Site Based Stormwater Management Plan Concrete …...concrete batching plant. 2. Site Description...

310 Gregors Creek Road, Gregors Creek

for

Edith Pastoral Company Pty Ltd

Date: 12 July 2016

Revision: 06

Site Based Stormwater Management Plan Concrete Batching Plant

STORMWATER MANAGEMENT PLAN

CONCRETE BATCHING PLANT

310 GREGORS CREEK RD

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

Contact Officer Amir Keshtgar (Water Engineer)

Phone: 07 3831 0800

Job No: LD-1030

Version history

Revision No. Date Details

01 November 2015 Draft

02 27 January 2016 Final

03 12 April 2016 RFI

04 14 April 2016 Peer Review – Peter Keane

05 27 April 2016 Revised Draft

06 12 July 2016 Finalisation

Final Report

Approved by: Cameron Currie (Senior Engineer) RPEQ # 6860

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


CONCRETE BATCHING PLANT 310 GREGORS CREEK RD

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Executive Summary Lockyer Designs was commissioned by Edith Pastoral Company to produce a stormwater management plan (SWMP) for the proposed Concrete Batching Plant 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 site 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 a combined sediment/detention dam for the purpose of quantity mitigation as well as quality treatment within the site. A 30m3 “first flush” pit will be located adjacent to the sediment/detention basin to capture the first flush of contaminated water from fly ash and cement storage, along with concrete loading areas. This basin captures the initial runoff generated from the batching plant and adjacent use area, before subsequent runoff is then directed to the combined detention and sediment basin.

The proposed basin captures the runoff generated from batching plant and associated haulage roads. The flow from this basin will discharge into the recycle dam downstream sized for extraction area then will flow into a grassed overland flow area with the discharge point into the Brisbane River more than 1.3km from the recycle dam.

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 650 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 6.

To meet these objectives modelling analysis was undertaken based on the stormwater concept which included a basin 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 8.

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, 2012.



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TABLE OF CONTENTS

Executive Summary ...................................................................................................................................... ii

1. Introduction .......................................................................................................................................... 1

2. Site Description ..................................................................................................................................... 1

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

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

4.1 Stormwater Quantity .................................................................................................................................. 4

4.2 Existing Condition ....................................................................................................................................... 5

4.3 Proposed Development Conditions ............................................................................................................ 6

5. Stormwater Quality Management ..................................................................................................... 10

5.1 Methodology ............................................................................................................................................ 10

5.2 MUSIC Modelling Results .......................................................................................................................... 11

5.3 Sediment Basins ........................................................................................................................................ 12

5.4 Wastewater Collection and Treatment .................................................................................................... 13

6. Conclusion .......................................................................................................................................... 13

6.1 Extractive Industry – Hard Rock Extraction .............................................................................................. 14

7. References .......................................................................................................................................... 15

APPENDICES

Appendix A Drawing Index

Appendix B Rational Method and MUSIC Model

Appendix C Sediment Basin Calculations



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1. IntroductionLockyer Designs was commissioned by Edith Pastoral Company to produce a stormwater managementplan (SWMP) for the proposed Concrete Batching Plant at 310 Gregors Creek Road, Gregors Creek aspart of the Development Permit Material Change of Use application to Somerset Regional Council. Theproposed site is currently farming land and adjoins pastoral land.

The aim of this management plan is to provide policies, performance criteria and procedures tominimise the impact of the development on the physical and social environment. This report identifiesthe stormwater quantity and quality management measures required for the construction andoperational phases of the proposed development.

This report will demonstrate the development can be undertaken in accordance with the currentSomerset Regional Council guidelines, Seqwater Development Guidelines 2012, the current QueenslandUrban Drainage Manual, State Planning Policy July 2014 and best management practices.

A stormwater quantity analysis has been undertaken to ensure peak flows resulting from thedevelopment do not exceed the pre-development peak flows. A water quality analysis has also beencompleted to determine the pollutant loads in the stormwater runoff as a result of the development.

Note: procedures and devices described in this management plan may require modification resultingfrom onsite survey to suit the detailed requirements for the construction and operational phases of theconcrete batching plant.

2. Site DescriptionThe proposed development site is located on the southern side of Gregors Creek Road approximately3km from the Brisbane Valley Highway intersection. The site is located approximately 2.8km fromGregors 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 flowcalculations.

The proposed fully developed site is located within the following parcels of land occupying an area of1498m2 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.

It is intended to batch the concrete onsite from imported or site extracted material.



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The proposed concrete batching plant will sit adjacent to the proposed extractive industry use on the same site, and will be co-located with the processing and stockpile area for that use, and the associated stormwater management infrastructure. Stormwater runoff from the concrete plant site, and any additional water runoff from the production process will be treated via a combined detention and sediment basin, along with a first flush pit to capture the initial runoff from the use area. The water treated by this process will then discharge to the recycle dam on the site, which also collects treated water from the extractive industry use. The recycled water in this dam will then be used in the production process whenever possible.

A concrete batching plant is proposed to be established on the site. Figure 1 page 5 shows the site layout.

Figure 1 – Site Layout




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3. Stormwater Management Plan The formulation and implementation of the stormwater management plan for the proposed concrete batching plant 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 management plan addresses Seqwater Development Guideline 2012. This Guideline requires runoff generated from the developed site to have 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 the concrete production process, stockpiling of the raw material and haulage to the site. It is proposed to build a separate stormwater network and treatment devices to the extractive industry also on-site so the runoff from the batching plant will not flow into the quarry, and the runoff from the quarry will not discharge into the batching plant area. The proposed stormwater management plan in this report aims to provide adequate quantity and quality mitigation devices and measurements for the concrete batching plant. To satisfy the Seqwater and DEHP requirements the following items have been discussed in this study:

Table 1 –Summary of Relevant Required Tasks

Guideline / Requirement Hydraulics/Quality Section

BCC Guide for Concrete Batching Part 6. Water Management 5.4

SEQ 2012 Table 8, Element 5 4.1, 4.2 and 4.3

Table 16, Element 13 4.3 and 5

Table 22, Element 17 4.3, Appendix D

DEHP 2014 – Code of Practice for Concrete Batching Industry

P.O 2.1 4.3, 5.3 and 5.4




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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 the ILSAX method for hydrological calculations which is based on time-area method and the Horton infiltration procedure. The 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. roof, car park) and grassed area. The Time of Concentration for each sub-catchment was calculated using the 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. 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-



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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 information extracted from Google Earth, aerial photos and the maximum allowable impervious areas according to QUDM.

Element 5 of Seqwater guideline compliments many existing accepted Water Sensitive Urban Design (WSUD) principles, 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 is indicated as an appropriate tool and resource for detail design of stormwater structures and devices. QUDM is a technical guideline, comprising principles which have been adopted to estimate stormwater quantity. Element 5 of the Seqwater guideline specifies the development shall not increase the stormwater quantity of flow velocity from the subject site.

4.2 Existing Condition

The Rational method calculations (as per QUDM guidelines) were undertaken to estimate the peak discharge during various storm events for the existing conditions. These calculated peak discharges were then used and compared to DRAINS results for calibration and verification.

The time of concentration for the existing condition was calculated for the entire catchment which includes the travel time due to overland flow, the calculation is provided in Appendix B.

The DRAINS program adopts the ILSAX model to calculate stormwater flows. The ILSAX method results in higher peak discharges for all investigated storm events, other than the 2 Year ARI, and has been adopted for conservatism in this study. It is noted that no further calibration is deemed necessary due to correlation to the rational method results.

The current site is almost entirely a rural catchment, with the access roads within the site have a negligible fraction impervious. There are no sheds and buildings within the development site, therefore the entire catchment area for the development site was considered pervious.

The proposed concrete batching plant and the adjacent area were analysed. The calculated flow rates using Rational Method and DRAINS are given in Table 2.



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Runoff from the proposed concrete batching plant site currently flows into a grassed overland flow area with the discharge point more than 1.3km from the recycle dam. Refer to sketch No SW101 in Appendix A.

Table 2 – Existing Site Peak Discharges – Rational Method

Table 3 – Existing Site Peak Discharges – DRAINS

4.3 Proposed Development Conditions The impervious area in post-development includes the existing access road, concrete batching plant, pad adjacent to the concrete batching plant as shown in Table 4.

The proposed total area covers an area of 4000m2 with fraction impervious of approximately 0%, however the fraction impervious in post-development stage will be increased to 100% which is due to paved area.

ARI Batching plant

Discharge(m3/s)

2 0.058

5 0.082

10 0.097

20 0.118

50 0.154

100 0.181

ARI Batching plant

Discharge (m3/s)

2 0.057

5 0.086

10 0.106

20 0.131

50 0.16

100 0.185



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Table 4 – Developed Catchment Details

Catchment Area (ha) Fraction impervious (%)

Concrete batching plant 0.15 100

Haul road 0.25 100

Total 0.4 -

For the purpose of this report the proposed concrete batching plant site will be called the proposed development. The proposed development flows have been calculated based on a developed site of which 100% of the catchment is impervious. Table 5 below shows the combined peak discharges from the site, after the site has been developed before any attenuation is undertaken.

Table 5 – Developed Combined Discharges without Attenuation

Table 5 shows an increase in the peak discharge from the site caused by the proposed development. To ensure the post development stormwater flows do not adversely affect downstream properties, 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 recycle dam downstream of the site.

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

Existing Developed without attenuation

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

2 0.057 0.139 144

5 0.086 0.18 109

10 0.106 0.206 94

20 0.131 0.243 85

50 0.16 0.284 78

100 0.185 0.324 75



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progressively adjusted until the peak detention basin discharge rate was equal to or less than the calculated pre-development value for each ARI event.

The proposed detention size has been reviewed for compliance with the specified requirements of the Code of Practice for the Concrete Batching Industry of Department of Environment and Heritage Protection (DEHP).

In compliance with the above guideline, it is proposed for the first flush of contaminated water from fly ash and cement storage, concrete loading and truck washing and slumping areas to be collected and stored in a 30m3 first flush pit to capture the initial site runoff, before subsequent runoff flows into the combined detention and sediment basin. The proposed first flush pit must be lined appropriately to ensure any contaminated water does not seep through the underground water and/or downstream river.

Furthermore, sufficient freeboard has been maintained to ensure the contaminated water will not leave the site after the first flush rain with 20mm depth.

Regular inspection, monitoring and desilting of the basin must be undertaken to maintain adequate sediment holding capacity. It is essential that any proposed reuse of this water does not have a potential to be released into the Brisbane River catchment.

A detention basin size with the total capacity of 650 m3 including the freeboard volume was modelled in the DRIANS program. Figure2 shows the stage – storage graph of the proposed basin.

Figure 2 – Stage Storage Graph - DRANS

The proposed detention basin is located to the southern side of the batching plant area. The proposed basin will capture all runoff generated from the site, with no bypass overland flow from this paved area. A proposed spillway structure will be provided for major flood events.



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Table 6 shows the peak flow estimates from the site after detention basin merging with runoff from screening and concrete batching plant area. As shown in the Table 6, all peak flows, other than the Q100 by a negligible extent, will be retained onsite.

Table 6 – Comparison of Peak Discharges after Attenuation

DRAINS Existing Post – development

(combined)

Decreased (%)

Q2 – Discharge (m3/s) 0.057 0 100.0

Q5 – Discharge (m3/s) 0.086 0 100.0

Q10 – Discharge (m3/s) 0.106 0 100.0

Q20 – Discharge (m3/s) 0.131 0 100.0

Q50 – Discharge (m3/s) 0.16 0 100.0

Q100 – Discharge (m3/s) 0.185 0.02 89.0

The invert level of the proposed basin is at RL117.5m and the top of wall at RL120m, allowing 1m for freeboard. The 5m long weir structure is to be installed at RL 119m at the south of the proposed basin.

As shown in Table 6, the proposed basin has the capacity to retain all storm event floods up to ARI 50 year. The overtopping flow from the basin for major storm of Q100 is only 20 l/s. This overtopping flow from the sediment basin will be directed into the existing farm dams downstream via the existing gullies and grassed swales.

Currently there is a series of farm dams on the site located downstream of the proposed recycle dam, which are connected by a grassed overland flow path that provides additional quality control for runoff from the proposed development, before being discharged into the Brisbane River more than 1.3km from the recycle dam.

Figure 3 – Inflow-Outflow Hydrograph for Detention Basin (50Yr-5min)

. Figure 3 shows the inflow-outflow hydrographs for the basin.



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5. Stormwater Quality ManagementThe State Planning Policy July 2014 requires development areas for industrial material change of usewithin 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 inthe Seqwater Development Guidelines.

This policy requires that we protect receiving water from adverse development impacts by managingdevelopment 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 todemonstrate compliance with the Seqwater Development Guidelines performance outcomes and toprovide quantifiable values for design.

The proposed detention size has been reviewed for compliance with the specified requirements of theCode of Practice for the Concrete Batching Plant compiled by Department of Environment and HeritageProtection (DEHP).

The State Planning Policy design objectives for managing stormwater are intended to:

• Manage stormwater quality• Improve waterway stability• Manage the frequency of flows

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 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 urban catchment. The rainfall data set for Esk from Pluviograph 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.



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Table 7– 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 developed unmitigated scenario, compared to the mitigated scenario

Gross Pollutants (GP) 90% reduction in average annual load pollutants leaving the developed unmitigated scenario, compared to the mitigated 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.

5.2 MUSIC Modelling Results A MUSIC model was set up to model the concrete batching plant site to determine the increase in total suspended solids, total phosphorus and total nitrogen as shown in Appendix B. The stormwater concept for the concrete batching plant is to capture flows from the paved area for treatment and detention and direct it to a grassed swale and existing farm dams downstream as shown on plan LD-1030-SW-102 in appendix A.

To mitigate the effects of the increased annual pollutant loads, an analysis was undertaken for concrete batching area using MUSIC model.

It is proposed the runoff generated from the concrete batching plant will be directed to a combined detention and sediment basin directly adjoining the southern end of the use area as shown on the attached plans.

The overtopping flow from this basin will then discharge to the recycle dam on the site via a grassed swale downstream of the concrete batching plant.

Any overflow from the recycle dam will discharge via an existing grassed overland flow path and through a series of existing farm dams that can provide additional downstream sediment control before flowing into the Brisbane River. The stormwater quality analysis of these farm dams is not included in the MUSIC modelling.



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It is noted that the discharge point from the site into the Brisbane River is more than 1.3km from the recycle dam, and any water leaving the recycle dam will already be of a standard that meets the water quality targets outlined in the State Planning Policy and the SEQ Water Development Guidelines. While additional sediment control will therefore not be necessary, the discharge of water from the recycle dam via the grassed overland flow path and farm dams ensures that there will be no adverse impact on the Brisbane River.

The MUSIC results indicate the above proposed devices will treat the contaminant items of TSS, TN and TP successfully. A summary of the results from the MUSIC modelling is provided in Table 7.

Table 8 – Best Practice Targets and Options for Reduction of Mean Annual Loads

Best Management Practice (Reduction %)

Proposed Development

TSS Reduction (%) 80% 96

TP Reduction (%) 60% 85

TN Reduction (%) 45% 78

Gross Pollutants Reduction (%) 90% 100

5.3 Sediment Basins The combined sediment and detention basin has been sized in accordance with the DEHP Code of Practice for the Concrete Batching Industry. 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 south of the batching plant area, which will be combined with the proposed detention basin. It is also proposed to use a spillway to convey the flow of extreme storm events. The water will be reused for washing purposes in the batching plant to assist in ensuring adequate capacity of the basin is maintained.

The proposed sediment basin has been sized to ensure the total required treatment for the whole concrete batching plant will be retained for all storm events up to and including Q50.

The sediment basin must be monitored after every rain event and cleaned as necessary. The build-up of sediment must be measured at least every 4 months and sediment must be removed every 12 months as a minimum. According to DEHP’s guideline the proposed basin must be lined appropriately to ensure any contaminated water does not seep through the underground water and/or downstream river.

According to Seqwater requirements the monitoring and water quality testing (in this case for ARI greater than 50 year) is essential at the location immediately before entering Brisbane River. The required tests are pH and Suspended Solid where water is entering downstream existing dams.



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5.4 Wastewater Collection and Treatment To prevent contaminated and dirty water entering Brisbane River downstream of the site, it is proposed to install a pit to collect the water from the first flush (d = 20mm) and then pump it to a storage tank with the same size for recycling.

A spillway (overflow drain) one meter upstream of the first flush pit should divert excess rainwater from the operational area when the pit fills due to heavy rain events, greater than 20mm. The excess runoff (more than 20mm) will flow into downstream sediment basin. The overflow from this basin will discharge into downstream dams in the extreme flood events.

The wastewater should be pumped from the first flush pit to the recycling tank. The first flush pit should have a primary pump triggered by a float switch and a backup pump that automatically activates if the primary pump fails.

Wastewater stored in the recycling tanks needs to be reused at the earliest possible time. Ideally, depending on production, the plant is able to use the full reserve storage capacity of the wastewater collection and treatment system within 72 hours of a downpour. However, if the water level exceeds the capacity of the recycling tank, the wastewater will need to be removed by a waste management contractor

The concrete batching area is 0.15ha, therefore the first flush pit will have 30m3 capacity to hold the stormwater from the areas generated by 20mm of rain over 24 hours inside the plant. The detailed sizes and location of the treatment devices will be provided in detail design stage.

6. ConclusionIt is recommended that a combined detention and sediment basin be built directly adjacent to theconcrete batching plant area for the purpose of quantity mitigation, as well as stormwater qualitytreatment from the use. A 30m3 first flush pit will be located adjacent to this basin to capture the firstflush of contaminated water from fly ash and cement storage, along with concrete loading areas. Thisbasin captures the initial runoff generated from the batching plant and adjacent use area, beforesubsequent runoff is then directed to the combined detention and sediment basin. The flow from thisbasin will then discharge to the recycle dam on the site downstream of the concrete batching plant areavia a grassed swale, with the water from the recycle dam to be reused within the concrete batching plantand adjacent extractive industry processing area whenever possible.

The main objective of the stormwater quantity analysis was to limit the post developed peak dischargeto the equivalent pre-developed peak flow discharging from the site for rainfall events up to the 100year ARI event. To achieve this objective on-site combined sediment and detention storage with thetotal volume of 650 m3 will be required for the site.

The analysis demonstrates that the total peak discharge from the proposed development will be equal toor less than the pre-development flows, as shown in Table 6.

The objectives for the stormwater quality analysis were to meet the operational phase performancecriteria outlined in Seqwater Guideline and in Brisbane City Council's Pollutant Export ModellingGuidelines (October 2003) and Healthy Waterways' Technical Design Guidelines (June 2006).



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To meet these objectives a MUSIC model was undertaken based on the stormwater concept which included a basin 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 8.

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.

6.1 Extractive Industry – Hard Rock Extraction The application also includes a proposed Extractive Industry use, with the proposed concrete batching plant and processing and stockpile area for the quarry being co-located on the site. A separate site based stormwater management plan has been prepared for the extractive industry use to detail how stormwater from both the extraction and processing areas will be managed and treated to ensure compliance with the relevant standards, before discharging to the proposed recycle dam on the site. The operation of the proposed concrete batching plant, in conjunction with the extractive industry as detailed in this report, will comply with all relevant stormwater quantity and quality control requirements. For further details regarding the stormwater management plan for the extractive industry use, please refer to the separate report prepared for that use.



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7. References

Department of Natural Resources and Water 2007, Queensland Urban Drainage Manual, 2nd Edition, Brisbane, QLD.

Department of Environmental and Heritage Protection, Code of Practice for the Concrete BatchingIndustry.

Institute of Engineers, Australia Queensland (1996). Soil Erosion and Sediment Control: EngineeringGuidelines for Construction Sites.

International Erosion Control Association (IECA) Australasia (2008). Best Practice Erosion and SedimentControl.

Brisbane City Council 2003, Guidelines for Pollutant Export Modelling in Brisbane, Version 7- Draft,Brisbane, QLD.

Brisbane City Council, Industry Environmental Guide for Concrete Batching

Healthy Waterways 2006, Water Sensitive Urban Design- Technical Design Guidelines forSouth East Queensland, Version 1 -June 2006, Brisbane, QLD.

Seqwater Development Guidelines, Development Guideline for Water Quality Management in DrinkingWater Catchments, 2008.

Ian

Polygon




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Appendix A Drawing Index

LD - 1030 – SW101 EXISTING CATCHMENT PLAN

LD – 1030 – SW102 CONCEPT PLANT LAYOUT

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Appendix B

Diagrammatic MUSIC Model




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Rational Method Calculation

Time of concentration - Friend's equation - Overland sheet flow Parameter Value Unit Description

Catchment Area 0.4 ha

Value Unit Description 2 yr discharge coefficient, C2 0.595 from equation 4.4, QUDM (Cy = Fy . C10)

50 m 5 yr discharge coefficient,C5 0.665

0.045 from Table 1 10 yr discharge coefficient, C10 0.7 from Tables 4.5.3 and 4.5.4, QUDM

2.5 % 20 yr discharge coefficient,C20 0.735

14.75 min 50 yr discharge coefficient,C50 0.805100 yr discharge coefficient,C100 0.84

Tc = 15 minutes

2 yr rainfall intensity, I2 87.1 127 from IFD curves - using BOM database

5 yr rainfall intensity, I5 110.45 mm/hr from IFD curves - using BOM database

10 yr rainfall intensity, I10 125 mm/hr from IFD curves - using BOM database

20 yr rainfall intensity, I20 145 mm/hr from IFD curves - using BOM database



2 yr runoff value, Q2 = 0.058 m3/s






Fraction impervious, fi 0.2 from Table 4.5.1, QUDM

Rational Method - Catchment Runoff Calculation - Batching Plant

Time of concentration, Tc =

Hydrological parameters

Overland sheet fow length, L

Hortons roughness, n

Slope of surface, S




R e v 06

Appendix C

Sedimentation Basin

Quarry : EDITH PASTORAL COMPANY

Detention BASIN - Concrete Batching

Sediment Basin Sizing

Soil Type = Dispersive

Basin Type = D

A = 4000 m2Catchment

D = 0.02 First flush rain depth (m) -P.O 2.1 DEHP code of practice

Vs = 80 m3 Storage Volume

Basin Area = 70 m2 Based on 0.6m depth and 1 in 5 batters

Width = 4.8 m Based on a 3:1 length to width ratio

Length = 14.4 m

Site Based Stormwater Management Plan Concrete …...concrete batching plant. 2. Site Description...

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