Broken Hill water supply upgrade to Mica Street water treatment plant environmental summary

Transcription

1 Broken Hill water supply upgrade to Mica Street water treatment plant environmental summary August 2015

2 Background New works are proposed at Mica Street Water Treatment Plant in Broken Hill to allow the treatment of the city s remaining water supplies that are predicted to become increasingly saline. A detailed environmental assessment has been completed for these works and the key outcomes of that assessment and described below. Why are these works required? The City of Broken Hill obtains part of its water supply from the Menindee Lakes. This water is pumped to the Mica Street Water Treatment Plant in Broken Hill. There it is treated to meet the Australian Drinking Water Guidelines before it is delivered to customers. The current drought affecting much of western NSW and Queensland has dramatically reduced inflows of water to the Menindee Lakes. Reduced inflows and water storage levels pose a risk to the security of the water supply to the 20,000 residents in Broken Hill and Menindee. There will be a critical shortage of water available to meet the city s water supply unless there are reasonable inflows to the lakes during In addition the quality of the remaining water stored in Copi Hollow will decline as storage levels fall. The water becomes increasingly saline and ultimately unfit for human consumption. These high amounts of salt in the water cannot be removed by the existing treatment processes at the water treatment plant. Action is being taken to address the predicted increasing salinity in the available stored water and to develop additional supplies of water should this water be exhausted. As a priority, Essential Water will recommission and upgrade the reverse osmosis treatment process at the water treatment plant to treat the saline water. WaterNSW is developing groundwater supplies from aquifers below Lake Menindee and the Talyawalka floodplain south of Menindee township. These sources will be an emergency reserve of water should the drought continue. Separate environmental assessments are being prepared should these new water sources be required. These measures are intended to extend the available water supply until there are substantial inflows to Menindee Lakes, while longer term options are investigated and implemented. What is proposed? During the last drought a reverse osmosis package plant was installed at the Mica Street Water Treatment Plant to treat increasingly saline water. This plant was designed to provide 6 million litres of desalinated water each day. The reverse osmosis components were housed in a series of shipping containers. When the drought broke much of this equipment was removed. A similar type of treatment process is now proposed to be reinstalled at the water treatment plant.

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4 Reverse osmosis is widely used to treat water, especially brackish and salt water, for drinking water supply. Water is pre-treated to remove suspended solids and dissolved metals that would reduce the effectiveness of the reverse osmosis process. This water is then forced under pressure to pass through artificial membranes that trap fine particles including dissolved salts. The treated water passes through the membranes whilst trapped salts are removed in a brine solution. The treated water can be blended with water that has been pre-treated to produce a water similar in character and taste to that usually supplied. Essential Water has determined that Broken Hill and Menindee need a minimum supply of 13.5 million litres of water per day when water restrictions are in operation. To meet this demand, Essential Water is proposing to reinstall and upgrade the reverse osmosis treatment. This will produce 10.5 million litres of desalinated water which will be blended with the pre-treated water to provide the required minimum supply. In developing the proposal, Essential Water, WaterNSW and consultants GHD considered a range of options. The best option was chosen and it comprises three main parts: 1. A reverse osmosis package plant at the Mica Street Water Treatment Plant. 2. Evaporation basins to manage the brine produced from the process. These will be constructed adjacent to Perilya Mine s tailings storage, south west of the city. 3. A pipeline, mainly in road reserves, to convey the brine from the water treatment plant to the evaporation basins The proposed works are temporary to get Broken Hill through the current drought. When no longer required the majority of the containers that make up the reverse osmosis package plant will be removed and the evaporation basin will be decommissioned. Location of reverse osmosis package plant at the Mica Street Water Treatment Plant. Location of proposed evaporation basin. (Perilya tailings storage at right) What environmental assessment was done? The proposal must be assessed in accordance with the Environmental Planning and Assessment Act The legislation specifies how the project is to be assessed and who can approved the proposal. In this instance, Essential Water is the determining authority for the proposal.

5 It has been established that the proposal will not have a significant impact on the environment. Therefore the required environmental assessment is documented in a Review of Environmental Factors. This has been prepared in accordance with Part 5 of the Act and it assesses the potential impacts of the proposal. Both positive and negative impacts have been identified and mitigation measures have been recommended to reduce or manage adverse impacts. The effects of other legislation on the proposal have also been examined. For example, the requirements of the following legislation were assessed: Native Title Act 1993, National Parks and Wildlife Act 1974, Protection of the Environment Operations Act 1997, Threatened Species Conservation Act 1995, Environment Protection and Biodiversity Conservation Act 1999 and the Heritage Act The community has been kept informed of the progress on the project through project bulletins and community information sessions, and the Community Consultative Committee. What environmental assessment studies were completed? A range of environmental investigations were completed in the preparation of the Review of Environmental Factors. This section identifies the key investigations and their findings. Aboriginal heritage A due diligence assessment was completed for the proposal to identify known Aboriginal cultural heritage places or objects or any areas of archaeological potential within the proposed project site. This assessment included consultation with representatives of the local Aboriginal community. A survey of the sites did not encounter any items or places of Aboriginal cultural heritage significance, and much of the area has been previously disturbed. The project will be managed to comply with requirements if Aboriginal cultural heritage places or objects are found during construction. Non-Aboriginal heritage Broken Hill is on the National heritage list. The Mica Street Water Treatment Plant includes items of local heritage significance. It contributes to the industrial history of Broken Hill and maintains relevance with its continued operation. The proposed new works at the plant will not affect the important heritage items on the site or affect the overall significance of the site. Noise Noise assessments were completed for the construction of the different parts of the project and their operations. Construction noise limits were assessed against Construction Noise Guidelines and noise limits established for the project. Some noisier construction related to the construction of portions of the pipeline will be short-term and within standard recommended construction hours. A noise assessment of the proposed operation of the reverse osmosis package plant was completed for a worst case scenario where the entire plant is assumed to be working at full capacity. It calculated that, with a worse case scenario, there would be a small (1dB) increase in noise from the treatment plant but that this would probably not be noticed against the current background noise at the plant. However, this will be checked during plant operation to ensure that the plant is conforming to the Environment Protection Authority s requirements.

6 Visual Although the evaporation basin would be a relatively large structure, it would not form a prominent part of any vistas. It would be located adjacent to the existing much larger tailings storages which would also partially screen views to the site. At the Mica Street Water Treatment Plant the containers housing the reverse osmosis package plant have the potential to result in visual impacts. These will be visible from the surrounding residential areas but they would be similar to existing structures on the site. It is unlikely to substantially alter the visual appearance or prominence of the water treatment plant. Ecology The ecological studies found that the proposal is unlikely to have a significant effect on threatened species, populations or communities, or their habitats. Five native vegetation communities were identified, none of which are listed as endangered. The Mica Street Water Treatment Plant Site is highly modified. Parts of the evaporation basin site are also heavily disturbed but other parts are covered by good condition native vegetation. The proposal would clear 35 hectares of native vegetation. One state listed protected flora species, Ptilotus obovatus var. obvatus (Silver Tails), was identified next to the basin site but none within the site. One national listed plant, Acacia carneorum (Purple-wood wattle) may occur in the area but the proposal was assessed as being unlikely to have a significant impact on that species. Habitat for eight listed fauna species is considered to be present within the pipeline route and at the evaporation basin site. However the seven-part tests for each of these species, including Major Mitchell s Cockatoo and the Dusky Hoping-mouse, found that there would not be a significant effect on the habitat of these eight species. Compared to the habitat available in the broader region, the proposal would only affect a small and degraded portion of habitat. Soil disturbance The assessment of soil disturbance during construction examined excavations required for footings and pipework at the treatment plant, trenching for the pipeline and the extensive earthworks required for the evaporation basin. It was established that impacts can be contained and disturbed areas readily stabilised after works are completed. Water and drainage Similarly the effects of the project on water and drainage were assessed. This identified that the erosion and sedimentation from excavation activities would be the main source of impacts on waterways. Controls will need to be implemented to manage these effects including sediment controls and positioning stockpiles away from waterways. The evaporation basin is designed to prevent surface water entering the basin. It will also have sufficient capacity to store any direct rainfall during an extreme rainfall event (the equivalent of a 72 hour storm with 220mm of rainfall). The basin is also lined with a geomembrane to control any seepage that might otherwise impact on groundwater. Traffic Traffic impacts were considered and the main impact is during the construction of the pipeline when either roadside parking or traffic flows may be temporarily affected. There will be a temporary increase in vehicle movements during construction. Heavy vehicles will also be required each day delivering plant, equipment and materials. It is estimated that up to there would be 80 small vehicle movements to and from sites each day and 100 heavy

7 vehicle movements each day during the peak construction period. This increase was assessed as relatively minor because there is sufficient capacity in the existing road network. A traffic management plan will be prepared for all works. Air quality The proposed earthworks and traffic movements have the potential to generate dust. Construction at the treatment plant is minor and only a small area will be disturbed. A 450m long section of the pipeline will be constructed along a residential street in close proximity to homes. The reminder of the pipeline will be through rural and industrial areas. The evaporation basin is adjacent to a mining operation with few sensitive receivers. Air quality effects in these latter areas will be similar to that which currently occurs in many rural areas. Dust will be controlled through measures such as minimising the time that land is disturbed and implementing dust suppression. What were the main findings of the environmental assessment? The proposal was found to have a significant benefit to the community as it would deal with deteriorating water quality and offer a continued supply of water that meets the Australian Drinking Water Guidelines. There will be minor adverse impacts on biodiversity and heritage values. There are likely to be short term, temporary and minor adverse impacts during the three month construction of the proposal. The main issues would be associated with impacts on: soil and water due to erosion and sedimentation during earthworks air quality due to dust from exposed surfaces noise due to the operation of machinery and equipment traffic and access to neighbouring properties. Impacts associated with pipeline construction would affect individual locations for a short period of time as the pipe is progressively laid. The most substantial construction activities would be associated with the evaporation basin which would be located adjacent to Perilya s tailings storage facilities. This location means that there are unlikely to be any significant construction impacts associated with noise or dust. Operational impacts would be also be short term as the proposal is intended to operate for two years in five, and would ultimately be decommissioned. Overall, potential negative impacts are considered to be minor and able to be readily managed by implementing the recommended mitigation measures. What happens next? Essential Water s endorsement of the environmental assessment will allow work to commence on the project. The environmental assessment details a number of safeguards and management measures to ensure that any impacts of the proposal are contained and consistent with the findings of the environmental assessment. Before any construction on site, a construction environmental management plan will be prepared that details how the works will proceed and how the environmental safeguards will be addressed.