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Kilcoy Solar Farm Stormwater Management Strategy

Reference: R.B22885.002.02.SMS.docx Date: April 2018 Confidential

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BMT WBM Pty Ltd Level 8, 200 Creek Street Brisbane Qld 4000 Australia PO Box 203, Spring Hill 4004 Tel: +61 7 3831 6744 Fax: + 61 7 3832 3627 ABN 54 010 830 421 www.bmt.org

Document: R.B22885.002.02.SMS.docx

Title: Kilcoy Solar Farm Stormwater Management Strategy

Project Manager: Brad Grant

Author: Paul Dubowski, Nigel Hardie, Adyn de Groot, Nicole Ramilo

Client: Ethos Urban

Client Contact: Morgan Randle

Client Reference:

Synopsis: This report presents a stormwater management strategy for the proposed Kilcoy Solar Farm development. A more detailed report is proposed once preliminary design drawings become available.

REVISION/CHECKING HISTORY

Revision Number Date Checked by Issued by

2 26/04/2018 Lucy Peljo

Paul Dubowski

1 23/04/2018 Lucy Peljo Paul Dubowski

0 06/04/2018 Lucy Peljo Paul Dubowski

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Destination Revision

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Kilcoy Solar Farm Stormwater Management Strategy i

Executive Summary


Executive Summary

BMT has been commissioned by Ethos Urban (in support of a preliminary approval for a Development

Application to Somerset Regional Council) to prepare a Stormwater Management Strategy for the proposed

Renewable Energy Facility (Solar Farm) development (hereafter referred to as ‘the site’).

The site has an approximate area of 2,055 hectares and is located approximately 15 kilometres west of Kilcoy.

The site is and is bounded to the north by the D’Aguilar Highway, to the west by Holland Road, and to the

south and east by private rural land.

The majority of the site drains to Neara Creek which then discharges into the Brisbane River approximately

3.6 kilometres downstream of the site. A small portion of the site drains south to Gregors Creek which then

discharges into the Brisbane River.

This conceptual Stormwater Management Strategy includes the following elements:

• Stormwater Quantity Management.

• Stormwater Quality Management.

The Stormwater Quantity Management strategy provides an assessment of the pre- and post-development

peak flows, and details the detention basin requirements to attenuate the peak flows to maintain pre-

development conditions.

The Stormwater Quality Management strategy provides a water quality assessment of the proposed

development and measures required to achieve design stormwater quality management objectives. Water

quality modelling results indicate that the proposed strategy will achieve the required load removal targets.

This Stormwater Management Strategy has also demonstrated how the proposed development will adhere to

the requirements of the State Planning Policy (DILGP 2017) and Somerset Regional Council’s Catchment

Overlay Code (Somerset Region Planning Scheme Version 2, 2016).

It is noted that a more detailed ‘Site Based Stormwater Management Plan’ will be prepared and submitted to

Council once design drawings become available.

Kilcoy Solar Farm Stormwater Management Strategy ii

Contents


Contents

Executive Summary i

1 Introduction 1

2 Site Details 2

2.2 Existing Zoning and Land Use 2

2.3 Site Topography and Drainage 8

2.4 Vegetation 8

3 Project Description 11

4 Stormwater Quantity Management 13

4.1 Preamble 13

4.2 Existing Case 13

4.2.1 Modelled Catchment 13

4.2.2 Rainfall Parameters 13

4.2.3 Hydrologic Parameters 14

4.3 Developed Case 14

4.4 Detention Basin Sizing 15

5 Stormwater Quality Management Strategy 16

5.1 Preamble 16

5.2 Stormwater Quality Management Objectives 16

5.2.1 Construction Phase 16

5.2.2 Operational Phase 17

5.2.2.1 Water Quality 17

5.3 MUSIC Modelling 18

5.4 Proposed Strategy 18

5.4.1 Option A 18

5.4.2 Option B 20

5.5 Model Results 23

5.6 Water Quality Monitoring 24

5.7 Maintenance Plans 24

5.8 Construction and Establishment 24

5.9 Asset Hand-over 24

6 Conclusions 25

7 References 26

Appendix A Conceptual Design Drawings A-1

Kilcoy Solar Farm Stormwater Management Strategy iii

Contents


Appendix B Somerset Regional Council Catchment Management Overlay Code B-1

Appendix C MUSIC Modelling Methodology C-1

List of Figures

Figure 2-1 Location of Site 4

Figure 2-2 Project Boundary 5

Figure 2-3 Somerset Regional Council Catchment Management Overlays Map 6

Figure 2-4 Images of the Existing Site 7

Figure 2-5 Site Topography and Digital Elevation Model 9

Figure 2-6 Stream Order Map 10

Figure 3-1 Proposed Development Area 12

Figure 5-1 Schematic of Stormwater Quality Management Strategy – Option A 18

Figure 5-2 Schematic of Stormwater Quality Management Strategy – Option B 20

Figure 5-3 Typical Arrangement of Swales and Bioretention Systems in Solar Subarrays (1ha) 22

Figure A-1 Site Context Map A-2

Figure A-2 Solar Subarray Layout A-3

Figure A-3 Solar Subarray Layout: Section A-A A-4

Figure C-1 Examples of Typical Constructed Wetlands C-5

Figure C-2 Typical Ephemeral Wetland – Plan View C-6

Figure C-3 Typical Ephemeral Wetland – Longitudinal Section C-7

Figure C-4 Examples of Swales C-8

Figure C-5 Examples of Streetscape Bioretention Systems C-9

Figure C-6 Typical Bioretention Cross Section C-10

List of Tables

Table 4-1 Existing Case Sub-Catchment Landuse Properties 13

Table 4-2 Rainfall Parameters 14

Table 4-3 Existing Case Hydrologic Parameters 14

Table 4-4 Developed Case Sub-Catchment Landuse Properties 14

Table 4-5 Developed Case Hydrologic Parameters 15

Table 4-6 Detention Basin Parameters 15

Table 5-1 Construction Phase Performance Criteria 16

Kilcoy Solar Farm Stormwater Management Strategy iv

Contents


Table 5-2 Operational Phase Performance Criteria 17

Table 5-3 Summary of Stormwater Quality Management Strategy – Option A 19

Table 5-4 Summary of Stormwater Quality Management Strategy – Option B 21

Table 5-5 Predicted Average Annual Flows & Pollutant Loads per representative 1 ha of Solar Subarrays (1980 to 1989) – Option A (Ephemeral Wetland) 23

Table 5-6 Predicted Average Annual Flows & Pollutant Loads per representative 1 ha of Solar Subarrays (1980 to 1989) – Option B (Swale & Bioretention) 23

Table 5-7 Predicted Average Annual Flows & Pollutant Loads per representative 1 ha of Substation Area (1980 to 1989) – With Proposed Treatment Strategy (Ephemeral Wetland) 23

Table C-1 Summary of Source Node Properties Applied in MUSIC Modelling for a 1-ha Representative Future Development Scenario C-2

Table C-2 Ephemeral Wetland Model Parameters C-4

Table C-3 Bioretention System Modelled Parameters C-9

Kilcoy Solar Farm Stormwater Management Strategy 1

Introduction


1 Introduction

1.1 Preamble

BMT has been commissioned by Ethos Urban, to prepare a ‘Stormwater Management Strategy’

(SMS) in support of a development application for a renewable energy facility (solar farm) at the

Kilcoy development site (hereafter referred to as ‘the site’). This section of the report provides a

background to the project and describes the objectives of the report.

1.2 Background

Sunshine Energy is proposing a renewable energy facility (solar farm) on a 2,055 hectare parcel of

land located approximately 15 kilometres west of Kilcoy. The development is proposed on land which

is predominantly cleared and currently used for grazing.

Ethos Urban has been engaged by Sunshine Energy Australia to undertake planning and project

coordination services, including undertaking the necessary planning applications for the

development. Ethos Urban has subsequently engaged BMT to prepare a SMS to assist in

understanding landuse constraints, potential impacts associated with the development and to

develop a preliminary mitigation strategy.

Two related reports have also been prepared by BMT including:

• Kilcoy Solar Farm ‘High-Level’ Flood Hazard Assessment (BMT 2018a).

• Kilcoy Solar Farm Preliminary Ecological Assessment Report (BMT 2018b).

1.3 Objectives of this Report

The objectives of this SMS include the following:

• Assess and describe the current condition of the site including drainage.

• Describe the potential impacts of the development on stormwater quality and hydrology.

• Identify potential stormwater management objectives.

• Outline a recommended strategy for onsite stormwater management which reflects contemporary

best management practice (BMP) to achieve the identified stormwater management objectives.

Given the preliminary stage of development and high level of design information currently available,

the treatment strategy proposed is based on a per hectare of development scale. It is intended that

a more detailed ‘Site Based Stormwater Management Plan’ will be prepared and submitted to Council

once design drawings become available.


Site Details


2 Site Details

2.1 Location

The site is a 2,055 hectare parcel of land made up of 17 allotments including:

• Lot 42 on SP218812;

• Lot 32 on SP203488;

• Lot 41 on SP218812;

• Lot 120 on CG2692;

• Lot 1 on RP28556;

• Lot 2 on SP210633;

• Lot 65 on CG463;

• Lot 1 on SP276622;

• Lot 135 on CG4460;

• Lot 10 on SP236175;

• Lot 2 on SP203488;

• Lot 26 on SP193038;

• Lot 144 on C311563;

• Lot 145 on C311563;

• Lot 48 on C31888;

• Lot 43 on SP218812; and

• Lot 127 on SP218812.

The site (centroid) is located approximately 15 kilometres west of Kilcoy, and is bounded to the north

by the D’Aguilar Highway, to the west by Holland Road, and to the south and east by private rural

land. The location of the site is presented in Figure 2-1 below while the project boundary is shown in

Figure 2-2. The allotments are shown in Appendix A.

2.2 Existing Zoning and Land Use

The site is located within the rural zone under the Somerset Region Planning Scheme Version 2

(SRPS) (Somerset Regional Council 2016). The site is also affected by a number of SRPS overlays

relevant to stormwater management, including:

• Catchment Management Overlay (OM005a), including:

○ 75 metre buffer to a watercourse in a Lower Risk Catchment Area.

○ 100 metre buffer to a watercourse in the Higher Risk Catchment Area.


Site Details


• Catchment Management Area.

• Flood Hazard Overlay (OM007a), with three western lots identified as Low Flood Hazard.

• High Impact Activity Management Area.

These overlays are shown in Figure 2-3.

The site is currently used for agricultural purposes. Grazing of nominally improved pastures along

with associated management infrastructure such as yards, sheds and dwellings is the only current

land use. Photos showing general conditions of the site are presented in Figure 2-4.


Site Details


Figure 2-4 Images of the Existing Site


Site Details


2.3 Site Topography and Drainage

The topography of the site can be separated broadly into two distinct areas including:

• The lowland alluvial plains/ gently undulating lower slopes. This topography is located in the

central and northern parts of the site and includes elevations of approximately 95 to 150 metres

Australian Height Datum (AHD).

• The steep mid to upper slopes. This topography is located along the southern part of the site and

includes elevations of approximately 150 to 360 m AHD.

A Digital Elevation Model (DEM) of the site is provided in Figure 2-5 below.

The site is located within the Brisbane River basin and Brisbane River sub-basin. The majority of the

site drains in a northerly direction towards Neara Creek which flows from an easterly to westerly

direction along the northern part of the site. Neara Creek discharges from the site’s western boundary

and then flows south where it flows into the Brisbane River approximately 3.6 kilometres downstream

of the site. Neara Creek is a freshwater, fifth order stream and expected to maintain permanent water

throughout the year. The only exception to the above is a very small part of the site which drains

south to Gregors Creek. Gregors Creek also flows towards the Brisbane River.

Figure 2-6 provides a stream order map at a 1:100,000 scale and also shows the drainage of the

site.

The Brisbane River flows into Wivenhoe Dam approximately 25 kilometres (geodesic distance)

downstream of the confluence of Neara Creek and the Brisbane River. The site therefore drains into

a water supply dam and is identified by the State Planning Policy interactive mapping system (SPP

IMS) to be located within a water resource catchment. The SPP IMS also identifies a small area of

the site to be located within a water supply buffer area (as shown in Figure 2-3).

2.4 Vegetation

As can be seen by the aerial photo on Figure 2-2, the site is predominately cleared although regrowth

vegetation remains along the steeper slopes and gullies along the southern parts of the site. A

number of large habitat trees are located on the site, however these are generally isolated from each

other across the site. For a more detailed description of vegetation please refer to the Kilcoy Solar Farm Preliminary Ecological Assessment Report (BMT 2018b).


Project Description


3 Project Description

As identified in Section 2 above, the development is a renewable energy facility (solar farm). The

proposal comprises the following:

• A 1500 MW energy facility, with approximately 5.19 million solar panels in total, built over two

stages.

• Stage 1 will require 867.6 hectares of land, while Stage 2 will require 295.7 hectares of land.

• The solar panels are proposed to be arranged in subarrays of 21 solar panels each in a 3 x 7

configuration (approximately 247,142 subarrays in total). Each subarray will be placed in a row

separated by 0.5 metres and columns separated by 6– 6.5 metres.

• Each subarray has dimensions of 11.9 x 3.016 metres and an area of 35.89 square metres.

• 125 battery module containers are proposed, each container storing 4 MW.

• Two substations are proposed, including one to be operated by Powerlink and the other by

Sunshine Energy. These substations are expected to be approximately 16.15 hectares and

16.8 hectares in area, respectively. The Sunshine Energy substation will also include the battery

storage for the whole site.

• No surface treatment beneath the panels is expected to be required and internal surfaced road

construction will be avoided.

• A fixed structure single post ground mounting system will be used and the panels will not rotate

during the day. Depending on the soil condition, there may be no need to concrete the mounting

poles.

Details of the proposed subarrays have been provided in Figure 5-3.

Figure 3-1 below shows the proposed development area.


Stormwater Quantity Management


4 Stormwater Quantity Management

4.1 Preamble

The proposed development is likely to increase the rainfall runoff from the site, leading to an increase

in peak flows entering the neighbouring waterways. This section provides a description of the

hydrologic model used to estimate the pre- and post-development peak flows, and determine the

detention basin requirements to attenuate the increase.

4.2 Existing Case

4.2.1 Modelled Catchment

To represent the hydrologic behaviour of the proposed development, four sub-catchments were

modelled using the XP RAFTS hydrologic modelling software. To estimate the per hectare

stormwater detention basin requirements of the solar panel installation area, three 1 hectare sub-

catchments were created with three different terrain slopes (1%, 5% and 10%) to represent the

varying terrain slope of the site. For the substations and battery storage area, a 37 hectare combined

sub-catchment was created.

The existing case sub-catchment landuse properties are presented in Table 4-1.

Table 4-1 Existing Case Sub-Catchment Landuse Properties

Sub-Catchment Name

Modelled Area

Slope Impervious Percentage

Manning’s Roughness ‘n’

Pervious Areas

Impervious Areas

EX_Slope1 1 ha 1% 2% 0.06 0.015

EX_Slope5 1 ha 5% 2% 0.06 0.015

EX_Slope10 1 ha 10% 2% 0.06 0.015

EX_Bldngs 37 ha 1% 2% 0.06 0.015

4.2.2 Rainfall Parameters

The rainfall parameters used in the XP RAFTS model were extracted from Australian Rainfall and Runoff (Institution of Engineers Australia, 1987) for the Kilcoy area. The adopted parameters are

presented in Table 4-2.




Table 4-2 Rainfall Parameters

Parameter Value

2 Year ARI 1 hour Rainfall Intensity 41.72 mm/hr




50 Year ARI 12 hour Rainfall Intensity 13.58 mm/h


Skew Coefficient 0.28

Geographical Factor F2 4.37

Geographical Factor F50 17.25

4.2.3 Hydrologic Parameters

The rainfall losses adopted for use in the XP RAFTS model for all events are presented in Table 4-3.

Table 4-3 Existing Case Hydrologic Parameters

Parameter Loss (mm)

Initial Loss (Pervious) (mm) 25

Initial Loss (Impervious) (mm) 1

Continuing Loss (Pervious) (mm) 2.5

Continuing Loss (Impervious) (mm) 0

4.3 Developed Case

The existing hydrologic model was revised to reflect the change in landuse and hydrologic

parameters associated with the proposed development.

For all the sub-catchments, the Manning’s roughness value for the pervious areas was reduced to

reflect a reduction in vegetation density. For the substations and battery storage sub-catchment, the

impervious percentage was increased to 100%, assuming these areas will either be paved or under

roof. The developed case sub-catchment landuse properties are presented in Table 4-4.

Table 4-4 Developed Case Sub-Catchment Landuse Properties

Sub-Catchment Name

Modelled Area

Slope Impervious Percentage

Manning’s Roughness ‘n’

Pervious Areas

Impervious Areas

DE_Slope1 1 ha 1% 2% 0.03 0.015

DE_Slope5 1 ha 5% 2% 0.03 0.015

DE_Slope10 1 ha 10% 2% 0.03 0.015

DE_Bldngs 37 ha 1% 100% 0.03 0.015




For the hydrologic parameters, the pervious area loss rates for the solar panel installation sub-

catchments were reduced to reflect an increase in rainfall concentration hitting the ground due to

deflection from the solar panels (Table 4-5).

Table 4-5 Developed Case Hydrologic Parameters

Parameter Loss (mm)

Initial Loss (Pervious) (mm) 15

Initial Loss (Impervious) (mm) 1

Continuing Loss (Pervious) (mm) 1.5

Continuing Loss (Impervious) (mm) 0

4.4 Detention Basin Sizing

To attenuate the increase in peak flow associated with the change in landuse and hydrologic

parameters, detention basins were sized for the four catchments. For this assessment, design storms

for the 2 year and 100 year ARI events were considered, with durations of 25min, 60min, 90min and

180min for each. The resultant detention basin parameters are presented in Table 4-6.

For the 1 hectare solar panel installation sub-catchments, it was found that the same per hectare

basin can be used for each of the terrain slopes. Allowing for 4:1 batter slopes and 300mm of

freeboard above a maximum storage depth of 1.4 m, a basin with a surface area of 7% of the total

sub-catchment area was required.

With the same batter slopes and freeboard, the substation and battery storage sub-catchment

required a maximum storage depth of 1.7 m and a surface area of 6% of the total sub-catchment

area.

Table 4-6 Detention Basin Parameters

Basin Parameter Per hectare of Solar Panel Installation Area

Substations and Battery Storage Area

Q100 Peak Storage Depth 1.4 m 1.7 m

Q100 Peak Stored Volume 466 m3 30,700 m3

Surface Area (assuming 4:1 batters and 300mm freeboard)

655 m2 20,450 m2

Percentage of Sub-catchment for Basin Surface Area

7% 6%


Stormwater Quality Management Strategy


5 Stormwater Quality Management Strategy

5.1 Preamble

This section provides a conceptual plan and assessment relating to the quality of stormwater runoff

from the site and how it will be possible to achieve the necessary stormwater quality management

objectives during the operational (post-construction) phase of the proposed development.

5.2 Stormwater Quality Management Objectives

5.2.1 Construction Phase

Performance criteria for the construction phase of the development have been adopted directly from

the State Planning Policy (DILGP 2017). These criteria are given in Table 5-1.

Table 5-1 Construction Phase Performance Criteria

Issue Design objectives

Drainage Control Temporary drainage works 1. Design life and design storm for temporary drainage works:

• Disturbed area open for <12 months—1 in 2-year ARI event

• Disturbed area open for 12–24 months—1 in 5-year ARI event

• Disturbed area open for > 24 months—1 in 10-year ARI event

2. Design capacity excludes minimum 150 mm freeboard

3. Temporary culvert crossing—minimum 1 in 1-year ARI hydraulic capacity

Erosion control Erosion control measure 1. Minimise exposure of disturbed soils at any time

2. Divert water run-off from undisturbed areas around disturbed areas

3. Determine the erosion risk rating using local rainfall erosivity, rainfall depth, soil-loss rate or other acceptable methods

4. Implement erosion control methods corresponding to identified erosion risk rating

Sediment control Sediment control measure

Design storm for sediment control basins

Sediment basin dewatering

1. Determine appropriate sediment control measures using:

• potential soil loss rate, or

• monthly erosivity, or

• average monthly rainfall

2. Collect and drain stormwater from disturbed soils to sediment basin for design storm event:

• design storm for sediment basin sizing is 80th% five-day event or similar

3. Site discharge during sediment basin dewatering:

• TSS < 50 mg/L, and

• Turbidity not >10% receiving waters turbidity, and

• pH 6.5–8.5




Issue Design objectives

Water quality Litter and other waste, hydrocarbons and other contaminants

1. Avoid wind-blown litter; remove gross pollutants

2. Ensure there is no visible oil or grease sheen on released waters

3. Dispose of waste containing contaminants at authorised facilities

Waterway stability and flood flow management

Changes to the natural waterway hydraulics and hydrology

1. For peak flow for the 1-year and 100-year ARI event, use constructed sediment basins to attenuate the discharge rate of stormwater from the site

The management strategy for achieving these criteria will be described as part of a detailed erosion

and sediment control (ESC) plan. Details of the ESC plan have not been provided as part of this

stormwater management strategy.

5.2.2 Operational Phase

The proposed development will adhere to the requirements of Somerset Regional Council’s

Catchment management overlay code (Somerset Region Planning Scheme Version 2, 2017).

Individual responses to this code are provided in Table 5-2.

5.2.2.1 Water Quality Performance criteria for the operational phase of the development shall be in accordance with the

State Planning Policy (DILGP 2017) as outlined in Somerset Region Planning Scheme Volume 2

(Somerset Regional Council 2017). These criteria are given in Table 5-2 below.

Table 5-2 Operational Phase Performance Criteria

Pollutant Criteria

Total Suspended Solids 80% reduction

Total Phosphorus 60% reduction

Total Nitrogen 45% reduction

Gross Pollutants (5mm or larger) 90% reduction

Additionally, as a very small area of the works (in Option 3 only) is located within a water supply

buffer area, the proposed development is required to avoid adverse impacts on drinking water supply

environmental values.




5.3 MUSIC Modelling

The MUSIC software has been used to assess the generation, transportation and management/

treatment of flows and pollutant loads from the site.

The following scenarios have been investigated in MUSIC:

• Developed site without the proposed stormwater management strategy in place.

• Developed site with the proposed stormwater management strategy in place.

Table 5-3 provides a detailed description of the MUSIC modelling methodology applied.

5.4 Proposed Strategy

There are a number of treatment options available for runoff from the site. For the purposes of this

application, two stormwater quality management options have been developed which are outlined in

the following sections. It should be noted that as the final layout of solar subarrays and substations

is not yet determined, the typical arrangement should be modified based on site specifics, such as

topography and waterways.

5.4.1 Option A

This option consists of a series of ephemeral wetlands to treat runoff from both the substations

(including battery storage areas) and solar subarrays. This is the preferred option. A schematic layout

of this option is shown in Figure 5-1. Table 5 3 provides a summary of the stormwater management

strategy for the site.

Figure 5-1 Schematic of Stormwater Quality Management Strategy – Option A

Solar Subarrays

Ephemeral Wetlands

Ephemeral Wetlands

Substations




Table 5-3 Summary of Stormwater Quality Management Strategy – Option A

Component Description

Ephemeral Wetlands (Solar Subarrays)

Ephemeral wetlands (that are temporarily inundated with water) are the preferred treatment strategy for treating runoff from the solar subarrays. It is envisaged that a series of wetlands (represented as one wetland in the MUSIC model) will be strategically located to capture and treat runoff prior to discharging to receiving waters.

The area of wetland required for treating one hectare of solar subarrays has been modelled in MUSIC as having a macrophyte surface area of 700m2 with an extended detention depth of 0.5m. It has also been modelled with an inlet pond volume of 70m3. Due to temporary inundation, the wetland has been modelled with a permanent pool volume of 210m3, however it is noted that this is expected to completely dry out during periods of no rainfall. An equivalent pipe diameter of 35mm has been assumed to achieve a notional detention time of 48 hrs.

Zero exfiltration and an overflow weir width of approximately 70m have been assumed.

Ephemeral Wetland (Substations, including Battery Storage Area)

Ephemeral wetlands are proposed for treating runoff from the solar subarrays. It is envisaged that a wetland will be located downstream of each of the proposed substations to capture and treat runoff prior to discharging to receiving waters.

The area of wetland required for treating one hectare of substation area has been modelled in MUSIC as having a macrophyte surface area of 600m2 with an extended detention depth of 0.5m. It has also been modelled with an inlet pond volume of 55m3. Due to temporary inundation, the wetland has been modelled with a permanent pool volume of 180m3, however it is noted that this is expected to completely dry out during periods of no rainfall. An equivalent pipe diameter of 32mm has been assumed to achieve a notional detention time of 49 hrs.

Zero exfiltration and an overflow weir width of approximately 60m have been assumed.

Wetland Extents

The extent of the wetland surface areas given in Table 5-4 only include the extent of the assumed

standing water level. It does not include any additional land required for other aspects of the wetland

external to the water level, including (but not limited to) batters and maintenance access.




5.4.2 Option B

This option consists of the integration of bioretention systems along the drip line of the solar

subarrays to treat runoff prior to entry into swales running alongside internal (unsurfaced) access

tracks. Swales would provide treatment of runoff from the access tracks as well as additional

treatment of runoff from the solar subarrays prior to ultimate discharge into Neara Creek and the

Brisbane River. This option has been investigated for the solar subarray area only if space is

constrained on site in the final adopted development layout. A schematic layout of this option is

shown in Figure 5-2. Figure 5-3 presents a typical arrangement of this option. Table 5 3 provides a

summary of the stormwater management strategy for the site.

Figure 5-2 Schematic of Stormwater Quality Management Strategy – Option B

Swales

Solar Subarrays Substations

Ephemeral Wetlands

Bioretention Systems




Table 5-4 Summary of Stormwater Quality Management Strategy – Option B

Component Description

Bioretention Basin (Solar Subarrays) Each bioretention basin under the drip line of the solar subarray will provide treatment to runoff from the subarray.

For each hectare representation, the total bioretention surface area is 1490m2, with no extended detention depth. The filter media depth is identified as 0.4m vegetated with effective nutrient removal plants. The basin is considered unlined, with no underdrainage present and no exfiltration assumed.

Swales (roadside for Solar Subarrays) The swales will primarily treat runoff from the access tracks, and convey treated runoff from the bioretention systems down the access tracks next to the solar subarrays.

For each hectare representation, a total swale length of 600m is modelled, with an average base width of 0.5m and top width of 2.9m. The swale has a depth of 0.3m and assumed bed slope of 1%. The swale is vegetated (0.25m vegetation height). Zero exfiltration has been assumed.




Figure 5-3 Typical Arrangement of Swales and Bioretention Systems in Solar Subarrays (1ha)




5.5 Model Results

The total predicted annual flow and pollutant loads from one hectare of representative land use on

the development site with the proposed stormwater management strategy is presented below.

Table 5-5 represents the flow and loads that are predicted to discharge from development site per

representative 1-hectare of solar subarrays with Option A (ephemeral wetland treatment).

Table 5-6 represents the flow and loads that are predicted to discharge from development site per

representative 1-hectare of solar subarrays with Option B (bioretention systems and swales). Table

5-7 represents the flow and loads that are predicted to discharge from the representative 1-hectare

of substation area (with ephemeral wetland treatment).

Table 5-5 Predicted Average Annual Flows & Pollutant Loads per representative 1 ha of Solar Subarrays (1980 to 1989) – Option A (Ephemeral Wetland)

Parameter Unmitigated Development

Developed Site With Treatment

% Removal % Removal Target*

Flow (ML/yr) 6.30 4.96 21 -

TSS (kg/yr) 655 119 82 80

TP (kg/yr) 1.3 0.4 67 60

TN (kg/yr) 14.0 6.8 51 45

Gross Pollutants (kg/yr) 157 0 100 90

*Refer to Table 5-2

Table 5-6 Predicted Average Annual Flows & Pollutant Loads per representative 1 ha of Solar Subarrays (1980 to 1989) – Option B (Swale & Bioretention)




Flow (ML/yr) 6.30 3.40 46 -

TSS (kg/yr) 635 59.8 91 80

TP (kg/yr) 1.34 0.44 67 60

TN (kg/yr) 13.8 5.2 63 45


*Refer to Table 5-2

Table 5-7 Predicted Average Annual Flows & Pollutant Loads per representative 1 ha of Substation Area (1980 to 1989) – With Proposed Treatment Strategy (Ephemeral Wetland)




Flow (ML/yr) 8.2 7.1 14 -

TSS (kg/yr) 1110 187 83 80

TP (kg/yr) 2.8 0.8 71 60

TN (kg/yr) 20.5 11.0 47 45


*Refer to Table 5-2




From Table 5-5, Table 5-6 and Table 5-7, it can be seen that the proposed stormwater quality

treatment strategy satisfies the required operational phase performance targets (refer to Table 5-2).

5.6 Water Quality Monitoring

No water quality monitoring is recommended for stormwater discharges from the site.

As there is no uncertain or untested stormwater quality best management practices proposed, the

need for stormwater quality monitoring is not considered to be required. The measures proposed for

water quality treatment are well understood and demonstrated in South East Queensland.

5.7 Maintenance Plans

Maintenance of the wetlands, bioretention systems and swales should be undertaken in accordance

with Maintaining Vegetated Stormwater Assets (Water by Design 2012).

5.8 Construction and Establishment

The wetlands, swales and bioretention systems will need to be constructed and established in

accordance with Water by Design (2010a) ‘Construction and Establishment Guidelines: Swales, Bioretention Systems and Wetlands’.

The appropriate construction and establishment of the proposed treatment devices will be critical to

maximising their ability to protect waterway health and minimise operational difficulties (and

maintenance requirements).

5.9 Asset Hand-over

It is anticipated that ownership and maintenance requirements of the proposed treatment devices

will be managed under private ownership by Sunshine Energy Australia. As the proposed

development will remain entirely on private land, treatment devices will not be ‘handed over’ to

Somerset Regional Council.


Conclusions


6 Conclusions

The conceptual Stormwater Management Strategy presented in this plan broadly outlines the

planning, management and maintenance for selected stormwater treatment measures.

Modelling results for the development site indicate that the proposed treatment strategy will attenuate

peak flows to pre-development levels and will also achieve given operational phase pollutant load

removal targets in accordance with the State Planning Policy (DILGP 2017).

This Stormwater Management Strategy has also demonstrated how the proposed development will

adhere to the requirements Somerset Regional Council’s Catchment Overlay Code (Somerset Region Planning Scheme Version 2, 2016).

It is noted that a more detailed ‘Site Based Stormwater Management Plan’ will be prepared and

submitted to Council once design drawings become available.


References


7 References

BMT (2018a). Kilcoy Solar Farm ‘High-Level’ Flood Hazard Assessment, prepared for Ethos Urban.

BMT (2018b). Kilcoy Solar Farm Preliminary Ecological Assessment Report, prepared for Ethos

Urban.

Department of Environment and Resource Management (DERM) (2010a). Environmental Protection (Water) Policy 2009 Plan WQ1438: Brisbane River, including all Tributaries of the Brisbane River, other than Bremer River, Lockyer Creek, Oxley Creek and Stanley River – Upper Brisbane River. The State of Queensland, Brisbane.

Department of Environment and Resource Management (DERM) (2010b). Environmental Protection (Water) Policy 2009 Upper Brisbane River environmental values and water quality objectives, Basin No 143 (part) including all tributaries of the Brisbane River above Wivenhoe Dam, Lake Wivenhoe, Lake Perseverance and Lake Cressbrook. The State of Queensland, Brisbane.

Department of Infrastructure, Local Government and Planning (DILGP) (2017). State Planning Policy, June 2017. The State of Queensland, Brisbane.

Department of State Development, Manufacturing, Infrastructure and Planning (DSDMIP). State Planning Policy Interactive Mapping System (SPP IMS)

https://spp.dsdip.esriaustraliaonline.com.au/geoviewer/map/planmaking Accessed 28/03/18

Somerset Regional Council (2016). Somerset Region Planning Scheme Version 2 (SRPS). Somerset Regional Council, Kilcoy.

Water by Design (2010a) Construction and Establishment Guidelines: Swales, Bioretention Systems and Wetlands. SEQ Healthy Waterways Partnership. Brisbane, Queensland.

Water by Design (2010b). MUSIC Modelling Guidelines. SEQ Healthy Waterways Partnership.

Brisbane, Queensland. ISBN 978-0-9806278-4-8.

Water by Design (2012). Maintaining Vegetated Stormwater Assets. Healthy Waterways Limited,

Brisbane.

https://spp.dsdip.esriaustraliaonline.com.au/geoviewer/map/planmaking

Kilcoy Solar Farm Stormwater Management Strategy A-1

Conceptual Design Drawings


Appendix A Conceptual Design Drawings

A.1 Preamble

This section contains the following conceptual design drawings:

• Site context map.

• Solar subarray configuration.

DAGUILAR HIG

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GREGORS

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SP

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OA

D

RO

AD

RIC

HTER ROAD

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OHLMANS

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ANG

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OA

DFO

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SINNAMONS LANE

OLEARYS LANE

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GAULTS

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4 11

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10812

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9

Sunshine Energ y – KilcoySite Context Map

0 1.50.75

km

7/12/2017

1:35,000

This product is for informational purposes and may not have beenprepared for, or be suitable for legal, engineering, or surveyingpurposes. The map layers displayed are compiled from varioussources. Therefore, no warranty is given relation to thedata displayed on this map (including accuracy, reliability,completeness, currency or suitability) and accepts no liability (including without limitation, liability in negligence) for any loss, damage or costs(including consequential damage) relating to any use of the data.

Disclaimer

GDA 94 Zone 56

Data Source: QGIS 2017 i

Subject site (site number - referto table)

CadastreHighway

# Lot des cription Area (Ha)1. Lot 42 on SP218812 179.2

2. Lot 32 on SP203488 115.4

3. Lot 41 on SP218812 199.5

4. Lot 120 on CG2692 64.719

5. Lot 1 on RP28556 89.985

6. Lot 2 on SP210633 246.978

7. Lot 65 on CG463 7.537

8. Lot 1 on SP276622 68.376

9. Lot 135 on CG4460 1.773

10. Lot 10 on SP236175 94.537

11. Lot 2 on SP203488 115.4

12. Lot 26 on SP193038 132.4

13. Lot 144 on C311563 94.59

14. Lot 145 on C311563 93.869

15. Lot 48 on C31888 258.999

16. Lot 43 on SP218812 200.6

17. Lot 127 on SP218812 91.3

2055.163Ha

HARLIN

HARLIN

KILCOY

0 105

km




Figure A-2 Solar Subarray Layout




Figure A-3 Solar Subarray Layout: Section A-A

Kilcoy Solar Farm Stormwater Management Strategy B-1

Somerset Regional Council Catchment Management Overlay Code


Appendix B Somerset Regional Council Catchment Management Overlay Code




Catchment Management Overlay Code

Requirements for accepted development and assessment benchmarks for assessable development

Performance outcome Acceptable outcome Response

For acceptable development subject to requirements and assessable development

PO1 Land use and development is:

(a) appropriately separated from watercourses and

waterbodies to avoid adversely impacting on water

quality; and

(b) connected to reticulated sewerage or is connected

to an on-site waste water treatment or effluent

disposal system that complies with Element 1 of the

Seqwater Development Guidelines – Development

Guidelines for Water Quality Management in

Drinking Water Catchments.

AO1.1 Development is setback a minimum of:

(a) 25 metres from the high bank of a watercourse

identified on Catchment management overlay maps

OM005a-b; and

(b) 100 metres from the full supply level or the upper

flood margin level of a waterbody (whichever is

greater) identified on Catchment management

overlay maps OM005a-b.

AND AO1.2 Buildings are connected to reticulated sewerage OR Where within a Higher Risk Catchment Area identified on Catchment management overlay maps OM005a-b AO1.3 The development, including effluent disposal areas is setback a minimum of:


identified on Catchment management overlay maps

OM005a-b; and


flood margin level of a waterbody, whichever is

greater, identified on Catchment management


OR

AO1.1 The project buildings and structures are set back from watercourses based on the setbacks set out in the table below. These are broadly consistent with the SPP State Interest Guidance Material – Water Quality (DILGP, 2017) which are best practice guidelines for achieve water quality outcomes through setbacks.

Adopted setbacks from waterway features

Stream order Setback

5 30m from high bank





AO1.2 Not Applicable





Where within a Lower Risk Catchment Area identified on Catchment management overlay maps OM005a-b AO1.4 The development, including effluent disposal areas is setback a minimum of:


identified on Catchment management overlay

maps OM004a-b; and




overlay maps OM004a-b

For assessable development

PO2 Higher risk land uses are appropriately sited, designed and managed to avoid adversely impacting on water quality.

Where within a Higher Risk Catchment Area identified on Catchment management overlay maps OM005a-b AO2.1 No acceptable outcome provided.

Complies with PO2 See response to PO1.

Protection of natural systems

PO3 Development maintains and rehabilitates the extent of riparian vegetation along the banks of a waterbody or watercourse so as to:

(a) maintain the natural drainage function;

(b) minimise erosion of banks and verges; and

(c) reduce sediment and nutrient loads.

Where within a Higher Risk Catchment Area identified on Catchment management overlay maps OM005a-b AO3.1 Vegetation clearing is not undertaken within:



maps OM004a-b; and

Complies with PO3 The project has adopted setbacks from waterways in which no clearing will occur, as shown the table below. These setbacks are lower than the 75-150m required for the Lower Risk Catchment Area but are broadly consistent with the SPP State Interest Guidance Material – Water Quality (DILGP, 2017) and adapted to the site conditions including the sparsity of vegetation on the









project site. No areas of regulated vegetation will be cleared at all. As a ‘value add’, the project will also involve revegetation of waterways in the Biodiversity Corridor to improve habitat values and waterway stabilisation.

Where within a Lower Risk Catchment Area identified on Catchment management overlay maps OM005a-b AO3.2 Vegetation clearing is not undertaken within:



maps OM005a-b; and





As above

Catchment Management Analysis

PO3 Development in the Higher Risk Catchment Area is undertaken in a sustainable manner that:

(a) contributes to maintaining and improving the water

quality of the major drinking water storages; and

(b) will not have an adverse impact on the

environment.

Where within the Higher Risk Catchment Area identified on Catchment management overlay maps OM005a-b AO3.1 For any development within the Higher Risk Catchment Area the water quality impacts of the proposal are addressed in a catchment management analysis report undertaken in accordance with Planning Scheme Policy 3 – Catchment Management Analysis Guidelines

A small area of option 3 is located within the higher risk catchment. The stormwater management strategy outlines on site treatment options for minimising adverse impacts from stormwater runoff from the proposed development. A more detailed catchment management analysis will be undertaken as design progresses if required.

Editor’s Note-The Higher Risk Catchment Area identified on the Catchment management overlay maps OM005a-b reflects the Seqwater and State planning policy Water Supply Buffer Area as identified on Strategic Framework Map SMF-006 – Water Quality.

Kilcoy Solar Farm Stormwater Management Strategy C-1

MUSIC Modelling Methodology


Appendix C MUSIC Modelling Methodology

As described in Section 5, the MUSIC software package has been used to assess the generation,

transportation and management/ treatment of flows and pollutant loads from a typical catchment on

the site.

This appendix provides a detailed description of the modelling methodology applied.

C.1 Software

The performance of possible stormwater treatment strategies in managing stormwater pollutants

(during the operational phase) has been assessed using the MUSIC software package (Version

6.2.1) developed by the CRC for Catchment Hydrology and now supported by eWater. MUSIC is

well suited to the assessments required for the proposed development, i.e. prediction of annual

discharge loads of total suspended solids (TSS) total phosphorus (TP), total nitrogen (TN) and gross

pollutants (GP). The software has been specifically designed to allow comparisons to be made

between different stormwater management systems and thereby function as a decision support tool.

C.2 Modelling Scenarios

The following scenarios were modelled:

The following scenarios have been investigated in MUSIC:

• Developed site without the proposed stormwater management strategy in place.

• Developed site with the proposed stormwater management strategy in place.

C.3 Source Nodes

The user is required to specify source nodes within MUSIC. The source nodes represent the pollutant

generating areas of the site. A summary of the source node properties used in the MUSIC modelling

(and the methodology used to derive them) is provided below.

C.3.1 Source Node Properties

Land use categories were selected to represent, as accurately as possible, how current conditions

and the future development will generate stormwater. The proposed land use for the site is detailed

inTable C-1. Rainfall-runoff and pollutant export characteristics for the existing and developed site

have been applied from the MUSIC Modelling Guidelines (Water by Design 2010a).




Table C-1 Summary of Source Node Properties Applied in MUSIC Modelling for a 1-ha Representative Future Development Scenario

Parameter Value Comments

Assumed land usage for the proposed development site: Solar Subarrays at ground level

Rural Residential Pollutant export and rainfall-runoff properties in accordance with the MUSIC Modelling Guidelines (Water by Design 2010a) for ‘Rural Residential’. Open space areas surrounding the solar subarray panels at ground level have been modelled using this land use classification.

Assumed land usage for the proposed development site: Solar Subarrays

Urban Residential Roof Pollutant export and rainfall-runoff properties in accordance with the MUSIC Modelling Guidelines (Water by Design 2010a) for ‘Urban Residential Roof’. Solar subarray panels only have been modelled assuming this land use classification.

Assumed land usage for the proposed development site: Substations

Industrial Pollutant export and rainfall-runoff properties in accordance with the MUSIC Modelling Guidelines (Water by Design 2010a) for ‘Industrial’. Proposed substations and battery storage areas have been modelled assuming the industrial land use classification.

Land Use Total

Impervious Fraction

Area (m2/ha)

Comments

Solar Subarray – “roof area”

100% 6,000 Assumes 60% of the representative 1 hectare land use is covered by solar subarrays. Impervious fraction in accordance with the MUSIC Modelling Guidelines (Water by Design 2010a). Area estimated from review of conceptual design notes as presented in Appendix A. All of the runoff is directed to treatment.

Rural Residential - access pathways

50% 2,000 Assumes 20% of the representative 1-hectare land use used as access pathways (unpaved) between the solar subarrays. Impervious fraction is however assumed as 50% due to possible compaction of the pathway surfaces. All of the runoff is assumed to be directed to treatment.

Rural Residential – open space areas

0% 2,000 All of the runoff is assumed to be directed to treatment.

Substations Battery storage area

100% 10,000 Assumes all the representative 1-hectare land use is identified as impervious area. All the runoff is directed to treatment nodes.

C.3.2 Meteorological Data

In accordance with the MUSIC Modelling Guidelines (Water by Design 2010a), meteorological data

was obtained for MUSIC from Kirkleigh (BOM Station no. 040318). Modelling of the site was

performed for a period of ten years (from 1 January 1980 to 31 December 1989) at 6-minute time

steps. Average potential evapo-transpiration data has been obtained from the MUSIC Modelling Guidelines (Water by Design 2010a).




C.4 Proposed Treatment Strategy Elements

As outlined in Section 0, two options were proposed for the stormwater quality management strategy.

The two options include the following elements:

Option A: This option consists of a series of ephemeral wetlands to treat runoff from both the

substations (including battery storage areas) and solar subarrays is proposed.

Option B: This option consists of bioretention systems and swales to treat runoff from the solar panel

subarrays if there are space constraints on site.

The individual elements of the above strategy options are described below. MUSIC requires the user

to specify stormwater treatment nodes. These nodes essentially represent the stormwater treatment

train.




C.4.1 Ephemeral Wetlands

Wetland systems are extensively vegetated, shallow water bodies that use enhanced sedimentation,

fine filtration and biological uptake processes to remove pollutants from stormwater (WBD, 2006).

An ephemeral wetland is a wetland that temporarily holds water after periods of rainfall. Ephemeral

wetlands periodically dry out, retaining no permanent pool like conventional constructed wetlands. In

addition to enhancing water quality, wetlands also provide improved habitat and amenity values.

The proposed ephemeral wetlands have been sized to capture and treat stormwater runoff prior to

discharge into receiving waters from both a typical hectare of the solar panel subarrays, and a typical

hectare of the substation land use. Due to the high-level nature of this assessment, no locations have

been identified.

The parameters modelled in MUSIC for the ephemeral wetlands are presented inTable C-2. It is

noted that the ephemeral wetlands were still modelled as having a permanent pool, as it is likely that

water will pond in the wetlands for extended periods of time, facilitating the treatment processes

modelled in a permanent pool arrangement. Examples of ‘typical’ stormwater wetlands are provided

in Table C-2.

Table C-2 Ephemeral Wetland Model Parameters

Parameter

Value

Per hectare Substation Landuse

Per hectare Solar Subarray Landuse

Inlet Pond Volume (m3) 55 70

Surface area (m2) 600 700

Extended Detention Depth (m) 0.5 0.5

Permanent Pool Volume (m3) 180 180

Initial Volume (m3) 180 180

Exfiltration rate (mm/hr) 0 0

Evaporative Loss as % of PET 125 125

Equivalent Pipe Diameter (mm) 32 35

Overflow weir width (m) 60 70

Notional Detention Time (hrs) 49.4 48.2




Figure C-1 Examples of Typical Constructed Wetlands

A typical plan view and longitudinal section of a constructed wetland can be seen in Figure C-2 and

Figure C-3 respectively.

North Lakes

Varsity Lakes Southport

Coomera Waters




Figure C-2 Typical Ephemeral Wetland – Plan View




Figure C-3 Typical Ephemeral Wetland – Longitudinal Section




C.4.2 Swales

Swales are shallow channels lined with vegetation (usually grass) and are often used in combination

with alternative kerb design to provide flow conveyance, minimising the use of piped stormwater

drainage systems. Vegetated swales tend to slow stormwater flows and retain sediment.

Swales are proposed on the site to provide two key stormwater management functions:

• Conveyance of stormwater flows: The swales will typically convey flows from upstream areas

into the ultimate receiving waterway.

• Treatment of stormwater flows: The swales will receive (and provide additional treatment to)

stormwater flows from upstream areas prior to discharge into the ultimate receiving waterway.

Examples of swales in South East Queensland are shown in Figure C-4.

Figure C-4 Examples of Swales

C.4.3 Bioretention Systems

A bioretention system is a soil and plant-based stormwater management measure. A typical system

consists of a porous medium such as sandy loam. Vegetation is also established within the

bioretention basin to promote evapo-transpiration, maintain soil porosity, encourage biological

activity, and promote uptake of some pollutants. Run-off is directed into the system and infiltrates

through the plant/mulch/soil environment Figure C-5 provides examples of bioretention systems.




Figure C-5 Examples of Streetscape Bioretention Systems

Bioretention systems are proposed as an option to be located underneath the drip line of all solar

subarrays if the further detailed investigations indicate space constraints for including ephemeral

wetlands. Each solar subarray requires a bioretention system with a filter area of approximately

7.45m2.

The parameters modelled in MUSIC for the various bioretention systems are presented in Table C-3.

An illustrated example of a bioretention system is shown in Figure C-6.

Table C-3 Bioretention System Modelled Parameters

Parameter

Value

Per Bioretention system

Per hectare solar subarray

Extended detention depth (m) 0 0

Surface area (m2) 7.45 1,490

Filter area (m2) 7.45 1,490

Unlined filter media perimeter (m) 29.18 5836

Saturated. hydraulic conductivity (mm/hr) 200 200

Filter media depth (m) 0.4 0.4

TN content (mg/kg) 400 400

PO4 content (mg/kg) 30 30

Exfiltration rate (mm/hr) 0 0

Lined base No No

Vegetated with effective nutrient removal plants Yes Yes

Overflow weir width (m) 14.9 2980

Victoria Park, Sydney

Southport, Gold Coast

Broadmeadows, Melbourne

Docklands, Melbourne




Figure C-6 Typical Bioretention Cross Section

C.5 Receiving Node

One node from the development has been used to represent the destination of runoff from each of

the scenarios investigated, including:

• A representative 1-hectare area of solar subarray development.

• A representative 1-hectare area of substation development (with battery storage).

These areas would both discharge to the ultimate receiving waterway.

1

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We aim to continue to enhance our services, capabilities and

areas of application to meet the community’s future development

and environmental protection needs.

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