Changed Concurrence agency response—with …...At all times 2. The development must be in...

SEQ WestLevel 4,117 Brisbane StreetPO Box 129Ipswich QLD 4305

Our reference: SDA-0316-029272(Previously SDA-0315-018787)

Your reference: DA14975

11 May 2016

The Chief Executive OfficerSomerset Regional CouncilPO Box 117ESK QLD [email protected]

Attention: Julie Bertsos

Dear Julie,

Changed Concurrence agency response—with conditions310 Gregors Creek Road, Gregors Creek(Given under section 285 of the Sustainable Planning Act 2009)

The referral material for the changed development application described below was received by the Department of Infrastructure, Local Government and Planning under section 272 of the Sustainable Planning Act 2009 on 31 March 2016.

Applicant details

Applicant name: Edith Pastoral Company

C/- I.B. Town Planning

Applicant contact details: PO Box 501Kallangur QLD [email protected]

Site details

Street address: 310 Gregors Creek Road, Gregors Creek

Lot on plan: Lot 1 and 2 on RP75267, Lot 1 RP15328, Lot 5 on RP41543, Lot 2 on RP99954, Lot 1 on CSH2113 and Lot 3 on RP84104

Local government area: Somerset Regional Council

mailto://[email protected]


SDA-0316-029272

Department of Infrastructure, Local Government and Planning

Application detailsProposed development: Development Permit for Material Change of Use for

Extractive Industry (hard rock extraction) Development Permit for Material Change of Use for Medium Impact Industry (Concrete Batching Plant) Development Permit for Material Change of Use for Environmentally Relevant Activity 16 Extractive and Screening Activities 16(b) and 16(c) for 5,000 – 100,000 tonnes per year

Aspects of development and type of approval being sought

Nature of Development

Approval Type Brief Proposal of Description

Level of Assessment

Material Change of Use

Development Permit Extractive Industry (hard rock extraction)

Impact Assessment


Development Permit Medium Impact Industry (Concrete Batching Plant)

Impact Assessment


Development Permit Environmentally Relevant Activity 16 Extractive and Screening Activities 16(b) and 16(c) for 5,000 – 100,000 tonnes per year

Impact Assessment

Referral triggers

The development application was referred to the department under the following provisions of the Sustainable Planning Regulation 2009:

Referral trigger Schedule 7, Table 3, Item 2 - Development impacting on state transport infrastructure

ConditionsUnder section 287(1)(a) of the Sustainable Planning Act 2009, the conditions set out in Attachment 1 must be attached to any development approval.

Reasons for decision to impose conditionsUnder section 289(1) of the Sustainable Planning Act 2009, the department must set out the reasons for the decision to impose conditions. These reasons are set out in Attachment 2.

Further adviceUnder section 287(6) of the Sustainable Planning Act 2009, the department offers advice about the application to the assessment manager—see Attachment 3.

SDA-0316-029272


Approved plans and specificationsThe department requires that the following plans and specifications set out below and in Attachment 4 must be attached to any development approval.

Drawing/Report Title Prepared by Date Reference no. Version/ Issue

Development Permits for Material Change of Use for Extractive Industry (sand and gravel extraction), Medium Impact Industry (Concrete Batching Plant) and Environmentally Relevant Activity 16 Extractive and Screening Activities 16(b) and 16(c) for 5,000 – 100,000 tonnes per year

Concept Site Development Lockyer Designs January 2016 LD-1030-SK01 C

Site Based Stormwater Management Plan

Lockyer Designs 27 January 2016

LD-1030-SK01 2

A copy of this response has been sent to the applicant for their information.

For further information, please contact Darren Cooper, Principal Planner, SARA SEQ West on (07) 3432 2405, or email [email protected] who will be pleased to assist.

Yours sincerely

Kieran HannaA/Manager

enc: Attachment 1—Conditions to be imposedAttachment 2—Reasons for decision to impose conditionsAttachment 3—Further adviceAttachment 4—Approved Plans and Specifications

cc: Edith Pastoral Company c/- I.B. Town Planning Pty Ltd, [email protected] of Transport and Main Roads, [email protected]

SDA-0316-029272


Our reference: SDA-0316-029272Your reference: DA14975

Attachment 1—Conditions to be imposed

No. Conditions Condition timing

Development Permits for Material Change of Use for Extractive Industry (Hard Rock Extraction), Medium Impact Industry (Concrete Batching Plant) and Environmentally Relevant Activity 16 Extractive and Screening Activities 16(b) and 16(c) for 5,000 – 100,000 tonnes per year

Schedule 7, Table 3, Item 2 - Development Impacting on State Transport Infrastructure - Pursuant to section 255D of the Sustainable Planning Act 2009, the chief executive administering the Act nominates the Director-General of Department of Transport and Main Roads to be the assessing authority for the development to which this development approval relates for the administration and enforcement of any matter relating to the following condition(s):

1. The development must be carried out generally in accordance with the following Plan:

Concept Site Development, prepared by Lockyer Designs, dated January 2016, drawing no. LD-1030-SK01, revision C.

At all times

2. The development must be in accordance with the Stormwater Management Plan entitled Site Based Stormwater Management Plan, prepared by Lockyer Designs, dated 27 January 2016, job no. LD-1030, revision 2. In particular:

Carry out construction of the proposed sediment basins as detailed in Section 4 and 5 of the Site Based Stormwater Management Plan.

At all times

3. The following road works are required: a Channelised Right Turn Treatment (CHR(s)) on the

Brisbane Valley Highway into Gregors Creek Road; and

a realignment of the Gregors Creek Road approach to the Brisbane valley Highway intersection to provide a conventional stand-up left turn treatment including removal of the existing low entry angle left turn

Approval under section 33 of the Transport Infrastructure Act 1994 must be obtained, and the road works must be designed and constructed in accordance with the Department of Transport and Main Roads’ Road Planning and Design Manual, 2013.

Prior to commencement of use and to be maintained at all times

T13

SDA-0316-029272



Attachment 2—Reasons for decision to impose conditions

The reasons for this decision are: To ensure the development is carried out generally in accordance with the plans of

development submitted with the application. To ensure that the impacts of stormwater events associated with development are

minimised and managed to avoid creating any adverse impacts on the state transport corridor.

To ensure the road works on or associated with, the state-controlled road network are undertaken in accordance with applicable standards.

T13

SDA-0316-029272



Attachment 3—Further advice

General advice

Road Works Approval

1. Under section 33 of the Transport Infrastructure Act 1994, written approval is required from the Department of Transport and Main Roads to carry out road works on a state-controlled road. Please contact the Department of Transport and Main Roads on [email protected] (reference TMR15-013405) to make an application for road works approval. This approval must be obtained prior to commencing any works on the state-controlled road reserve. The approval process may require the approval of engineering designs of the proposed works, certified by a Registered Professional Engineer of Queensland (RPEQ).

The road works approval process takes time – please contact Transport and Main Roads well in advance to ensure that gaining approval does not delay construction.

Bonding of Works

2. A bond will be required to ensure that the works required in Condition 3 are completed to the standard required by the Department of Transport and Main Roads. The bond requirement will be included as a condition of the road works approval (section 33 of the Transport Infrastructure Act 1994). If you would like any further information about the Department of Transport and Main Roads’ policy with regard to bonding please contact the North Coast District Development Assessment Team of the Department of Transport and Main Roads via [email protected] (or phone 5451 0755) (please quote TMR16-016860).

T13


SDA-0316-029272



Attachment 4—Approved plans and specifications

T13

310 GREGORS CREEK ROADPROPOSED EXTRACTIVE INDUSTRY

CONCEPT SITE DEVELOPMENT

LD-1030

LD-1030-SK01C

LSSK07

cooperd

Stamp

310 Gregors Creek Road, Gregors Creek

for

Edith Pastoral Company Pty Ltd

Date: 27 January 2016

Revision: 02

Site Based Stormwater Management Plan

Extractive Industry

cooperd

Stamp

STORMWATER MANAGEMENT PLAN

EXTRACTIVE INDUSTRY

310 GREGORS CREEK RD Lockyer Designs

R e v 02 P a g e 1

Document control sheet

If you have any questions regarding this document, please contact:

Contact Officer Amir Keshtgar (Water Engineer)

Phone: 07 4639 4188

Job No: LD-1030

Version history

Revision No. Date Details

01 November 2015 Draft

02 27 January 2016 Final

52 Crescent Street (PO Box 383),

Gatton Qld 4343

P: 07 5462 4785 F: 07 5462 1823

230 James Street (PO Box 18132)

Toowoomba Qld 4350

P: 07 4639 4188 F: 07 4646 2408


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Executive Summary

Lockyer Designs was commissioned by Edith Pastoral Company to produce a stormwater management plan (SWMP) for the proposed Extractive Industry (hard rock extraction) at 310 Gregors Creek Road, Gregors Creek as part of the Development Permit Material Change of Use application to Somerset Regional Council. The proposed site is currently farming land and adjoins pastoral land. The proposed development site is located on the southern side of Gregors Creek Road approximately 3km from the Brisbane Valley Highway intersection. The extraction area is located approximately 2.8km from Gregors Creek Road along an existing access road. The development site is bound by pastoral lands with external upstream catchment.

This report identifies the stormwater quantity and quality management measures required for the construction and operational phases of the proposed development. It is recommended to build two new basins for the purpose of quantity mitigation as well as quality treatment within the site. It is proposed that the basin downstream of the hard rock area will be a sediment basin to treat the runoff from hard rock extraction area. The second basin downstream will be a combined recycle/detention basin. This basin captures the runoff overtopping from a series of sediment basins around the crushing, washing and screening area. The flow from this basin will discharge into a series of “Stage Polishing” ponds downstream before flowing into the Brisbane River. The main objective of the stormwater quantity analysis was to limit the post developed peak discharge to the equivalent pre-developed peak flow discharging from the site for rainfall events up to the 100 year ARI event. To achieve this objective it was estimated that an on-site combined sediment and detention storage with the total volume of approximately 19,000 m3 will be required for the site. The analysis demonstrates that the total peak discharge from the proposed development will be equal to or less than the pre-development flows, as shown in Table 5. It is intended to use the stored water in the sedimentation basin as well as recycle/detention basin for watering and washing purposes within the development.

To meet the quality objectives modelling analysis was undertaken based on the stormwater concept which included two sediment basins as part of the treatment train. The model demonstrated that the reduction in pollutants will satisfy the recommendations in Australian Runoff Quality as shown in Table 7. The proposed measures and devices in this report will satisfy the requirements and specific outcomes outlined in Seqwater Development Guidelines, Development Guideline for Water Quality Management in Drinking Water Catchments, 2008.


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TABLE OF CONTENTS

Executive Summary ...................................................................................................................................... 2

1. Introduction .......................................................................................................................................... 4

2. Site Description ..................................................................................................................................... 4

3. Stormwater Management Plan ............................................................................................................ 6

4. Design Philosophy and Methodology ................................................................................................... 7

4.1 Stormwater Quantity .................................................................................................................................. 7

4.2 Existing Condition ....................................................................................................................................... 8

4.3 Proposed Development Conditions .......................................................................................................... 10

5. Stormwater Quality Management ..................................................................................................... 15

5.1 Methodology ............................................................................................................................................ 16

5.2 MUSIC Modelling Results .......................................................................................................................... 17

5.3 Sediment Basins ........................................................................................................................................ 18

6. Conclusion .......................................................................................................................................... 19

7. Concrete Batching Plant ..................................................................................................................... 20

8. References .......................................................................................................................................... 21

APPENDICES

Appendix A Drawing Index

Appendix B Rational Method and MUSIC Model

Appendix C Sediment Basin Calculations


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1. Introduction

Lockyer Designs was commissioned by Edith Pastoral Company to produce a stormwater management plan (SWMP) for the proposed Extractive Industry (hard rock extraction) at 310 Gregors Creek Road, Gregors Creek as part of the Development Permit Material Change of Use application to Somerset Regional Council. The proposed site is currently farming land and adjoins pastoral land. The aim of this management plan is to provide policies, performance criteria and procedures to minimise the impact of the development on the physical and social environment. This report identifies the stormwater quantity and quality management measures required for the construction and operational phases of the proposed development. This report will demonstrate the development can be undertaken in accordance with the current Somerset Regional Council Guidelines, Seqwater Development Guidelines, the current Queensland Urban Drainage Manual, State Planning Policy July 2014 and best management practices. A stormwater quantity analysis has been undertaken to ensure peak flows resulting from the development do not exceed the pre-development peak flows. A water quality analysis has also been completed to determine the pollutant loads in the stormwater runoff as a result of the development. Some procedures and devices described in this management plan may require modification or clarification from the onsite survey to suit the detailed requirements for the construction and operational phases of the extractive industry.

2. Site Description

The proposed development site is located on the southern side of Gregors Creek Road approximately 3km from the Brisbane Valley Highway intersection. The extraction area is located approximately 2.8km from Gregors Creek Road along an existing access road. The development site is bound by pastoral lands with external upstream catchment. The existing site is undeveloped farming land which is the basis for the pre-development flow calculations. The proposed fully developed site is located within the following parcels of land covering approximately 22.5ha of the total area of 369ha:

Lot 1 RP75267

Lot 2 RP75267

Lot 1 RP15328

Lot 5 RP41543

Lot 2 RP99954

Lot 1 CSH2113 and

Lot 3 RP84104.


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The proposal provided by Ian Buchanan Town Planning incorporated the geological report undertaken by Groundwork indicate an extraction area of hard rock material from the northeast area of the site as shown Drawing No LD-1030-SW01.

It is intended to transport the extracted material to an on-site crushing, screening and washing plant located adjacent to the extraction area as shown Drawing No LD-1030-SW01. The crushing, screening and washing of the material will predominately be a dry process with water sprinklers and water truck use to reduce dust. A wet process will be used when product is required to meet specific quality requirements. Stormwater and water used during the production process running off the site will be treated through a series of sediment ponds before discharging into a recycle dam. Recycled water will be used in the production process when available. Material extracted from the hard rock deposits will be transported to the onsite crushing, screening and washing plant. The processed material will be stored in stockpiles immediately surrounding the plant. Site layout for crushing, screening and washing plant is shown in Figure 1.


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Figure 1 – Site Layout

3. Stormwater Management Plan

The formulation and implementation of the stormwater management plan for the proposed extractive industry is based on the following key principles.

• Utilisation of existing drainage flow paths to reduce impacts. • Structures to ensure no increase in peak flows leaving the site. • Measurement to ensure the acceptable reduction in contaminants has been achieved.

Due to the site being situated within the storage and intake catchment for Wivenhoe Dam, the development application has been addressed under Seqwater’s stated guidelines. Thus, this section will address the requirements specified in the Seqwater Development Guideline 2012 ensuring the runoff generated from the developed site has no adverse impact on downstream catchments and neighbouring properties. The following processes have been used to develop the stormwater management plan for the subject site.

• Identify the on-site and surrounding catchment areas contributing to the site; • Consider the types of stormwater management practices available and assess which

practices would be appropriate for use within the development site; and • Demonstrate that best practice management measures have been implemented to meet

the nominated water quality objectives. It is recognised that the majority of adverse water quality impacts are likely to occur during catchment disturbance, particularly where significant earthworks are involved on steep land.


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The proposed stormwater management plan in this report is aiming to provide adequate quantity and quality mitigation devices and measurements for material extraction process for both hard rock extraction area and crushing, screening and washing plant.

4. Design Philosophy and Methodology

The DRAINS program performs design and analysis calculations for stormwater drainage systems and models the flood behaviour of rural and urban catchments. DRAINS displays the components of a drainage system as “objects”, and presents information about these and the results of calculations pictorially. DRAINS adopts ILSAX method for hydrological calculations which is based on time-area method and Horton infiltration procedure. ILSAX method is an event model, in which the sub-catchments of a stormwater drainage area are divided into the following land uses:

Impervious areas directly connected to the main drainage system,

Impervious areas not directly connected (supplementary), and

Pervious areas (grassed areas).

For each land use, a time of travel of stormwater is specified or may be calculated by the program. The infiltration model for pervious areas is based on Horton’s equation as used in the ILSAX method. The model employs parameters that define the soil type and its antecedent moisture condition. These can be easily defined from knowledge of the local soils and climate. DRAINS calculates the full hydrographs of flows resulting from the specified rainfall hyetographs. Multiple storm burst patterns can be selected, with the worst case results reported. DRAINS models for the existing and developed phases were developed to calculate the peak runoff from the site’s catchments. The sub-catchments were defined as paved areas (e.g. crushing, screening and washing plant area, hard rock extraction area) and grassed area. The Time of Concentration for each sub-catchment was calculated using Bransby Williams’s equation for overland sheet flow in accordance with Queensland Urban Drainage Manual. The Intensity, Frequency and Duration chart was generated for the region using the Australian Bureau of Meteorology website tool.

4.1 Stormwater Quantity

Element 5 of the Seqwater guideline specifies the development not increase the stormwater quantity of flow velocity from the subject site.


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The Queensland Urban Drainage Manual (QUDM) specifies that any proposed development, must demonstrate that the development shall have a lawful point of stormwater discharge and the proposed development must not cause ‘achievable nuisance’, or, as per QUDM, ‘non-worsening’ must be achieved. Attenuation of stormwater to pre-developed conditions is required due to the expected increase in volume of stormwater run-off generated by increasing the impervious area. To achieve this ‘non-worsening’, the development was modelled with DRAINS for pre-development and post-development for Annual Recurrence Intervals of 2, 5, 10, 20, 50 and 100 years. The fraction impervious values and sub-catchment areas used in the DRAINS model were based on the aerial survey plan, aerial photos and the maximum allowable impervious areas according to QUDM. Element 5 of Seqwater guideline compliments many existing accepted Water Sensitive Urbane Design (WSUD) principals, with a rural context. Referring Table 8 within this Element there are two major sections of quantity and quality. WSUD is a holistic approach to the planning and design of urban development that aims to minimise negative impacts on the natural water cycle and protect the health of aquatic ecosystem. WSUD is a guideline for quality devices and does not cover the quantity aspects of the stormwater management plan. However, in the scope of WSUD guideline, QUDM has been indicated as one of the tools and resources for detail design of stormwater structures and devices. QUDM is a technical guideline that we are using its principals here to estimate the stormwater quantity. The Seqwater guideline in Element 5 specifies the development shall not increase the stormwater quantity of flow velocity from the subject site. The Queensland Urban Drainage Manual (QUDM) specifies that any proposed development, must demonstrate that the development shall have a lawful point of stormwater discharge and the proposed development must not cause ‘achievable nuisance’, or, as per QUDM, ‘non-worsening’ must be achieved. Attenuation of stormwater to pre-developed conditions is required due to the expected increase in the volume of stormwater run-off generated caused by increasing the impervious area. To achieve this ‘non-worsening’, the development was modelled with DRAINS for pre-development and post-development for Annual Recurrence Intervals of 2, 5, 10, 20, 50 and 100 years. The fraction impervious values and sub-catchment areas used in the DRAINS model were based on aerial survey information extracted form Googlearth, aerial photos and the maximum allowable impervious areas according to QUDM.

4.2 Existing Condition


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Rational method calculations (as per QUDM guidelines) were undertaken to estimate the peak discharge during various storm events for the existing stage. These calculated peak discharges were then used and compared to DRAINS results for calibration and verification. The time of concentration for the existing phase was calculated for the entire catchment which includes the travel time due to overland flow, the calculation is given Appendix B. The DRAINS program adopts ILSAX model to calculate stormwater flows. As the ILSAX method tends to calculate higher peak discharge for most of the investigated storm events it was considered to be conservative in nature and no further calibration is deemed necessary as the results still correlate to the rational method. The current site is completely within a rural catchment. The access roads within the site have a negligible fraction impervious. There are a no sheds and buildings within the development site. Thus, the entire development site was considered pervious. The runoff generated in the pre-development phase for the contributing catchments was split into two catchments:

1. Hard rock extraction area (20ha) 2. Crushing, screening and washing area. (2.5ha)

The proposed hard rock extraction area and the crushing, screening and washing area are analysed separately. The calculated peak flows for the investigated storm events using Rational Method and DRAINS are given in Table 1. Runoff from the proposed extractive industry site currently flows into several natural gullies which discharge to Brisbane River southward. These natural gullies/watercourse also cater for runoff from the external catchment upstream of the extractive industry. Refer sketches SW02 in Appendix A. Currently there are several farm storage dams onsite capturing the runoff generated from the gullies before discharge into the Brisbane River. It is intended to use these dams as “polishing stage dams”.

Table 1 – Existing Site Peak Discharges – Rational Method

ARI Screening and washing

plant

Hard rock area

Discharge(m3/s) Discharge(m3/s

2 0.278 3.306

5 0.393 4.692

10 0.467 5.600

20 0.569 6.819


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Table 2 – Existing Site Peak Discharges – DRAINS

4.3 P

roposed Development Conditions

The geological investigation undertaken by Groundwork Plus on June 2015 revealed that an area of approximately 64 ha has the potential of hard rock extraction. However this area has been reduced to 20ha for the development stage. The material extracted from this hard rock area will be transported to the crushing, screening and washing plant. The post-development impervious area includes the screening plant, the existing access road and the disturbed area due to hard rock extraction and are shown in Table 3.

50 0.738 8.900

100 0.866 10.407

Screening and washing

plant

Hard rock area Combined

ARI Discharge (m3/s) Discharge(m3/s) Discharge(m3/s)

2 0.265 3.59 3.855

5 0.417 5.8 6.217

10 0.522 7.15 7.672

20 0.652 8.98 9.632

50 0.82 10.2 11.02

100 0.948 11.9 12.848


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The proposed extractive industry site covers an area of 20ha with fraction impervious of approximately 0%, however the fraction impervious in post-development stage will be increased to 90% which is mainly due to removal of topsoil and overburden.

Table 3 – Developed Catchment Details

Catchment Area (ha) Fraction impervious

(%)

Crushing, Screening, Washing plant and stockpile 2.5 100

Hard rock extraction 20 90

Total 22.5 -

For the purpose of this report the proposed extractive industry site will be called the proposed development. The proposed development flows have been calculated based on a developed site of which 90% of the catchment is impervious. Table 4 below shows the combined peak discharges from the site, after the site has been developed before any attenuation is undertaken.

Table 4 – Developed Combined Discharges without Attenuation

Table 4 shows an increase in the peak discharge from the site caused by the proposed development. It is recommended that the post development stormwater flows do not adversely affect downstream properties. To ensure compliance with this, on-site detention storage is proposed within the site to detain any increase in peak flows generated from the developed site. Discharge from the site currently is via the natural gully running south-west towards the Brisbane River. It is proposed to utilise the natural terrain to construct the detention basin to ensure all surface runoff from the development will flow to the basin. Discharge from the detention basin will flow to the existing discharge point from the development via a series of existing farm dams and gullies.

Existing Developed without attenuation

Increased (%) ARI Discharge (m3/s) Discharge (m3/s)

2 3.855 7.719 100.2

5 6.217 10.05 61.7

10 7.672 11.56 50.7

20 9.632 13.61 41.3

50 11.02 15.68 42.3

100 12.848 17.95 39.7


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As the extraction area is located on hillside it is proposed to divert the overland flow from upstream of the catchment via catch drains. For layout of the basin, catch drain and the existing discharge location refer drawing LD-1030- SW02 and SW03 in Appendix A. A detailed analysis of the detention behaviour of the proposed basin was carried out for the proposed development using DRAINS. The program routes the inflow hydrograph into the detention basin and iteratively solves the storage equation for each of the individual standard duration storm burst patterns defined in Australian Rainfall and Runoff and for each Average Recurrence Interval (ARI). The peak flows for the pre and post development were assessed to determine the required detention basin size. Detention basin parameters such as storage, height/volume and outlet characteristics were progressively adjusted until the peak detention basin discharge rate was equal to or less than the calculated pre-development value for each ARI event. Furthermore, the Stormwater Guideline for Environmentally Relevant Activities of Department of Environment and Heritage Protection (DEHP) was sought ensuring the proposed detention size will comply with the specified requirements. Based on the above guideline the proposed site was considered High Erosion Hazard Site. Thus, the basin was sized to retain a 24 hour storm event with an ARI 1 in 5 years using the provided formula. Refer Appendix C for sedimentation basin calculation. A detention basin size with the total capacity of approximately 19,000m3 including the freeboard volume was inserted into the DRAINS program. Figure 2 shows the stage – storage graph of the proposed basin.

The recycle/detention basin as detailed on Figure 2 located downstream of the extraction area will be required to be constructed at the start of the project.


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Figure 2 – Stage Storage Graph – DRAINS

The proposed sediment basin is located downstream of the extraction area as shown on drawing LD-1030-SW03. A storage volume of 13,000m3 meets the required settling volumes for the sedimentation purposes as specified by DEHP guidelines. The overtopped flow from the basin will flow into the recycle/detention basin. Table 5 shows the combined peak flow estimates from the site after the detention basin merging with runoff from the crushing, screening and washing plant area.

Table 5 – Comparison of Peak Discharges after Attenuation

DRAINS Existing Post – development

(combined)

Decreased (%)

Q2 – Discharge (m3/s) 3.855 0.92 76.1

Q5 – Discharge (m3/s) 6.217 1.2 80.7

Q10 – Discharge (m3/s) 7.672 1.36 82.3

Q20 – Discharge (m3/s) 9.632 1.61 83.3

Q50 – Discharge (m3/s) 11.02 1.88 82.9

Q100 – Discharge (m3/s) 12.848 2.15 83.3

The invert level of the proposed detention basin is at 104.0 and the top of bank will be at 109.5, the spillway structure with 35m long will be installed at RL 116.0. The basin has been designed with a 450mm diameter RCP culvert outlet at RL108.0. It is proposed to use scour protection and energy dissipater structures at the outlet of the culvert and the spillway. The detail of these structures will be provided in detailed design stage. For typical section of the detention basin refer Appendix A. The proposed recycle/detention basin will capture the overland flow generated from the hard rock excavation area. The runoff from the impervious areas of crushing, screening and washing plant area plant will discharge into a series of sediment ponds around the pad. Refer drawing LD1030-SW03. The overtopping flow from the sediment basins will be directed to the proposed recycle/detention basin and a series of polishing dams downstream of it. It is intended to install a pump to use the stored water in the recycle/detention basin for washing purposes in the screening pad, dust control and general uses around the site.


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As shown on the proposed plans (Appendix A) currently there are three farm dams on site located downstream of the proposed recycle dam labelled “polishing dams”. These dams incorporating the grassed swales connection between them will provide additional quantity control to runoff from the proposed development before flowing some further 800m down an existing natural gully and discharging into Brisbane River. Hydrological analysis indicates the proposed detention basin will accommodate a storm event with ARI 50 year onsite without overtopping and discharging into downstream ponds. Figure 3 shows the inflow-

outflow hydrograph for storm event 50 year ARI and 15min duration.

Figure 3 – Inflow – Outflow Hydrograph Detention Basin (50Yr-15min)

The overland flow from the crushing, screening and washing plant will be directed into a recycle. This recycle dam is located downstream of a series of sedimentation basins.


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The hydrological analysis show that this basin will contain the storm event with ARI 50 year generated from the developed site. Figure 4 shows the inflow – outflow hydrograph for storm event of 50 year ARI.

Figure 4 – Inflow – Outflow Hydrograph of Recycle Dam (Q50-15min)

As shown in Table 5, the DRAINS modelling results indicate that the peak discharge from the proposed development site has been successfully attenuated to non-worsening levels from the existing situation for all investigated storm events.

5. Stormwater Quality Management

The State Planning Policy July 2014 requires development areas for extractive industry material change of use within the water supply catchment in South East Queensland to provide stormwater quality treatment. This requires that stormwater quality improvement works be provided to achieve targets as outlined in the Seqwater Development Guidelines. This policy requires that we protect receiving water from adverse development impacts by managing development and construction activities in accordance with various stormwater design objectives. Table B, Appendix 3 of State Planning Policy July 2014 for South East Queensland was adopted to demonstrate compliance with the Seqwater Development Guidelines performance outcomes and to provide quantifiable values for design. The State Planning Policy design objectives for managing stormwater are intended to: • Manage stormwater quality • Improve waterway stability • Manage the frequency of flows


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Compliance with the above mentioned design objectives are contained herein

5.1 Methodology

The design objectives for stormwater quality management are outlined in Table 1 of the SEQ Regional Plan, Implementation Guideline Number 7. The following water quality objectives have been adopted for the site as they are deemed to be the most relevant to the type of development:

Treatment modelling for this site was undertaken using MUSIC (Model for Urban Stormwater Improvement Conceptualisation) software. MUSIC is an industry standard program that simulates pollutant removal potential for various stormwater treatment devices. Brisbane City Council Guidelines for Pollutant Export Modelling in Brisbane Version 7 were used to determine the calibrated runoff generation parameters and base and storm flow pollutant concentrations for an Industrial catchment. The rainfall data set for Esk from Pulviograph Rainfall Data tools were obtained from eWater website. Gold Coast City Council Music Modelling Guidelines 2006 and Brisbane City Council Guidelines for Pollutant Export Modelling in Brisbane Version 7 suggest that industrial areas consist of approximately 85% total impervious area.

Table 6– Load based Reduction Targets

INDICATOR LOAD BASED REDUCTION TARGETS (%)

Total suspended Solids (TSS) 80% reduction in average annual load of pollutants leaving the

developed unmitigated scenario compared to the developed

mitigated scenarios

Total Phosphorus (TP) 60% reduction in average annual load pollutants leaving the

developed unmitigated scenario, compared to the mitigated

scenario

Total Nitrogen (TN) 45% reduction in average annual load pollutants leaving the


scenario

Gross Pollutants (GP) 90% reduction in average annual load pollutants leaving the


scenario

Due to the large areas of existing land remaining relatively undisturbed, with no increases in post development pollutant discharge compared to pre development levels, it is considered that any increases in pollutants due to the proposed development will be limited to disturbed areas only. Therefore the reduction values will only apply to the pollution generated from the runoff of stormwater from the proposed development.


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5.2 MUSIC Modelling Results

A MUSIC model was set up to model the extractive industry site to determine the increase in total suspended solids, total phosphorus and total nitrogen as shown in Appendix B. The stormwater concept for the extractive industry is to capture flows from the rock extraction area for treatment and direct it to the combined recycle/detention basin as shown on plan LD-1030-SW-03 in appendix A. To mitigate the effects of the increased annual pollutant loads, an analysis was undertaken for the hard rock extraction area, crushing, screening and washing plant area using MUSIC model. It is proposed the runoff generated from the crushing, screening and washing plant area will be directed to a series of sediment basins around the site. The overtopping flow from these sediment basins will discharge into a recycle/detention basin downstream of the site for further treatment. This stored water will be re-used for dust control and washing purposes. The discharge from the 20ha catchment of hard rock extraction area will be captured by a sediment basin located downstream of the catchment which is connected to a recycle/detention basin via a 450mm RCP outlet. The recycle/detention basin will discharge into a series of polishing ponds downstream of the development before flowing into the Brisbane River. The modelling of the polishing ponds is out of scope of stormwater quality analysis and is not included in the MUSIC model, however the quality model was performed for minimum required size of sediment basin based on DEHP Guidelines. The MUSIC results indicate the above proposed devices will treat the contaminant items of TSS, TN and TP successfully, so the polishing ponds downstream will provide extra treatment. A summary of the results from the MUSIC modelling is provided in Table 7.

Table 7 – Best Practice Targets and Options for reduction of Mean Annual Loads

Best Management Practice (Reduction %)

Proposed Development

TSS Reduction (%) 80% 90

TP Reduction (%) 60% 74

TN Reduction (%) 45% 53

Gross Pollutants Reduction (%) 90% 100


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5.3 Sediment Basins

Sediment basins have been sized in accordance with the Stormwater Guideline for Environmentally Relevant Activates of Department of Environment and Heritage Protection. As recommended for dispersive soils the sediment basins will store the storm event with ARI 5 years and duration of 24 hours to enable the stormwater runoff to be treated before release to meet the DEHP requirements. The release of water will be controlled to enable the treatment required for each rainfall event. It is recommended that water be stored for at least 48 hours after a rain event. It is proposed to construct a sediment basin downstream of the rock extraction area, this sediment basin will be outlet into the proposed recycle/detention basin. It is also proposed to use five small sediment basins located around the crushing, screening and washing plant area. The proposed sediment basins have been sized to ensure the total required treatment for the whole extractive industry is achieved. The sediment basins should be monitored after every rain event and cleaned as necessary. The build-up of sediment should be measured at least every 4 months and sediment should be removed every 12 months as a minimum. According to DEHP guideline each sediment basin must be operated in such a manner that within 120 hours (5 days) of the most recent rainfall event, the required design capacity of the upper settling volume is available for capture and storage of stormwater runoff from the next rainfall event. Calculations for the sediment basin are attached in Appendix C. Figure 5 shows a visual concept of series of sedimentation basins arrangements within a similar sand extractive industry currently operating by the applicant. The same type of treatment arrangement is proposed for the Gregor Creek extractive industry in this stormwater management plan. This current site produces higher fine contents than the proposed site in Gregor Creek according to the Geological report.


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Figure 5 – Sediment Basin Series – Work Example

6. Conclusion

It is recommended to build two new basins for the purpose of quantity mitigation as well as quality treatment within the site. It is proposed that the basin downstream of the hard rock area will be a sediment basin to treat the runoff from hard rock extraction area. The second basin downstream will be a combined recycle/detention basin. The proposed second basin captures the runoff overtopping from a series of sediment basins around crushing, washing and screening area. The flow from this basin will discharge into a series of “Stage Polishing” ponds downstream before flowing into the Brisbane River. In preparing this stormwater management plan, stormwater quantity analysis and stormwater quality analysis were undertaken for the subject site. The main objective of the stormwater quantity analysis was to limit the post developed peak discharge to the equivalent pre-developed peak flow discharging from the site for rainfall events up to the 100 year ARI event. To achieve this objective it was estimated that an on-site combined sediment and detention storage with the total volume of approximately 19,000 m3 will be required for the site.


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The analysis demonstrates that the total peak discharge from the proposed development will be equal to or less than the pre-development flows, as shown in Table 5. It is intended to use the stored water in the sedimentation basin as well as recycle/detention basin for watering and washing purposes within the development. The objectives for the stormwater quality analysis were to meet the operational phase performance criteria outlined in Brisbane City Council's Pollutant Export Modelling Guidelines (October 2003) and Healthy Waterways' Technical Design Guidelines (June 2006).

To meet these objectives a MUSIC model was undertaken based on the stormwater concept which

included two sediment basins as part of the treatment train. The music model demonstrated that the reduction in pollutants will satisfy the recommendations in Australian Runoff Quality as shown in Table 7. The proposed measures and devices in this report will satisfy the requirements and specific outcomes outlined in Seqwater Guidelines for Water Quality in Drinking Water Catchments.

7. Concrete Batching Plant

Edith Pastoral Company is submitting a Development Permit Material Change of Use application to Somerset

Regional Council for a Concrete Batching Plant to be located to the southern side of the crushing, screening and

washing area. Refer to “dashed” outline on Lockyer Designs Sketch LD-1030-SK05 in the appendix.

This operation in conjunction with the development as detailed in this report will have minimal impact on the

stormwater quality and quantity requirements. The area has been taken into account when sizing sedimentation

and detention basins.

For details refer to the separate Development Application.


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8. References

Department of Natural Resources and Water 2007, Queensland Urban Drainage Manual, 2nd Edition, Brisbane, QLD. Department of Environmental and Heritage Protection, Stormwater Guideline for Environmentally Relevant Activities, February 2014. Institute of Engineers, Australia Queensland (1996). Soil Erosion and Sediment Control: Engineering Guidelines for Construction Sites. International Erosion Control Association (IECA) Australasia (2008). Best Practice Erosion and Sediment Control. Brisbane City Council 2003, Guidelines for Pollutant Export Modelling in Brisbane, Version 7- Draft, Brisbane, QLD. Healthy Waterways 2006, Water Sensitive Urban Design- Technical Design Guidelines for South East Queensland, Version 1 -June 2006, Brisbane, QLD. Seqwater Development Guidelines, Development Guideline for Water Quality Management in Drinking Water Catchments, 2008.


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APPENDIX A

Drawing Index

LD - 1030 - SW01 EXISTING CATCHMENT PLAN

LD – 1030 – SW02 DEVELOPED CATCHMENT PLAN

LD – 1030 – SW03 EXTRACTIVE INDUSTRY


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& SONS Lockyer Designs

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Appendix B Diagrammatic MUSIC Model


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& SONS Lockyer Designs

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Appendix C Sedimentation Basin Calculation

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