Surface Water Assessment Report

6583830 GRWP Works Approval Application

Appendix K

Surface Water Assessment

Report

Memorandum

To: Western Water Date: 17 December 2020

From: Sarah Hale, Emily Cray Our Ref: 6583830

Copy: Simon Treadwell

Subject: Gisborne RWP Upgrade - Surface Water Risk Assessment (Construction Activities)

1 Introduction

1.1 Overview and scope

Gisborne Recycled Water Plant (RWP) is owned and operated by Western Water (WW) and is located on Haywood Drive, Gisborne approximately 15 km west of Sunbury and 40 km north-west of Melbourne. The site is bordered by rural and agricultural land to the north, low density rural living to the east and south and the Calder Freeway to the west.

The Gisborne RWP treats wastewater from Gisborne, New Gisborne and Macedon townships and treated effluent produced by the plant is either supplied to customers through the Gisborne recycled water network or discharged under an EPA licence to Jacksons Creek. The plant is currently reaching the limit of its capacity. Growth in flows and loads to the plant are projected to increase in line with population from approximately 14,000 people to approximately 21,000 in 2035. To avoid negative impacts on Jacksons Creek, it is proposed to undertake the following upgrades to the plant:

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New common inlet screening and grit removal facility

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New odour control facility for inlet works consisting of a biotrickling filter with activated carbon

polishing

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New membrane bioreactor (MBR) activated sludge process with provisions for future capacity

augmentations

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Ferric sulphate dosing facility (or other suitable chemical phosphorus removal chemical)

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New effluent discharge pipework to Jacksons Creek

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Sludge dewatering, including polymer dosing facilities

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Electrical and ancillary services

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Site power supply upgrade

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Discharge outlet upgrade (in Jackson’s Creek)

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Site road works

The concept design layout of the Stage 1 upgrade works is shown in Figure 1-1. This layout may be modified during detailed design, so this assessment has considered potential impacts associated with general construction activities based on the concept design only.

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The scope of the surface water and aquatic ecology assessment is to consider the key

environmental risks associated with the construction activities for the proposed Stage 1 upgrade of the Gisborne RWP. This includes general site run-off to surrounding surface water bodies. The assessment includes a qualitative risk assessment based on available data for relevant beneficial uses, indicators and objectives for water quality as well as a description of ecological conditions. A range of risk mitigation measures are recommended to manage identified risks and to address compliance with the relevant SEPPs.

1.2 Construction activities

The proposed Stage 1 upgrade works at the Gisborne RWP, listed in Section 1.1, will result in ground disturbance which has the potential to impact on the surface water and aquatic ecology values in the surrounding surface water bodies. The ground disturbance activities will include (but are not limited to) the following:

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Excavations for the purpose of installing new building foundations

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Creation of new or modification of existing access tracks

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Installation of new pipelines (either above or below the ground)

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Upgrade of existing discharge outlet in Jackson’s Creek

The proposed Stage 1 upgrade works at the Gisborne RWP and associated ground disturbance activities have the potential to impact on surface water and aquatic ecology values in the following ways:

▪

The passive discharge of sediment or settleable matter to surface water from general

construction activities. General construction activities include the installation of new pipelines as well as other water treatment infrastructure and associated buildings at the existing Gisborne RWP. Exposure of soil during construction activities could result in sediment laden surface water run-off entering Jacksons Creek and/or Stephens Creek under existing drainage arrangements.

▪

Local erosion and discharge of sediment to surface water run-off from the construction of new

effluent discharge pipework/outlet in Jacksons Creek and pipe from the RWP to the header pit across Stephens Creek (trenched or above ground on a bridge). Construction of the pipework may create instability and erosion of the Jacksons Creek and Stephens Creek embankment and bed, causing local erosion and sediment laden run-off entering the drainage line.

▪

Construction of a new access road may also result in additional run-off causing local erosion and

sediment laden water entering surface water system.

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Chemical and/or fuel spill during construction, resulting in pollution to local water bodies. The

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2 Relevant environmental legislation and guidance

The following section provides a summary of the legislative requirements for surface water

applicable to the construction phase of the proposed Stage 1 upgrade works to the Gisborne RWP. 2.1 Environment Protection Act 1970 (Vic)

The overall purpose of the Victorian Environment Protection (EPA) Act 1970 is to create a

legislative framework for the management and protection of the Victorian environment, including the environmental values associated with surface water quality. The EPA Act stipulates that discharges to the environment must be managed such that they “do not adversely affect the receiving

environment (for example, land, surface water or groundwater).”

State environment protection policies (SEPPs) are subordinate legislation made under the

provisions of the EPA Act and provide more detailed requirements and guidance for the application of the EPA Act.

Western Water is committed to managing their activities to minimise their impact on the

environment, including the environmental values and beneficial uses of surface waters as discussed further in this section.

2.2 State Environment Protection Policy (Waters) (Vic)

State Environment Protection Policies (SEPPs) provide measures for the protection and

maintenance of environmental quality of Victoria’s land and water environments. The key regulatory instrument of relevance to construction discharge to waterways is the SEPP (Waters).

The SEPP (Waters) sets the framework for government agencies, businesses and the community to work together to protect and rehabilitate Victoria’s surface water environments. It aims to “protect

and maintain the level of environmental quality required to sustain the beneficial uses of Victoria’s water environments” and sets out:

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The beneficial uses and environmental quality objectives for waters, and;

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Obligations to protect beneficial uses and improve water quality, and;

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The rules for decision-making by protection agencies to protect beneficial uses and improve

water quality.

The SEPP (Waters) identifies beneficial uses that reflect the different ways surface waters are used across Victoria. A beneficial use, as defined in the EPA Act, includes a current or future

environmental value or use of surface waters that communities want to protect. The SEPP (Waters) outlines beneficial uses for waterways based on the environment type, location and the applicable regional ‘segment’.

Jackson Creek at Gisborne, is within the Central Foothills and Coastal Plains segment of the SEPP (Waters) - uplands of the Maribyrnong basin. The community values1 relevant to this assessment

include the beneficial uses specified under SEPP, namely:

1 The term “Community Values” is defined in the updated Australian and New Zealand Marine and Freshwater Water Quality

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 Water dependent ecosystems and species that are slightly to moderately modified  Agriculture and irrigation

 Human consumption of aquatic foods  Industrial and commercial

 Water based recreation (primary contact, secondary contact and aesthetic enjoyment)  Traditional Owner cultural values

 Cultural and spiritual values

2.3 National Water Quality Management Strategy and Australian & New Zealand guidelines for Marine & Freshwater Quality

The National Water Quality Management Strategy (NWQMS) is an Australian Government initiative in partnership with state and territory governments which develops and maintains a voluntary, nationally coordinated water quality management framework to facilitate the productive and sustainable use of Australia’s water resources (Australian Government, 2018). Although the primary responsibility for water quality management lies with state governments (through implementation of the SEPP (Waters) for example), the NWQMS aims to provide best available information to support the overall objective of delivery of water that is ‘fit for purpose’ and supports community values (inclusive of both environmental values and beneficial uses).

The NWQMS contains tools and information to support water quality management, central to which is the Water Quality Management Framework (WQMF). A key component of the WQMF is the determination of suitable water/sediment quality guideline values. Guideline values are intended to provide information for water quality managers to assess whether water quality is ‘fit for purpose’. Primary guidance documents referred to in the NWQMS include:

◼ Australian & New Zealand guidelines for fresh & marine water quality (ANZG); ◼ Australian Drinking Water Guidelines (ADWG), and;

◼ Guidelines for managing risks in recreational waters.

These primary guidelines are considered to be key documents for the protection of human health and the environment. The ANZG is relevant to potential impacts to water quality associated with construction and are discussed further below.

2.3.1 Australian & New Zealand guidelines for fresh & marine water quality

The ANZG published by the Australian and New Zealand Environment and Conservation Council (ANZECC) in 1992 was the first joint guidance for assessment of water quality in Australia and New Zealand. The 1992 ANZECC guidelines collated a vast body of scientific literature and

management experience on water quality required to sustain environmental values within aquatic ecosystems. These guidelines became an important reference tool for assessing and managing water quality in natural and semi-natural water resources, providing default guideline values for toxicants and ecosystem stressors.

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also an increased emphasis placed on integrated water management through use of both chemical and biological water quality indicators.

The water quality guidelines were updated again in 2018 as part of an update to the overarching NWQMS. Rather than publication of guidelines in paper (or fixed electronic) format, the 2018 ANZG guidelines are a web-based database which can be updated as new information becomes available. Over thirty default toxicant guideline values have been flagged for revision as part of the ANZG update, however as yet none have been released on the Water Quality Australia website.

Another important change in ANZG is an increased focus on use of a weight of evidence approach towards water quality management. The ANZECC 2000 guidelines introduced a risk-based approach for integrated water quality assessment for the protection of aquatic ecosystems. This concept is further strengthened in the ANZG which adopts formulation of Pressure-State-Ecosystem Receptor (PSER) model as means by which multiple lines of evidence pertaining to a potential water quality issue can be combined. Evaluation of these multiple lines of evidence, including the quality of the available information, is referred within the ANZG as a “weight of evidence” approach. By consideration of factors other than exceedances of default guideline values (or trigger values in the ANZECC 2000 guidelines), assessment conclusions and subsequent management decisions, if required, can be made with greater certainty.

2.4 Water Act 1989

Works and activities in, under, on or over the bed and banks of Designated Waterways in Victoria require a Works on Waterways Permit from the relevant Catchment Management Authority (CMA). Designated waterways are declared under the Water Act 1989 and are named or unnamed, permanent or seasonal waterways, ranging in size from a river to a natural depression. In the Port Phillip and Westernport catchment region, Melbourne Water has the CMA responsibilities. Works and/or activities requiring a Works on Waterways Permit may include:

 Access crossings including bridges, culverts and fords  Services/utility crossings

 Stormwater/discharge outlets

 Stabilisation works such as bank protection, bettering and retaining structures  Removal of silt deposits or silt from around structures

 Vegetation and debris removal  Sand and gravel extraction

 Bore hole testing, monitoring or other works

3 Baseline environmental condition

The Gisborne RWP is located adjacent to Jacksons Creek (Figure 3-1 and Figure 3-2), downstream of Rosslynne Reservoir in which Jacksons Creek flows into, and discharges into the creek’s

receiving environment. There is a tributary of Jackson Creek called Stephens Creek (Figure 3-3) which runs along the eastern boundary of the RWP, however there is little public information available on Stephens Creek, therefore the baseline environmental conditions have been described for Jacksons Creek only.

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and Sunbury. Jacksons Creek meets Riddells Creek between Gisborne and Sunbury and forms the Maribyrnong River at its confluence with Deep Creek downstream of Sunbury. The Maribyrnong River subsequently flows into the Yarra River estuary, at the northern end of Port Phillip Bay. According to the Victorian Healthy Waterways Strategy (2018), the Maribyrnong River and its tributaries are important bio-links – corridors of secure, high quality habitats that allow plants and animals to move and adapt to changes in catchment conditions and climates.

Jacksons Creek supports a number of aquatic fauna species that are threatened, endangered or are regionally significant, including Platypus (Ornithorhynchus anatinus), Water Rats (Hydromys

chyrogaster), Lesueur’s Frog (Litoria lesueurii), Growling Grass Frog (Litoria raniformis) and

possibly Yarra Pygmy Perch (Nannoperca obscura) (GHD 2013) and River Blackfish (Gadopsis

marmoratus) (EarthTech 2006). Jacksons Creek likely also supports a range of other native fish

species including Southern Pygmy Perch (Nannoperca australis), Short-finned Eels (Anguilla

australis), Australian Smelt (Retropinna semoni) and Flat-headed Gudgeon (Philypnodon grandiceps) (reviewed in GHD 2013).

The Jacksons Creek catchment has been significantly modified from natural, with land use primarily consisting of agriculture, including broad acre cropping and livestock grazing. There has also been significant urban development, including the townships of Gisborne and Sunbury on Jacksons Creek and Riddells Creek township, which is located north of Riddells Creek. The condition of Jacksons Creek has been significantly altered from natural primarily as a result of land use change and the operation of Rosslynne Reservoir.

The Index of Stream Condition (ISC), a Statewide program that provides a benchmark of river health in Victoria, rated the four ‘reaches’ (assessment locations) in Jacksons Creek as being in poor or very poor condition (based on information collected from 2004 to 2010). Across the four reaches, the physical form score was comparatively high (ranging from 5 to 9) indicating that the channel is broadly in good condition and that physical habitat (e.g. instream habitat) is present. Streamside zone, which considers the width, nativeness and connectivity of the riparian zone, declined with distance downstream (from 9 to 5). Aquatic life and water quality was moderate (where data was collected). The major factor in the low overall score was hydrology (seasonality, streamflow, variability), which was rated as 3 or less for each reach.

There has been recent efforts to remove willow tree infestations along a portion of the Jacksons Creek adjacent to the Gisborne RWP. Some of these areas have been revegetated with tree species in an effort to improve the extent and quality of the Riparian Woodland (EVC 641) and Stream Bank Shrubland (EVC 851) vegetation communities that are currently present.

Ambient water quality in Jacksons Creek (upstream of the Gisborne RWP) was investigated as part of a Human Health and Ecological Risk Assessment developed as part of the works approval (exemption) application. Using the publicly available water quality data from the closest water quality gauge in Jacksons Creek (gauge 230245A, upstream Sunbury – Riddles Creek, downstream of the Gisborne RWP) it concluded that ambient water quality generally met the water quality objectives for beneficial uses during the 2019/2020 period except for:

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Total Phosphorus

– Water dependent ecosystems: WQO = 0.055 mg/L, ambient value = 0.114 mg/L – Irrigation: WQO = 0.05 mg/L, ambient value = 0.24 mg/L

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E. coli

– Irrigation: WQO = 10 orgs/100mL, ambient value = 11 orgs/100mL

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Figure 3-1: Looking downstream Jacksons Creek at the Gisborne RWP

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Figure 3-3: Looking downstream Stephens Creek towards the Gisborne RWP

4 Assessment findings

Impacts and issues

The key impacts and issues associated with the construction works associated with the proposed upgrade of the Gisborne RWP:

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The passive discharge of sediment or settleable matter to surface water run-off and associated

impact of turbidity on the Jacksons Creek and Stephens Creek during high rainfall events. Water quality and aquatic habitat could be impacted by a small plume of turbidity in the drainage line from surface water run-off from existing drainage pathways.

▪

The construction of the new effluent discharge pipework/outlet in Jacksons Creek and pipe from

RWP to header pit in Stephens Creek may create instability and erosion of the creek

embankment causing local erosion and sediment laden run-off entering the drainage line. Water quality and aquatic habitat could be impacted by the sedimentation of the drainage line.

▪

The pollution of Jacksons Creek or Stephens Creek as a result of chemical and/or fuel spill

during construction. Localised spills to either creek could impact the water quality.

The following relevant beneficial uses of Jacksons and Stephens Creek have the potential to be impacted by surface water run off containing sediment, settleable matter or general construction pollutants/ toxicants:

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Maintenance of slightly to moderately modified ecosystems: Water quality, aquatic fauna and

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Water based recreation – Primary contact: Recreational use of Jacksons Creek may be

impacted by a small plume of turbidity or presence of general toxicant levels from surface water run-off transported directly to the creek or via Stephens Creek.

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Agricultural and irrigation water supply – Stock water: Water quality for unregulated downstream

stock watering may be impacted by a small plume of turbidity or presence of general toxicant levels in the drainage line from surface water run-off.

4.1 Risk assessment

4.1.1 Methodology

The key risks to surface water and aquatic ecology associated with the construction activities for the proposed Stage 1 upgrade of the Gisborne RWP outlined in this chapter have been identified through:

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Qualitative environmental risk assessment undertaken prior to completion of the design

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Taking into consideration that heavy rainfall events that generate surface water run-off during the

construction and operation phase will correspond to moderate to high flows in Jacksons Creek. Therefore, there will likely be significant dilution of any pollutants in the run-off in the receiving waterways.

The overall risks to surface water and aquatic ecology have been predicted by determining the likelihood of a risk occurring (Table 4-1) and the consequence if it does occur (Table 4-2). The risk matrix (Table 4-3) and criteria (Table 4-4) have been adopted from EPA Publication 1695.1 Assessing and controlling risks for business (EPA, 2019).

Table 4-1: Likelihood criteria

Likelihood Frequency

Certain Expected to happen regularly under normal circumstances Likely Expected to happen at some time

Possible May happen at some time

Unlikely Not likely to happen in normal circumstances Rare Could happen but probably never will

Table 4-2: Consequence criteria

Likelihood Description

Severe Permanent or long-term serious environmental harm / life threatening or long-term harm to health and wellbeing

Major Serious environment harm / high-level harm to health and wellbeing Moderate Medium level of harm to health and wellbeing or the environment over an

extended period of time

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Table 4-3: Risk matrix

Consequence Likelihood

Certain Likely Possible Unlikely Rare

Severe Extreme Extreme High High Medium

Major Extreme High High Medium Medium

Moderate High High Medium Medium Low

Minor High Medium Medium Low Low

Low Medium Medium Low Low Low

Table 4-4: Risk ratings

Risk Level Description

Extreme Totally unacceptable level of risk

High Unacceptable level of risk. Controls must be put in place to reduce or lower levels

Medium Can be acceptable if controls are in place. Attempt to reduce to low Low Acceptable level of risk. Attempt to eliminate risk but higher risk levels take

priority

4.1.2 Results

Results of the risk assessment undertaken for the construction works associated with the proposed upgrade of the Gisborne RWP are provided in Table 4-5.

Overall, the level of impact from the proposed construction activities was rated as Medium

assuming no mitigation measures have been put in place i.e. pre-mitigation risk. With mitigation measures put in place, this risk is reduced to Low. The most likely impact activities include

Surface Water Risk Assessment (Construction Activities) Technical Memorandum

Table 4-5: Impacts assessment of proposed construction activities on water quality (turbidity and beneficial uses Relevant

Beneficial Uses Activity Potential impact (Pre-mitigation) Impact severity (Pre-mitigation) Mitigation Impact severity (With

mitigation)

Site access preparation

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Maintenance of modified ecosystem

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Water based recreation – Primary contact

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Agricultural water supply – Stock water

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Creation of new temporary operations access track at south west corner of site

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Potential upgrade of

existing access tracks

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Clear and grub surface

material for new access road

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Import and placement of engineering fill material for access road

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Exposure of soil during construction of access road may result in sediment laden run-off entering Stephens Creek (and potentially flowing in to Jacksons Creek) during high rainfall periods.

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Water quality and aquatic habitat may be impacted by a small plume of turbidity in the drainage line from surface water run-off. Sedimentation may reduce the effectiveness of the drainage line.

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Potential road upgrade activities may disturb soil and gravel on road verge, causing localised erosion and sediment laden run-off entering Jacksons Creek during high rainfall periods. Consequence Minor

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Development and implementation of an appropriate construction environmental management plan that includes mitigation measures outlined in Section 4.2. Consequence Minor Likelihood Possible Likelihood Unlikely Risk Medium Risk Low Site preparation

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Maintenance of modified ecosystem

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Water based recreation – Primary contact

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Agricultural water supply – Stock water

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Clear and grub surface material for construction

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Stockpile excavated

topsoil, subgrade, vegetation and other material

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Excavate pre-loaded material from potential on-site borrow area and temporary stockpile

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Import and stockpile

crushed rock,

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Exposure of soil during site preparation activities may result in sediment laden run-off entering Jacksons Creek or Stephens Creek during high rainfall periods.

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Stockpiling of materials may result in

sediment laden run-off entering Jacksons Creek or Stephens Creek during high rainfall periods.

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Water quality and aquatic habitat

may be impacted by a small plume of turbidity in the drainage line from surface water run-off. Sedimentation

Surface Water Risk Assessment (Construction Activities) Technical Memorandum

engineering fill and other

construction material may reduce the effectiveness of the drainage line.

Construction

▪

Maintenance of modified ecosystem

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Water based recreation – Primary contact

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Agricultural water supply – Stock water

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Import and temporary stockpile crushed rock, engineering fill and other construction material

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Install permanent pipe

from RWP to header pit, across Stephens Creek (trenched or above ground on a bridge)

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Install permanent effluent

discharge pipeline and outlet to Jacksons Creek

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Stockpile excavated

material

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Construction of

hardstand surfaces, plant, equipment and associated infrastructure

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Construction of crushed

rock pathways and internal access track

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Stockpiling of materials may result in sediment laden run-off entering Jacksons Creek or Stephens Creek during high rainfall periods.

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Construction of pipe within Stephens Creek may create instability and erosion of creek bed, causing local erosion and sediment surface run-off into the creek and potentially flow in to Jacksons Creek.

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Construction of sub-soil outlets may create instability and erosion of Jacksons Creek embankment, causing local erosion and sediment surface run-off into the drainage line.

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Operation of heavy machinery may

expose soil and result in sediment laden run-off entering Jacksons Creek or Stephens Creek during high rainfall periods

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4.2 Recommendations and mitigation measures

The following actions are recommended to reduce the potential risks (from Medium to Low) of the proposed construction activities associated with the upgrade of the Gisborne RWP on Jacksons Creek and Stephens Creek and downstream environment values and beneficial uses:

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Develop and implement an appropriate construction environmental management plan that shows

existing and proposed works, site gradients, closely spaced contour lines, drainage systems, easements, boundaries, direction, and other relevant features and provides the following mitigation measures:

– Installation of a site drainage system prior to commencement of site disturbance activities. – Scheduling of construction activities to avoid high rainfall periods.

– Staging construction works to minimise the surface area disturbed at any one time. – Implementation of appropriate silt/sediment control measures to minimise sediment laden

run-off entering waterways or drainage lines (refer to EPA Publication 275: Construction techniques for sediment pollution control). This is of particular importance due to the steepness of the Jacksons Creek embankment.

– Installation of energy dissipaters at discharge point

– Maintenance of buffers of ground cover vegetation at least 30 metres wide alongside creeks and drainage lines, where practical

– Storage of temporarily stockpiled materials at approved sites within the works area at least 20 m away from Jacksons Creek and Stephens Creek and to heights not exceeding 2.0 m (excluding preload areas). Protective covers recommended for any loose erodible material. – Minimising the access and use of heavy machinery in the Jacksons Creek and Stephen

Creek area

– Rehabilitation and revegetation of areas affected by the construction of the new effluent discharge pipework in Jacksons Creek and pipe from RWP to header pit in Stephens Creek.

▪

Undertake regular environmental site inspections to evaluate effectiveness of erosion and

sedimentation controls

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Undertake visual inspections of the water quality conditions in Jacksons Creek and Stephens

Creek (if wet) daily and after significant rainfall (> 10 mm in 24 hours) by the construction superintendent (or appointee). The observer should note any turbidity plumes or oil slicks in the vicinity of the works or downstream. If such impacts are detected, the turbidity and general toxicant levels should be verified (via probe) and recorded and construction should cease while the source is identified and adaptively managed. If oil slicks are detected, water samples should be collected and sent to the laboratories for analysis of oils and greases.

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Review of the construction environmental management plan by Western Water and/or audited by

a suitably qualified professional:

5 Summary

The construction activities associated with the upgrade of the Gisborne RWP are unlikely to result in an impact on beneficial uses outlined in the SEPP (Waters), assuming mitigation measures are implemented. The application of typical silt/sediment controls measures through the

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The exposure of soil during the construction of the Gisborne RWP upgrade or erosion of Jacksons Creek or Stephens Creek embankment (from construction of new effluent discharge pipework in Jacksons Creek and pipe across Stephens Creek from RWP to header pit) may lead to sediment laden run-off entering the creeks during high rainfall periods. Water quality and aquatic habitat may be affected. However, any potential impact on the associated beneficial uses will be minor and infrequent and can be controlled through silt/sediment control measures. The mitigated risk is considered to be low.

6 References

EarthTech (2006) Environmental Flow Determination for the Maribyrnong River – Site Paper. Report by EarthTech for Melbourne Water.

Environment Protection Authority Victoria (2019). Assessing and controlling risks for business. EPA Publication 1695.1.

Jacobs (2017). Jacksons Creek Ecological Benefit and Risks Assessment – Assessment of the

Benefits and Risks of Recycled Water Releases to Jacksons Creek. Report by Jacobs for

Melbourne Water.

GHD (2013). Ecological Risk Assessment of Gisborne, Sunbury and Woodend Recycled Water