (near Pennant Hills Station and within the Beecroft Village Green) may potentially be impacted by construction. The impacts to these bores would be determined during detailed design with a view to avoidance of impacts if at all possible. PR_5709 Rev0 Page 263 Epping to Thornleigh Third Track Environmental Impact Statement 14.2.2 Operation Surface water quality During operation, there is the potential for stormwater run-off to be contaminated by oils, greases and gross pollutants from the operation

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