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Leaching Facili ties DesignRosemont Copper

June 2007

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Leaching Facili ties DesignRosemont Copper

Prepared for:

Augusta Resource Corporat ion

4500 Cherry Creek South Drive, Suite #1040Denver, Colorado 80246(303) 300-0138Fax (303) 300-0135

Prepared by:

3031 West Ina RoadTucson, Arizona 85741(520) 297-7723Fax (520) 297-7724

Tetra Tech Project No. 320614

June 2007

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Leaching Facilities Design Augusta Resource Corporation

Tetra Tech June 2007 i

TABLE OF CONTENTS

1.0 INTRODUCTION...............................................................................................................1

1.1 General..................................................................................................................1

2.0 PROJECT DESCRIPTION................................................................................................2

2.1

General..................................................................................................................2

2.2 Ore Production ......................................................................................................2

2.3 Leach Pad Site ......................................................................................................2

2.4

Solution Collection Ditch and Ponds .....................................................................3

3.0

SITE CONDITIONS........................................................................................................... 4

3.1

General..................................................................................................................4

3.2 Surface and Subsurface Conditions ......................................................................4

3.3

Climatology............................................................................................................5

3.4

Surface Water Hydrology ......................................................................................5

3.5

Site Geology..........................................................................................................5

3.6 Site Seismicity .......................................................................................................6

4.0 ENGINEERING ANALYSES ............................................................................................8

4.1 General..................................................................................................................8

4.2 Slope Stability........................................................................................................8

4.2.1

General .................................................................................................................. 8

4.2.2

Stability Analyses Parameters ............................................................................... 8

4.2.3

Stability Analyses Results...................................................................................... 8

4.3 Water Balance and Design Flows .........................................................................8

4.3.1 General .................................................................................................................. 8

4.3.2

Pond Sizing............................................................................................................ 9

4.3.3 Water Balance Results ..........................................................................................9

4.3.4 Process Design Flows ......................................................................................... 10

4.4 Liner Design ........................................................................................................10

4.4.1 General ................................................................................................................10

4.4.2 Composite Liner Parameters ............................................................................... 10

4.4.3 Geomembrane Liner Selection ............................................................................ 11

4.4.4

Liner Testing ........................................................................................................ 11

4.5

Pad Drain Design ................................................................................................11

4.5.1 General ................................................................................................................11

4.5.2 Pad Drain Pipes and Fill ......................................................................................11

4.5.3

Drain Rock Testing ..............................................................................................12

5.0 CONSTRUCTION QUANTITIES ESTIMATE .................................................................13

6.0

GENERAL INFORMATION ............................................................................................14

7.0

REFERENCES................................................................................................................15

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Tetra Tech June 2007 ii

LIST OF TABLES

Table 2.1:

Predicted Yearly Ore Schedule .............................................................................2

Table 3.1: Summary of Insitu Permeability Test Results........................................................ 5

Table 4.1: Predicted Monthly Freshwater Makeup Requirements..........................................9

LIST OF FIGURES

Figure 1: Title Sheet and Location MapFigure 2: General Facilities ArrangementFigure 3: Phase 1 Leach Pad Layout and Grading PlanFigure 4: Phase 1 Leach Pad SectionsFigure 5: Phase 1 Leach Pad DetailsFigure 6: Phase 2 Leach Pad Layout and Grading PlanFigure 7: Phase 2 Leach Pad SectionsFigure 8: Phase 2 Tie-in Plan & DetailsFigure 9: Phase 1 Drain Pipe Layout, Sections & DetailsFigure 10: Phase 2 Drain Pipe Layout, Sections & DetailsFigure 11: Phase 1 Pond Layout Sections & DetailsFigure 12: Phase 1 Pond Sections & DetailsFigure 13: Geotechnical Investigation Plan

LIST OF APPENDICES

Appendix A Detailed Design Criteria Appendix B Construction Quantities Appendix C Engineering Analyses

Appendix C1 Water Balance and Pond Sizing Analyses Appendix C2 Stability Analyses Appendix C3 Pad Drain System Analyses Appendix C4 Liner System Analyses Appendix C5 Geotechnical Data

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Tetra Tech June 2007 1

1.0 INTRODUCTION

1.1 General

This report presents the leaching facilities engineering analyses and design documents

provided by Tetra Tech, Mining and Manufacturing (Tetra Tech) to Augusta ResourceCorporation (Augusta) for the Rosemont Copper Project (Project).

The Project site is located approximately 30 miles southeast of Tucson, west of State Highway83 on the east slope of the Santa Rita Mountains (Figure 1). In geographical terms, theRosemont Property location coordinates are approximately 31º 50’N and 110º 45’W. Access tothe Property can be gained from Interstate 10 to State Highway 83 south, then west on ForestRoad (FR) 231.

A feasibility-level crushing and plant facility design has been prepared by M3 Engineering (M3).The location of the proposed open pit, crusher plant, solution process plant, and mill facilitieshave been considered for tie-in to the leach pad and pond limits. General mine site and leachfacility layouts are shown on Figure 2.

Pertinent site information and meeting discussions with Augusta and M3 have beenincorporated into this feasibility design report, figures, and attachments. The detailed designcriteria list is included in Appendix A. The feasibility design construction quantity estimates areincluded in Appendix B. The supporting engineering analyses for site conditions, leach padslope stability, water balance, liner system, and pad drainage system design are included in

Appendix C.

This report is part of a compendium of reports presenting the feasibility-level design of theProject. The list of reports below present the results of field investigations, laboratory testing,and engineering analyses and design activities carried out in support of the Project.

● Leaching Facility Design (Tetra Tech, June 2007)

●

Dry Tailings Facility Design (Tetra Tech, June 2007)● Site Water Management Plan (Tetra Tech, June 2007)

● Geotechnical Study Report (Tetra Tech, June 2007)

● Geologic Hazards Assessment (Tetra Tech, June 2007)

● Baseline Geochemical Characterization (Tetra Tech, June 2007)

● Reclamation and Closure Plan (Tetra Tech, June 2007)

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2.0 PROJECT DESCRIPTION

2.1 General

Current plans by Augusta include copper leaching of approximately 50 million tons (Mt) of oxideore in an approximate 6 year leaching operation life concurrent with milling operations.

The leach pad is designed to accommodate the planned ore tonnage with a lined pad built inone construction phase. The lined leach pad, collection ditch, and pond design, as well as thesolution pumping systems, and pipelines, will provide full containment of operational solutionsand the design storm event. References to site information and a detailed list of design criteriaand design approach information are presented in Appendix A.

2.2 Ore Production

The heap leach ore production schedule is variable with the maximum rate occurring in year 1of the schedule. The current ore production schedule indicates a total of 50 Mt of oxide ore tothe leaching operation. The peak ore stacking rate is approximately 51,000 tons per day (tpd)of Run-of-Mine (ROM) ore to the leach pad in Year 1 with no stockpiling of ore. Table 2.1presents the ore stockpile schedule based on information provided by WRL Consulting.

Table 2.1: Predicted Yearly Ore Schedule

Time Oxide Leach Ore

Period (Year) Ktons Cumulative

Pre-Production 14,979 14,979

1 18,244 33,223

2 5,320 38,543

3 937 39,480

4 2,602 42,082

5 5,002 47,084

6 2,195 49,279

2.3 Leach Pad Site

Tetra Tech, Augusta, and M3 personnel selected the leach pad site during initial internal studiesfor the Project. The site is located southeast of the planned open pit. Alternate sites wereconsidered for the heap leach operation and considerations and selection criteria aredocumented (Vector 2006). A setback distance of 450 feet from the ultimate pit limit wasrequired by M3 for placement of the leaching operation.

The leach pad site includes a Phase 1 pad for up to 50 Mt of ore with an expansion pad with upto 50 Mt of additional storage stacked to a maximum ore heap height of 300 feet. Figures 3through 5 describe the leach pad layout, grading, sections for this phase. The Phase 2 pad isincluded in anticipation of additional ore reserves. Figures 6 through 8 describe the leach padlayout, grading, sections, details, and tie-in plans for Phase 2.

The lined leach pad will utilize gravity solution drainage via perforated drain pipelines to thedownhill perimeter berm and a collection ditch pipeline system to the pregnant leach solution(PLS) pond. A schematic cross section of the Phase 1 leach pad is shown on Figure 4 with paddrain pipe sections and details shown on Figure 9.

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The Phase 1 leach pad and pond limits include approximately 522,000 cubic yards of sitegrading cut/fill to achieve positive drainage to the ponds, provide suitable slopes and surfacesfor geomembrane lining, and to allow for a relatively level surface for downstream heap stability.Temporary diversion ditches are not required as the heap layout utilizes natural drainageboundaries to a large extent.

Both pad phases drain by gravity flow to the collection pipe network and the downhill linedcollection ditch and PLS pond. The Phase 1 and Phase 2 leach pad and pond site grading limitsare shown on Figures 3 and 6.

2.4 Solution Collection Ditch and Ponds

The lined collection ditch contains solid collection pipelines along the downhill toe heap limits forgravity drainage in a lined channel to the double lined PLS pond. The solid pipelines (primarycontainment) together with the composite lined collection ditch (secondary containment) providedouble containment of solutions from the leach pad and prevent ponding of solution flows in thecollection ditch. The collection ditch pipeline sections and details are shown on Figures 9 and10. The collection pipe network is divided into several cells or drainage areas per leach padphase and allows for solution monitoring of separate areas of the heap. The pad grading and

natural terrain will separate flows into these cells to a large extent therefore internal cell dividerberms will not be required.

In addition to 24 hours of standby drain down flows, the double lined PLS pond is sized to storeup to 8 hours of operational flows. Any PLS leakage through the top pond liner will be detectedin the underlying leak detection system, and the leakage will be contained by the bottom pondliner until the pond can be drained for liner repair. In addition, a pump is planned for installationbetween the two liners so collected leakage can be evacuated as necessary.

Temporary solution overflows from the double lined PLS pond, if filled to capacity, will dischargeinto the single lined storm pond during any upset operational or storm overflow events. Averageyear storm events will likely be fully contained within the PLS pond. This assumes the operatingPLS pond level can be maintained at far less than 8 hours of solution storage.

The storm pond overflow solutions will be temporarily stored in the single-lined pond limits for upto 72 hours before being pumped back to the PLS or barren (raffinate) pond for reuse in theheap leach operation. The ponds include a corner sump area lower than the pond bottom levelsto assist in low pond level pumping operations. Rub sheets will be placed over the pond liners inthe sump corner areas to protect the pond liners during pumping operations. The Phase 1 linedpond system layout is shown on Figure 11. Pond sections and details are shown on Figure 12.

In addition to the solution collection ponds, a raffinate pond is located nearby. This pond willcontain the raffinate solutions from the solvent extraction operations prior to being pumped tothe drip emitters on the leach dump. Because all solutions are pumped to this pond anddischarge into the pond is not subject to storm flows, the raffinate pond is separated from theother ponds by a berm. The raffinate pond was sized for 4 hours of operational flows resulting

in a storage capacity of 8 acre-feet (ac-ft).

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3.0 SITE CONDITIONS

3.1 General

This section provides a summary of surface and subsurface conditions, climatology, surfacewater hydrology, site geology, and seismicity. The proposed Phase 1 pad and process pondarea is located southeast of the planned open pit within a tributary of the Barrel drainage basin.The Phase 2 pad expansion is located in the Wasp drainage just south of the Phase 1 pad area.The Phase 1 leach pad area is characterized by terrain sloping generally north and east fromthe pit area to the Barrel drainage which runs generally north-south in this area. A network ofsmall arroyos feed the main Barrel drainage. The leach pad limits follow the major ridgelinesdelineating several of the arroyo networks.

Vegetation at the proposed leach pad site consists of a poor coverage of native grasses andshrubs. Groundwater levels observed within the floodplain of the Barrel drainage range from 46feet to 81 feet below the existing ground surface based on borehole observations. Groundwaterlevel conditions in the pad area is anticipated to be deep, at more than 100 feet below theexisting ground surface. Existing structures in the proposed leach pad study area include the

Rosemont camp located in the northeast portion of the site, and a small power line supplyingpower to the camp.

A geotechnical investigation was performed under the direction of Tetra Tech to characterizethe site soil and rock conditions and provide engineering parameters for feasibility design. Thisinvestigation consisted of 10 geotechnical borings, 33 test pits, and over 18 miles of geophysicalsurvey lines located throughout the site. Additionally, several rock and soils samples were sentfor laboratory testing. Results of the site investigation program are presented in theGeotechnical Study Report (Tetra Tech, June 2007).

A total of 4 of the geotechnical borings, 13 test pits, and approximately 2.3 miles of geophysicalsurvey were completed within the vicinity of the leach pad and ponds. Figure 13 shows thegeotechnical site investigation plan and includes locations of the completed geophysical surveys

and completed and proposed borings and test pits.

3.2 Surface and Subsurface Conditions

Surface soils within the proposed leach pad area are comprised primarily of alluvial deposits inthe drainages and floodplains. The thickness of the alluvium ranges from 20 feet to 80 feetbased on borehole and geophysical data. The two major rock units found within the area are theWillow Canyon and Apache Canyon Formation. Locally, the Willow Canyon Formation consistsof a fine to coarse grained arkosic sandstone to conglomerate and the Apache CanyonFormation is a series of calcareous siltstones and sandstones. Bedrock depth varies from 80 ftwithin the drainages and floodplains to at ground surface within the hills. Where topsoil ispresent, depths vary from 1 foot to 2 feet across the site.

Standard Penetration Tests (SPT) conducted during geotechnical borings indicates mediumdense materials (SPT blow count of 10 to 30) near the surface and very dense materials (SPTblow count of 50) from 20 to 40 ft in depth. Rock Quality Designation (RQD) measurements of

Apache Canyon Formation varied greatly from 10 to 100% with an average value of 62%. RQDvalues for the Willow Canyon Formation located within the leach pad area, are not currentlyavailable. However, a geotechnical boring approximately 1 mile to the north recorded that theRQD values in Willow Canyon material ranged from 0 to 55% with an average of 20%.

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In-situ permeability testing was conducted in the boreholes using the double packer and fallinghead method at depths ranging from 19 to 63 feet. The results indicate fairly low permeabilitysurficial soils (alluvium) with values between 2x10-4 to 5x10-5 centimeters per second (cm/s) andbedrock permeabilities in the 4x10-5 cm/s range. Table 3.1 lists results of field permeabilitytesting completed within the heap leach pad footprint.

Table 3.1: Summary of Insitu Permeability Test Resul ts

Borehole No. Testing

Interval (ft) Estimated

Permeability (cm/s)Geologic Unit

VABH-06-05 0-18.7 1.65x10-4

Alluvium

VABH-06-04 53.5-63.1 4.3 x10-5

Apache Canyon Formation -Fine grained sandstone andsiltstone (contact at ~55.3')

3.3 Climatology

Meteorological records for the immediate vicinity of the Rosemont Project are of limited durationand are available for a period covering 56 to 75 years ago. The U.S. Forest Service obtained

measurements of rainfall and temperature at Rosemont during the period from August 1914 toJune 1931 (University of Arizona, 1977). The elevation of the meteorological station atRosemont was 4,800 feet above sea level. Daily temperature and precipitation at Helvetia,located a few miles to the west at 4,400 feet elevation, are available through the WesternRegional Climate Center (WRCC, 2006) for the period from June 1916 through April 1950. Morerecent meteorological records are available for weather stations in the region and provide abasis for projecting climatic conditions for the Rosemont Project area. These weather stationsinclude: Canelo, located about 25 miles to the southeast at elevation of 5,010 feet; and SantaRita Experimental Range, located about 8 miles to the southwest at 4,300 feet.

More than half of the precipitation recorded at these stations fell during the summer months ofJuly, August, and September. The months with the least recorded precipitation are April, May,and June. In general, annual precipitation has been less than average for the past 10 years,resulting in severe drought conditions.

3.4 Surface Water Hydrology

Annual average precipitation for Rosemont, estimated by Sellers (University of Arizona, 1977)for the period 1931 through 1970, was approximately 16 inches. Based on records availablefrom the Western Regional Climate Center (2006), average annual precipitation for Helvetia forthe period 1916 through 1950 was 19.73 inches. For comparison to more recent information, theaverage annual precipitation for Santa Rita Experimental Range for the period from 1971through 2000 was 22.22 inches. Average annual precipitation for Canelo for the period 1971through 2000 was 18.01 inches (Western Regional Climate Center, 2006).

For feasibility design purposes, average climate data from WRCC data were used for waterbalance calculations and NOAA data was used to develop storm event precipitation depths.

Appendix C1 presents the hydrologic data and water balance analysis.

3.5 Site Geology

The proposed Rosemont mine site lies in the southwestern region of North America, specifically,in the Basin and Range physiographic province. The Basin and Range is characterized byrelatively evenly spaced, subparallel mountain ranges separated by broad, thick alluviatedbasins, the boundaries of which are defined by high-angle extensional faults. This irregularly

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shaped region encompasses an area greater than 1,500 kilometers in length and up to1,000 kilometers in width extending from the southern portions of Idaho and Oregon through themajority of Nevada, parts of western Utah, eastern California, western and southern Arizona,southern New Mexico, and northern Mexico.

The Santa Rita Mountains comprise a relatively small horst consisting of Paleozoic/Mesozoic-

age rocks bounded on the east by the Davidson Canyon graben and a small uplifted rangeknown as the Empire Mountains.

As previously mentioned, the proposed leach pad site is underlain by rocks of the EarlyCretaceous Willow Canyon and Apache Canyon formations. These formations consist oflimestones, siltstones, mudstones, sandstones, and conglomerates. There are known faultsunderlying the heap leach site.

3.6 Site Seismicity

The Arizona Department of Environmental Quality (ADEQ, 1998) has published guidelines formining project design criteria in a publication entitled “Arizona Mining Guidance Manual, Best

Available Demonstrated Control Technology (BADCT).” This manual sets forth

recommendations for minimum standard design criteria with the interest of protectinggroundwater aquifers in the State of Arizona. Accordingly, the BADCT manual recommendsdesign criteria for seismic hazards as follows:

“The minimum design earthquake is the maximum probable earthquake (MPE).The MPE is defined as the maximum earthquake that is likely to occur during a100 year interval (80% probability of not being exceeded in 100 years) and shallnot be less than the maximum historical event. This design earthquake mayapply to structures with a relatively short design life (e.g., 10 years) and minimumpotential threat to human life or the environment.

Where human life is potentially threatened, the maximum credible earthquake(MCE) should be used. MCE is the maximum earthquake that appears capableof occurring under the presently known tectonic framework.”

In accordance with these recommendations, two distinct levels of ground motion are defined forthe proposed Rosemont site: the MPE and the MCE. The maximum ground accelerationexpected at the proposed Rosemont mine site is 0.326g associated with a maximum credibleearthquake on the Santa Rita fault zone, where g is the acceleration due to gravity. Accordingly,the MCE design peak ground acceleration (PGA) equals 0.326g. The site seismicity study ispresented in the Geologic Hazards Assessment (Tetra Tech, June 2007).

The MPE definition requires the larger of the maximum historical event or one having a returnperiod of approximately 448 years, corresponding to the 80% probability of non-exceedanceevent in 100 years. The seismic hazard curve for the Rosemont site indicates that the 80%probability of non-exceedance event in 100 years corresponds to a peak ground acceleration of0.045g. In comparison, the largest earthquake ground motion recorded in the Project area wasassociated with the 1887 Bavispe, Mexico event. The estimates of peak ground accelerationpresented in the Geologic Hazards Assessment indicate that this event would result in anacceleration of 0.036g. Therefore, the design MPE for the proposed Rosemont mine site wouldbe the greater of these two accelerations or 0.045g.

The leach pad ore stack will be designed as a low hazard facility, with fully drained ROM oreplaced in controlled lifts and wetted (partially saturated with no excess pore pressure conditions)during leaching. The wetted ore lifts will densify under successive controlled lift placementoperations, resulting in an increase in the lower lift fill strength over time. Considering the fully

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drained conditions within the ore heap fill, and the low hazard nature of the facility over anapproximate 19 year facility life, the MPE has been selected for the feasibility design.

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4.0 ENGINEERING ANALYSES

4.1 General

The following sections present the engineering analyses conducted for the Rosemont leach paddesign which included slope stability, water balance, liner selection, and pad drain design.

4.2 Slope Stabili ty

4.2.1 General

The leach pad slope stability analyses included an evaluation of the planned foundation, padliner, and ore stack conditions, as shown on Figures 3 and 4. The stability analyses consideredmaximizing the ROM ore tonnage for construction and operation with stable stacked heapslopes on the pad liner system. Final heap slopes for closure may require some slope flatteningfor long term erosion and revegetation conditions, but were not considered for this feasibilitydesign.

4.2.2 Stability Analyses Parameters

The assumed parameters for the ore heap slope stability analyses were developed from a sitereview of surface and subsurface conditions, literature review information, planned construction,and past leach pad construction performance experience.

The planned ore stack limits were evaluated for both static and pseudo-static (earthquake)conditions using the Maximum Probable Earthquake (MPE) and a 50% horizontal groundacceleration factor for the analyses.

4.2.3 Stability Analyses Resul ts

Adequate factors of safety at 1.3 static and 1.1 psueudo-static were obtained from the stabilityanalyses, with the slope geometry as described in this section. (See Appendix C2.)

The slope stability analyses indicate the heap stacking operations can be constructed withstable overall 2H:1V slopes to a total height of 300 feet. The actual ore heap slopes will include30 foot ROM ore lifts stacked at the angle-of-repose (estimated at about 1.3H:1V) with asetback bench as required to develop the overall slope angle. The analysis is based on themaximum ore stack section through the downstream portion of the Phase 1 configuration.Steeper ore stack slopes may be acceptable in uphill areas of the Phase 1 and Phase 2 orestack. Optimization of slopes will be performed during final design, as required.

Some surficial slumping or raveling of the individual angle-of-repose ore lift slopes may occurduring storm runoff or earthquake events. Considering the low hazard nature of the fully drainedgranular ore heap fill structure, and the low probability of an earthquake event at this site duringthe relatively short life of the mine project, the pad liner system should remain intact and the

surficial slope erosion, if any, can be controlled by periodic maintenance around the perimeter ofthe pad.

4.3 Water Balance and Design Flows

4.3.1 General

The leach pad water balance evaluation included available climatology data, estimated oremoisture and production conditions, and planned construction for the Phase 1 leach pad and

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pond operations. A spreadsheet computer model was developed for predicting the averageyearly water balance for storm pond sizing. Leaching operations were simulated for averageprecipitation conditions to validate the PLS pond sizing and to estimate the monthly fresh watermake-up requirements for the heap leach facility and for establishing the maximum processdesign flows. The water balance and pond sizing analyses are presented in Appendix C1.

4.3.2 Pond Sizing

Water balance calculations included sizing of the ponds proposed for the heap leach facility,including the PLS pond, raffinate pond, and storm pond.

The PLS pond is sized to store up to 8 hours of operational flows, including 24 hours of standbydrain down flows. Temporary solution overflows from the PLS pond, if filled to capacity, willdischarge to the storm pond during any upset operational conditions or storm overflow events.The raffinate pond was sized for 4 hours of operational flows, resulting in a storage capacity of 8acre-feet (ac-ft) assuming a minimum operational depth of 10 feet.

The water balance results indicate a required PLS Pond storage capacity of 48 ac-ft and aPhase 1 storm pond storage capacity of approximately 50 ac-ft. All ponds are designed with aminimum 3 foot dry freeboard above design pond levels.

4.3.3 Water Balance Results

The water balance analyses indicate that the average year precipitation conditions result in amakeup water requirement throughout the operational year. The total makeup water required inan average year of precipitation is approximately 800 ac-ft of water corresponding to an averageflow rate of about 500 gallons per minute (gpm). The maximum makeup water rate occurs in themonth of June at up to 600 gpm. Table 4.1 presents the monthly makeup water requirementspredicted by the water balance model and were based on average monthly precipitation andevaporation and the operating parameters presented herein and in Appendix C1.

Table 4.1: Predicted Monthly Freshwater Makeup Requirements

Month Ac-Ft gpm

Jan 57.4 419

Feb 55.0 445

Mar 65.5 478

Apr 69.9 528

May 79.3 579

Jun 79.1 597

Jul 71.0 518

Aug 70.0 511

Sep 67.3 507Oct 66.0 482

Nov 59.9 451

Dec 56.8 414

Total 797.3 -

Average 66.4 494

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It should be noted that the water balance results are very sensitive to the chosen ore fieldcapacity (drain down) moisture value. A value of 7% was used based on previous experiencewith this ore type and material size. The water balance should be revisited upon final design toincorporate retained ore moisture values obtained from the ongoing metallurgical columntesting.

4.3.4 Process Design Flows

Design PLS circulation rates were given by M3 as 2,500 gpm (nominal) and 3,000 gpm(design). The water balance calculations indicate a required average raffinate flow rate ofapproximately 2,900 to 3,100 gpm including evaporation and moisture retention within the ore.

4.4 Liner Design

4.4.1 General

The liner design considered the use of sodium bentonite geosynthetic clay liners (GCL) due tothe low quantity of offsite clay borrow materials available for the Phase 1 leach pad and pondliner system. The GCL liner provides an equivalent 1 foot minimum thickness of 1 x 10-6 cm/sec

or lower permeability soil layer. The higher cost for GCL material can be offset by cost savingsin construction time due to the relatively rapid deployment of the GCL rolls during geomembraneliner installation with no moisture conditioning or compaction required. The GCL surfaceprovides rock puncture protection to the overlying geomembrane liner and only requires asmoothed and compacted subgrade surface to support the composite pad liner system.

The leach pad liner includes an overliner gravity drain fill and pipe system to minimize hydraulicheads on the pad liner and reduce any risk of leakage. The PLS pond includes a doublegeomembrane liner system with leak detection and bottom composite liner for monitoring andcontainment of any leakage through the top pond liner. The single lined (composite liner) stormpond will be dry except during for short periods during storm events or upset operational flows.The storm pond will be drained within 72 hours to provide storm storage capacity throughout theyear. The leach pad and pond liner details are shown on Figures 5 and 12, respectively. Thepad drain system analysis is presented in Appendix C3.

4.4.2 Composite Liner Parameters

Some of the more important technical aspects in liner selection for this Project site includegeomembrane liner resistance to rock puncture, adequate liner friction strengths for slopestability, elongation capacity to withstand earthfill and rock fill foundation settlements under highheap loads, and long-term exposure to climatic conditions (temperature expansion andcontraction, wind forces, and UV sunlight exposure in the collection ditch and pond areas).

Settlement under the pad liner will be minimal with medium dense to dense overburden soils,and the site grading fill will consist of fairly competent rocky materials placed in controlled lifts,moisture conditioned, and compacted by heavy vibratory rollers. The compacted soil and rock

fill should settle at approximately 1 percent or less based on past settlement experience on rockfill dams under similar planned placement and fill load conditions.

The proposed composite liner system incorporates GCL beneath the geomembrane in place ofa compacted clay subliner. The GCL provides an equivalent 1 foot minimum thickness of 1 x10-6 cm/sec or lower permeability soil layer. Appendix C4 presents the equivalency evaluationof this system to the prescribed Arizona BADCT standard.

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4.4.3 Geomembrane Liner Selection

A 60 mil (1.5 millimeter) Linear Low Density Polyethylene (LLDPE) geomembrane liner hasbeen selected for the leach pad based on engineering performance requirements and pastdesign and construction experience. The pad liner will have double textured surfaces forstability. The collection ditch, pond spillway, and PLS and storm pond top liners will include 80

mil (2.0 millimeters) single textured sheet High Density Polyethylene (HDPE) geomembraneliners (textured side facing up for traction) with the secondary PLS and raffinate pond liner toinclude a composite 60 mil LLDPE smooth sheet geomembrane liner in contact with theunderlying GCL.

Conveyor rub sheets will be provided by the owner over the top pond liners in the sump cornersas needed for any foot traffic or pump related operations. A leak detection geonet, sump, andwell pipe will be included between the PLS pond top and bottom liner system with a submersiblepump installed within the leak detection well pipes in each pond sump corner.

4.4.4 Liner Testing

Large scale puncture tests have been completed on representative subsoil, GCL,geomembrane liner, and overliner gravel. Representative samples of subgrade soil werecompacted into a mold and covered with GCL, LLDPE geomembrane, and drain fill gravelproduced from rock taken from the proposed quarry site. Tests were performed for both 60 milLLDPE at a normal stress of 260 pounds per square inch (psi) applied for 48 hours. The linerdid not show evidence of punctures when observed visually and when tested with a vacuum boxtest with a negative pressure of 6 psi. Results of the liner puncture testing indicate verificationof the liner selection performance under simulated loading and site-specific conditions.

Large scale direct shear interface testing was performed on the liner system to provideengineering parameters for heap slope stability. The results indicate a friction angle of 19degrees for textured LLDPE liner to GCL interface and about 12 degrees for smooth LLDPE toGCL interface. Appendix C5 presents the results of the liner testing.

4.5 Pad Drain Design

4.5.1 General

The leach pad drain design includes a 3 foot loose lift thickness of crushed minus 1.5 inch cleanore supplemented by drain pipes above the pad liner for gravity drainage to the collection ditchand ponds. The pad drain pipe design plan, sections, and details are shown on Figure 9. Thepad drain system analyses are presented in Appendix C3.

The leach pad is divided into several cells which generally follow the natural terrain drainagewith the bottom limits of each pad cell site graded to 3 percent toward the northeast corner ofthe pad. Primary collector pipes convey flow to headers at the downgradient edge and allow foroperational monitoring of flows from each cell area. The Phase 2 leach pad will drain to pre-

installed pipes placed during Phase 1 construction.

4.5.2 Pad Drain Pipes and Fill

The corrugated and perforated drain pipe system includes a dual wall 18 inch diameter N-12 PEheader drain pipe along the downhill toe berm limits connected uphill to dual wall 8 inchdiameter N-12 PE primary pipes overlapping with a network of 4 inch diameter PE secondarydrain pipes placed at a 30 foot maximum pipe spacing. This arrangement maintains an averagehydraulic head of less than 20 inches on the pad liner system. The drain pipe system is sized to

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handle the planned operational solution application flows, including 100 year storm event flowsover 24 hours.

A temporary quarry crushing circuit will require commissioning prior to stockpiling or directplacement of a 3 feet thick drain fill cover over the pad liner and drain pipes in advance ofstacking operations. The pad liner system requires complete drain fill coverage as soon as

practical to avoid any potential wind movement damage. The overliner drain fill will also provideliner and drain pipe protection during the initial ore lift placement operations.

4.5.3 Drain Rock Testing

Samples of material (silica-rich Arkose rock) were taken from the proposed quarry area locatedwithin the pit limits for testing for suitability as liner cover drain fill. Appendix C5 presents theresults of the laboratory testing. The drain fill material was used in liner interface and puncturetesting (Section 4.4.4), and a sample was subjected to slake durability (ASTM D4644) testingwith sulfuric acid soaking to simulate acid leaching and verify chemical resistance to theleachate solution. The slake durability test results indicate no loss of durability upon soaking in0.5% sulfuric acid solution and minimal loss upon soaking in 5.0% solution strength. The resultsof the testing indicate the material will exhibit negligible degradation under the expected

operational conditions and is suitable for drain rock fill.

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5.0 CONSTRUCTION QUANTITIES ESTIMATE

Site grading cut and fill calculations were estimated using an Autocad Land Desktop computerprogram and existing topography at 10 foot contour intervals. No bulk or shrink factors wereapplied to the cut and fill estimates. The quantity calculations and details are presented in

Appendix B. Design plans, sections, and details for the feasibility quantity estimate are shownon Figures 3 through 12.

Quantity estimates for the Phase 1 and Phase 2 pad limits include construction of the leach pad,collection ditch, ponds, and uphill diversion systems. The leach pad, collection ditch, and pondfoundation preparation and site grading cut and fill quantities are included as a generalconstruction work item that will be constructed concurrently with both the pad and pond sitegrading fill placement. Other quantity items, including the pad liner, pad drain cover, pond liners,and pipelines, are separated into individual work items, as presented in Appendix B.

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6.0 GENERAL INFORMATION

Recommendations are based on an evaluation of the findings of the site investigations notedearlier. Due to the complexity and variability of natural earth and rock formations and materials,significant variations may occur between or around the boring or geophysical test locations.

Because the test borings and geophysical test areas represent a very small statistical samplingof subsurface conditions, it is possible that conditions may be encountered during constructionthat are substantially different from those indicated by the site investigation results. In theseinstances, design adjustments and construction modifications may be necessary. If conditionsother than those reported are noted during subsequent phases of the Project, Tetra Tech shouldbe notified and be given the opportunity to review and revise the current recommendations, ifnecessary. Recommendations may not be valid if an adequate level of review or inspection isnot provided during construction.

This report has been prepared for the exclusive use of Augusta Resource Corporation forspecific application to the area within this report. Any use of this report by a third party of thisreport, or any reliance on or decisions made based on it, are the responsibility of such thirdparties. Tetra Tech accepts no responsibility for damages, if any, suffered by any third party as

a result of decisions made or actions based on this report. This report has been prepared inaccordance with generally accepted engineering practices. No other warranty, expressed orimplied, is made.

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7.0 REFERENCES

Arizona Department of Environmental Quality, 1998, Arizona Mining Guidance Manual BADCT

(ADEQ Publication Number TB-04-01).

University of Arizona, 1977, An environmental inventory of the Rosemont area in southern

Arizona, Volume I: The present environment: Edited by Davis, R., and Callahan, J.R.

Vector Colorado, LLC, Conceptual Heap Leach Pad Design Layout, June 5, 2006.

Western Regional Climate Center, 2006, Arizona climate summaries:http://www.wrcc.dri.edu/summary/climsmaz.html, May 16, 2006.

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FIGURES

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APPENDIX A

DETAILED DESIGN CRITERIA

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Tetra Tech603 Park Point Drive, Suite 250, Golden, CO 80410

Tel 303.217.5700 Fax 303.217.5705 www.tetratech.com

Technical Memorandum

To: Troy Meyer

Cc: File

From: Joel Carrasco

Project No: 320614

Subject: Detailed Design Criteria – Rosemont Leaching Facil ity

Date: February 22, 2007

1.0 General

This section lists pertinent design criteria and planned approach information for the feasibilitydesign of the Augusta Rosemont copper leach pad and pond facilities. Pertinent design criteria andapproach information includes the following:

• pad and pond borrow development;

• pad and pond foundation preparation;

• pad liner system;

• pad drain cover system;

• ore stack construction;

• solution application;

• solution collection ditch;

• solution process ponds;

• diversion system; and

• solution return pump system.

2.0 Pad and Pond Borrow Development

Borrow development typically includes providing site grading fill for the leach pad, suitable soilsfor a state-of-practice composite liner system, and a drain cover fill above the pad liner for

geomembrane liner protection and drainage of pregnant leach solutions by gravity flow to theexterior process ponds. Pertinent borrow development criteria include the following:

Site Grading Fill Design will balance cuts and fills to the extent possiblefor site grading. Import of borrow material may be

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Detailed Design Criteria 2

necessary from required excavations during sitedevelopment or pit pre-stripping activities

Moisture condition as required for soil compaction tominimum 90 percent of maximum Modified Proctor drydensity (ASTM D-1557) or specified compactive effortor performance specification for rock fills, asdetermined by the engineer

Clayey Soil Fill Suitable borrow sources for clayey soil fill have notbeen located on site. The design will utilize bentoniteGeosynthetic Clay Liner (GCL) in place of acompacted clayey soil liner for the pad and ponds

Liner Bedding Fill Liner bedding fill for GCL liner placement to be

relatively fine grained materials with no rocks largerthan 1.5 inches in the upper 6 inches of the fill.Subgrade to be compacted to minimum 90 percent ofmaximum Modified Proctor dry density (ASTM D-1557)and rolled with minimum 10 tonne vibratory smoothsteel drum compactor to produce suitable surface forGCL deployment

Drain Cover Fill Borrow source to be crushed waste rock fromidentified quarry within pit limits screened as needed toproduce particle sizes between 1.5 inch and 0.5 inchwith less than 5% fines.

No moisture conditioning required

3.0 Pad and Pond Foundation Preparation

Foundation preparation includes removing vegetation and unsuitable materials for constructingsite grading fills and berms as listed below.

Vegetation Clear and grub vegetation (remove as part of strippingexcavation)

Structures Remove buildings and infrastructure at RosemontCamp. Plug any condemnation boreholes in top 100ft depth within the lined leach pad, collection ditch andpond limits

Surface Soils Strip and remove organic surface soils and vegetationto approximate 6 inch depth within leach pad, pondand process plant phase limits and place in temporarytopsoil stockpiles for final reclamation

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Scarify, moisten, and recompact the stripped soilsurface to minimum 90 percent of maximum Modified

Proctor dry density (ASTM D-1557) prior to fillplacement

Bedrock cut or existing rock outcrop surface to becleared of loose rock fragments greater than 8 inchesand wetted in preparation for a transition fill cover asneeded for GCL liner placement

Underdrains Current leach pad layout extents to top of localdrainage boundaries with exception of small drainageon western perimeter. French drain will be required inthis area to convey any water under the pad liner

Site Grading Construct pad phases and perimeter berms with sitegrading cut and fill balance for gravity drainage tosolution collection ditch and PLS pond

Compact site grading fill and final cut surfaces to aminimum 90 percent of Modified Proctor dry density(ASTM D-1557)

Perimeter Berm 3-foot minimum height above pad grade

6-foot minimum crest width along side hill and up hillsections

25-foot minimum road crest width along down hill sideadjacent to collection ditch

2H:1V maximum lined interior slopes, 1.5H:1Vmaximum unlined exterior slopes

Interior Toe & Cell Berms Cell separation will utilize natural terrain drainageareas within the pad area to the extent possible. Cellberms, where required, to be 3 ft minimum heightabove pad grade with 2 ft minimum crest width and2H:1V maximum side slopes

4.0 Pad Liner System

The pad liner system provides an impervious boundary to contain leach solutions and protect theunderlying groundwater. The composite geomembrane and GCL composite system is the state ofpractice in leach pad design where clayey soils are not available for constructing a compactedclay sub-liner and meets Arizona BADCT requirements for site-specific conditions. Componentsof the pad liner system are listed below.

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Soil Liner Fill Geosynthetic clay liner (GCL) for leach pad andprocess ponds (GSE-Gundseal or Bentomat-STM

bentonite GCL product or equivalent)

Minus 1.5 inch maximum rock particle size on finalcompacted and smoothed subgrade surface inpreparation for GCL placement

Geomembrane Pad Liner 1.5 mm (60 mil) textured sheet LLDPE padgeomembrane liner for ore slope stability

Liner Anchor Trench 2 ft wide by 2 ft minimum depth trench for liner backfillanchorage

5.0 Pad Drain Cover System

The pad drain cover system provides liner protection from exposure to the climate, vehicle tracks,foot traffic, and conveyor or haul truck ore placement. The drain cover also reduces hydraulicheads on the pad liner when constructed in combination with supplemental drain pipes at aspacing determined by the leaching solution application rate and the permeability characteristicsof the drain rock. Components of the pad drain cover system are listed below.

Drain Pipes 4 inch diameter corrugated and perforatedpolyethylene (PE) lateral pipes in herringbone fashionon 30 ft maximum centers (to be verified withoverdrain permeability testing)

8 inch diameter corrugated and perforated dual wallN-12 PE collector pipes spaced as necessary tohandle the solution application flows plus estimatedflows from the design storm event

18 inch diameter corrugated and perforated dual wallN-12 PE header pipe at downhill collection ditch toroute flows to pregnant pond

Drain Cover Fill 3 feet minimum thickness of minus 1.5 inch mine pitore crushed and screened as needed for drain coverfill with less than 5 percent fines passing the No. 200

ASTM sieve size. Thickness to be verified based onliner puncture tests.

6.0 Leach Pad Construction

Leach pad construction involves controlled ore placement by trucks and leaching of successivelifts to the maximum design height and slope limits. Components of the planned construction arelisted below.

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Expected Ore Tonnage Startup pad at 50 million dry tons

Total startup and expansion pad at 100 million drytons

Ore Production 51,000 ton per day (peak)

Ore Processing Run of Mine

Ore Height 300 ft maximum design height (to be verified based onore percolation testing)

Ore Slope Individual ore lifts stacked at natural angle-of-reposebetween benches

Target 2H:1V overall slopes with benches with optionfor steeper side hill and up hill slopes, as determinedin stability analyses

Closure requirements to consider covering final spentore limits with mine overburden or waste rock toflatten slopes as required by regulations

Ore Setback 6 ft minimum setback from inside edge of perimeterberm limits

Ore Density 125 pcf bulk density

Ore Moisture Content 2 percent typical as-mined for pond sizing

7 percent drain down for pond sizing

10 percent for makeup water estimates

Leach Pad Phasing Startup lined pad area at about 4,500,000 square ftbased on 300 ft max ore stack height

Ultimate pad expansion lined area at about 9,400,000square ft

Ore Stack Factor of Safety Static factor of safety = 1.5

Psuedo-static factor of safety = 1.1

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7.0 Solution Application

Solution application involves the uniform application of raffinate solution to the ore stack surfacefor controlled infiltration and leaching of the ore. The enriched pregnant leach solution (PLS) ispumped from the collection ponds to the plant for metal recovery. The planned leach solutionapplication components are listed below.

Raffinate Irrigation Rate 0.004 gpm/sf by drip emitters

Pregnant (PLS) Flow Rate 2,500 gpm nominal, 3,000 design

Raffinate Circulation Rate 4,000 gpm (TBD)

Drain Down Flow Rate 2,500 gpm in 24 hours with standby emergencybackup pumping system to top surface

Active Leach Surface 1,000,000 sq ft

Leach Cycle 45 days

8.0 Solution Collection Ditch

The solution collection ditch will route the leach pad drain pipe solutions by pipeline to thepregnant pond with the ditch lined for double containment. The collection ditch will be backfilledwith drain fill for locating application pipelines on the backfill surface as needed. The solutioncollection ditch components are listed below.

Ditch Slopes 2.5H:1V

Ditch Bottom Grade 0.5% minimum to pregnant pond

Ditch Liner 60 mil HDPE

Pad Cell Flow Monitoring Flow measurement and sampling as required byowner

Ditch Liner Anchor Trench 2 ft wide by 2 ft minimum depth trench for liner backfillanchorage

Ditch Backfill Screened drain fill to cover collection pipe and provide

surface area below ditch freeboard for locating returnapplication pipeline to ore stack

Ditch Freeboard 1 ft minimum below perimeter access road level forstorm containment

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9.0 Solution Process Ponds

The solution collection ponds will collect and store 100 percent of the operational solutions, aswell as any temporary drain down and design storm flows within the lined leach pad, collectionditch and process pond areas. The planned solution process ponds include a double linedPregnant (PLS) pond and Raffinate pond and a single lined Stormwater pond for any temporarystorm and operational upset events. The solution process pond components are listed below.

Pond Design Depth Target 25 ft maximum including 3 ft freeboard

Pond Bottom Grade Grade to drain to 3 ft deep corner sumps

Berm Crest Width 25 ft minimum for security fencing and access topumps

Berm Slopes 2.5H:1V maximum lined interior and 2H:1V maximumexterior

Soil Liner Fill GCL

Top Geomembrane Liner 80 mil HDPE

Bottom Geomembrane Liner 60 mil LLDPE (Pregnant and Raffinate Ponds only)

Leak Detection System Geonet and geofabric on pond bottom and geofabricon pond slopes

Leak detection well at 6 inch diameter PVC pipebetween top and bottom liners on pond slope

Pond Liner Anchor Trench 2 ft wide by 2 ft minimum depth trench for liner backfillanchorage

Pond Sizing PLS process pond to store temporary 24 hr draindown and 8 hr operational flows + 3 ft freeboard

Storm Event pond to store temporary excess waterbalance from storm and process pond upset eventsfor 72 hrs maximum + 3 ft pond freeboard

Raffinate pond to store 4 hrs of retention time flow + 3ft freeboard

Emergency 24 hour backup pump system includingpower supply for process pond flows and portable gasoperated pump for storm event pond drained back toPLS pond within 72 hours

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10.0 Fencing

A security fence and posted signs are planned around the leach pad and pond facilities, asdesigned by others. The leach pad limits will include a perimeter access road with a 5-foot highfour-strand barbed wire fence. The process ponds will include a 10-foot high chain-link fence with asecurity gate for access by authorized personnel.

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APPENDIX B

CONSTRUCTION QUANTITES

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APPENDIX C

ENGINEERING ANALYSIS

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APPENDIX C1

WATER BALANCE AND POND SIZING ANALYSIS

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To: File

Cc:

From: Todd Lewis

Project No: 320614

Subject: Water Balance Pond Sizing- Rosemont Leach Facility

Date: 1/26/2007

1.0 Objective

Perform feasibility-level sizing of the various ponds proposed by Augusta Resource (Augusta) forconstruction as part of the Rosemont Copper Project heap leach facility, which entails:

• Pregnant Leach Solution (PLS) Pond,

• Raffinate Solution Pond, and

• Storm Water Pond (for runoff from the heap leach pad; Phases 1, 2, and 1+2separately).

Once the feasibility-level sizing is complete, simulate one year of heap leach operations underaverage climate conditions to validate the pond sizing and to estimate the monthly fresh water

make-up requirements of the Rosemont heap leach facility.

2.0 Method

Feasibility-level sizing of ponds involved in a heap leach water cycle follows a four-step process:

1. Create a schematic diagram of the heap leach water cycle focusing on inflows to thesystem, outflows from the system, and portions of the system where water storageexists.

2. Identify the subset of the water cycle on the schematic diagram that must becomputed (using the principle of conservation of mass) in order to determine allnormal inflows to the pond that is being sized.

3. Estimate maximum inflow rates to the pond that is being sized (in an average year)then compute design volumes by multiplying the aforementioned inflow rates byprescribed design durations.

4. Assume a base width and then compute the dimensions of the pond by stacking thedesign volumes and computing the height associated with each “slice” subject to thegeometric constraints of the pond (side slopes, length to width ratio, etc.)

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Water Balance Pond Sizing 2

Water balance calculations to validate the pond sizing and estimate the monthly fresh water

make-up requirements of the heap leach water cycle are based on the principle of conservation ofmass, which may be expressed in its most basic form as:

∆S = (ΣI – ΣO) x ∆t

Where:∆S = Change in system volume,ΣI = Sum of inflows to system,ΣO = Sum of outflows from system, and∆t = Elapsed time.

For storage structures within the Rosemont heap leach water balance model, normal operationsmay entail changes in the volume of water stored at the end of a simulated time increment

(months). The estimated pond sizes are validated if their respective capacities are not exceededduring simulated operations in an average year.

At the system-wide level, the Rosemont heap leach water balance must operate under the criteriathat ∆S = 0. At the Rosemont site, local climatic conditions dictate that additional fresh make-upwater has to be added to the system in given months, i.e. the Rosemont heap leach waterbalance cycle is a net evaporative system.

3.0 Assumptions

• Leach ore properties Leach ore production rate = 38,000 tons per day (tpd), Leach ore “as-mined” moisture content = 2.0%, and

Leach ore field capacity = 7.0%.• Raffinate solution application

Raffinate application method = drip emitters, Raffinate application evaporative loss rate = 3.0% (of the raffinate application rate), and Target PLS flow rate to PLS Pond = 2,500 gallons per minute (gpm).

• Heap leach pad design Active leach surface = 1,000,000 square feet (ft

2), and

Phase 1 lined area = 4,370,161 ft2,

Phase 2 lined area = 4,511,933 ft2, and

Ultimate lined area = 8,882,094 ft2.

• Pond design PLS Pond is sized for 8 hours of operational flow plus 24 hours of heap drain-down flow

with an additional 3 feet (ft) of dry freeboard,

PLS drain-down flow rates are assumed equivalent to the estimated PLS Pondoperational flow rates, Raffinate Solution Pond is sized for 4 hours of operational flow with an additional 3 ft of

dry freeboard, Storm Water Pond is sized for the 100 year (yr), 24 hour precipitation event, which equals

4.68 inches (in), over the lined heap leach pad area (Phases 1, 2, and 1+2 are doneseparately) with an additional 3 ft of dry freeboard,

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Process pond (PLS and Raffinate) minimum operating depth = 10 ft, Pond side slopes = 2.5 horizontal to 1 vertical (2.5:1),

Variable pond length to width ratio of between 2.5 long to 1 wide (2.5:1) and 1.5:1, and Pond shapes are frustums of inverted rectangular pyramids.

• Climate Pond surface evaporation coefficient = 0.70 (of Pan) as given in Handbook of Applied

Hydrology (Chow, 1964), Wetted leach surface evaporation coefficient = 0.85 (of Pan) to account for the additional

area exposed on the surface of the heap leach pad, and Average year precipitation and evaporation values were taken from Santa Rita

Experimental Range, Arizona: Monthly Total Precipitation (inches) (WRCC, 2005) andMaximum, Normal and Minimum Daily Evaporation and Average Monthly EvaporationFrom Open Water Surfaces (ADWR, 2005) as given in Table 1.

4.0 Calculations

A schematic diagram of the Rosemont heap leach balance cycles is shown on Figure 1.

PLS Pond sizing focused on the subset of the Rosemont heap leach water balance cyclecentered on the PLS Pond. As shown in Figure 1, normal inflow rates to the PLS Pond includethe pregnant leach solution flow from the heap leach pad (Ghl) and direct precipitation on the PLSPond (Ppp). Details of the PLS Pond sizing are given in Attachment 1, with associated waterbalance formulas taken from Figure 1. (Note that since the normal inflow rate (Ghl) is specified,average precipitation and evaporation data are not required for sizing the PLS Pond.)

Sizing of the Storm Water Pond for Phases 1, 2, and 1+2 was performed using three parameters:the lined area of the heap leach pad, design storm runoff from the heap leach pad, and directprecipitation on the Storm Water Pond during the design storm event. Details of the Storm Water

Pond sizing are given in Attachments 2, 3, and 4 for Phases 1, 2, and 1+2, respectively.

Raffinate Solution Pond sizing focused on the subset of the Rosemont heap leach water balancecycle centered on inflows and outflows from the Raffinate Solution Pond. Referring to Figure 1,the barren raffinate solution outflow rate to the heap leach pad (B rp) can’t exceed the sum of thebarren raffinate solution inflow rate (Bsx), direct precipitation on the Raffinate Solution Pond (Prp),and the fresh water make-up rate (Ffs). Accordingly, the normal inflow rate to the heap leach padwas taken as Brp. Details of the Raffinate Solution Pond sizing are given in Attachment 5, withassociated water balance formulas taken from Figure 1. (Note that for this calculation, thegreatest required solution application rate is in the month of June at 3,073 gpm in order to sustainthe target 2,500 gpm PLS flow rate.)

One year of Rosemont heap leach water cycle operations was simulated under average

precipitation conditions using a water balance model based on the schematic and water balanceequations shown on Figure 1. This model, detailed in Attachment 6, was used to verify pondsizing and to determine monthly fresh water make-up required at the site.

5.0 Conclusions/Results

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For the sizing of each pond, various alternative configurations were computed in order to providea range of possible dimensions. These results are detailed in Table 2 and are summarized below:

• PLS Pond – depending on the selected geometric configuration (in Table 2), the PLS Pondshould have an ultimate capacity between 44 and 60 acre-feet.

• Phase 1 Storm Water Pond – depending on the selected geometric configuration, the Phase1 Storm Water Pond should have an ultimate capacity of about 50 acre-feet.

• Phase 2 Storm Water Pond – depending on the selected geometric configuration, the Phase2 Storm Water Pond should have an ultimate capacity between 54 and 55 acre-feet.

• Phase 1+2 Storm Water Pond (if one combined pond is built) – depending on the selectedgeometric configuration, the Phase 1+2 Storm Water Pond should have an ultimate capacitybetween 110 and 116 acre-feet.

• Raffinate Solution Pond – depending on the selected geometric configuration, the RaffinateSolution Pond should have an ultimate capacity between 5 and 11 acre-feet.

The Rosemont heap leach water balance cycle was simulated with average year climate valuesand pond configurations as indicated in Table 2 to validate the pond sizing and determine thefresh water make-up requirements at the site. The heap leach water balance results are detailedin Table 3. Key results are summarized below:

• As was mentioned in the Method Section, the Rosemont heap leach water balance cycle is anet evaporative system. The water balance results agree with this assertion as fresh watermake-up is predicted year-round for all scenarios investigated.

• The results show that the consumptive maximum fresh water requirements for the RosemontCopper Project are 600 gpm.

6.0 References

Arizona Department of Environmental Quality (2005). Arizona Mining BADCT Guidance Manual, Aquifer Protection Program. Publication TB-04-01. Phoenix, AZ: ADEQ.

Arizona Department of Water Resources (2005). Maximum, Normal and Minimum DailyEvaporation and Average Monthly Evaporation From Open Water Surfaces. File name“EvaporationRates.tif” provided by Augusta Resource Corp. Phoenix, AZ: ADWR.

Chow, V.T. (1964). Handbook of Applied Hydrology. New York, NY: McGraw-Hill.Western Regional Climate Center. (2005). Santa Rita Experimental Range, Arizona: MonthlyTotal Precipitation (inches). File name “SantaRitaPrecip.tif” retrieved on October 4, 2005 by

Augusta Resource Corp. from URL: http://www.wrcc.dri.edu/cgi-bin/cliMONtpre.pl?azsant. Reno,NV: WRCC.

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APPENDIX C2

STABILITY ANALYSIS

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To: Alyssa Kohlman

Cc:

From: Ana Mohseni

Project No: 310306

Subject: Stability Analyses- Rosemont Leach Facility

Date: April 12, 2007

1.0 Introduction

This memo presents the results of slope stability analyses of the proposed heap leach facility atthe Rosemont Mine in Arizona. The heap leach facility will be constructed on natural ground witha grade ranging from 3% to 7%. Structural fill composed of ROM ore will be used to flatten thenatural grade near the toe of the heap to 3% to 4%, as shown in the attached sections. The mostcritical (steepest natural grade and pad grade) maximum section of the Stage 1 heap leachfacility was analyzed.

2.0 Design Criteria

Design of the heap leach facility is governed by the requirements of the Arizona Mining GuidanceManual BADCT. Based on these requirements, the minimum stability criteria adopted for theheap leach facility are presented in Table 1.0.

Table 1.0 Minimum Stability Requirements

Analysis Condit ionRequired Minimum

Factor of Safety

Static 1.30

Pseudostatic 1.10

The site seismicity was analyzed for two levels of ground motion: the maximum probableearthquake (MPE) and the maximum credible earthquake (MCE). These values are 0.045g for

the MPE and 0.200g for the MCE. Since the facility life is relatively short and no threat to humanlife is anticipated, the MPE ground motion was utilized for pseudostatic analyses of the heapleach facility.

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Stability Analyses 2

3.0 Methods

The stability analyses were performed using the Slope/W component of GeoStudio 2004 (Version6.20) by Geo-Slope International, Ltd. Slope/W was used to conduct limiting equilibrium analysesusing the general limit equilibrium (GLE) method, which satisfies both force and momentequilibrium. This program incorporates search routines to determine the critical, lowest factor-of-safety failure surface.

Slope/W was used to conduct analyses of slope stability considering block sliding on the linerinterface and global (rotational) stability of the ore and the foundation materials. Full height failuresurfaces, intersecting the crest of the ore, were considered for all analyses. The heap wasmodeled with one foot of head on the liner.

To evaluate the performance of the heap under seismic loading a pseudo-static analysis was

performed. The pseudo-static analyses subject the two-dimensional sliding mass to a horizontalacceleration equal to an earthquake coefficient multiplied by the acceleration of gravity. To allowfor damping and attenuation of the bedrock acceleration within a slope or embankment, and toaccount for the rigid body pseudo-static model, the pseudo-static coefficient used in the modelwas a conservative estimate of horizontal ground motion of 2/3 of the peak ground acceleration ofthe design earthquake (the MPE in this case), or 0.030g.

A yield acceleration analysis was also performed, to determine the critical level of horizontalground motion for the heap leach facility. The yield acceleration is the horizontal groundacceleration that results in a factor of safety equal to unity using limit equilibrium methods ofstability analysis. This yield acceleration was compared to the design ground acceleration todetermine a factor of safety against pseudostatic failure of the heap leach.

Material properties for the heap materials were determined from field and laboratory testing,experience with similar materials, published literature, and professional judgment. The bilinearstrength model used for the ROM Arkose Ore is a conservative adaptation of the industrystandard Leps (1970) rock strength model. Leps’ strength model of the weakest type of rock fillwas adapted for these analyses. The Leps strength of the ore is conservative when comparedwith laboratory testing of the Arkose material at the site. The material properties for the alluvium,structural fill, and liner interface were based on site-specific laboratory testing. The materialproperties for the weathered bedrock were based on field and laboratory testing and subsequentanalysis. The material properties used in the analyses are presented in Table 2.0.

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Stability Analyses 3

Table 2.0 Material Properties

Phi Cohesion UnitWeightMaterial # Descript ion Strength Model

degrees psf pcf

1 ROM Arkose Ore Bilinear

0-60': 38degrees60'+: 34degrees

0 140

2 Structural Fill Mohr-Coulomb 39 2000 140

3LL/GCL Liner Interface

(Textured)Mohr-Coulomb 19 0 95

4 Alluvium Mohr-Coulomb 39 2000 127

5 Weathered Bedrock Mohr-Coulomb 40 3500 160

4.0 Results

Both the static and pseudostatic factors of safety against a full-height failure of the heap leachwere found to be adequate for a block failure sliding on the liner interface and for global stability.Failure through the foundation materials does not represent a critical failure mode for the heapleach with the material properties used in the analysis. Table 3.0 shows the results of theanalyses.

The yield acceleration for the heap leach for sliding on the liner was found to be 0.14g. This givesa factor of safety against pseudostatic failure, when presented as the ratio of the yieldacceleration to the design acceleration (2/3 of the MPE for pseudostatic analyses), of 4.67. Sincesliding on the liner is the more critical failure mode (versus global failure of the ore), applying the

yield acceleration to a global failure scenario results in a safety factor greater than unity. Theanalyses discussed in this memorandum are attached.

Table 3.0 Results of Slope Stability Analyses

Safety Factor

Ore Slope Scenario Static PseudostaticYield/Design

Accelerat ion

2H:1V Block sliding on liner 1.41 1.30 4.67

2H:1V Global Failure of Ore 1.70 1.58 N/A

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ATTACHMENT A

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1.41

OSEMONT FEASIBILITY STUDY

EAP LEACH FACILITYMaterial #: 1Description: ROM Arkose OreWt: 125Cohesion: 0Phi 1: 38Phi 2: 34Bilinear Normal: 7200

(Normal load equivalent to approx. 60 feet of

Material #: 2Description: Structural FillWt: 140Cohesion: 2000Phi: 39

Material #: 3Description: LLDPE/GCL Liner Interface (textWt: 95Cohesion: 0Phi: 19

250' @ 7% 3%

450' @ 4%

2H:1V

3%

ethod: GLEp Surface Option: Block

orz Seismic Load: 0tatic)

Distance (ft) (x 1000)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1

H e i g h t ( f t )

0

100

200

300

400

500

600

700

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1.30

ROSEMONT FEASIBILITY STUDY

HEAP LEACH FACILITY

Material #: 1Description: ROM Arkose OreWt: 125Cohesion: 0Phi 1: 38Phi 2: 34Bilinear Normal: 7200(Normal load equivalent to approx. 60 feet of o


Material #: 3Description: LLDPE/GCL Liner Interface (textuWt: 95Cohesion: 0Phi: 19

250' @ 7% 3%

450' @ 4%

2H:1V

3%

Method: GLElip Surface Option: Block

Horz Seismic Load: 3.e-002Horizontal Component of the MPE)


0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1

H e i g h t ( f t )

0

100

200

300

400

500

600

700

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1.70


HEAP LEACH FACILITY




250' @ 7% 3%

450' @ 4%

2H:1V

3%

Method: GLElip Surface Option: EntryAndExit

Horz Seismic Load: 0Static)


0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1

H e i g h t ( f t )

0

100

200

300

400

500

600

700

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1.58


HEAP LEACH FACILITY




250' @ 7% 3%

450' @ 4%

2H:1V

3%

Method: GLElip Surface Option: EntryAndExit

Horz Seismic Load: 3.e-002Horzintal Component of the MPE)


0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1

H e i g h t ( f t )

0

100

200

300

400

500

600

700

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1.01

OSEMONT FEASIBILITY STUDY

EAP LEACH FACILITYMaterial #: 1Description: ROM Arkose OreWt: 125Cohesion: 0Phi 1: 38Phi 2: 34Bilinear Normal: 7200

(Normal load equivalent to approx. 60 feet of


Material #: 3Description: LLDPE/GCL Liner Interface (textWt: 95Cohesion: 0Phi: 19

250' @ 7% 3%

450' @ 4%

2H:1V

3%

ethod: GLEp Surface Option: Block

orz Seismic Load: 0.14ield Acceleration)


0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1

H e i g h t ( f t )

0

100

200

300

400

500

600

700

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APPENDIX C3

PAD DRAIN SYSTEM ANALYSIS

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Client: Augusta Resource Corp. Job No.: 320614

Subject: Rosemont Project By: JAC

Details: Heap Leach Pipe Sizing Date: May 10, 2007

Slotted ADS Pipe

Mannings n: 0.015

Pipe Slope (m/m): 0.050

Pipe Inside Diameter

(mm)

ow

(m3/s)

Flow Depth

(mm)

Flow Velocity

(m/s)

75 0.005 65 1.19

100 0.010 85 1.45

Slotted ADS Pipe

Mannings n: 0.015


Pipe Diameter

(mm)

ow

(m

3

/s)

Flow Depth

(mm)

Flow Velocity

(m/s)75 0.007 65 1.69100 0.015 85 2.05

Slotted ADS N12 Pipe

Mannings n: 0.012Pipe Slope (m/m): 0.080

Pipe Diameter

(mm)

ow

(m3/s)

Flow Depth

(mm)

Flow Velocity

(m/s)

100 0.016 85 2.29

150 0.048 128 3.00

200 0.104 170 3.64

250 0.188 213 4.22

300 0.305 255 4.77

375 0.554 319 5.53450 0.901 383 6.25

600 1.939 510 7.57

760 3.641 646 8.86

Mannings n: 0.012


Pipe Diameter

(mm)

ow

(m3/s)

Flow Depth

(mm)

Flow Velocity

(m/s)

100 0.010 85 1.40

150 0.029 128 1.84

200 0.063 170 2.23

250 0.115 213 2.59300 0.187 255 2.92

375 0.339 319 3.39

450 0.552 383 3.83

600 1.187 510 4.64

760 2.230 646 5.43

HeapPipeSizingCalcs_rev4.xls

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Client: Augusta Resource Corp. Job No.: 320614

Subject: Rosemont Project By: JAC

Details: Heap Leach Pipe Sizing Date: May 10, 2007

Avg. Solution Outflow Rate (m3/hr): 681.4 3,000 gpm (From Water Balance)

100-Year 24-Hour Precipitation (m): 0.119 4.68 inches (From NOAA Atlas 14)

Total Area

(m2)

Total Area

(ft2)

Primary Pipe

Design Slope

(m/m)

Header Pipe

Design Slope

(m/m)

Phase 1 - North: 181,685 1,955,644 0.030 0.030

Phase 1 - South: 224,316 2,414,516

Total Phase 1: 406,001 4,370,160

Phase 2 - West: 272,301 2,931,021 0.030 0.030

Phase 2 - East: 147,009 1,582,396

Total Phase 2: 419,310 4,513,417

To tal Pad A rea: 825,311 8,883,577

Header Pipes

PLS Solution + 100-Year Storm Flow

Area

PLS Flow

(m3/hr)

Storm Flow

(m3/hr)

Total Flow

(m3/hr)

Total Flow

(gpm) No. Pipes

Pipe

Diameter

(mm)

Phase 1 681 2011 2692 11854 2.0 450

Phase 2 681 2077 2758 12144 2.0 450

Primary Pipes


Area

PLS Flow

(m3/hr)

Storm Flow

(m3/hr)

Total Flow

(m3/hr)

Total Flow

(gpm) No. Pipes

Pipe

Diameter

(mm)

Phase 1 - North 681 900 1581 6962 7 200

Phase 1 - South 681 1111 1792 7892 8 200

Phase 2 - West 681 1349 2030 8938 9 200

Phase 2 - East 681 728 1410 6206 7 200

Check Secondary Pipe Capacity

Calculated Pipe Spacing = 10 m (based on McWhorter equation)

Controlling Design Pipe Slope = 0.05 m/m


Phase

PLS Flow

(m3/hr)

Storm Flow

(m3/hr)

Total Flow

(m3/hr)

Total Flow

(gpm) No. Pipes

Pipe

Diameter

(mm)

Phase 1 - North 681 900 1581.26 6962 92 75

12m spacing ok for capacity


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CLIENT: Augusta Resources Corp.

PROJECT: Rosemont Project JOB NO: 320614SUBJECT: Heap Leach Pad Pipe Sizing BY: JAC

DETAILS

Pipe Spacing - McWhorter & Sunada, 1977

Date:

May 10, 2007

Units: Metric Application Rate: 0.0050 gpm/ft2

Application Rate: 0.29 m^3/day/m^2 12.2242 l/hr/m2

Maximum Desired Head on the Liner: 1.0 m 0.0122 m3/hr/m

2

Hydraulic Conductivity: 8.64 m/day 0.29 m3/day/m

2

10.36 ft /day/ft

Pipe Spacing: 10.9 m

Average Hydraulic Head on Liner: 0.5 m

Hydraulic Conductivity 0.0100 cm/s

28.35 ft/day

8.64 m/day

Where:

H = Maximum Hydraulic Head on Liner at Midpoint between Pipes

L = Drain Pipe Spacing

W = Application Rate

K = Hydraulic Conductivity

1) Assumes permeability in drain layer of 1 x 10 -2 for a fully loaded scenario with lift height at 60 meters

Pipe Spacing App lic ation Rate Conv erter

Hydraulic Conductivity Converter

5.0

*2

⎟ ⎠

⎞⎜⎝

⎛ =

K

W L H


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APPENDIX C4

LINER SYSTEMS ANALYSIS

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To: Troy Meyer

Cc:

From: Alyssa Kohlman

Project No: 320614-200-30

Subject: BADCT Equivalence- Rosemont Heap Leach Liner

Date: April 17, 2007

1.0 Introduction

This memorandum has been prepared in order to demonstrate the equivalence of the proposedheap leach liner system at the Rosemont mine in Pima County, Arizona to the BADCTPrescriptive requirements set forth in the Arizona Department of Environmental Quality’s “ArizonaMining Guidance Manual BADCT” (ADEQ Publication Number TB-04-01).

Under the BADCT Prescriptive criteria, engineering equivalents to specific elements are deemedacceptable as long as supporting evidence is provided to ADEQ. The following sections provide asummary of the proposed design of the heap leach liner system and discussions of engineeringanalyses demonstrating the equivalence of the certain aspects of the proposed design toacceptable BADCT standards.

2.0 Background

Rosemont is a proposed copper-molybdenum mining project (Project) in Arizona. The project siteis located approximately 35 miles southeast of Tucson, Arizona on the east slope of the SantaRita Mountains. The Project will be developed as an open pit mine with a milling and processingplant for sulfide ores and a leaching facility for oxide ores. The leach pad and associated pondsare proposed to be located just east of the open pit.

3.0 Proposed Design

Some of the more important technical aspects in liner selection for this project site includegeomembrane liner resistance to rock puncture, adequate liner friction strengths for slopestability, elongation capacity to withstand rock fill foundation settlements under high heap loads,and long-term exposure to climatic conditions (temperature expansion and contraction, windforces and UV sunlight exposure in the collection ditch and pond areas).

Settlement under the pad liner will be minimal with medium dense to dense overburden soils, andthe site grading fill will consist of fairly competent rocky materials placed in controlled lifts,moisture conditioned, and compacted by heavy vibratory rollers. The compacted soil and rock fill

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BADCT Equivalence 2

should settle at approximately one percent or less, based on past settlement experience on rockfill dams under similar planned placement and fill load conditions.

The basic design of the Rosemont heap leach liner system consists of prepared subgrade,overlain by a geosynthetic clay liner (GCL), overlain by 60-mil double-textured LLDPE. Three feetof overliner drain fill and an internal drainage pipe network will be placed over the 60 mil liner.Each of the liner components is intended to maintain the constructability and performance of theliner system to protect the environment and limit undesired seepage of process fluids. Thefollowing sections contain details on each of the liner components. A schematic showing theleach pad liner section is presented in Figure 1.0.

Figure 1.0 Schematic of Proposed Leach Pad Liner Section

3.1 Overliner Drain

The heap leach overliner drain rock is proposed to consist of a three-foot thickness of processeddrainage material (clean crushed rock), with 100% passing a 1.5” screen. The function of thislayer is to protect the geomembrane from damage that might occur from construction oroperations activities, and to collect leachate drainage from the overlying heap, thus limitinghydraulic head on the geomembrane liner.

The use of minus 1.5-inch material for the drainage layer rather than the BADCT specified minus¾-inch material is based upon a site specific approach for Rosemont, rather than the prescriptivestandards in BADCT. This use of material is supported by laboratory testing, as described below.

The pipe network in the overdrain material consists of four-inch diameter corrugated perforatedPE N-12 drain pipe at typical 30 foot herringbone spacing. These pipes feed to a series of largerdiameter collector pipes. The system has been designed to minimize head on the liner. Average

head on the liner is expected to be approximately one foot.

3.2 LLDPE Geomembrane

A 60 mil (1.5 mm) Linear Low Density Polyethylene (LLDPE) geomembrane liner has beenselected for the leach pad, based on engineering performance requirements, and past design and

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BADCT Equivalence 3

construction experience. The pad liner will have double textured surfaces in order to enhance theheap leach stability and the safety of construction workers working on the liner in irregular terrain.

LLDPE provides superior puncture resistance compared to HDPE. A 60-mil liner was deemedadequate based on site-specific liner puncture testing for the project.

The collection ditch, pond spillway, and pregnant and storm pond top liners will include 80 mil (2.0mm) single textured sheet HDPE geomembrane liners (textured side facing up for traction) withthe secondary PLS and Raffinate pond liner to include a composite 60 mil LLDPE smooth sheetgeomembrane liner in contact with the underlying GCL liner. Schematics of the single- anddouble-lined ponds are shown in Figures 2.0 and 3.0. Conveyor rub sheets will be provided bythe owner over the top pond liners in the sump corners and anchored at the pond crest asneeded for any foot traffic or pump related operations. A leak detection geonet, sump and wellpipe will be included between the pregnant pond top and bottom liner system with a submersiblepump installed within the leak detection well pipes in each pond sump corner. The ponds will beleak tested before operation using a standard procedure of filling the ponds with fresh water and

monitoring the leak detection sump. Any significant leaks that would transfer hydraulic head tothe primary liner will be repaired prior to operation of the pond. During operations, the pond willbe monitored and repaired if leakage rates greater than the threshold level established by theEngineer are exceeded.

Figure 2.0 Schematic of Single-Lined Pond Liner Section

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BADCT Equivalence 4

Figure 3.0 Schematic of Double-Lined Pond Liner Section

3.3 Geosynthetic Clay Liner (GCL)

A sodium bentonite geosynthetic clay liner (GCL) was selected for the low-permeability layer inthe liner system due to the absence of available onsite clay borrow materials for the leach padand pond liner system. The GCL liner provides the equivalent of a one-foot minimum thickness of1 x 10

-6 cm/sec or lower permeability soil layer.

The higher cost for GCL can be offset by cost savings in construction time due to the relativelyrapid deployment of the GCL rolls during geomembrane liner installation with no moisture

conditioning or compaction required. The GCL surface provides rock puncture protection to theoverlying geomembrane liner, and only requires a smoothed and compacted subgrade surfacegraded to drain and support the composite pad liner system.

The direct contact between the geomembrane liner and low permeability subliner GCL reducesthe seepage through the liner system, and is the state-of-practice liner system for copper heapleach pads. As discussed above, the leach pad liner includes an overliner gravity drain fill andpipe system to minimize hydraulic heads on the pad liner and limit leakage.

4.0 Engineering Analyses

4.1 Geochemical Compatib ility

Geochemical compatibility with leachate was addressed for both the LLDPE and for the bentoniteGCL product. Technical literature indicates that sulfuric acid in the concentrations that will bepresent in the heap (approximately 0.5% concentration) will have little or no effect on the LLDPE.While low pH and high ionic strength solutions can be detrimental to the performance of sodiumbentonite, these detrimental effects are minimal under high confining pressures and low acidlevels at Rosemont. In addition, the expected confining pressures at Rosemont are well above

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BADCT Equivalence 5

those shown to minimize the detrimental effects of acidic and high ionic strength solutions onbentonite (Thiel and Criley, 2005).

A chemical resistance summary chart provided by Sierra Geosynthetics and Agru technicalliterature regarding LLDPE chemical resistance are provided in Attachment A.

4.1.1 Puncture Resistance

LLDPE was selected for the geomembrane material in the liner system because of its superiorpuncture resistance in comparison to other available geomembrane types. It should be noted thatplacement of the GCL layer under the geomembrane liner generally increases the punctureresistance of the LLDPE to the underlying material (prepared subgrade). GCL also has the addedbenefit of sealing off punctures that occur in overlying geomembranes (Narejo et. al., 2002).

Laboratory testing on site-specific material was conducted to ensure that components of the linersystem will have adequate puncture resistance under the project loads. The testing was

conducted on 60-mil smooth LLDPE. The overdrain layer consisted of a composite ofrepresentative on-site materials screened through a 1.5-inch sieve. The bedding layer consistedof on-site arkose rock screened over a 1.5-inch sieve. A layer of CETCO GCL was placedbetween the geomembrane and bedding layer (woven side of GCL facing the LLDPE). The testload used was 390 psi, which corresponds to an ore heap height of 450 feet, which is higher thananticipated ore heights in order to incorporate a factor of safety against puncture.

Although two “major” indentations were observed in the geomembrane, no holes were observedby visual inspection or with a vacuum box. Full puncture test results are included in the heapleach report for this project.

4.1.2 Leakage

Vector calculated the expected hydraulic performance of two leach pad liner options:

• BADCT prescriptive geomembrane/clay system and

• site-specific geomembrane/GCL system proposed for Rosemont.

Theoretical leakage calculations were performed using the Giroud (1997) equations. Giroud andBonaparte (1989) indicate that the 1 cm

2 (“large”) hole is appropriate to size components of the

liner system, such as LCRS systems in double-lined impoundments. This is conservativecompared to the smaller hole recommended for evaluating the performance of the liner system.One (1) 1 cm

2 circular puncture per acre of liner is an appropriate estimate of the number of

defects for liners placed using very good installation practices and QA/QC. More information onthis subject can be found in Giroud and Bonaparte (1989).

Using the Giroud (1997) equation and an average of one foot of hydraulic head on the liner, thecalculations resulted in an estimated liner leakage as follows for the evaluated options:

• 4.6 gal/acre/day for the BADCT prescriptive geomembrane/compacted clay system and

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BADCT Equivalence 6

• 0.70 gal/acre/day for a geomembrane/GCL composite liner system proposed for

Rosemont.

Since the lined area for Phase 1 is approximately 104 acres, this results in a flow ofapproximately 73 to 479 gallons per day, using a GCL or clay system, respectively. Leakagecalculations are presented in Attachment B.

4.1.3 Slope Stability

Potential slip planes internal to the ore, through the foundation materials, and along the planescreated by the liner system were considered. Laboratory testing on the site-specific materialsincluding the liner system components was conducted under loads of 25, 50, and 100 psi. Theweakest interface is expected to be between the GCL and the geomembrane. Large-scale directshear testing of this interface indicated a friction angle of 11 degrees.

Slope stability analyses indicate that the current design of the facility has adequate factors ofsafety against global, full-height failure and against block sliding on the liner interface for both thestatic and pseudostatic conditions. Material properties used and details of the heap leach stabilitytesting are included in a separate memorandum.

5.0 References

Agru America, undated, Chemical Resistance Information for HDPE and Polypropylene,qualitative information brochure.

Chevron Phillips Chemical Company LP / Marlex Polythylene Premium Extrusion and RigidPackaging Resins, 2005, PE TIB-2 Packaging Properties, product technical data.

Giroud, J.P. and R. Bonaparte, 1989, Leakage through Liners Constructed with Geomembranes -Part I. Geomembrane Liners and – Part 2. Composite Liners, Geotextile and Geomembranes 8.

Giroud, J.P., 1997, Equations for Calculating the Rate of Liquid Migration Through GeocompositeLiners Due to Geomembrane Defects, Geosynthetics International, Vol. 4, Nos. 3 – 4, pp. 335 –348.

Narejo et. Al., 2002, An evaluation of geosynthetic clay liners to minimize geomembrane leakagecaused by protrusions in subgrades and compacted clay liners, in Clay Geosynthetic Barriers,Zanzinger, Koerner & Gartung (eds.), (c) 2002 Swets & Zeitlinger, Lisse

Thiel, R. and Criley, K., 2005, Hydraulic Conductivity of a GCL Under Various High EffectiveConfining Stresses for Three Different Leachates, Presented at Geofrontiers 2005, WasteContainment and Remediation

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ATTACHMENT A

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ATTACHMENT B

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ATTACHMENT B

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Giroud's Equation (1997)

Cqo= 0.21 contact quality factor (dimensionless, 0.21 for good contact, 1.15 for poor contact)

h= 0.3049 height of liquid on top of geomembrane (m, must be less than or equal to 3 m)

d= 1.00E-02 diameter of circular defect (m, must be between 0.0005 and 0.025 m)

ts= 0.0060 thickness of low-permeability soil component (m)

ks= 1.00E-09 hydraulic conductivity of low-permeability soil component (m/sec)

Q= 3.17E-08 Rate of liquid migration (m3/sec)

Q= 0.72 Rate of liquid migration (gal/defect/day)

1 Number of installation defects per acre

Q= 0.7 Rate of liquid migration (gal/acre/day)

LEAKAGE RATE CALCULATIONS THROUGH CIRCULAR DEFECTS IN A GEOMEMBRANE/GCL COMPOSITE

LINER

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Giroud's Equation (1997)

Cqo= 1.15 contact quality factor (dimensionless, 0.21 for good contact, 1.15 for poor contact)

h= 0.3048 height of liquid on top of geomembrane (m, must be less than or equal to 3 m)

d= 1.00E-02 diameter of circular defect (m, must be between 0.0005 and 0.025 m)

ts= 0.3049 thickness of low-permeability soil component (m)

ks= 1.00E-08 hydraulic conductivity of low-permeability soil component (m/sec)

Q= 2.03E-07 Rate of l iquid migration (m3/sec)

Q= 4.63 Rate of liquid migration (gal/defect/day)

1 Number of installation defects per acre

Q= 4.6 Rate of liquid migration (gal/acre/day)

LEAKAGE RATE CALCULATIONS THROUGH CIRCULAR DEFECTS IN A GEOMEMBRANE/COMPACTED CLAY

COMPOSITE LINER

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APPENDIX C5

GEOTECHNICAL DATA

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A B C

Normal (psf) 2880 5760 11520

Shear (psf) 3375 4815 9974

Displacement 1.1 1.1 1.1

49.5 39.9 40.9

Direct Shear phi (degrees) c (psf) R2

Arkose02 y = 0.7826 + 795.5x 38.0 795.5 0.9846

Arkose02 y = 0.8747 x 41.2 0 0.9671

Points

Direct Shear:Density/MCSample

Arkose 02 98.5 pcf, air-dried

trendline:

phi calculated by point -1.1" displ.

Direct Shear Test

1.1" Displacement (3 Points)

Linear Trendline (c=0):

y = 0.8747x

R2 = 0.9671

Linear Trendline:

y = 0.7826x + 795.5

R2 = 0.9846

0

2000

4000

6000

8000

10000

12000

0 2000 4000 6000 8000 10000 12000 14000

Normal Stress (psf)

S h e a r S t r e s s

( p s f )

Arkose02

Linear (Arkose02): cohesion = 0

Linear (Arkose02)

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A B C

Normal (psf) 2880 5760 11520

PEAK Shear (psf) 2410 5492

Displacement 1.216 1.625 N/A

39.9 43.6 0.0

Direct Shear phi (degrees) c (psf) R2

Arkose02 y = 1.0701 x - 672 46.9 -672 1 NOT VALID

Arkose02 y = 0.9301 x 42.9 0 0.981

Sample Density/MC Direct Shear:

Points

Arkose 02 98.5 pcf, air-dried

phi calculated by point -1.1" displ.

trendline:

Direct Shear Test

Peak Strength (2 Points )

Linear Trendline (c=0)

y = 0.9301x

R2 = 0.981

Linear Trendline:

y = 1.0701x - 672

R2 = 1

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Normal Stress (psf)

S h e a r S t r e s s

( p s f )

Arkose02

Linear (Arkose02)

Linear (Arkose02)

7/23/2019 011897


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