REPORT ON THE PRELIMINARY DESIGN FOR THE PHASE 2 For ...

Golder Associates (UK) Limited IS’ Floor Clyde House Reform Road Maidenhead Berkshire, SL6 8BY England

Tel: [44] (0)1628 771731 Fax: [44] (0)1628 770699 E-mail: [email protected] http://www.golder.com

REPORT ON

THE PRELIMINARY DESIGN FOR THE PHASE 2

BAUXITE RESIDUE DISPOSAL AREA AT AUGHINISH ALUMINA

Submitted to:

Aughinish Ahnninia Limited Askeaton

Co.Limerick Ireland

DISTRIBUTION:

1 copy - Aughinish Alumina Limited 2 copies - Golder Associates (UK) Ltd

May 2005 03511318.511

Oppms IN UK, FINLAND, GERMANY, HUNGARY, fffiy, FRANCE, SPAIN, SWEDEN, CANADA USA, PERU, CHILE, BRAZIL, AUSTRALIA, NEW ZEALAND, INDONESIA, HONG KONG, THAILAND

COmPanY Registered In England No 11~~1~. At I* Floor Clyde HOW+ Reform Road, Maidenhead, Berkshire, SLY w-f

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SECTION PAGE 1.0

2.0

3.0 4.0 5.0

6.0 7.0

8.0

TABLE OF CONTENTS

INTRODUCTION ......................................................................................... 1 1.1 General.. ................................................................................................. .I

1.2 Scope of the Works ................................................................................ .1

RESIDUE PRODUCTION ........................................................................... 3

2.1 General . . . ..*............................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.2 Operation.. .............................................................................................. .4

SITE ............................................................................................................. 6

SITE WORK ................................................................................................ 9 HYDROLOGY AND HYDROGEOLOGY.. ................................................ 11 5.1 General.. ................................................................................................ I?

5.2 Climate .................................................................................................. 12

5.3 Flood Flows ........................................................................................... 12

5.4 Hydrogeology ........................................................................................ 14

5.4.1 Estuarine .................................................................................... 14

5.4.2 Glacial Till ................................................................................. .I5

5.4.3 Limestone Bedrock ................................................................... .I5

SEISMICITY .............................................................................................. 17

PHASE 2 BAUXITE RESIDUE DISPOSAL AREA DESIGN .................... 18 7.1 7.2 7.3 7.4 7.5 7.6 7.7

;;

7.10 7.11 7.12 7.13

7.14

General.. ............................................................................................... .I8

Outer Perimeter Embankment Wall ....................................................... 19

Inner Perimeter Embankment Wall ........................................................ 21

Perimeter Interceptor Channel .............................................................. 22

Composite Lining ................................................................................... 24

Stack raise ............................................................................................. 25 Upper Level Interceptor Channel ........................................................... 27

Flood Tidal Defence Berm ..................................................................... 28

Construction Materials and Quantities ................................................... 30

Storm Water Pond Raising ................................................................... .31

Liquid Waste Pond Raising ................................................................... 33

Stability .................................................................................................. 34

7.13.1 Outer and inner perimeter embankment walls and the flood tidal defence berm ................................................................................. 34

7.13.2 Storm water pond and liquid waste pond.. ................................ .36

Dusting .................................................................................................. 38

SEEPAGE MODELLING ........................................................................... 39 8.1 BRDA ..................................................................................................... 39

8.2 Perimeter interceptor Channel ............................................................. .41

8.3 Storm Water Pond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

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8.4 Seepage Summary ................................................................................ 42

9.0 CONTAMINANT MODELLING ................................................................. 43

9.1 General .................................................................................................. 43

9.2 Process .................................................................................................. 43

9.3 Modelling .............................................................................................. .46

10.0 SURFACE WATER MANAGEMENT ........................................................ 51

IO. 1 General ................................................................................................. .51

10.2 Storm Water Management .................................................................... 51

10.3 SWP and PIC Volumes ........................................................................ .54 10.4 Water Balance.. .................................................................................... .56

10.5 Upper Level Interceptor Channel .......................................................... .57

11 .O CONSTRUCTION MONITORING ............................................................ 58

11 .I General ....................................................................................... . ......... .58

11.2 Site Preperation ..................................................................................... 58 11.2.1 Removal of Trees, Vegetation and Stumps .............................. .58 II ,2.2 Backfilling Existing Drains ......................................................... .59 II .2.3 Removal of Topsoil .................................................................... 59

11.2.4 Removal of Unsuitable Stockpile .............................................. .59 11.3 Earthworks ............................................................................................. 60 II .4 Geomembrane.. .................................................................................... .61 11.5 Leak Detection.. .................................................................................... .61

12.0 MCNITORING ........................................................................................... 62

12.1 General .................................................................................................. 62 12.2 Vibrating Wire Piezometers ................................................................... 62 12.3 Casagrande Standpipe Piezometer.. .................................................... .63 12.4 Monitoring Wells ................................................................................... .63

12.4.1 Preliminary ................................................................................. 64

12.4.2 Detail.. ........................................................................................ .64 12.5 Inclinometers ......................................................................................... 64

12.6 Settlement Spiders ................................................................................ 64

j2.7 Survey Monuments ................................................................................ 64

12.8 Intrusive Investigation ............................................................................ 65

12.9 Additional Monitoring ............................................................................. 65

13.0 REFERENCES .......................................................................................... 66

LIST OF TABLES

Table 1 Table 2 Table 3

30 Year Averages Shannon Airport True Evaporation at Ardnacrusha Water Balance Output Computations

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LIST OF FIGURES

Figure 1.1 General Location Plan Figure 1.2 Site Location Plan

Figure 3.1 Topographic Plan of the Site Phases 1 and 2

Figure 5.1 Figure 5.2 Figure 5.3

Shannon Extreme Precipitation vs Return Event 1995 Rainfall Comparison 1997 Rainfall Comparison

Figure 7.1 Figure 7.2 Figure 7.3 Figure 7.4 Figure 7.5 Figure 7.6

Plan of Bauxite Residue Disposal Area Phase 2 Plan of Bauxite Residue Disposal Area Phase 1 and 2 Sections Through Embankment Wall Phase 2 Sections Through Embankment Wall Showing 10 Stage Raises Detailed Section Through Perimeter Embankment Walls Plan Showing Connection Between the Phase 2 and Phase 1 BRDA along Eastern Flank

Figure 7.7

Figure 7.8 Figure 7.9 Figure 7.10 Figure 7.11 Figure 7.12 Figure 7.13

Plan Showing Location of Decant Pipes/Culverts and Flow Direction from the Interceptor Channels Longitudinal Profile Interceptor Channel Phase 1 and 2 Stage Raises Final Surface Profile. Upper Level Interceptor Channel Decant and Spillway Details Detailed Section Through the Flood Tidal Defence Berm Plan of Storm Water Pond Details of Storm Water Pond Raise

Figure 10.1 Figure 10.2 Figure 10.3

FigmeN Figure 10.5 Figure 10.6 Figure 10.7

Mud Stack Water Inventory Pumping and Storm Volumes vs Duration Estimated Operating Storage in the SWP and PIC between 1992 and 2003

StormWaterPonQStorage\rolumevsWater SurfaceElevation Phase 1 Perimeter Interceptor Channel Storage Volume vs Elevation Flow Chart For Water Balance SWP and PIC Operating Volume and Rate vs Month

Figure 11.1 Figure 11.2

Surface Drainage Backfill Detail Topsoil and Unsuitable Stockpile Area

Figure 12.1 Plan Showing Location of Monitoring Points

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1 .O INTRODUCTION

I .I General

Golder Associates UK Ltd (Golder) was appointed by Aughinish Alumina Limited (AAL) in November 2003 to undertake the design of the Phase 2 Bauxite Residue Disposal Area (BRDA).

AAL is a subsidiary of the Swiss based commodities trading and manufacturing group Glencore and employs some 500 permanent employees together with approximately 200 contractors at the Aughinish plant.

AAL operates the alumina refinery situated on Aughinish Island on the south side of the Shannon estuary. The Island is located between Askeaton and Foynes and is some 30km west of Limerick and 1Okm south west of Shannon Airport (Figure 1.1). The Island is approximately 400 hectares in area and is bounded by the River Shannon to the north, the Robertstown river to the west and south west and the Poulaweala creek to the east and south east (Figure 1.2) The existing Phase 1 BRDA is located south west of the existing process plant. The proposed Phase 2 BRDA is located immediately to the south of the existing Phase 1 BRDA.

The plant and ancillary structures were constructed between 1978 and 1983 representing an investment of some EO.8 Billion which is the largest single private investment in the Irish economy. Plant production has continually increased since commissioning of the plant in 1983 and the 2004 production is approximately 1.7 million tonnes of alumina per annum (MTA).

The existing Phase 1 BRDA will provide storage to the year 2009 based on their current planning permission condition which allows AAL to raise the facility to Stage 7 (elv. 18mAMSL) which equates to a central elevation of 27.5mAMSL or 26m above original

punQ level, It ia now proposed that three m.x %ages will, be added (8agc 8-elevation 2OmAMSL, Stage g-elevation 22mAMSL and Stage lo-elevation 24mAMSL) resulting in a maximum central elevation of 32mAMSL.

1.2 Scope of the Works

The scope of the works for the Phase 2 BRDA study is detailed in Part III Appendices to Terms and Conditions Appendix A (Reference 1). These are summarised below;

l engineering design related services,

l services for regulatory processes and

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a construction stage services.

This report presents the preliminary design for the Phase 2 BRDA. The site investigation data and the borrow assessment are presented in Reference 2 together with a review of previous work carried out within the footprint of the Phase 2 BRDA.

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2.0 RESIDUE PRODUCTION

2.1 General

AAL extracts alumina (aluminium oxide) from the imported bauxite raw material and exports the alumina to various altiium smelters in the UK and Continental Europe. The bauxite is shipped in 65,000 tonnes bulk ore carriers from bauxite mines, principally Boke in West Africa, but also from Brazil. The bauxite is unloaded at the Aughinish marine terminal on the Shannon Estuary. At the current production levels, over 60 ships a year are offloaded and 150 alumina export ships are loaded each year. In addition to bauxite and alumina, the ships offload caustic soda, sulphuric acid and heavy fuel oil as consumables for the operating plant.

The production of alumina from bauxite involves 5 stages;

Preparation Bauxite is crushed and ground and mixed with caustic soda solution and pumped into digester pressure vessels. ’

Digestion Under high pressure and heat, the alumina (within the bauxite slurry) is dissolved by and combines with the caustic soda to produce sodium aluminate.

Clarification The solid residues (red mud and process sand) in the digested bauxite shury are separated by settling out of the sodium aluminate solution. The residues are washed and the red mud is thickened by vacuum filtration and pumped to the bauxite residue disposal area.

Precipitation As the soluble sodium aluminate is cooled, it is agitated and seeded with aluminium hydroxide crystals. These form larger crystals which gradually settle out of solution. Seed crystals and sodium aluminate remaining in solution are recirculated.

Calcinations The ahuninium hydroxide crystals are calcined at over 1100 degrees centigrade to remove the water of crystallisation. A fine white powder, alumina is produced and this product is exported by ship to overseas smelters.

The process consumed in 2004, approximately 9,414 tonnes/day (t/d) of bauxite, 281t/d of caustic soda, 14,35lt/d of water, 143t/d of lime and 972MW/d of electrical power. After repeated washings to remove entrained caustic liquor, the residue is delivered to the, BRDA. Two main residue streams are produced, the finer material is called red mud and is approximately 90% to 95% of the waste stream. The remainder is a coarser material termed process sand. The properties of these materials are discussed in Reference 3 and 4.

Current production of alumina is approximately 1,600,OOO tonnes per annum which will progressively rise to 1,950,OOO tonnes per annum by 2010. The anticipated alumina production together with the waste products are tabulated below to the year 2010.

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The tonnage of residue produced is dependent on the grade of alumina in the bauxite and the efficiency of the process recovery. These parameters are variable and an average factor of 0.7 has been adopted by AAL for production values to derive the residue throughput in the future. The volume of residue produced is also dependent on the dry density of the red mud and sand and a conservative value of 1.35tlm3 and 1.45t/m3 have been used respectively in determining these volumes.

2.2 Operation

The red mud is dewatered in the plant using vacuum drum filters. The dewatered mud slurry or filter cake has a pulp density of 65% and is scraped from the drum filters. Water is added to reduce the pulp density (solids content) to 57% and by shear thinning, the red mud is pumped to the BRDA by positive displacement pumps. The mud is discharged into the facilities as a paste from fixed spigot points.

The processed sand is trucked out from the plant and will be used to construct ramps and access roads inside the Phase 2 BRDA,

At a pulp density of 57% the red mud flows down the slope with the appearance of lava at an average slope of 2.5%. Reductions in the pulp density results in a reduction in viscosity which in turn reduces the slope angle. At the target pulp density, no bleeding of water should occur and no segregation of the solids is likely to occur either. As the pulp density decreases, bleeding will occur and some segregation of the red mud particles will also occur. As the pulp density decreases further, erosion of existing deposited red mud will become an issue and therefore it is important to maintain consistently the design pulp density of 57%. A separate report by Golder (Reference 5) discusses issues relating to consistency of the red mud production.

At a pulp density of about 57% the moisture content of the red mud is approximately 75%. After deposition, the moisture content decreases and the in situ density increases. Typically,

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the moisture content decreases to about 45% and the in situ solids content increases to about 70%. As the moisture content of the red mud decreases both its undrained shear strength and dry density increases whilst its volume decreases (Reference 3).

The maturing of the red mud is achieved by the following principal methods;

l air drying of the surface of the red mud by evaporation,

l consolidation of the red mud under its own weight.

Air drying by evaporation is the most important process in dewatering the red mud and improving undrained shear strength. Both wind and sun contribute to evaporation although wind is the main process and therefore occurs throughout the year.

Air drying results in the formation of a desiccated crust which is typical of wet fine grained materials. The desiccated cracks extend to maximum depths of between 200mm and 250mm. The desiccated cracks fill with water during rain periods although the water tends to be displaced once the red mud is deposited.

It is important to prevent ponding of water on the red mud surface in order to promote the maturing of the red mud. It is also important to place the mud in relatively thin layers, typically less than 3OOmm in thickness and allow it to be exposed as long as possible. In the past, recommendations of between 3 and 6 months have been given for the upper red mud layer to be exposed before placement of the next layer. However, at three months, this restricts the maximum number of layers that could be placed to four equating to a total thickness of 1200mm in a year.

The rate of rising will increase as a result of increased production, lower bauxite grades and reduced disposal area. Initially, for Phase 2, the rate of raising will be about 1429mm per annum. By the end of its life, the rate of raising will have increased to 1815mm per annum. The rate of raising could be reduced by alternating disposal with the Phase 1 facility although this could be only undertaken for a limited time whilst there is still storage capacity in Phase 1. It may also be possible to restrict the raising of Phase1 in order that they are both completed at the same time. The rate of rising is discussed in Section 7.

The mud can be directed into selected areas by hydraulically actuated rotating pipes at the end of the discharge points. The placement and direction of movement of the red mud is also strongly influenced by the level and distribution of the previously deposited material. Also, bunds can be constructed from the red mud to direct mud flows to specific areas.

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3.0 SITE

A site investigation was carried out in the area of the proposed Phase 2 BRDA (Reference 2). The proposed footprint of the BRDA is located to the south of the current Phase 1 BRDA and covers an area of approximately 80 hectares (Figure 3.1).

The following section describes topography and groundcover along the proposed flanks of the BRDA, the internal area and the potential borrow area outside the footprint.

The northern flank of the area abuts the southern flank of the Phase 1 BRDA.

The western flank of the area runs parallel with the Robertstown River. There is an existing flood tidal defence berm (FTDB) and a drainage channel within the footprint of the BRDA along this section of the alignment. The FTDB is at an approximate elevation 4.OmAMSL, but varies between 3.25mAMSL and 4.5mAMSL and over the years, has settled differentially. The drainage channel, immediately behind the FTDB, has an invert level of generally between OmAMSL and -O.SmAMSL. Part of the Phase 2 embankment wall alignment will encroach on the mud flats of the Robertstown river, beyond the existing FTDB and this will be investigated prior to the detailed design by piezocone testing, vane testing and delft sampling.

The southern flank of the area runs along the northern side of a railway line on the Island Mac Teige. This railway connects Silvermines with the port of Foynes and has not been used for a number of years. The railway runs along an embankment, with a maximum height of about 4m, over approximately two thirds of the flank. The remaining third of the railway is in a cutting. The elevation of the railway is approximately SmAMSL, with a maximum depth of cutting of approximately 5m. Ground levels vary considerably along this flank. There is a hill of glacial till along approximately one third of the flank with elevations of up to lO.OmAMSL. To the west of the hill the ground is relatively level with an elevation of approximately l.OmAMSL, whereas to the east of the hill the ground is at an approximate

fdmi~nof1,%ViMSL, The eastern flank of the proposed facility runs parallel with the Limerick County Council (LCC) rising water main in Glenbane West, past the LCC water treatment plant and towards the main access road to the AAL Plant. The facility then runs parallel to the main access road crossing the reclaimed Poulaweala Creek which was backfilled during the construction of the access road. The ground level along this flank varies typically between 6mAMSL and 1OmAMSL although drops to 2mAMSL where the creek has been reclaimed. Some additional topographic survey is required in this area which is being undertaken.

At the northern east section of the foot print, there is a stockpile of predominantly unsuitable glacial tiU ant\ estuarine materials ana ‘00ulders. This material was placed in the area during construction of the Phase 1 extension and the stockpile attains an elevation of +lGmAMSL.

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Within the footprint of the proposed BRDA, bounded by the flanks described above, the

ground elevations and vegetation coverage varies. There is a reclaimed water course (Poulaweala Creek); flooded by spring tides; running south-west to north-east, with numerous drainage ditches, generally running north-south directed towards the water course. Drainage from the site exits to the Robertstown River via the drainage channel and a one way flap valve in the FTDB wall. The valve is currently not closing tightly which allows some tidal water to enter the drainage channel.

There is a north-east to south-west running seam of glacial till commencing at the security fence along the northern flank, approximately 200m long by 1OOm wide. Ground levels vary from approximately 1.7mAMSL at the flanks to a maximum of 4.5mAMSL. The northern end of this area was used as a borrow source during construction of the previous mud stack.

Along the western flank, approximately 200m south of the existing BRDA stack there is a small area, approximately 1OOm by 50m, of elevated glacial till. The maximum elevation is approximately 3.OmAMSL, with elevation on the fringes and surrounding ground of 1 .SmAMSL. The drainage channel is located along the western side of this area.

As mentioned above, there is a hill of glacial till along the southern flank of the area. The hill has a maximum elevation of lOmAMSL, with ground levels of 1 .OmAMSL to l.SmAMSL around the fringes. The hill covers an area of approximately 220 m long by 220 m wide, runs north-south and is flanked at the northern end by the reclaimed water course and by the railway cutting to the south.

Ground levels between the higher ground, discussed above, vary, but generally are less than 2mAMSL.

Ground coverage varies. The higher ground, where glacial till is present, is generally covered in grasses with hedgerows along the fringes. The high ground at the southern end of the site is divided into four fields by hedgerows.

The low lying ground is generally covered by reeds and grasses, with hedging along the edges of drains and water courses. There is a woodland plantation area, covering approximately 8.5 hectares of ground in the north west part of the site. The ground elevations based on the old survey data indicate a range generally between 1mAMSL and 2mAMSL. Plantation timber is present along the edge of the majority of the reclaimed Poulaweala Creek. It is understood that the LCC water treatment plant disposes its sludges from the process into the Poulaweala Creek.

An area to the south of the railway cutting was investigated for potential borrow material. The elevation at the top of the cutting is approximately 9.5mAMSL. The ground falls to the

south, east and west towards the Robertstown River. The ground cover is predominantly grasses with hedgerows on field boundaries.

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The farm land forming the eastern flank of the old alignment was included in the investigation as a potential source of borrow material. However, this excluded the cSAC area The ground is undulating with elevations of up to 12mAMSL. There are numerous outcrops of limestone across this area and the ground cover is predominantly grasses with stone walls and hedgerows along the boundaries. Some additional site investigation will be required in this area to determine the potential for ripping and blasting of the limestone to remove high spots and determine the suitability of the rock for construction.

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4.0 SITE WORK

A site investigation was undertaken within the footprint of the proposed Phase 2 BRDA at the location of the perimeter embankment walls and at the location where material could be borrowed. No site investigation work was undertaken at the retained cSAC/SPA and where the delisted cSAC was located. These are the mud flat areas on the shoreline of the Robertstown River and the eastern flank of the footprint which is mostly scrub land and believed to be rock at shallow depth. These areas will be investigated prior to the detailed design phase.

The results of the site investigation are reported in Reference 2 and the site work consisted of 11 boreholes and 43 trial pits.

The site investigation work confirms the presence of soft to firm estuarine deposits forming the low topographic areas (below approximately 2.0m AMSL). The higher ground comprises firm to very stiff glacial till which overlies the limestone bedrock. To the east, the bedrock is expected to outcrop near surface.

The volumes of materials estimated from the trial pits are tabulated below and are based on the borrow areas being excavated to average depths of between lm and 3m below ground level as discussed in Reference 2. The table below gives an upper, lower and median assessment and is based on the variability of the percentage material greater than 75mm and on the potential for the moisture content being outside the design limits.

Material Type

Processed Glacial Till

Topsoil Stripping

Volume of Borrow (m3)

Lower Bound Median Upper Bound

150,000 200,000 250,000

180,000 200,000 230,000

It is apparent that there is only a limited vohune of glacial till available on site and largely confined to the higher ground. Typically the limestone/glacial till contact will be extremely undulating and generally characterised by numerous boulders with a varying proportion of glacial till matrix.

Additional rotary drilling and excavations will be carried out prior to the detailed design in order to confirm the glacial till quantities. Also, additional investigation work will be required on the Robertstown River mud flats using CPT and piezocone equipment together with vane testing and Delft sampling. Rotary drilling in the rock will be required to determine its potential to be excavated by ripping or blasting and to locate the bedrock interface witi tie glacial till on the southern flank. Trial pitting will be required to determine the amount of unsuitable material to be removed in the stockpile areas which encroach on the

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embankment footprint at the north east flank. Trial pitting and probing will also be required to determine the volume of sludges discharged into the reclaimed Poulaweala Creek from the water treatment plant.

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5.0 HYDROLOGY AND HYDROGEOLOGY

5.1 General

The BRDA will occupy some low lying ground that has been claimed from tidal flats through the construction of a flood tidal defence berm (FTDB) and a land drainage system. The majority of the BRDA footprint is on Aughinish West which is bounded by the Shannon to the north, the Robertstown River to the west and the Poulaweala Creek to the south and east (Figure 1.2). The remainder of the BRDA footprint encroaches onto the Island Mac Teige and Glenbane West south and south east of the Poulaweala Creek.

The Shannon is Irelands major river and its catchment covers approximately 20% of the entire area of the country. It is tidal from a point a short distance upstream of Limerick. The flow of the River Shannon is of the order of lMm3/day and at Foynes the sea water mix is some 88% (Reference 6).

The Robertstown River flows into the Shannon Estuary and is tidal in the area of the Aughinish Island. Previous flow measurements indicate a minimum flow of 2600m3/day with normal flow in the order of 78,000m3/day (Reference 6). The catchment area of the Robertstown River south of the Poulaweala Creek is about 6500Ha. The footprint of the Phase 2 BRDA is approximately 80Ha and therefore contributes to about only 1% of the discharge into the Robertstown River.

The Poulaweala Creek separates Aughinish Island from the townland of Island Mac Teige to the south and Glenbane West to the east (Figure 1.2). The Phase 2 BRDA will cross the Creek and encroach on the Island Mac Teige and Glenbane West. The Poulaweala Creek has been backfilled at the point where the main access road to the plant site crosses the Creek. To the north east of the access road, the Poulaweala Creek is tidal. To the south west and within the foot print of the BRDA, the Poulaweala Creek has been reclaimed. There are a number of small discharges that enter the creek from the limestone outcrop to the north east and south east of the creek as well as some drainage ditches.

Some 3km of drainage ditches have been installed to assist in draining the area behind the FTDB. The drainage ditches either discharge directly into the main drainage channel behind the FTDB or to the Poulaweala Creek and then into the main drainage channel. Water collected in the drainage channel discharges to the Robertstown River, via a flap valve. The flow through the flap valve occurs generally during wetter periods and is estimated to be between lOl/sec and 80Vsec for rainfall events of up to 1Omm per day. The current catchment area of the drainage ditches including the limestone outcrops is less than lOOHa which will be reduced to 30Ha once the Phase 2 BRDA is constructed. It can be expected that there wiil be a corresponding reduction in flow of about 70%.

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Farmers have previously used freshwater wells on the south-eastern portion of Aughinish island. However, there is currently no abstraction of water for beneficial uses on the island. Freshwater on the island is derived from rainfall, which has infiltrated and become perched above brackish seawater. The distribution of water over the Aughinish Island is not uniform, and is distributed as a lens with a +9 m AMSL. maximum elevation, which is centred upon the East Ridge in the central portion of Aughinish Island (eastern boundary of Phase 1). The interface between freshwater and brackish waters undergoes seasonal level adjustments, with

some wells yielding fresh water in the winter, but brackish water in the summer. The non- saline groundwater on the Aughinish Island and the Island Mac Teige are not believed to be

connected hydrologicallly to freshwater aquifers on the mainland and discharge as springs around the margins of the islands. This is not the case for groundwater on Glenbane West, where the eastern and south eastern sectors of the Phase 2 BRDA are sited, which is on the main land. Fortunately, virtually all the ground water flow is to &west and north west from the elevated limestone outcrops, beneath the Phase 2 BRDA and towards the saline ground waters of the Poulaweala Creek.. Further, site investigation work will be undertaken along this section to determine the regional groundwater flow, together with the mass in situ permeability of the limestone and presence and thickness of any glacial till capping the limestone. Also, the topographical survey needs to be completed in this area.

5.2 Climate

The climate in the area is temperate characterised by mild winters and cool summers. The mean daily maximum temperatures for the summer months are between 18 and 19 degrees centigrade. The mean daily minimum during the winter months are between 2 and 3 degrees centigrade

The average annual precipitation of the area is 930mm with a general range of between 709mm and 1178mm. The majority of rain falls between August and February.

5.3 Flood Flows

The BRDA must be designed to withstand peak rainfall events. Run off from the BRDA will contain suspended particles of red mud and contaminants. This run off is collected, stored, and treated at the process plant prior to discharge into the environment. The amount of run off is primarily a function of the rainfall and in particular extreme events.

Design storm rainfalls and run-offs have been estimated for the BRDA to determine flood flow using standard techniques which are outlined in the following paragraphs. The data are used to determine the capacity and operating level for the perimeter interceptor channel and storm water pond and pumping requirements to the water treatment plant.

The accuracy of the results are dependent upon the length of records. The derivation of a 100 year return period storm requires some extrapolation from the data covering some fifty years.

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However, considerable extrapolation is required to determine design storms with return periods of 500 years, 1,000 years, 5,000 years and 10,000 years. The choice of extreme event to be used in design is generally based on the risk that this event will be exceeded and the impact of this exceedanoe on the design, environment, health and safety (fatalities) political or economic etc. For instance, if the active life of the facility is another 20 years, then the probability that a 1 in 200 year storm event is exceeded is approximately 10%. Aughinish have accepted this level of risk and this value has been used in design.

If the design criteria is exceeded, then the result would be an overflow of effluent into the environment via a spillway on the perimeter interceptor channel.

Ideally, actual flood flow data should be used to determine these design flows but such records are rare, particularly for small catchments. However, some data are available from the site and has been used in the analysis. The majority of the analysis is based on data derived from Shannon Airport and from the local weather station at Aughinish.

A previous study (Reference 6) to determine extreme rainfall used data derived from Shannon Airport between 1941 and 1992, some 50 years of data. The results are tabulated below and have been extrapolated by Golder to include the 10,000 year event.

Maximum Precipitation in mm for Specific Event Durations Return Event Years 1 day 7 days 14 days 10,000 100 159 210. 5.000 93 150 202 1,000 80 133 183

500 73 127 174

100 58 100 156 50 1 53 1 96 1 148

Met Eireann (Reference 7) also supply extreme rainfall for Shannon Airport up to durations of 48 hours and for return events up to 100 .years. Golder have extrapolated these data to 10,000 year events and included for 7 day and 14 day periods. The results are presented in Figure 5.1 and are tabulated below.

/ y;.;; Event Years Maximum Preciuitation in mm for Suecific Event Durations

1 day 122

7 days 174

14 days 193

114 164 182 98 140 156 90 130 145

74 107 119

65 96 107

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These results are reasonably similar as expected from essentially the same data base.

AAL have monitored rainfall at site for nearly 10 years and have been accredited since 1999. A review of the data indicates two particularly wet years, 1995 and 1997. On the 4* August 1997, 84.8mm of rainfall were recorded in a day. Based on the data provided by Met Eireann and extrapolated by Golder, this equates to at least a 1 in 300 year event. On the 5* April 1995, 67.9mm of rainfall were recorded equating to a 1 in 60 year event. It was also shown that both the 7 day and 14 day duration events were also extreme as shown in the table below.

Maximum Precipitation Site for Specific Durations 1 day 7 days 14 days

84.8mm 162.4m1-n 195.61x-m

Return Event 1 in 300 year I in 5,000 years 1 in 10000 years

The data from these extreme events were compared with data derived from the station at Shannon Airport. For the specific dates on the 5” April 1995 and the 4’ August 1997, the rainfall measured at Shannon Airport was 0.4mm and 38.7mm respectively. A yearly comparison for 1995 and 1997 are presented in Figures 5.2 and 5.3. The comparisons are good particularly in 1997. Based on the Shannon data, it has been assummed that the extreme values recorded by AAL are anomalous.

For design purposes, the data supplied and statistically derived from the Met Eireann has been used in the water balance analyses.

5.4 Hydrogeology

The foundation materials encountered beneath the footprint of the Phase 2 BRDA will be:

0 &wine soils, l glacial till and

l limestone bedrock.

54.1 Estuarine

The recent estuarine soils will be found extensively along the western flank of the facility, adjacent to the glacial till ridge found in the central and southern flank of the footprint and along the reclaimed Poulaweala Creek. The depth of the estuarine within the. footprint of the embankment wall will vary fkom absent to about 7.2m. They are typically encountered below an elevation of 1 .SmAMSL.

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The estuarine soils are generally clays and silts of low to intermediate plasticity with rare bands of compressed peat. The laboratory permeability values generally vary between lE- lOm/s and lE-7m/s but higher values were obtained from the in situ tests, presumably because of the bedded nature of the estuarine soils and the possibility of more permeable bands encountered in the test zone. Typical ranges between 5E-9m/s and 5E-6m/s were measured. For analysis, a range between lE-7m/sec and lE-8m/sec has been used in the analyses. The estuarine deposits show evidence of desiccation to a depth of about 3m.

Groundwater within the estuarine soils will fluctuate during the seasons but can be expected to be within lm of the surface. There is an ongoing monitoring programme recording the groundwater fluctuations in the estuarine soils.

5.4.2 Glacial Till

The glacial till is found underlying the estuarine soils and also out cropping on surface within the footprint of the BRDA. It is generally outcrops above an elevation of 1 .SmAMSL.

The glacial till is primarily a sandy gravely clay to silty sandy gravely clay constituting some 90% of the volume. The clay content of the glacial till typically varies between 8% and 10% and the material is classified as a clay of low plasticity.

There are minor amounts of more gravely glacial till and more clayey material with the latter generally found directly beneath the topsoil. The more granular material can be expected at depth as bedrock is encountered although it can occur as lenses throughout the glacial till. Limestone cobbles and boulders were encountered and the quantity of the cobbles and boulders varied and estimated at between 5% and 10% of total volume based on visual inspection. ’ It can be expected that the permeability of the glacial till will be highly variable.

The laboratory permeabilities carried out on recompacted glacial till indicated values between 2.2E-9m/sec to 4.7E-lOm/sec with all but one test being greater than 9E-lOm/sec. Previous work indicates the permeability of the in situ glacial till measured in the laboratory generally ranging from 5.5E-9m/sec to 3.2E-llmsec from 12 results. Two results indicated a permeability of 5.1E-6m/sec and 4.lE-6m/sec.

In situ permeability tests carried out in the glacial till (Reference 8) gave values between 2.5E-6m/sec to 3.9E-9msecglacial till. A recent test (Reference 9) gave an insitn permeability for the glacial till of 9.3E-7m/sec. Based on the available data, the in situ permeability of the glacial till is likely to range from lE-6m/sec to lE-9m/sec.

5.4.3 Limestone Bedrock

The bedrock encountered on the site is the Waulsortian Limestone, which is part of the Lower Carboniferous Limestone Group. The limestone is found beneath the glacial till but

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also found extensively out cropping to the east of the Phase 2 BDRA where it forms the high ground up to an elevation of approximately 12mAMSL. The limestone is near the top of the Waulsortian (Reference 10). It occurs on the limb of the Shannon Anticline, a broad fold formed as a result of the Hercynian mountain building phase, which plunges gently west- south west along the Shannon Estuary. The limestone generally is massive, grey, crystalline with bedding dipping in the range of 5 degrees to 30 degrees. The limestone is fractured with the main trends NNE-SSW and WNW-ESE.

The Waulsortian Limestone in Ireland, typically weathers along fractures and joints which then tend to be inlilled with the weathered debris. These structures are typically termed palaeokarstic features. The permeability of the limestone is a function of the number, size, infilling and continuity of the discontinuities and palaeokarstic features. Without any structural discontinuities, the limestone has a very low permeability. This was shown by the detailed hydrogeological study (Reference 11) carried out in the eastern part of the Aughinish Island where the plant is sited. Seven of the eighteen boreholes drilled were dry and one of the dry boreholes was within 3m of a borehole with one of the maximum yields.

Recovery tests carried out on the groundwater observation wells (Reference 6) indicate permeability of the limestone ranging from 8.OE-6m/sec to l.lE-9m/sec. Additional studies (Reference 9) indicate permeability values of 1.9E-5rn/sec and 3.3E-6m/sec for the fractured limestone.

The permeability for the fractured limestone has been taken as between lE-5m/sec and lE- 7ndsec for analyses.

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6.0 SEISMICITY

The seismicity of Ireland is very low, particularly in the western part of the country and virtually the whole of Ireland is practically free of earthquakes (Reference 12). The last reported earthquake was in Wicklow on 28* April 1992 with a magnitude of 1.4 which is a very small event.

The design criteria for the site has been evaluated using seismic data of the region to derive the Design Base Earthquake (OBE) and the Maximum Credible Earthquake (MCE). These are equated to a peak ground acceleration (PGA) for the site. This procedure follows international guidelines as set out by the International Commission on Large Dams (ICOLD) (Referencel3). The DBE equates to an earthquake event that usually has a return period equal to the life of the facility (25 years) and when occurring will not affect the performance of the structure. The MCE has a return period of some 10,000 years and when occurring will not cause total failure of the embankment wall but will result in severe damage i.e slumping of the crest. The MCE is particularly applicable to the long term situation such as the close out phase of the facility.

It should be noted that, unlike a water retaining dam or conventional upstream raised tailings dam, the BRDA does not retain any water other than which is retained in the perimeter interceptor channel and storm water pond. The volume of water contained by these structures is relatively small and typically less than 350,000m3 and the embankment walls are less than 5m in height.

Generally, an earthquake has the potential to liquefy the tailings materials (i.e. catastrophic loss of strength induced by rapid shaking) or cause settlement of the dam crest resulting in a reduction in freeboard and overtopping of the dam.

Based on the laboratory data (Reference 3), the red mud is not prone to liquefaction particularly at the very low PGA anticipated. Also, settlement of the stack wall of the BRDA would not result in any release of water.

The DBE has been taken as 0.03g which is very low and would have little or no effect on any of the structures constructed. The MCE has been taken as 0.06g and has been used to determine potential crest settlement in the long term of the storm water pond and perimeter interceptor channel. The MCE has been used in the long term stability analysis as a horizontal force acting on the stack wall of the BRDA. This is termed the pseudo static method of stability analysis and is a very conservative approach.

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7.0 PHASE 2 BAUXITE RESIDUE DISPOSAL AREA DESIGN

7.1 General

The design of the Phase 2 BRDA will be based on the design criteria developed for the construction and raising of the Phase 1 and Phase 1 Extension with some modifications based on the ongoing performance of these facilities. The key components of the Phase 2 BRDA are;

0 Low Permeability Outer Perimeter Embankment Wall

l Permeable Inner Perimeter Embankment Wall

l Perimeter Interceptor Channel

l Composite Lined System Throughout

l Stage Raises

l Upper Level Interceptor Channel

In addition, the storm water pond and liquid waste pond will be raised to accommodate runoff from both Phases 1 and 2 and a new flood tidal defence berm will be constructed to replace the existing section which is within the footprint of the facility.

The new Phase 2 BRDA will be completely composite lined and surrounded by a perimeter interceptor channel which is formed by constructing the outer and inner perimeter embankment walls. The channel will connect to the Phase 1 perimeter interceptor channel on the western section. The two facilities will also be connected and the outline of Phase 2 is presented in Figure 7.1 and combined with Phase 1 in Figure 7.2.

The ground level within the footprint of the TMF varies from OmAMSL to 16mAMSL and therefore the perimeter interceptor channel, the inner and out perimeter embankment walls and future raising of the stack walls will need to accommodate these changes of elevation.

General sections through the proposed Phase 2 BRDA showing the outer and inner perimeter embankment walls with some initial stack raises are presented in Figure 7.3. A section showing all ten raises from the inner perimeter embankment wall is presented in Figure 7.4.

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03511318.5 11

7.2 Outer Perimeter Embankment Wall.

This structure forms the outer wall of the perimeter interceptor channel and is the main access road around the facility and is designed with a crest width of 5m. Details of the structures are present on Figure 7.5 and are described below.

The upstream and downstream sides slopes vary depending on the foundation materials the structure is placed on. On the weaker foundation materials, which are likely to be encountered on the mud flats, the side slope will be 4H:lV. The strength of the foundation materials beneath the embankment wall on the mud flats will be investigated prior to the detailed design The structure founded on the estuarine soils and glacial tills on dry land will be constructed with upstream and downstream side slopes of 3H:lV. These will be found on the southern and western flanks. In all these cases the crest elevation is at 5mAMSL.

Along the central section of the southern flank, the outer perimeter interceptor embankment wall is constructed in cut with a side slope of 3H:lV and a crest elevation of 5mAMSL (Figure 7.5).

On the eastern flank, the ground rises and the foundation material is likely to be on bedrock or glacial till. The sides slopes of the structure have been steepened to reflect these stronger foundation materials to 2H:lV. The exception is where the embankment wall crosses the backfilled Poulaweala Creek. At this locality, the current ground elevation is 2mAMSL. It may be necessary to remove any unsuitable soft foundation material which formed the base of the creek, reinforce the foundations or reduce the side slopes. The strength of the foundations materials beneath the causeway will be investigated prior to the detailed design.

On the eastern flank the crest level of the outer perimeter embankment wall rises from 5mAMSL to 8mAMSL, from 8mAMSL to 1OmAMSL and from 1OmAMSL to 16mAMSL at ’ which elevation it connects to the access road of the Phase 1 extension. At 16rnAMSL it also forms the outer wall of the upper interceptor channel (Figure 7.6). The outer perimeter embankment wall cuts across the unsuitable stockpile area prior to connecting with the access road of the Phase 1 extension. The unsuitable material forming the stockpile will be removed from this area and depending on the quality could be used for restoration, landscaping or backfilling drainage ditches. Some trial pitting will be undertaken in this area to determine the thickness and quality of the unsuitable materials.

The change in elevation of the outer perimeter embankment walls will be accommodated by a series of ramps at maximum side slopes of 6H: 1V.

The construction detail of the outer perimeter embankment wall on he eastern flank is similar to the structure proposed on the southern and western sides. Where the crest elevation is at SmAMSL, water may be against the upstream face. In these cases, the composite lining on the upstream face will consist of a minimum of lm thick of processed glacial till (4m

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horizontal width) underlying 2mm smooth HDPE geomembrane (Figure 7.5). The surface of the processed glacial till will be prepared prior to placement of the geomembrane. Previously, the stones have been hand picked. This is an option provided the hollows created by the removal of stones greater than 19mm are filled with a 10% bentonite sand mix.

Alternatively, where stones are exposed, the glacial till could be covered by geosynthetic clay liner (GCL). The bulk of the structure will consist of random rockfill. To prevent migration of fines from the glacial till into the rockfill, a filter consisting of Ten-am 2000 over a 500mm thick processed rockfill will be designed for. The grading of the processed rock will be dependent on the general grading of the rockfill but is generally equivalent to a well graded sand and gravel with a maximum particle size of 60mm.

It is preferable to avoid a composite lining consisting only of GCL directly beneath a geomembrane containing water which is subject to wind action and possible damage by operators/plant. If the membrane is damaged, wave action can wash out the bentonite from the GCL. The wave action can then migrate to behind the geomembrane lifting it off from the upstream face.

The 2mm geomembrane would require a permanent surcharge load to prevent wind uplift as previously undertaken for Phase 1.

The embankment footprint for the processed rockfill and random rockfill zones will be placed on Terram 2000 when founded on the estuarine on dry land. On the mud flats, further reinforcing of the surface foundations may be required under the full width of the embankment wall using a material such as a Tensar geogrid. These details will be finalised during the detailed design and after the completion of the site investigation in the mud flat area.

During construction, pore pressures induced in the estuarine foundation soils will be monitored to ensure these materials are not over stressed as discussed in Sections 7.12 and 11.3.

A similar design is applicable to the outer perimeter walls at crest elevations above 5.OmAMSL (Figure 7.5). However, there is the possibility of replacing the processed glacial till forming the upstream face with a GCL placed on Terram 2000 over processed rockfill. The gradient of the invert level of the perimeter interceptor channel along these sections will prevent build up of standing water in the channel.

It may be necessary to raise the crest elevation of the outer perimeter wall above the current design level of SmAMSL, as discussed in section 7.8, in order that the structure can act as a flood tidal defence berm. The downstream slope will also require protection from wave erosion if the existing flood tidal defence berm fails.. The erosion protection will comprise

interlocking gabion mattresses and the design will be finalised during the detailed design phase.

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7.3 Inner Perimeter Embankment Wall

This structure forms the inner wall of the perimeter interceptor channel and is designed with a crest width of either 4m or 8m. The wider crest is to support the mud distribution pipe and water supply pipe for the sprinkler system on the eastern and southern sectors. Details of the structures are present on Figure 7.5 and are described below.

The upstream and downstream sides slopes vary depending on the foundation materials the structure is placed on. The structure founded on the estuarine soils and glacial tills on dry land will be constructed with upstream and downstream side slopes of 2H:lV. These structures are located on the southern and western flanks. For these cases, the crest elevation is at 4 5mAMSL. ’

Along the central section of the southern flank, the inner perimeter interceptor embankment wall is constructed in a cut. and will be founded on glacial till or bedrock. In this area, the side slopes are constructed at 2H: 1V in order to align with the two embankments constructed on the estuarine soils either side of the cut.

On the eastern flank, the ground rises and the foundation material is likely to be weathered bedrock. The sides slopes of the structure have been steepened to reflect the stronger foundation materials to 3H:2V.

Where the inner perimeter embankment wall runs parallel to the main plant side access road (causeway), the ground elevation drops to about 2mAMSL at the backfilled Poulaweala Creek. Rather than construct the inner perimeter wall on the natural ground which would mean an 8m high embankment wall, it is proposed to construct it on the red mud once it has reached an elevation of 8mAMSL (Figure 7.3).

On the eastern flank, the crest level of the inner perimeter embankment wall rises from 4.5mAMSL to 8mAMSL and from 8mAMSL to 1OmAMSL. A section will be built to 16mAMSL which will connect to the inner perimeter embankment wall of the Phase 1 extension and form the upper level interceptor channel (Figure 7.6). The change in elevation will be accommodated by a series of ramps.

The construction detail of the inner perimeter embankment walls is similar. They are constructed from random rockfill placed on a minimum thickness of 3OOmm of processed rockfill overlying a 1OOOgrm geotextile which overlies 2mm thick rough faced HDPE which in turn overlies lm thick layer of processed glacial till. The processed glacial till will either be stone picked or GCL placed over the glacial till prior to receiving the geomembrane. A series of cylinder tests would be undertaken to determine the most suitable weight of geotextile to receive the processed rocktill.

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A filtering system will be required upstream of the rockfill to prevent the migration of particles of red mud due to water erosion. The filter system is required to retain the fine mud particles but have sufficient permeability to allow the passage of water. The initial design work incorporated a granular filter system although this has not been constructed during later stages of the stack wall construction. The filter system would be either constructed from a combination of processed rocktill and sand or processed rockfill and a geotextile such as Terram 2000. A series of trials will be undertaken on Phase 1 to optimise the method and material types to be employed. In the past, the process sand as a filter has been prone to slumping and wind erosion unless protected. Slumping was particularly prevalent in areas where water could temporarily pond as observed in the corners of the facility or behind the disused sludge pond. The sand would have to be protected with a layer of processed rockfill. Geotextiles tend to clog with the fine red mud more readily than natural materials.

If a geotextile is used it would be fixed at the crest beneath the 200mm access road capping and on the base by sand bags. To prevent damage through wind action, processed rockfill would be selectively placed over the geotextile.

During construction, pore pressures induced in the estuarine foundation soils will be monitored to ensure these materials are not over stressed as discussed in Sections 7.12 and 11.3.

A similar design is applicable for the inner perimeter walls at crest elevations above the 4.5mAMSL. The exception is where it is constructed on red mud and follows the design section for the raise which is discussed later, and where it joins the inner perimeter wall of the Phase 1 extension. At the connector point (Figure 7.6) it will be necessary to cut through the existing perimeter access road of the Phase 1 extension.

7.4 Perimeter Interceptor Channel

The perimeter interceptor channel collects all the runoff from the stack walls and seepage

R~rn the red mud, It is Rxm~d by the constmctiion of the outu aul inner perimeter embankment walls which are discussed above.

For much of its length and for all the western and southern flanks, the perimeter interceptor channel has a top width of 25m and a minimum base width of 4m. Along the southern and western flanks the invert level falls from approximately 1 .SmAMSL to 1 .OmAMSL.

The base of the interceptor channel is composite lined with a working top surface and the sequence is listed below:

Concrete Working Surface 1 OOmm thick

1 OOOgrms geotextile

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Smooth 2mm HDPE 2mm thick

Processed Glacial Till .Minimum 1OOOmm thick on the side slopes and 3OOmm thick at the base.

Geosynthetic Clay Liner GCL 1omm

The concrete working surface will be installed at the base of the southern and western sections of the perimeter interceptor channel to allow machine access. The concrete lining will extend to a height of lm on the upstream side of the lined section of the outer perimeter dam wall. This is to protect the lining from machine damage during de-sludging of the channel. The problems of accumulating red mud sediment in the base of the perimeter interceptor channel observed in Phase 1 will virtually be eliminated by installing a filter system on the upstream face of the stack raises. The concrete working surface has been used for the interceptor channel for the Phase 1 extension. In the detailed design phase, alternative working surfaces will be considered. A layer of 1OOOgrms geotextile is placed above the geomembrane to prevent the concrete damaging the 2mm HDPE on the base, on the toe of the upstream slope of the outer perimeter embankment wall and the toe of the downstream slope of the inner perimeter embankment wall.

The thickness of the processed glacial till will be a minimum of 300mm and underlain by the GCL which is keyed into the processed clay of the inner and outer perimeter embankment walls. This detail, while somewhat inconvenient to construct, allows the minimum thickness of construction material to achieve the design invert levels. To increase the thickness of processed glacial till to lm may require the removal of the desiccated estuarine crust and the exposure of softer and possible wetter material. For the reasons stated before, it is recommended to avoid where possible forming a composite’ lining by placing the GCL directly beneath the geomembrane where water is to be stored in the long term. However, it is less problematic at the base where there would be a continuous coverage of water or sediment.

The surface of the processed glacial till will be prepared prior to placement of the geomembrane. For the Phase 1 extension, the stones were hand picked. This is an option

’ provided the hollows created by the removal of stones greater than 19mm are filled with a 10% bentonite sand mix. Alternatively, where stones are exposed, the glacial till could be covered by a layer of GCL.

Where the Phase 2 perimeter interceptor channel connects to the Phase 1 perimeter interceptor channel, there is a difference in invert elevation of about 0.9m. The invert level of the Phase 1 perimeter interceptor channel is about 1.9mAMSL. It is preferable to connect the two interceptor channels by culverts and it is proposed to install four 600mm diameter HDPE.pipes at an invert elevation of 2.OmAMSL to allow the passage of the effluent water. Because the invert elevation is high at this point in the Phase 1 perimeter interceptor channel,

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it is possible to keep the base dry during construction. However, two coffer dams will be constructed in the Phase 1 perimeter interceptor channel to allow for the installation of the culverts and for connecting the linings. Some trials will be undertaken involving welding 2mm HDPE to the existing lining of the Phase 1 perimeter interceptor channel. Previous construction work has indicated that welding new to old geomembrane is achievable. Pumping will be required to empty the Phase 2 perimeter interceptor channel for maintenance.

On the eastern flank, the perimeter interceptor channel collects the runoff and seepage water from the eastern sector of the BDRA. This is directed to the south via a system of 600 mm diameter culverts prior to discharging into perimeter interceptor channel constructed along the southern flank (Figure 7.7).

Along the eastern flank and parallel to the main plant access road, the perimeter interceptor channel will not be in operation until much later and once the red mud is built up to an elevation of 8mAMSL.

Finally, where the Phase 2 meets the Phase 1 extension at the north east comer, the perimeter channel formed at a crest elevation of 16mAMSL (Figure7.6), takes water from the upper interceptor channel of Phase 2 to the Phase 1 extension.

A longitudinal profile of the perimeter interceptor channel is presented on Figure 7.8. An emergency spillway will be installed to discharge excess flood water from a storm event exceeding the design 1 in 200 year event. The water would be spilled via a spillway constructed on the outer perimeter wall at an invert level of 4.5m AMSL. The contaminant water will spill into a holding area between the outer perimeter embankment wall and the flood tidal defence berm. The storage capacity is approximately 20,000m3. The details will be confirmed during the detailed design phase.

7.5 Composite Lining

The sections above have dealt with the composite lining incorporated in the outer and inner perimeter embankment walls and the perimeter interceptor channel.

The largest area to be composite lined is the basin area of the BRDA. This will cover an area of nearly 65Ha. There is insufficient glacial till to form a lm thick lining underneath the proposed 1.5mm HDPE geomembrane. The alternative is to use the GCL to form the second lining or a combination of bentonite and sand to form BES (bentonite enriched soil) which would be compacted like a conventional soil to form a 3OOmm layer. Unless sand is readily available and relatively cheap, it tends to be more expensive than GCL. It is proposed to use GCL. The composite system using HDPE on top of GCL was used on some sections of the

Phase 1 extension.

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A combination of smooth 2mm HDPE over GCL and 3OOmm of processed glacial till will be used to form a composite lining on top of the downstream slope of the Phase 1 and Phase 1 extension embankment walls. This is shown on Figure 7.5. The surface of the processed glacial till will be prepared prior to placement of the geomembrane. Previously, the stones have been hand picked. This is an option provided the hollows created by the removal of stones greater than 19mm are filled with a 10% bentonite sand mix. Alternatively, where stones are exposed, the glacial till could be covered by GCL.

Approximately a third of the Phase 2 BRDA footprint encroaches on Glenbane West. Of this area, there is approximately 7Ha where the seepage could migrate away from the BRDA and further inland on Glenbane West. In this area, a double composite lining is being considered.. The double composite lining system will consist of two composite linings of 2mm HDPE underlain by GCL with a drainage blanket in between. Any leakage through the upper composite lining system would be collected in a 500mm thick drainage blanket above the lower composite lining system and pumped to the perimeter interceptor channel. This is a very conservative approach and during the detailed design phase additional site work, topographical survey work and detailed contaminant modelling will be undertaken to determine whether the double composite lining system is required and its lateral extent. The majority of seepage from the Phase 2 BRDA located on Glenbane West will migrate towards the Poulaweala Creek underneath the facility and will be buffered by the saline ground water.

7.6 Stack raise

The method of raising the stack wall retaining the red mud is by the upstream method which involves founding on previously deposited red mud. The red mud is allowed to mature for as long as possible (approximately 3 months) prior to placing the next layer. The success of this method of stack raising is very much dependent on the design of the facility and its ongoing performance. The performance of the facility, which is compared to the design criteria, is determine from a comprehensive geotechnical monitoring system within the stack wall together with an intrusive site investigation carried out prior to any &ure raising.

The original design of the Phase 1 BRDA was based on the undrained shear strength of the red mud and the effective strength parameters of the underlying estuarine deposits. Based on an assumed average undrained shear strength of 30kPa for the red mud, the height of the mud stack wall could be raised to an elevation of 18mAMSL (Stage 7) at a slope of 6H:lV (9.5 degrees) with a resultant factor of safety of 1.3. The recommendation from the designer was that the undrained shear strength of the red mud should be monitored and compared against the design criteria. A site investigation was undertaken in 2002 (Reference 14) and 2004 (Reference 3) to determine the undrained shear strength of the red mud using in situ vane equipment and continuous cone penetration testing.

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Using the lower bound undrained shear strength values obtained from beneath the stack wall of Phase 1, a factor of safety of 1.4 was obtained for Stage 4 and 1.3 for Stage 5. The factor

of safety further reduced to 1.2 for Stage 6 and 1.1 for Stage 7.

The factor of safety for Stages 6 and 7 are low and as a consequence, the proposed scheme for raising the wall involves reducing the overall slope by incorporating an upper level interceptor channel some 20m wide at Stage 6 (elv.lGmAMSL). In addition, it is proposed to strengthen the red mud where required beneath the stack walls by installing a reinforcing geotextile. This would allow the facility to be raised to Stage 10 at an elevation of

24mAMSL and a central discharge elevation of 32mAMSL (Figure 7.9) The technical issues relating to the raising are presented in the Phase 1 Preliminary Design Report (Reference 15) The performance of the Phase 1 BRDA will be continuously monitored throughout its life and an intrusive investigation will be undertaken after each raise to assess the strength gains in the red mud and compared to previous years and the design criteria. The outcomes from the monitoring of Phase 1 BRDA will be used to form the basis of the design for raising the Phase 2 BRDA.

The stack wall raises will be constructed of random quarried rockfill placed either on approximately 600mm layer of process sand (minimum required to support the dump trucks) or Terram 2000. The sand is primarily used in low spots but also, as with the Terram, prevents the imported rockfill punching through the red mud. The rockfill side slopes for each stage are designed at 3H:2V (Figure 7.4).

A filtering system will be required upstream of the rockfill embankment walls to prevent the migration of particles of red mud due to water erosion. The filter system is required to retain the fine mud particles but have sufficient permeability to allow the passage of water. The initial design work for the starter dam (inner perimeter dam wall) incorporated a granular filter system although this design feature was not included during later stage raises of the stack wall construction. The filter system would be either constructed from a combination of processed rockfill and sand or processed rockfill and a geotextile such as Ten-am 2000. A

series of~~arialswillbeundertakento optimisethemethod andmaterialtypestobe employed. In the past, the process sand as a filter has been prone to slumping and wind erosion unless protected. Slumping was particularly prevalent in areas where water could temporarily pond as observed in the comers of the facility or behind the disused sludge pond. The sand would have to be protected with a layer Of processed rockfill. Geotextiles tend to clog with the fine red mud more readily than natural materials.

The visual impact of the facility can be improved by dressing the rockfill slopes and adjacent benches, that form the stack wall, with a combination of granular material, topsoil grass and shrubs. Initially, these materials would cover the lower slopes and benches between Stages 1 and 6, after completion of the upper level interceptor channel. To improve the immediate visual impact of the stack wall on the south and south east sectors, these will be landscaped

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as the walls are raised. These aspects are discussed in the closure plan update of the BRDA (Reference 16).

7.7 Upper Level Interceptor Channel

The upper level interceptor channel is installed when the stack wall is raised to an elevation of 16mAMSL (Stage 6) and the red mud is at a maximum elevation of 14mAMSL. The width of the channel is 20m at the top and 14m at the base and the depth is 2m (Figure 7.4).

The channel collects surface runoff from the exposed red mud at a high elevation rather than allowing the water to cascade and erode its way down to the perimeter interceptor channel. ‘It also allows the downstream slopes of the first 5 stage raises to be rehabilitated.

The outer perimeter Stage 6 stack wall of the interceptor channel is lined with a 2mm HDPE rough geomembrane overlying Terram 2000 which overlies processed rockfill. The bulk of the fill forming the wall is random rockfill overlying process sand or directly on the red mud with Terram 2000 separating the two materials.

The HDPE geomembrane extends along the base of the channel to the downstream toe of the inner perimeter Stage 6 stack wall and is conventionally anchored into the red mud. The geomembrane is protected from the random rockfill by a minimum thickness of 500mm of process sand from the AAL plant or a combination of 1OOOgrrn geotextile and 300mm processed rockfill.

The Phase 2 upper level interceptor channel connects with the Phase 1 upper level interceptor channel at two localities. On the western flank, the transition is relatively straightforward. On the eastern flank (Figure 7.6), the Phase 2 inner wall of the upper level interceptor channel will have to be built to an elevation of 16mAMSL and connect with the inner wall of Phase 1 at Stage 6.

The Phase 2 upper level interceptor channel during normal operations stores only a limited volume of water. It is designed to discharge, from various points along its alignment (Figure 7.7) into the perimeter interceptor channel below and also connects with the upper interceptor channel of Phase 1 in two localities by a series of 4x 600mm culvert pipes. At three locations, a 500mm diameter HDPE decant pipe is to be installed near the base of the upper interceptor channel for Phase 2 (Figure 7.10). A similar arrangement is proposed for Phase 1. At one of the locations of the decant pipe, a small spillway 500mm x 2000mm at an elevation of 15.5mAMSL will be installed. The Phase 1 upper interceptor channel also has a number of discharge points along its alignment and has two ends which discharge water by a series of 600mm decant culverts into a lined channel adjacent to the eastern ridge road (Figure 7.6). One of the ends is at an elevation of 15mAMSL and acts as the main spillway for the upper interceptor channel.

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The filter system on the upstream wall of each raise, including and above Stage 6, will reduce the solids entering the upper level interceptor channel and desludging should not be normally required. However, if very wet material is discharged due to problems in the plant and the red mud level is close to the crest level, over topping could occur. The red mud deposited would eventually be washed into the channel. This could be removed readily by high pressure water washing and the slurry discharged down one of the decant pipes or culvert forming the northern outlet or the open end forming the southern outlet.

7.8 Flood Tidal Defence Berm

The Island of Aughinish is protected from flooding from the Shannon River by a flood tidal defence berm (FTDB). The design elevation for the FTDB as provided by the Office of Public Works (OPW) varies from a maximum height along the Shannon and mouth of the Robertstown River of 27 feet Poolbeg (approximately 5.56mAMSL), reducing to 25 feet (4.95mAMSL) and then 24 feet (4.65m) along the Robertstown River. The slope of the FTDB also varies with location and height as tabulated below.

Crest Elevation mAMSL 5.56 4.95

Seaward Slope 2.5H:lV 2.OH: IV

Landward Slope 3H: 1V

2.5H: 1V 4.65 1.5H:lV 2H:lV

Stone pitching has been observed along certain sections of the seaward slope of the FTDB and based on information provided by the OPW, these are constructed to an elevation of approximately 1.86mAMSL to prevent wave erosion.

The EPA have recommended that the structure should accommodate a 1 in 200 year

storm/flood event (UKEnvironmental Agency Standard) and consideration shouldbe given to rises in sea level as a consequence of global warming. The detailed design phase of the study will evaluate the height of the flood tidal defence berm for various return periods.

The existing FTDB structures along the Robertstown River range from elevations approximately between 3.25mAMSL and 4.5mAMSL and over the years, have settled both uniformly and differentially. The crest of the FTDB is typically between 2m and 3m wide. The FTDB was constructed from locally sourced mud flat deposits and estuarine soils borrowed immediately in front of the FTDB using a drag line. Thus, the structure is prone to consolidation settlement of the foundation soils and self settlement of the construction fill.

The south west footprint of the Phase 2 BRDA will encroach on the existing FTDB and this will have to be replaced. The design of new FTDB will only be finalised after the completion

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of the geotechnical site investigation of the mud flats and underlying estuarine soils and the study on height of protection required to accommodate at least the 1 in 200 year event. The location of the new section of the FTDB is shown on Figure 7.1.

A section through the proposed FTDB embankment wall is presented in Figure 7.11. The upstream and downstream side slopes are designed with an overall slope of 4H:lV to accommodate the potentially soft estuarine deposits forming the mud flats. The crest elevation is designed at 5.OmAMSL.

The sea ward slope incorporates a stepped gabion mattress to an elevation of 2mAMSL to prevent toe erosion from the water. The remaining platform base of the embankment wall will be constructed with random rockfill with a central processed glacial till core protected by filters of processed rockfill. This initial platform will be constructed to an elevation of 2mAMSL and be used to provide access for the placement of the upstream gabions. A 3OOmm layer of processed rocktill followed by Terram 2000 Would be placed prior to placing the glacial till to complete the embankment wall.

The gabion mattress, random rockfill and processed glacial till would be placed on a geogrid overlain by Ten-am 2000 subject to the results of the site investigation. The Terram 2000 will prevent the rockfill Corn punching through the very soft foundation materials.

The existing flood tidal defence berm has a flap valve incorporated into the structure to allow surface runoff water to be discharged into the Robertstown River. Because of the limited catchment area remaining after the Phase 2 BRDA is in operation and the need to have an emergency discharge area at this point, it is proposed that no valve is installed and discharge is prevented into the Robertstown River.

The responsibility for maintaining the FTDB adjacent to Phase 1 BRDA is AAL’s. AAL will also be responsible for the maintenance of the FTDB adjacent to Phase 2 BRDA once construction commences. The current condition of the existing FTDB will not meet the design criteria proposed for the new FTDB. Therefore, to protect the outer perimeter wall of the BRDA for both Phases 1 and 2, either the existing FTDB is strengthen and raised or the outer perimeter wall is used as a secondary defence and protected by gabion mattresses. The optimum solution is to protect the outer perimeter wall. This will be finalised at the detailed design phase.

7.9 Disposal Capacity, Life and Rate of Rise of the Red Mud.

The storage capacity of the Phase 2 BRDA, together with the life and rate of rise are tabulated below for a red mud disposal volume of 1 ,000,000m3 per annum;

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Phase 2 Elevation Area Act. Volume Life mAMSL (Ha) Mm3 (yeas) 4.5 58 1.44 1.4 6.0 65 2.74 2.7 8.0 69 4.11 4.1 10.0 72 5.56 5.6

Starter Dam

Stage 1 Stage 2

Stage 3 Staee 4 12.0 I 70 1 6.95 I 7.0 Stage 5 14.0 68 8.31 8.3 Stane 6 16.0 62 9.55 9.6 Stage 7 18.0 61 10.78 10.8 Stage 8 20.0 59 11.94 11.9 Starre 9 22.0 I 57 1 13.08 I 13.1 1756 I

24.0 1 55 ) 14.18 1 14.2 1858 1 Stage 10

The life of 14.2 years is from the commencement of discharge of red mud into Stage 8 of the Phase 1 BDRA and subject to the performance of the structure during its life.

These values relate to all the red mud being discharged into Phase 2 BRDA. The rate of rising could be reduced if some of the red mud was discharged into the Phase 1 facility.

If the red mud disposal to the Phase 2 BDRA is restricted to 8 16,000m3 per annum, with the remainder (184,OOOms) being discharged to the Phase 1 BDRA from Stage 8 onwards, the rate of rising will decrease. The changes in the rate of rising and life of facility are tabulated below.

I

I Starter Dam

Rate of Rise

(years) 1.4

(mm/yr) 1429

Stage 1

Stage 2 E Stage Stage 4

Stage 5

3.4 1 1258

5.1 I 1184 Stage 7 1 13.2 I 1340

10.2 1 1198

The life of 17.4 years is from the commencement of discharge of red mud into Stage 8 of the Phase 1 BDRA and subject to the performance of the structure during its life..

7.10 Construction Materials and Quantities

The sections through the embankment walls are presented in cross section in Figures 7.3 and 7.5.

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The provisional quantities of the main construction materials are given below: It excludes any materials associated with subsequent raises.

1000grms 5oogrms

Geogrid GCL Tarmac Access Road

m2 50,000

m2 10,000 m2 15,000 m2 720,000 m2 16,000

Based on the above table, the fill volumes for construction of the embankment walls are relatively small.

A total of some 125,000m3 of processed glacial till and 125,OOOm3 of non processed glacial till will be required for construction. Based on the borrow assessment it is likely that more glacial material will be required from the borrow areas immediately to the north and south of the railway line.

7.11 Storm Water Pond Raising

The current crest elevation of the storm water pond (SWP) is 4.7mAMSL on the external wall with the Bird Sanctuary, the internal dividing wall between the SWP and the Liquid Waste Pond (LWP) and between the SWP and central access ramp. The internal wall between the SWP and the PIC is at an elevation of 3.85m. A plan of the SWP is presented on Figure 7.12.

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The current storage of the SWP needs to be increased as outlined in Section 10. It will be necessary to raise the crest level to an elevation of 6.OmAMSL which could be achieved by a combination of steepening the existing embankment side slopes and with gabions. The raising of the SWP will have to be carried out with both the PIC and the LWP in operation. These sides will be raised using gabions. However, the level in the PIC will be maintained as low as possible. Details of the scheme are presented in Figure 7.13.

The side slopes on the upstream side of the SWP and the downstream side of the dividing wall with the bird sanctuary could be steepened from 4H: 1V to 2.5H: lV, provided the rate of construction is controlled by monitoring pore water pressure development in the foundation estuarine soils. The fill used for construction would be glacial till which would need to be keyed into the existing embankment wall.

Depending on the condition of the existing gabions they could be reused in construction.

The residual effluent water will be removed from the SWP by pumping and either discharged directly into the plant effluent treatment system or into the completed Phase 2 BRDA. The discharged effluent water will migrate to the low area of the Phase 2 BRDA which is the south western sector of the Poulaweala Creek The basin of the SWP would be cleaned of all sediment. The sediment would be placed into geotextile bags to dewater and placed on the BRDA of either Phase 1 or Phase 2. The existing lining system would be removed and buried in Phase 1. The raising operation and relining will be challenging and the operation will require considerable careful planning and coordination. There is a strong possibility of leakage from either the adjacent PIC and the LWP and therefore the operation will require a comprehensive health and safety risk assessment. Considerable softening of the estuarine soils could have occurred within the basin area of the SWP and the extent will only be evaluated once the construction phase starts.

The water level in the PIC will be reduced to as low as possible by pumping it into the completed Phase 2. The water level in the LWP should be dropped as far as practically

pos'sible KI reQncc any sxpage into the excavation of the SW!, The conmuim work should be undertaken in the summer.

The SWP would be composite lined with combination of GCL and processed glacial till on the side slopes overlain by 2mm HDPE. The surface of the processed glacial till will be prepared prior to placement of the geomembrane. For the Phase 1 extension, the stones were hand picked. This is an option provided the hollows created by the removal of stones greater than 19mm are filled with a 10% bentonite sand mix. Alternatively, where stones are exposed, the glacial till could be covered by a layer of GCL.

If the floor of the basin is dry, GCL could be placed directly on a prepared floor or over a protective geotextile. However, if the basin floor shows any signs of seepage or water it would be preferable to use a lm thick layer of processed glacial till (screened at 75mm).

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Contaminant seepages from the adjacent structures (Phase 1 DRDA, PIC and LWP), if observed would have to be assessed and remediation instigated during construction. This may take the form of collecting and pumping from beneath the lining.

The quantities of earth materials required to raise the SWP are tabulated below;

Description Glacial Till

Unit m3

Quantity 14,000

Processed Glacial Till Processed Rocktill

m3 36,000 m3 1,000

Gabion Wall HDPE 2mm GCL Geotextile 1OOOgrms Road Topping Tarmac

m3 3,000 m2 70,000 m2 65,000 m2 4,000 m2 3,500

7.12 Liquid Waste Pond Raising

The current crest elevation of the liquid waste pond (LWP) is 4.7mAMSL on the external wall with the Bird Sanctuary, the internal dividing wall between the LWP and the SWP and between the LWP and central access ramp. A plan of the LWP is presented on Figure 7.12.

The current storage of the LWP is to be increased to accommodate the increase in production of red mud. AAL require the LWP to be raised to a crest elevation of 6.OmAMSL which could be achieved by a combination of steepening the existing embankment side slopes and with gabions. The raising of the LWP will have to be carried out with the facility operating which means that all upstream slopes will have to be raised by gabions. These sides will be raised using gabions. Details of the scheme are presented in Figure 7.13.

The side slopes on the downstream side of the LWP where it adjoins the bird sanctuary could be steepened from 4H:lV to 2.5H:lV, provided the rate of construction is controlled by monitoring pore water pressure development in the foundation estuarine soils. The fill used for construction would be glacial till which would need to be keyed into the existing embankment wall.

The existing lining will be extended up the natural slope although a bench would, be cut into the natural ground to provide a degree of safety to the lining crew.

The raising of the LWP will be composite lined using a combination of GCL overlain by 2mm HDPE for the gabion raise and on the natural ground.

The quantities of earth materials required to raise the LWP are tabulated below;

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Description

Processed Glacial Till Unit m3

Quantity

3.000 Processed Rockfill Gabion Wall

m3 m3 1000

HDPE 2mm GCL

mz 3500 m2 3500

Geotextile 1000grms Road Topping Tarmac

m2 1600 m2 1200

The LWP will be raised before the raising of the SWP. After the completion of the raising of the SWP, the effluent in the LWP will be temporarily stored in the SWP. This will allow inspection and repair of the existing basin lining in the LWP.

7.13 Stability

7.13.1 Outer and inner perimeter embankment walls and the flood tidal defence berm.

Stability analyses have been undertaken for the outer perimeter wall (OPW), inner perimeter wall (IPW) and the flood tidal defence berm (FTDB). Three conditions have been evaluated:

e total stress analysis reflecting the short term condition and rapid rate of construction;

. effective stress analysis with generated construction pore pressures (ru values) in the foundation estuarine soils for the short term and controlled rate of construction;

. effective stress analysis with residual zero pore pressures (ru =0) in the foundation estuarine soils to reflect the long term conditions.

The parameters used for the analyses are tabulated below.

EST O-3m 1.8 0 30 30 0 EST 3-7m 1.8 0 20 28 0 EST Mudflat O-4m 1.7 0 15 28 0

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EST Mudflat 4-8m 1.7 0 20 28 0 EST Mudflat 8-12m 1.8 0 25 26 0 Note * Short term only

The undrained shear strength of the estuarine soils beneath the mud flats have been based on the lower bound values obtained from samples tested from the boreholes drilled on dry land.

The maximum height of the outer perimeter wall (OPW) will only be 5m and the majority of the embankment will be between 3.5m and 4m high. Similarly for the inner perimeter wall, the maximum height is 4.5m with the majority of the embankment between 3m and 3.5m high. The flood tidal defence berm (FTDB) is 5.0m high.

The results of the stability analyses are tabulated below.

TOTAL STRESS ANALYSIS-SHORT TERM Embankment

OPW

Side Slopes

3H:lV

Foundation Material EST

1 4H:lV 1 EST Mud Flat Geo Grid

EFFECTIVE STRESS ANALYSIS-SHORT TERM

EST Mud Flat 1 Geo Grid

Bedrock N/A EST Mud Flat Geo Grid 0.5 1.6

ru value Factor of Safety

0.5 1.6 0.4 1.3

EFFECTIVE STRESS ANALYSIS ru = O-LONG TERM Embankment Side Slopes Foundation Foundation Factor of Safety

Material Geofabric OPW 3H:lV EST 2.0

4H:lV EST Mud Flat Geo Grid >2.0 IPW 2H: 1V EST 1.6

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FPDB

2H:lV GT 3H:2V Bedrock 4H: 1V EST Mud Flat Geo Grid

1.5 >2.0 >2.0

The results indicate that during construction, the pore pressures generated in the estuarine and glacial till foundation soils should be monitored and not allowed to exceed the ru values given in the table above. For the inner perimeter wall constructed to side slopes of 2H: IV, the ru values should not exceed 0.4 and 0.3 for the estuarine and glacial foundation soils respectively. For the shallower slopes, the ru should not exceed 0.5.

For the long term condition (ru=O), the factors of safety for all structures are adequate.

7.132 Storm water pond and liquid waste pond

Stability analyses were also undertaken on the raised storm water pond (SWP) and liquid waste pond (LWP). Three conditions have been evaluated:

l total stress analysis reflecting the short term condition and rapid rate of construction;

. effective stress analysis with generated construction pore pressures (ru values) in the foundation estuarine soils for the short term and controlled rate of construction;

. effective stress analysis with residual zero pore pressures (ru =0) in the foundation estuarine soils to reflect the long term conditions.

The parameters used for the analyses are similar to the previous table except that some improvement of the estuarine soils can be expected as a result of consolidation due to the existing walls of the SWP and LWP. The values are tabulated below.

j

GT Insitu 2.0 EST 0-4m 1.7

Shear StrengthParameters Total Stress Effective Stress

a) C a.)’ C’ 45 0 45 0 40 0 40 0 35 0 35 0 0 60 32 0

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TOTAL STRESS ANALYSIS-SHORT TERM

EFFECTIVE STRESS ANALYSIS-SHORT TERM

2.5H:lVlGabions

The results indicate that during construction, the pore pressures generated in the estuarine soils should be monitored and not allowed to exceed the ru values given in the table above.

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For the long term condition, the factor of safety for all structures are adequate.

7.14 Dusting

Dusting is proactively managed on the Phase 1 BRDA by a system of sprinklers which cover the entire exposed mud surface on approximately a 30m grid. The fixings of the sprinkler system is periodically extended as the red mud is raised. Although the red mud is very fine and forms a relatively stable crust, it is prone to dusting. Firstly, by the formation of salt crystals on the surface as the caustic soda reacts with the carbon dioxide in the atmosphere which blisters the red mud and secondly in winter time after a sharp frost which blisters the surface and in both case the agglomerated red mud particles can be picked up in a strong wind.

The process sand which forms much of the access roads on the BRDA is prone to dusting during trafficking in dry conditions and during strong winds at any period of the year. During dry conditions the haul roads are systematically wetted with bowsers.

The current system used for the Phase 1 BRDA will be adopted for Phase 2. Initially the’ base of the sprinkler points will be fixed to a steel plate on top of a minimum thickness of 0.6m of red mud protecting the HDPE geomembrane. The size and weight of the steel plate and the initial vertical height of sprinkler pipe will be finalised after field trials on Phase 1.

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03511318.511

8.0 SEEPAGE MODELLING

8.1 BRDA

With the composite lining, seepage from the base of the Phase 2 BRDA will be minimised

and will be dependent on the following key factors;

l Defects in the liner after installation,

l The permeability and thickness of the basal clay liner (glacial till/GCL),

l The hydraulic head acting across the composite liner,

l The permeability of the red mud.

Even with the most thorough quality control and quality assurance procedures carried out during the installation of the geomembrane, some defects will occur. There is a considerable amount of data on the potential number and size of holes (Reference 17) that can be expected for a competently supervised and quality assured geomembrane installation. The number of defects can be further reduced by undertaking a geophysical leak detection survey after the geomembrane has been installed.

The inner perimeter embankment wall is to be constructed on top of the protected geomembrane. Internal acess roads constructed of process sand and topped with processed aggregate and piped services will also be constructed on top of the protected membrane. Whilst the leak detection survey will be carried out before and after the installation of these structures, the increase activity on top of the geomembrane could result in some additional defects. The seepage analysis has taken this into account.

The permeability of the processed glacial clay forming the basal liner will be a minimum of 1x10-‘m/set and constructed to a thickness of l.Om. The permeability of the GCL is 1x10- “m/set and is approximately 1Omm thick. It has the equivalent property of a lm thick clay at 1x10-‘m/set. The hydraulic head acting across the liner will be controlled by the phreatic surface in the red mud which is currently 1 to 2m below surface for the Phase 1 BRDA.

Recharge to the base of the facility is controlled by the permeability of the red mud. Permeability testing on the red mud indicate values generally between 1x10-‘m/set and 1x10- ‘m/set Generally, the deposition of the red mud as paste does not lead to segregation so there should be little difference between the horizontal and vertical permeabilities. However, occasionally the red mud is discharged at lower pulp densities and some segregation does occur.

The volume of seepage that can be expected through the composite lining system for given elevations of the BRDA has been assessed. The defects in the geomembrane will be

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May 2005 - 40 -

Aughinish Alumina Ltd Version B .2

03511318.511

minimised because a detailed leak detection survey will be carried out after installation and all defects logged and repaired. The holes assumed were as follows;

No. of Holes per Ha. Defect Type Hole Size Min. Av Max. Pin Holes 0.1 to 5mm2 1 2 4 Holes 5 to 100 mm2 0 1 2 Tears 100 to 1000mm2 0 0 0.5

Because of the variability of the permeability of the red mud and the number of likely defects, the seepage emanating from the BRDA has been determined probabilistically. The method uses the Monte Carlo simulation technique to select randomly from a pre-defined range of possible input values to create parameters for use in the calculations. Repeating the

process many times gives a range of output values and enables the likelihood of the estimated output levels being achieved. For presentation, the 90%, 50% and 10% probability of occurrence are reported in the text. The 90% probability means that there is a 90% probability that the seepage value will be exceeded. The 10% probability means that there is a 10% probability that the seepage value will be exceeded. The 50% probability is the likely seepage value.

The seepages through the base of the composite lining system for the Phase 2 BRDA at various Stages are tabulated below.

Stage Stack Elv.mAMSL Seepage m?day 90% 50% 10%

1 6 5 15 40 4 12 10 40 95 7 18 20 70 175

10 24 30 90 225

The volume of seepages tabulated above are relatively low and reflect the composite characteristics of the GCL and a quality installed HDPE geomembrane. The seepage

volumes increase slowly as the BRDA is raised due to the increase in hydraulic gradient across the composite lining.

Further analysis was carried out on the section of the Phase 2 BRDA which overlies the area on Glenbane West which is on the main land. The total area of the BRDA foot print is some 23 Ha on Glenbane West and based on the above table approximately 30rn3/day is the mean value of seepage that could emanate through the composite lining. The majority of the seepage from the BRDA will migrate to the Poulaweala Creek and the marsh area between

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03511318.511

Glenbane West and the Island Mac Teige. There is the possibility however, of a limited amount of seepage migration from the BRDA eastwards towards the mainland. As discussed in Section 5.1, additional site work will be required to determine the extent of this area. Conservatively, the area is estimated to be approximately 7 Ha and the potential mean seepage value will be approximately 9m3/day.

AAL require this seepage to be reduced because of the potential contamination issues and it is proposed that over an area of 7 Ha a double composite lined facility is installed as outlined in section 7.5. This will reduce the seepage drastically to less than IOU-es/day.

8.2 Perimeter Interceptor Channel

Seepage through the Phase 2 perimeter interceptor channel will be minimised by the composite lining containing the effluent. This will consist of 2mm HDPE and a lm minimum thickness of glacial till on the channel side slopes and 300 mm of glacial till over a GCL on the base.

After the geomembrane is installed, a leak detection survey would be undertaken and any defects repaired.

The estimated seepage emanating from the interceptor channel is small and there is only a 10% probability that it is greater than 3m31day and a 50% probability of less than lms/day.

8.3 Storm Water Pond

The storm water pond (SWP) will also be composite lined with a combination of HDPE lining, GCL and processed glacial till. The geomembrane will be surveyed for leaks once installed.

The defects attributed to the geomembrane are tabulated below. The values used in the

analysis fur the stum waler pond and perimeter intmxpx channel are greater than used for the basin of the Phase 2 BRDA and take into account the geomembranes exposure adjacent to the access roads.

No. of Holes per Ha. Defect TvDe Hole Size Min. 1 Av 1 Max. Pin Holes 0.1 to 5mm* 1 5 10 Holes 5 to 100 mm2 1 3 6 Tears 100 to lOOOmm* 0 1 2

The estimated seepage emanating from tie SWP is relatively small compared to the BRDA and the values are tabulated below.

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03511318.51 1

SeeDage m3/dav

8.4 Seepage Summary

The 1974 planning approval for Phase 1 BRDA for ponded storage of the wet unfiltered red mud was 4.3E-3m3/sec or 371m3/day.

The total seepage emanating from the Phase 2 BRDA at Stage 10 and including the SWP and perimeter interceptor channel bounding Phase 2 is given below.

Structure

Phase 2 BRDA PIG SWP TOTAL

90% 30 1 1 32

Seepage m3/day 50% 10% 90 225 1 3 3 8 94 236

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9.0 CONTAMINANT MODELLING

9.1 General

The primary objective of the contaminant modelling is to determine the likely concentration of key contaminants emanating from the Phase 2 ERDA. This is carried out probabilistically using software developed by Golder termed LandSim (Reference 18). Deterministic methods for resolving contaminant modelling are not considered appropriate because many of the factors which influence the passage of contaminants between the source and the receptor are both poorly quantified and highly variable. A realistic assessment of the Phase 2 BRDA site should adequately reflect the large range of possible outcomes arising fiom these variables. The advantage of a probabilistic approach is that the potential for any such outcome can be measured; this potential is given in terms of percentiles and as minimum, maximum and most likely target values. The percentiles of the output distribution specify the probability with which a certain value will not be exceeded.

The model uses the Monte Carlo simulation technique to select randomly from a pre-defined range of possible input values to create parameters for use in the calculations. Repeating the process many times gives a range of output values and enables the likelihood of the estimated output levels being achieved. For presentation, the 90%, 50% and 10% probability of occurrence are reported in the text. The 90% probability means that there is a 90% probability that the actual value will be exceeded. The 10% probability means that there is a 10% probability that the actual value will be exceeded. The 50% probability is the likely mean value.

9.2 Process

There are four main elements to the risk assessment model for the contaminant migration from a tailings facility, with a series of internal processes for each element, and the output of one element forming the input to the next. The elements are:

l source term; 2

l engineered barrier;

l geosphere;

l biosphere.

The red mud contained in the BRDA facility is referred to as the source term. The source supplies contaminants that potentially will impact the environment and is the hazard component of the risk equation. The description of the source term consists of a list of contaminants, their concentrations, and how these concentrations will vary with time.

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The engineered barrier for the BRDA is a composite liner consisting of a geomembrane directly on a lm thick layer of processed glacial till or GCL. Factors considered in assessing the reliability of the engineered barriers include the reliability of the design equations, to what degree the design objectives are achieved, and subsequent degradation of the constructed elements. Leakage through the engineered barrier which is closely linked to the hydraulic head across the barrier corresponds to input to the geosphere.

The geosphere is the soil, rock, and groundwater system into which contaminants from the BRDA migrate. The contaminants released through the engineered barrier travel along pathways in the geosphere towards the biosphere.

The hydrogeological regime existing beneath the BRDA is variable consisting of low permeability estuarine soils and glacial till underlain by limestone, or glacial till underlain by limestone or limestone outcropping at or very close to the surface. The limestone is an aquifer. The permeability of the limestone is controlled by discontinuities. A range of permeability values for the estuarine soils, glacial till and limestone have been used in the analysis.

Given the close proximity of the Shannon Estuary and Robertstown River, less than 50m from the downstream toe of much of the embankment wall, the zone of water activity is unlikely to extend beyond 40m below ground level before reaching the denser saline waters.

Important processes in the geosphere include advection and dispersion of contaminants (how the contaminants spread outward in the groundwater), retardation (the soil and rock adsorbs contaminants so that the contaminants move at a slower speed than the groundwater itself) and possible breakdown (decay) of the contaminants to other species. The output of the geosphere calculation is a contaminant concentration at the receptor, as a function of time.

The biosphere is the environment in which exposure to the contaminants occurs. In the case of the BRDA site, the natural contaminant background level of the ground water is very high

atdeplk'oeca~s~ofsalineintIusionandthishasamakedinflueenceonspecificconl~a~nas, Monitoring wells adjacent to and on the west and south side of the Phase1 BRDA (Reference 19) indicate saline water with a maximum conductivity of 29,00OmS/cm and maximum soda value of 8.6g/l. The maximum aluminium value was measured at 2.45mgll and pH between 7.0 and 7.3. This compares markedly with the wells monitored on the eastern and northern sectors of the Phase 1 BRDA where the maximum conductivity value is l,157mS/cm and maximum soda value of between O.lg/l. The maximum aluminium value was 0.6mg/l with an average pH of 7.2.

The 2004 monitoring of the storm water pond indicated conductivity values between 12,000 and 28,00OmS/cm, soda values between 3.8 and 9.14g/l and pH values between 12.2 and 13.0. Two monitoring wells (Owl and OW2) immediately downstream of the SWP indicated a maximum conductivity value for 2004 of between 13,000 and 13,50OmS/cm, soda

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03511318.511

of between 5.9 and 6.Og/l, pH of between 11.1 and 11.5 and aluminium between 92 and 145mg/l. The high soda values and conductivity are a consequence of leakage from the salt cake area into the perimeter interceptor channel and then via pumping into the storm water pond.

Chemical analysis indicated (Reference 20) an aluminium content of between 11 and 3Og/kg for red mud and 25g!kg for process sand. The sodium content for the red mud ranged between 19 to 28g/kg for the red mud and 9g/kg for the process sand. The pH for the red mud and process sand were between 12.3 and 12.5.

The pH measured in the monitoring wells in the mud stack (Reference 20) indicated pH values between 12.8 and 13.4 which is considered very high by AAL. Recent tests carried out on the red mud, process sand and salt cake indicate the following values;

Determinand

PH Soda (mglkg) Total Alkininity (mglkg) CaC03 Aluminium (mglkg)

Red Mud

12.1 4,956

9,145 27,250

Sand Salt Cake

Leachate Leachate from from Process

Red Mud Sand

12.2 : 13.4 11.8 11.7 4,288 241,120 3,870 1,156

7,431 341,905 6,980 3,327 18,557 221,870 1,084 745

Note mg/kg tar solid samples, mg/l tar leached samples.

Further testing of contaminant water within the pores of the red mud and measured from piezometers installed into the Phase 1 BRDA indicated the following values.

Determinand

PH Soda (g/l) Conductivity (uS/cm) Aluminium (mgll) Aluminium (ma/l\

Laboratory

AAL 12.54 AAL 3.24

AAL 12,040 AAL 252

TELLAB 365

Perimeter Piezometer InterceotoChannel North Side

Piezometer South Side

12.57 12.97 3.88 14.22

13,060 43,100 307 484 406 558

The high values in the piezometer installed on the south side is probably due to the presence of process sand which is being recharged with high soda liquor from the salt cake waste area. This will be confirmed with the on going sampling regime.

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Three key determinants have been used in the contaminant model; soda, aluminium and pH. The seepages used in the analyses are given in Section 8. The values used in the contaminant analyses are based on the relevant values from the north side piezometer and the leached values from the red mud test work..

There is also a time element relating to the transportation of the contaminants. This is dependent on the mobility of the contaminant, the hydraulic head across the composite lining, the gradient of the regional ground water table and the permeability of the host materials.

The magnitude of the peak concentration is very much dependent on the dilution from the groundwater. The dilution beneath the BRDA will be dependent on the regional groundwater gradient, which is generally low because of the low relief of the area and proximity to the sea, the permeability of the fractured limestone and reasonably high infiltration due to rainfall. The dilution factor will result in the peak concentration at a receptor being reduced from the concentration in the BRDA.

The life of Phase 2 is 20 years at which time the facility will be closed out. After closure, the renewal of the source of the contamination is cut off although the peak contaminant plume may not have arrived at the downstream toe receptor. However, this peak will occur, driven by the regional ground water gradient and by the head acting across the liner of the BRDA. Lower concentrations, below the peak value, will arrive initially. These lower values result from lower seepage rates and greater dilution as the head across the composite liner increases during the early life of the facility. Also, the front of the contamination plume will mix to some extent with the ground water as it moves through the strata.

9.3 Modelling

The receptor for estimating the contaminant concentrations in the ground water are assumed to be immediately above the limestone aquifer at the downstream of the embankment wall toe of the BRDA. The peak contaminant levels are tabulated below for the 90%, 50% (mean)

and N% probability of exceedance, Two moQels were Nn, the first model assumes a thickness of 5 to 10m of estuarine soils and glacial till overlying the limestone which prevails over much of the footprint of the Phase 2 BRDA. The second model assumes only 0 to lm of glacial till over the limestone which is expected to be the stratigraphy beneath the footprint of the Phase 2 BRDA located on the mainland of Glenbane West and parts of the Island Mac Teige. Because of the limited thickness of the low permeability glacial till over the limestone, the travel time of the contaminant plume to the top of the aquifer and to the downstream toe of the outer embankment wall will be considerably faster.

The determinant concentrations used are tabulated below for a triangular distribution of probability of occurrence.

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Species Aluminium

Minimum (mgh) 200

Average (mg/l) 400

Maximum (mg/l) 600

Soda 3500 4000 4500 DH 12 12.5 13.0

The results of the analysis are presented below for time intervals of 10 years, 30 years and 100 years for the 5 to 1 Om of estuarine soils and glacial till over the limestone.

10 years 5 to 10m of Estuarine Soils/Glacial Till over Limestone Single Composite Liner

90% Peak Cont. 50% Av. Peak Cone. 10% peak Cont. 0-W) (mgn) hgn)

Species D/S toe D/S toe D/S toe BRDA BRDA BRDA

Aluminium 0 0 0 Soda 0 0 20 PH 7.5 7.5 12.2

30 years 5 to 10m of Estuarine Soils/Glacial Till over Limestone Aluminium 0 10 190 Soda 20 100 2350 PH 10.2 12.1 12.7

100 years 5 to 10m of Estuarine Soils/Glacial Till over Limestone Aluminium 20 190 350 Soda 300 2570 3500 PH 12.0 12.2 12.8

Virtually all the seepage emanating from Phase 2 BRDA will be directed towards the saline groundwater between the Robertstown River and the Poulaweala Creek. The contaminant plume will be neutralised by buffering of soda ions from the saline groundwater. The saline groundwater has very high soda content and very high conductivity. The pH values at the receptor are conservative and do not take into account any dilution by rainfall infiltration. It is likely that the contaminant plume will take between 10 and 30 years to reach a receptor some 50m away.

The thinner soils overlying the limestone in Glenbane West and areas of the Island Mac Teige will allow for the rapid migration of contaminants and this is indicated by the results of the analysis. These are presented below for time intervals of 3 years, 10 years, 30 years and 100 years for 0 to lm thickness of glacial till over the limestone.

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Species

Aluminium Soda

PH

Aluminium Soda

PH

Aluminium

Soda

PH

Aluminium Soda

PH

3 years 0 to lm of Glacial Till over Limestone Single Composite Liner

90% Peak Cont. 50% Av. Peak Cont. 10% peak Cont.

(w/)1 @g/l) (mg/l) D/S toe D/S toe D/S toe BRDA BRDA BRDA

0 0 40 0 10 300

7.5 7.5 11.8 10 years 0 to lm of Glacial Till over Limestone

0 30 150 0 250 1500

7.5 11.3 12.5 30 years 0 to lm of Glacial Till over Limestone

20 90 250 200 1000 2500 10.8 11.9 12.7

100 years 0 to lm of Glacial Till over Limestone

30 130 290 350 1500 3000 11 12.4 12.8

It is likely that the contaminant plume will take between 3 to 10 years to reach a receptor some 50m downstream of the BRDA. Virtually all of the contaminant plume will mix with saline groundwater adjacent to the Poulaweala Creek and Robertstown River.

The average potential seepage that could migrate to the mainland on Glenbane West based on a single composite lined facility is estimated to be 9m3/day. The resulting contaminant concentrations at the downstream toe of the outer embankment wall are tabulated below.

10 years 0 to lm of Glacial Till over Limestone Migrating Towards Glenbane West

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Soda 95 550 2045 PH 10.4 11.6 12.7

100 years 0 to lm of Glacial Till over Limestone Migrating Towards Glenbane West Aluminium 15 90 245 Soda 180 970 2150 PH 10.7 11.9 12.8

With a double composite lined facility, the potential seepage through the bottom lining is reduced significantly as indicated by the table below.

90% 0

Seepage litres/day 50% 10% 10 75

The resulting contaminant concentrations at the downstream toe of the outer embankment wall based on the double composite lining are tabulated below.

Further contaminant modelling will be undertaken during the detailed design phase on this sector of Glenbane West and after the completion of the particular site investigation and topographical survey of that area. After the completion of the modelling, a decision will be made on whether a single composite or double composite will be required in this area. The decision will be based on consideration of the ground water flow direction, and the criteria that any contaminated seepage into the environment should not exceed the back ground count by more than 10% and the mean pH should not exceed 9.

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03511318.511

During operations of the Phase 2 BRDA, the monitoring well system at 1OOm spacing along the outer perimeter embankment wall of this section of the BRDA will measure the quality of the groundwater on a regular basis as outlined in Section 12.

I

.

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: :

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/ , “ : I . . , ‘ , , . , . 3,

: , - 1 ‘, ‘I , : , , . : l r

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10.0 SURFACE WATER MANAGEMENT

10.1 General

The water management of the BRDA includes the key issues of:

a Storm water management,

l Total storage, flood storage and maximum operating level for the storm water pond (SWP) and perimeter interceptor channel (PIG),

l Water balance and,

l Upper level interceptor channel.

Water collected in the Phase 2 PIC is discharged ‘into the Phase 1 PIC by four 600mm diameter culverts although pumping will be undertaken periodically to empty the Phase 2 PIC. The invert level of the Phase 2 PIC is approximately lm lower than the Phase 1 invert level where they join. The water is pumped from the Phase 1 PIC to the SWP. From the SWP, this pond water is then pumped to the south pond before being treated in the buffer tank and then the 35m clarifier. Some water is sent to the plant for use in the process. From the clarifier, the water is pumped to the liquid waste pond (LWP) prior to discharge into the Shannon

Some water is returned to the SWP if the west pond at the plant site is greater than 50% full. Over the last four years the rate of water return has averaged some 54m3/hour. Based on the 2004 estimates, the sprinkler system, which is used to prevent dusting for the total Phase 1 BRDA, was operational for a period of 45 days. The sprinklers were on for an average of 8hrs per day at an approximate rate of 1000m3/hour. Since the sprinkler system is used when the weather conditions are dry and windy it can be expected that evaporation is at a maximum. Observations indicate that a limited amount of water from the sprinkler system finds it way to the perimeter interceptor channel with the majority evaporated fi-om the surface of the red mud. In the future, improved monitoring of the volume of water used by the sprinkler system with time using a series of flow meters will be adopted. Other inflows to either the SWP or Phase 1 PIC amount to approximately 9.5m3/hour.

10.2 Storm Water Management

The majority of the water from the mud stack is derived from direct precipitation. As discussed above, some is via the sprinkler system which is used to prevent dusting during dry and windy spells. Additional water to the SWP is derived from the west dam at the plant site and a small amount from miscellaneous inflows. Some water is collected in the PIC via

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seepage from the red mud as a result of consolidation but the majority of seepage migrates through the base of the facility.

The total area of the Phase 1 and Phase 2 BRDA and SWP are approximately 180 Ha. The volume of runoff from a storm event will be dependent on the duration and intensity of the storm.

Tabulated below are the expected volumes that could be generated based on the rainfall data presented in Section 5.

During normal operations and during any storm events, water would be pumped from the SWP back to the processing/treatment plant. AAL have a license to discharge treated effluent into the Shannon at 900m3/hr. Some of this water would be derived from the SWP via the treatment plant and LWP. Based on the 2002/2003 Mud Stack Water Inventory (Figure1 0. l), the maximum effluent flow to the Shannon has been 700m3/hr corresponding to high water levels in the SWP and PIC. Normal average for discharge of effluent to the Shannon is between 300m3/hr and 500m3/hr. Water pumped from the SWP to the treatment plant over the period between Ott 1995 and Feb 2003 has averaged 185m3/hr and peaked at 584mJ/hr. Over the 7 day and 14 day periods, the maximum volumes of water pumped were 546m3/hr and 507m3/hr respectively.

The volume of water that couldtheoreticallybe pumped over the 1 day, 7 day and 14 day periods based on specific pump capacities are tabulated below.

Pumping Rate 300m3/hr 500m3/hr 750m3/hr 1000m3/hr Volume Volume Volume Volume

Duration Day x1000m3 x1000m3 x1000m3 x1000m3 1 7.2 12 18 24 7 50.4 84 126 168 14 100.8 168 252 336

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These pumping volumes together with the volume generated during the storm events are presented graphically (Figure10.2). The difference between the two represents the flood storage required to accommodate the storm water in order to prevent the facility overtopping.

These differences equating to the flood storage required are tabulated below.

750m3/hr F

Rtn Period 200 year 500 year 1000 year Day xlOOOm3 xlOOOm3 xlOOOm3 1 132 150 164 7 128 150 168 14 66 93 112 1 126 144 158 7 86 108 126 14 None 9 28 1 120 138 152 7 44 66 84 14 None None None

5000 year xlOOOm3 3 193 211 z-i G-i None I

Based on the historic data, a maximum pumping value of 584m3/hr has been achieved and for longer periods this has reduced to 546m3/hr and 507mJ/hr for 7 days and 14days respectively. AAL want to evaluate two pumping scenarios from the SWP in future, 500m3/hr and 750m3/hr during critical storm events. A pumping rate of 500m3/hr has been achieved in the past but the average rate is much lower at 185m3ihr. Also, discharge into the Shannon is restricted to 9OOm?hr and therefore treated water pumped originally from the SWP a rate of 5OOm3/hr will comprise approximately 55% of the rate to the Shannon. This increases to 83% at a rate of 75OmYhr from the SWP via the treatment plant.

AAL preference is to design for the 1 in 200 year storm event, and assuming a 500m3/hr pump rate, the required flood storage for the SWP and PIC, is approximately 132,000m3 for a 1 day period which appears to be the worst case. To be added to the flood storage volume, is the normal operating volume to determine the total storage capacity required.

The flood storage is generally defined as the volume between the maximum operating pond level and the freeboard. The freeboard is normally protected by a spillway and the maximum operating level is maintained by a decant structure or by pumping. At Aughinish, the maximum operating pond water level of the SWP will be controlled by pumping. If the flood storage is exceeded, the SWP overtops and the water discharges in an uncontrolled manner into the environment. There is currently no spillway on the existing SWP or the PIC and this will be rectified.

The normal operating level for the SWP tends to fluctuate through the year and is higher during the wet winter months and lowest during the dry summers. Based on the historic data

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for Phase 1 (Figure 10.3) for the water estimates in the SWP and PIC, there is a 50% probability that the operating volume in the two facilities would be greater than 180,000m3. The Phase 2 BRDA will increase the combined surface area of the BRDA by 70% which would require the average operating volume to be of the order of 306,000m3 based on the historic data. However, the average pumping rate from the SWP is less than 40% of its existing potential rate and average discharge to the Shannon is only 46% of its maximum allowed rate. Therefore, significant improvements could be made to the water inventory by increasing existing pumping rates.

The current operating volume is likely to include red mud sediment that has settled out in the base of these structures. Estimates in the past have put this volume of sediment as high as 50,000m3. The total combined storage capacity for the SWP and PIC should be at least equal to the current operating volume and the flood storage requirement which equates to a volume of 312,000m3 to accommodate the 1 in 200 year storm event. This assumes that the maximum operating volume and not the average does not exceed 18O,OOOm3. However as discussed earlier, based on the increase in surface area of the BRDA the operating volume should be 306,000m3 although in the past, pumping rates have been significantly lower than they should be. Therefore some improvement in the water management of the SWP is required as discussed in Section 10.4-water balance.

For a 750m3/hr pump rate, the required flood storage for the SWP and PIC, is approximately 126,000m3 for a 1 day period. The total combined storage capacity for the SWP and PJC should be at least 3 18,000m3 to accommodate the 1 in 200 year storm event. This again assumes that the maximum operating volume and not the average does not exceed 180,000m3.

10.3 SWP and PIC Volumes

The SWP is to be completely refurbished by replacing the existing lining where present with a composite lining and increasing the storage capacity by raising the crest height.

The current storage capacity for the SWP for given elevations are presented graphically in Figure 10.4. Allowing for a l.Om freeboard the storage capacity with water elevation is tabulated below.

Crest Elv. mAMSL 5.0

5.5 6.0

Water Elv. mAMSL 4.0

4.5 5.0

Storage Volume m3 160,000

190,000 220.000

6.5 5.5 245,000 7.0 6.0 275,000

7.5 6.5 305,000

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Raising the SWP from its current maximum elevation to 6mAMSL and operating a lm freeboard, gives a storage capacity of 220,000m3. Operating with a reduced fieeboard increases the storage capacity to 245,000m3. With no freeboard, the maximum storage capacity prior to over topping the facility is 275,000m3. These volumes would be confirmed after the refurbishment of the SWP has been complete.

Reducing the freeboard below lm for the SWP could result in waves surging up the smooth lining in strong winds and spraying contaminated effluent over the crest. This in itself should not have a detrimental effect on the integrity of the dam wall but may impact on the downstream monitoring wells or the quality of the adjacent liquid waste pond. The PIC is long and narrow and less likely to be influenced by wave action and a freeboard of 0.5m (4.2mAMSL) would be acceptable.

The storage capacity for the Phase 1 PIC for given elevations are presented in Figure 10.5. The maximum storage capacity assuming a freeboard of 0.5 m is 90,000m3. The Phase 2 PIC has a storage capacity of 65,OOOm3 allowing for a freeboard of 0.5m. The total storage for both the Phase 1 and Phase 2 PIC is around 155,000m3. These volumes will be confirmed during construction.

The total storage volume capacity of the SWP at a top water elevation of 5mAMSL and the PIC at a top water elevation of 4.2mAMSL is approximately 375,000m3 . This is sufficient to accommodate the 1 in 200 year and allow the maximum operating volume to increase from 180,000m3 to 243,000m3 for the 500m3/hr’ pump rate. The maximum operating volume can increase from 180,000m3 to 249,000m3 for the 750m3/hr pump rate. From the current data, the water level in the SWP and the PIC should not exceed about 4.OmAMSL. However, the SWP can operate at a different level than the PIC and therefore a combination of levels in the two structures could provide the maximum operating level. After the raising of the SWP and construction of the Phase 2 PIC, the total volume of the structures will be determined from the survey data. ‘Plimsoll’ lines indicating the elevation will be painted on the HDPE lining of the SWP and PIC. The maximum operating level should not be exceeded and a trigger level system needs to be installed to inform the operators if this level is approached.

AAL operates a set of emergency procedures if the SWP exceeds its current design capacity. These procedures need to be revised once the SWP has been raised and the Phase 2 BRDA is in operation.

It will be essential to install a spillway on the SWP and PIC to protect the walls from severe erosion if the facility is ever over topped. It is designed to accommodate the 1 in 200 year event which has an approximate probability of 5E-03 of being exceeded on an annual basis. Downstream of the SWP is the bird sanctuary and this is a protected area. It is therefore proposed that the spillway should discharge effluent from the SWP back into the perimeter interceptor channel. This can be best managed by controlling the discharge into the SWP from the pumps in the PIC. These could be throttled back so they do not exceed the water

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pumped from the SWP to the treatment plant and water inflowing from the west pond. The depth of the invert level of the spillway for the SWP should be at 5.OmAMSL. A spillway will be installed on the north west sector of the Phase 2 PIC (Section 7.4) and discharge will occur into the area bounded by the downstream toe of the outer perimeter embankment wall and the flood tidal defence berm which has a capacity of some 20,000m3. An accurate volume will be determined during the detailed design phase when addition topographical survey data will be available.. The effluent will be contained and temporarily stored prior to pumping back into the perimeter interceptor channel once the level has been lowered.

10.4 Water Balance

The capacity of the storm water pond and perimeter interceptor channel together with pumping to the treatment plant are able to cope with a 1 in 200 year storm event. For normal operations the amount to be pumped from the SWP to the treatment plant would be significantly less than 5OOm3/hr required to accommodate an extreme storm event.

A flow chart is presented in Figure 10.6 delineating the main components of the water balance. Golders has developed a computer program (Watbal) which determines inflows and outflows on a monthly basis. The water balance analysis includes the Phase 1 and Phase 1 extension facilities.

The red mud production has been taken as the future production of 3700 tonnes/day and discharged to the BDRA at a pulp density of 57%. Average 30 year monthly rainfall (Table 1) derived from the Shannon Airport has been used together with monthly evaporation data from Ardnacrusha (Table 2). *

The moisture content retained in the red mud has been taken as 45%. Seepage losses for Phase 1 have been taken as 4400m3/month (Reference 15) and is controlled entirely by the average permeability of the red mud at SE-Bm/sec. A seepage value of 1800m3/month has been used for the Phase 1 extension (Reference 15). A seepage value of 2800m3/month has

The wetted red mud area has been restricted to 5% of the surface area of the facility at any one time.

The results of the water balance are presented in Table 3 for average rainfall conditions. The analysis assumes that the start date for operation is October, at the end of the construction season, and is tilled to its maximum operating volume of 180,OOOma in the SWP and PIC. To maintain the volume at about 180,OOOms through the year, pumping from the SWP has to vary between 250m3/hr during summer to 370m?hr in winter for average rainfall conditions. The average annual pumping rate is 306m3/hr. Current average pumping rate for the Phase 1 BRDA is I85ms/hr. The operating storage volume in the SWP and PIC and pumping rate with time is presented on Figure 10.7.

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10.5 Upper Level Interceptor Channel

The Phase 2 upper interceptor channel during normal operations stores only a limited volume of water. It is designed to discharge from various points along its alignment into the perimeter interceptor channel and also connects with the upper interceptor channel of Phase 1 in two localities by a series of 4 x 600mm culvert pipes. The Phase 1 upper interceptor channel also has a number of discharge points along its alignment and has two ends which discharge water by a series of 600mm decant culverts into a lined channel adjacent to the eastern ridge road Figure 7.7. One of the ends is at an elevation of 15mAMSL and acts as the main spillway for the upper interceptor channel. The water is discharged into the PIC before being discharged into the SWP.

The catchment area for the upper interceptor channel is 130 Ha for both Phases 1 and 2 combined. The total storage volume for the upper interceptor channel is lOO,OOOm3. The total volume of water generated for various storm durations are tabulated below together with the volume to be spilled and rate of spilling for the 1 in 10,000 year event. _

Duration 6 hour

Flood Volume m3 Volume to be Spilled m3 Rate of Spilling m3/hr 115.000 15,000 2,500m3/hr

12 hours 137,000 37,000 3,100m3/hr 1 day 159,000 59,000 2,500m3/hr 7 dav 227.000 127.000 750m3/hr

As previously discussed in Section 7, at three locations a 500mm diameter HDPE decant pipe is to be installed near the base of the upper interceptor channel’ for Phase 2. A similar arrangement is proposed for Phase 1. At one of the locations of the decant pipe, a small spillway 5OOmmx2OOOmm at an elevation of 15.5m4MSL will be installed. The total capacity of the decant structures is considerably in excess of the 3100ms/hour requirement. This is a precautionary approach to allow for 50% of the decant pipes inoperative and the main discharge outlets on the east ridge road being blocked by sloughing of the red mud during these extreme storm events.

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Aughinish Alumina Ltd Version B .2 03511318.511

11 .O CONSTRUCTION MONITORING

11 .I General

A considerable amount of site preparation will be required prior to the construction of the embankment walls and placement of the composite lining. Both the earthworks and the installation of the composite lining will be quality controlled and quality assured as discussed below together with an outline of the monitoring required.

II 2 Site Preperation

The key components of the site preparation required prior to construction are:

l Removal of trees;

l Removal of hedges and shrubs/vegetation;

l Removal of tree stumps;

l Removal of organics from the existing surface drainage ditches;

l Reshaping and backfilling existing surface drainage ditches;

l Removal of topsoil;

l Removal of existing unsuitable stockpiles beneath the embankment footprint;

l Rerouting of 33kV and 1 OkV lines;

11.2.1 Removal of Trees, Vegetation and Stumps

Part of the BRDA footprint is covered with plantation trees. They are a mixture of xxxxx and xxxxx. These trees, which are spaced approximately lm to 3m apart are generally less than 4m high and have trunk diameters between 50mm and 1OOmm. Occasionally larger pines are present with trunks in excess of 300mm although this is less than 5% of the tree population. The roots tend to be confined to shallow depth. A report is being prepared relating to the felling of these trees.

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The trees are owned by AAL and are deemed by them to have no economic value. It should also be noted that burning of the wood on site may not be allowed by the regulatory authorities..

It is estimated that between x to x number of trees will be felled to clear the BRDA site. If possible, the trees will be felled and the trunks transported to a timber processing facility, Otherwise the tree trunks will be turned into wood chippings and the branches shredded. These products will be mixed with the topsoil for latter use in the restoration of the facility.

The chippings and shreddings generated will be transported to the proposed topsoil stockpile area periodically during the operation.

As the trees are being felled, the roots and stumps will need to be removed and where appropriate will be shredded and mixed with topsoil. Stumps and roots which would be difficult to shred will be placed in the unsuitable stockpile for later restoration use.

I I .2.2 Backfilling Existing Drains

There is some 3000m of existing drainage ditches that need to be backfilled prior to the placement of the composite lining. The drainage ditches will need to be cleaned of all vegetation and organic debris from the sides and base. The drain will be cut back to side slopes no steeper than 3H:2V, Ten-am 2000 placed and cobbles and boulders placed from the processing of the glacial till and from the unsuitable stockpile as shown in Figure 11.1.

11.2.3 Removal of Topsoil

The topsoil will be stripped and temporary stockpiled for use in the restoration of the side slopes of both Phases 1’ and 2. Topsoil designated for the rehabilitation of the lower slopes in Phase 1 will be placed immediately. The remaining topsoil will be stockpiled in the designated areas shown on Figure 11.2. The stockpiles shall not exceed a height of 5m and side slopes shall not exceed 2H:lV. The total volume of topsoil to be removed is approximately 200,000m3.

.

1 I .2.4 Removal of Unsuitable Stockpile

The existing unsuitable stockpile located in the northeast sector of the Phase 2 BRDA at the location where it connects to the Phase 1 BRDA will be removed. Based on the old survey data the stockpile could be in excess of 5m in depth and wet. A series of pits will be excavated through the stockpile to determine the condition of the foundation materials which is expected to be bedrock limestone with possibly a thin layer of glacial till.

The volume of material which may require to be removed is expected to be of the order of 50,000m3. The organic and soft estnarine would be mixed in with the topsoil stockpile

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whilst the cobbles and boulders from the processing of the glacial till will be used for backfilling the existing drainage ditches.

11.3 Earthworks

The BRDA would be constructed in accordance with a technical specification and construction drawings. The implementation of the technical specification, and associated construction drawings during the construction phase is essential to ensure that the facility will function according to the design intent. A comprehensive quality control and assurance programme would be carried out during the construction of the facility. The following aspects will be carefully monitored during the construction phase by suitably qualified personnel:

l Embankment footprint foundation preparation;

l Selection of suitable materials for embankment wall;

l Moisture conditioning and compaction of embankment wall fill materials;

l Alignment and level of any pipework;

o Selection and installation of pipes, bedding and drainage material;

l Pore pressure monitoring in the estuarine and glacial foundation materials.

Quality control tasks including classification tests, gradations, moisture content, permeability and density tests will be carried out throughout the construction phase to ensure compliance with the technical specifications and construction drawings.

The dry density and moisture content of the embankment fill materials will be measured

using anuclear Qensometerwhich willbe continually calibratedagainstthesandreplacement test, The nuclear densometer testing will be carried out every 2000m2 of lift placed and the sand replacement test every SOOOm2 lift placed.

The permeability of the clay lining will be tested every 10000m2 of glacial clay lift placed. The plasticity of the clay will be tested every 4000m2 of clay lift placed.

The pore pressure development in the estuarine and glacial till foundation materials during construction will be monitored using vibrating wire piezometers. The development of pore pressures will be checked against the design. Where necessary, construction will be slowed down or halted to allow for the dissipation of pore pressures in the estuarine soils. At least

six sections of the embankment alignment will be monitored with two vibrating wire

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piezometers installed beneath the OPW and IPW each. At least two sections of the FTDB embankment will be monitored with two vibrating wire piezometers installed per section.

11.4 Geomembrane

The installation of the gemembranes forming the composite lining and protection/filter geotextiles for the BRDA would be in accordance with the technical specification, manufactures guidelines, the Contractors method statements and the construction drawings. The implementation of these procedures during the construction phase is essential to ensure that the facility will function according to the design intent. A comprehensive quality control and assurance programme would be carried out during the construction of the facility and would be discussed in the detailed design phase.

II .5 Leak Detection

A leak detection survey will be carried out after the geomembrane is installed using direct (DC) electric current. The technique used is closely related to the electrical resistivity method. Electric current is passed between two electrodes, one placed in the water inside the cell and the other in the peat outside the cell. With the geomembrane intact, the water in the cell will be electrically isolated from the external environment. The resulting potential field, measured as a potential difference between two non-polarising electrodes, is small but uniformly distributed over the geomembrane. If the geomembrane is defective, current will flow through the point of leakage and the measured potential will peak around the position of the defect. All defects will be recorded, repaired and retested.

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12.1 General

A comprehensive monitoring system will be installed beneath the inner and outer perimeter embankment walls and flood tidal defence berm and in the stack wall to measure the performance of the structure during its life.

The monitoring system will consist of the following:

l Vibrating Wire Piezometers,

l Casagrande Standpipe Piezometers,

l Perimeter Monitoring Wells

03511318.511

0 Inclinometers,

l Settlement Spiders,

l Survey Monuments.

The approximate locations of the majority of instruments are shown in Figure 12.1.

In addition to the monitoring, an intrusive site investigation will be undertaken which will consist of:

l Cone Penetration Tests,

l Geonor Insitu Vane Testing.

12.2 Vibrating Wire Piezometers

The vibrating wire piezometers are used to measure the increase in the pore pressure during the construction of the inner and outer perimeter embankment walls and the flood tidal defence berm and twenty four areas will be monitored. Each area will consist of a near surface piezometer at approximately 1.5m to 2m depth and a lower piezometer at approximately 4m to 6m depth depending on the thickness of the estuarine soils. They would be positioned beneath the centreline of the embankment walls. They would be measured prior to loading, every 5 minutes during loading and every hour for the next 24 hours after loading and then every 12 hours for the next week. Readings would then be taken daily until the piezometric pressures dissipated 50% from its peak. From then, the piezometric pressures would be monitored weekly until dissipation had reached 90% and from thereafter

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every month. The time interval for taken readings will be adjusted depending on the rate of loading and the rate of pore pressure dissipation. The location of the vibrating wire piezometers will be determined by the designer and the Engineer on site supervising the works

From the results, the coefficient of consolidation for the estuarine soils will be obtained and compared to the design value.

Vibrating wire piezometers will also be installed in the red mud beneath the rockfill embankment walls forming the stack raises as outlined in Reference 15 for the Phase 1 BRDA.

12.3 Casagrande Standpipe Piezometer

Casagrande standpipe piezometers will be installed to monitor the phreatic surface in the stack wall and in the estuarine soils in the Phase 1 BRDA at specific depths. This is essential to assist in evaluating the stability of the stack wall and foundations. A complete profile of the phreatic surface within stack wall will be obtained from eight sections given in Figure 12.1. These would be measured monthly.

12.4 Monitoring Wells

The monitoring system for Phase 2 will consist of monitoring wells at approximate spacing of 200m. Along the section of Phase 2 in the area of Glenbane West from the railway line, past the Limerick County Council water treatment works and along the main plant access road to Poulaweala Creek the wells will to be installed at a maximum spacing of 100m. The boreholes will be positioned downstream of the perimeter interceptor channel. However, their final location will be determined with the assistance of a resistivity survey which will enable the fractures in the limestone to be located. Seepage from either the base of the BRDA and perimeter interceptor channel will preferentially migrate along the fractures in the limestone. The wells would be then drilled 3m to 4m into the fi-actured limestone beneath the estuarine soils or to a minimum depth of 15m. A shallower well, adjacent to the limestone well and in a separate borehole, would be drilled into the estuarine soils on the east and south sides of the BRDA.

The monitoring wells will consist of a 1OOmm ID perforated pipe installed in a 2OOmm borehole. The response zone will consist of fine gravel and plugged with bentonite/concrete either in the limestone or, for the estuarine soils, near ground surface.

The proposed water quality sampling programme to be adopted is subdivided into two based on a time interval and types of testing. The subdivisions are termed preliminary and detailed. The scheme is outlined below.

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12.4.1 Preliminary

A sample should be collected (following standard practice) each time the water level from the monitoring wells is measured on a monthly basis. This sample should be tested on site using a hand-held instruments for pH and conductivity.

12.4.2 Detail

On a bi annual basis, a sample should be collected from each monitoring well and submitted for laboratory analysis to determine major and minor ions, key total and dissolved metals indicators, together with the basic parameters. In addition, alkalinity and acidity determinations should be carried out by titration in the laboratory.

The monitoring wells should have simple dedicated water sampling devices installed (eg Waterra pumps), to aid sampling and minimise the risk of cross contamination.

12.5 Inclinometers

Inclinometers will be installed into the stack wall to measure any deformation in the red mud. A probe is sent down the inclinometer tube and a gravity sensing transducer measures the inclination with respect to the vertical. A total of 30 inclinometers will be installed, four per section line except for one line in which two will be installed. It is not proposed to install the inclinometers beneath the lining and therefore the base cannot be fixed. The top of the access tube would be monitored by GPS, as will all the other instruments, but the interpretation of the results will be more problematic. The performance of the inclinometer installed above the lining of the Phase 1 extension will be evaluated to establish the difficulties of interpretation of the data resulting from no fixed base. The inclinometers would be measured quarterly.

12.6 Settlement Spiders

The internal settlement of the red mud, which is necessary for the undrained shear strength to increase with time, will be measured from settlement spiders installed at 2 to 3m intervals along the inclinometer tubes. A probe sent down the tube records the exact location of the spiders and this is compared to previous readings. Again, care will be required to interpret the data as the base of the inclinometer cannot be fixed. The settlement spiders would be measured quarterly.

12.7 Survey Monuments

To measure the surface movements on the stack wall in three dimensions, a comprehensive system of survey monument stations would be installed along nine sections of the BRDA. These survey monument stations would be monitored by GPS quarterly.

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03511318.511

12.8 Intrusive Investigation

After the filling of each stage and prior to the construction of the next stage rocktill wall, cone penetration testing and in situ vane testing will be undertaken to determine the strength and strength gain of the red mud. Three piezocone tests will be carried out on each section and in situ vane testing would be selectively carried out on the weaker zones identified by the CPT equipment. In addition to the in situ testing, samples of the red mud will be taken to measure moisture content and these will be correlated with the undrained shear strengths obtained from the vane tests.

12.9 Additionat Monitoring

The water levels in the Phase 2 perimeter interceptor channel and storm water pond should be measured on a weekly basis and it is recommended that a ‘plimsoll line’ showing elevations is installed on the lining at each locality.

The surface area of the red mud will be surveyed after the completion of each raise to determine the volume placed and predict the remaining storage volume in the facility.

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03511318.511

13.0 REFERENCES

1 AAL Part 111 Appendices to the Terms and Conditions of the Specialist Appointment. Consulting Engineer Services for Tasks Associated with Red Mud Tailings Storage at Aughinish Alumina Limited, Askeaton Appendix A Scope of Service. November, 2003.

2 Golder Associates Geotechnical Investigation and Borrow Assessment for the Phase 2 Bauxite Residue Disposal Area at Aughinish Alumina, 2004.

3 Golder Associates Geotechnical Investigation for the Optimisation Capacity of the Phase 1 Bauxite Residue Disposal Area at Aughinish Alumina, 2004.

4 Delft Geotechnics Mud Stack. 1988.

Final Report Recommendations for Optimum Capacity of Red

5 Golder Associates Review of Mud Distribution System, 2004.

6 Ove Arup & Partners Ireland. Extension to Bauxite Residue Storage Area at Aughinish Island, Askeaton, Co. Limerick Environmental Impact Statement Volumes 1 to 3 1993.

7

8

9

10

11

12

13

14

Met Eireann Shannon Airport Monthly and Annual Mean and Extreme Values 2004

Soil Mechanics Limited Site Investigation for a Feasibility Study of a Bauxite Beneficiation Plant at Aughinish Island, Co. Limerick, Eire Volumes 1 and 2 Mud Waste Disposal Pond 1971 and 1973.

URS Dames and Moore Mudstack Site Investigation Drilling and Groundwater Modelling 2002

Soil Mechanics Limited Further Site Investigation for a Bauxite Beneficiation

b--tat Aughinish~s~anQ,Co.Limerick,Eire\Jolumes 1 to 4MuQ anNasteDisposa\ Lagoon 1974 and 1975

Engineering and Resources Consultants Limited (Ercon) Bauxite Beneficiation Plant, Aughinish Island, Report on Hydrogeological Investigation 1974.

Roger Musson Seismic&y and Earthquake Hazard in the UK British Geological Survey 2002.

ICOLD Dam Design Criteria, 1988.

Lankelma 2003.

Factual Report on Site Investigation in the Existing Phase 1 Mud Stack

Golder Associates

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- 67 - Version B.2

03511318.511

15

16

17

18 Golder Associates LandSim Manual ~2.5 2004.

19

a 20

Golder Associates, The Preliminary Design for the Optimisatidn Capacity of the Phase 1 Bauxite Residue Disposal Area at Aughinish Alumina, 2005

RPS Closure Plan Update for the Aughinish Alumina Ltd. Site Aughiniih Island, Askeaton, Co. Limerick, 2004.

Giroud, J. P and Bonaparte, R., Leakage Through Liners Constructed with Geomembranes Parts 1 Geomembranes and Part 2 Composites. Geotextiles and Geomembranes, 1989.

Aughinish Alumina Ltd. AER Report 2003.

URS Groundwater Flow Modelling within the Mud Stack Area of Aughinish Alumina in Support of the Site Closure Plan. 2002.

GOLDER ASSOCIATES (UK) LTD

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May 2005 Aughinish Alumina Ltd Version B.2

03511318.511

.i :‘O

‘. ‘,

TABL’ES”

Golder

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Table 130 Year Averages Shannon Airport.

mean no. of da

16 19 16 I I

17 18 18 1 20 1 19

dec

8.9 - 3.6

- 6.3

15.2

-8.3

5.0

11.0

- 89

84

- 1.42

7.1

99.6

50.4

20

16

7

YI

veal

13.5

6.8

10.1

31.6

25.4

68.6

84

73

3.48

15.8

62

926.8

50.4

214

160

66

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max. mean lo-

WEATHER (mean

isnow orsleet 1.8

snow lying at 0.1

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TABLE 2

“TRUE” EVAPORATION AT ARDNACRUSHA (mm)

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC YEAR

1962 46.4 29.2 -0.7 1.7

1963 24.6 36.9 70.7 78.0 61.0 73.6 42.4 4.0 9.2 ‘9.7 410

1964 4.4 18.4 28.5 48.1 80.1 67.2 72.5 65.0 42.5 18.5 7.2 5.6 458

1965 5.8 26.0 49.6 37.1 70.9 83.3 82.2 65.4 27.7 18.9 3.3

1966 5.9 16.3 32.0 49.0 120.9 77.5 94.0 68.9 46.4 17.8 1.7 -9.5 521

1967 2.5 12.3 32.6 63.7 78.9 83.1 70.5 65.6 40.6 25.5 9.8 -4.8 480

1968 5.1 9.2 27.0 50.1 1.9 93.6 93.0 88.2 49.7 20.1 9.9 3.7 522

1969 2.8 4.9 30.0 58.8 69.8 94.9 93.7 73.3 44.0 28.7 -1.4 1.0 501

1970 -0.4 -0.5 33.4 44.8 78.8 114.6 89.2 50.4 35.6 19.8 5.1 -1.0 470

1971 2.8 5.5 25.1 57.8 81.0 85.3 106.3 76.2 48.0 22.1 2.4 4.7 517

1972 2.1 11.6 22.6 56.1 69.0 78.1 89.7 70.9 53.7 24.7 -4.7 3.3 477

1973 -2.5 -2.3 38.4 66.4 84.4 98.5 69.6 43.0 16.1 4.5 1.2 473

1974 16.6 16.3 31.3 73.2 79.0 105.9 71.8 76.4 40.3 30.5 16.1 10.2 568

1975 15.6 17.1 37.7 51.6 104.8 119.1 110.9 83.4 44.3 26.1 9.1 623

1976 8.6 19.4 36.1 71.4 72.7 117.0 91.7 101.6 70.6 33.1 633

1977 -2.2 10.7 37.3 53.8 90.1 100.3 104.0 87.0 55.3 23.7 572

1978 5.7 10.0 52.0 61.6 80.3 97.9 84.2 55.0 31.7 561

1979 -2.7 21.9 19.6 45.9 64.1 91.7 98.7 61.1 40.0 30.9 11.9 6.0 489

1980 6.9 11.9 31.4 55.1 93.7 67.7 75.5 61.1 35.4 18.2 8.4 6.1 471

1981 4.9 16.1 30.2 63.3 79.9 82.0 79.7 72.9 45.1 15.1 12.5 5.7 507

1982 2.6 12.5 42.3 60.6 87.7 82.8 109.1 84.1 43.9 23.0 7.0 -12.9 543

1983 7.5 14.6 27.1 44.8 53.0 89.7 121.4 102.0 43.0 20.1 11.5 6.4 541

1984 11.1 14.1 27.5 70.0 89.5 83.6 138.5 92.8 37.2 26.0. 7.3 2.3 600

1985 -3.3 21.1 31.2 82.4 74.2 76.8 71.3 52.6 48.9 22.9 2.4 2.4 483

1986 25.3 51.5 53.3 69.1 69.4 64.3 66.5 48.2 21.0 15.6 495

1987 12.2 23.2 49.8 80.9 38.7 72.8 75.7 46.6 16.1 4.3 432

1988 18.4 31.8 51.3 72.4 92.3 68.9 60.7 38.1 21.1 6.8 476

1989 14.3 10.9 33.1 45.9 112.6 98 129.2 62.1 55.4 20.8 0.1 2 584

1990 7.2 37 40.7 57.2 94.6 88.7 94.8 57.5 47.5 19.1 8.5 5.0 558

Average 4.9 14.5 33.1 55.3 80.6 87.2 90.6 72.8 45.3 22.2 6.5 3.2 517

NOTE: Shaded values are not available (assumed average)

(a) True evaporation is understood to mean net evaporation from a free water surface

such as a lake, etc. as opposed to pan evaporation

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TABLE 3 WATER BALANCE AVERAGE CONDITIONS

UMULATION INFLOWS LOSSES PUMPING

‘ROM SWP

Rate m3lhr

349 360 371 367 294 294 250 257 257 246 312 316

:m3/mo.)

Decant

( m3/mo.)

Seepage

(m3/t Misc.

Inflows

m3 Accum. Volume

180000 180398 178387 178915 177496 178884 180134 179108 178149 179148 179125 179698 180000

)*) railings Basin

Pond Net Evao. I

Total Inflow

Change railings Water

Total Retained

in Tailings Water

Iisplace Net

Change

86528 63000 166320 315848 51615 9000 3552 64167 251681 0 251681 251283 398 83737 63000 170460 317197 49950 9000 1040 59990 257207 0 257207 259218 -2011 86528 63000 179280 328806 51615 9000 512 61127 267681 0 267681 267153 528 86528 63000 174960 324488 51615 9000 784 61399 263089 0 263089 264508 -1419 78154 63000 129780 270934 46620 9000 2320 57940 212994 0 212994 211606 1388 86528 63000 129240 278768 51615 9000 5296 65911 212857 0 212857 211606 1251 83737 63000 99900 246637 49950 9000 8848 67798 178839 0 178839 179866 -1027 86528 63000 108180 257708 51615 9000 12896 73511 184197 0 184197 185156 -959 83737 63000 112320 259057 49950 9000 13952 72902 186155 0 186155 185156 999 86528 63000 102780 252308 51615 9000 14496 75111 177197 0 177197 177220 -23 86528 63000 148140 297668 51615 9000 11648 72263 225405 0 225405 224832 573 83737 63000 147240 293977 49950 9000 7248 66198 227779 0 227779 227477 302

607725 108000 82592 1 798317 2645081 0 2645081 2645081 0 Ave.=306

INITIAL Ott Nov Dee Jan Feb Mar Apr May Jun Jul Aw Sep

TOTAL :018798 756000 1668600 3443398

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