NI 43-101 Technical Report – Mt. Todd Gold Project 50,000 ... VI_Appendix... · 3.2 Surface and Subsurface Conditions ... RWD Raw Water Dam . SPT Standard Penetration Test

Report to:

VISTA GOLD CORP.

7961 Shaffer Parkway, Suite 5, Littleton, CO 80127 Phone: (720-981-1185)

NI 43-101 Technical Report – Mt. Todd Gold Project

50,000 tpd Preliminary Feasibility Study Northern Territory, Australia Appendix J Raw Water Dam Enlargement

PROJECT NO. 114-311285 DATE: JUNE 2013

350 Indiana Street, Suite 500, Golden, CO 80401

Phone: 303-217-5700 Fax: 303-217-5705

Appendix J – Raw Water Dam Enlargement Vista Gold Corp. 50,000 tpd Preliminary Feasibility Study – Northern Territory, Australia Mt. Todd Project

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Tetra Tech June 2013 11431128500-REP-R0002-01

T A B L E O F C O N T E N T S

EXECUTIVE SUMMARY ............................................................................................................. 1

1.0 INTRODUCTION ............................................................................................................ 3

1.1 General .............................................................................................................................................. 3 1.2 Site Location ...................................................................................................................................... 3 1.3 Previous Studies................................................................................................................................ 3

2.0 SITE CONDITIONS ......................................................................................................... 5

2.1 General .............................................................................................................................................. 5 2.2 Climate and Hydrology ...................................................................................................................... 5 2.3 Geology ............................................................................................................................................. 6 2.4 Site Seismicity ................................................................................................................................... 7 2.5 Geologic Hazards .............................................................................................................................. 7

3.0 SITE INVESTIGATIONS ................................................................................................... 8

3.1 2012 Geotechnical Investigation ....................................................................................................... 8 3.2 Surface and Subsurface Conditions .................................................................................................. 9

4.0 EXISTING DAM ........................................................................................................... 10

4.1 Original Design and Existing Conditions.......................................................................................... 10 4.2 Performance Assessment ............................................................................................................... 10

5.0 RAW WATER DAM RAISE ............................................................................................ 12

5.1 General ............................................................................................................................................ 12 5.2 Design Criteria ................................................................................................................................. 12 5.3 Embankment Construction .............................................................................................................. 12

5.3.1 Excavation and Foundation Preparation .............................................................. 12 5.3.2 Embankment Raise .............................................................................................. 13 5.3.3 Slope Protection ................................................................................................... 13

5.4 Engineering Analyses ...................................................................................................................... 13 5.4.1 General ................................................................................................................ 13 5.4.2 Filter Compatibility................................................................................................ 13 5.4.3 Seepage Analysis ................................................................................................ 13 5.4.4 Slope Stability Analyses ....................................................................................... 14

6.0 SPILLWAY ................................................................................................................... 16

6.1 General ............................................................................................................................................ 16 6.2 Hydrologic and Hydraulic Analysis .................................................................................................. 16 6.3 Spillway Design ............................................................................................................................... 18 6.4 Existing Spillway Removal ............................................................................................................... 19

7.0 OUTLET WORKS .......................................................................................................... 20

7.1 General ............................................................................................................................................ 20


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8.0 SADDLE DAMS ............................................................................................................ 21

8.1 General ............................................................................................................................................ 21 8.2 Saddle Dam Design ......................................................................................................................... 21

9.0 MORRIS DAM REMOVAL ............................................................................................ 22

9.1 General ............................................................................................................................................ 22

10.0 CONSTRUCTION CONSIDERATIONS ............................................................................ 23

10.1 Borrow ............................................................................................................................................. 23 10.2 Water Control .................................................................................................................................. 23 10.3 Construction Schedule .................................................................................................................... 23

11.0 COST ESTIMATE BASIS ................................................................................................ 24

11.1 General ............................................................................................................................................ 24 11.2 Quantity Estimates .......................................................................................................................... 24 11.3 Construction Cost Estimates ........................................................................................................... 24

11.3.1 Raw Water Dam Raise, Saddle Dams and Morris Dam Breach: Site and Foundation Preparation ....................................................................................... 25

11.3.2 Raw Water Dam Raise: Embankment Zones A, B, and C Construction ............. 25 11.3.3 Outlet Works Extension: excavate toe and salvage valve, pipe extension, valve

box and valve replacement .................................................................................. 25 11.3.4 Spillway Construction: excavation, concrete, grout, and riprap ........................... 25 11.3.5 Other Construction ............................................................................................... 26 11.3.6 Engineering and Design Services ........................................................................ 26 11.3.7 Construction Management ................................................................................... 26 11.3.8 Temporary Construction Facilities ....................................................................... 26

12.0 CONCLUSIONS AND RECOMMENDATIONS ................................................................. 27

12.1 Conclusions ..................................................................................................................................... 27 12.2 Recommendations ........................................................................................................................... 27

13.0 REFERENCES ............................................................................................................... 29


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L I S T O F T A B L E S

Table ES-1: RWD Raise Capital Cost Estimate Summary .............................................................................. 1 Table 3-1: 2012 Mt. Todd Geotechnical Investigation Borehole Location, Depth, Date and Testing ........ 8 Table 3-2: 2012 Mt. Todd Geotechnical Investigation Laboratory Testing Results ................................... 9 Table 5-1: RWD Minimum Factors of Safety for Design ........................................................................... 12 Table 5-2: RWD Material Properties for Seepage Analysis ...................................................................... 14 Table 5-3: RWD Material Properties for Slope Stability Analyses ............................................................ 15 Table 6-1: HEC-HMS Model Input Parameters for RWD Drainage Basin ................................................. 17 Table 6-2: RWD Stage-Storage Data ......................................................................................................... 17 Table 6-3: Summary of HEC-HMS Model Results for RWD ...................................................................... 18 Table 6-4: Proposed RWD Spillway Sizing Parameters ............................................................................. 18

L I S T O F A T T A C H M E N T S

Attachment A Figures Attachment B 2012 Investigation Borehole Logs and Laboratory Test Results Attachment C Hydrologic and Hydraulic Analyses Attachment D Seepage and Slope Stability Analyses


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L I S T O F U N I T S

g acceleration of gravity

cm/s centimeters per second

km kilometers

kN/m3 kilonewton per cubic meter

kPa kilopascals

masl meters above mean sea level

m/day meters per day

m meters

m3 cubic meters

m3/s cubic meters per second

mm millimeter

t/m3 tonnes per cubic meter

tpd tonnes per day


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L I S T O F A C R O N Y M S

ANCOLD Australian National Committee on Large Dams

AS Australian Standards

AUD Australian Dollars

c’ effective apparent cohesion

CM Construction Management

EP Engineering Procurement

φ’ effective angle of internal friction

FoS Factor of Safety

FS Feasibility Study

GLE General Limit Equilibrium

ID identification

Kh horizontal hydraulic conductivity

Kv vertical hydraulic conductivity

LL Liquid Limit

Ma Million Years Ago

NAG Non-Acid Generating

NI National Instrument

NRCS Natural Resources Conservation Service

PCO Pine Creek Orogen

PFS Preliminary Feasibility Study or Prefeasibility Study

PGA Peak Ground Acceleration

PI Plasticity Index

PL Plastic Limit

PMP Probable Maximum Precipitation

RWD Raw Water Dam

SPT Standard Penetration Test


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USACE United States Army Corps of Engineers

USGS United States Geological Survey

WSEL Water Surface Elevation


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E X E C U T I V E S U M M A R Y

This report presents Raw Water Dam (RWD) Raise design and plans in support of a Canadian National Instrument NI 43-101 compliant Preliminary Feasibility Study (PFS) for Vista Gold Corporation’s (Vista) proposed Mt. Todd Gold project located in Northern Territory, Australia. The PFS for the Mt. Todd project is a collaborative effort between several engineering consulting firms with individual responsibilities as listed below:

Tetra Tech (Tt) – Process, Metallurgy, Infrastructure, Tailings, Reclamation, Process Water Management, 43-101 Report Compilation and Cost Analysis

Mine Development Associates (MDA) – Mining and Reserves

GHD - Environmental

The RWD Raise design and plans for the current PFS include raising of existing embankment and spillway, relocating of the downstream outlet works valves, constructing two saddle dams and breaching Morris Dam. The purpose of the RWD Raise is to increase the capacity of the reservoir and upgrade the existing spillway, which has developed some cracks and experienced significant erosion in downstream areas.

The RWD Raise was not included in the PFS published to date. The following tasks were completed for the RWD Raise by Tt as part of the current PFS:

An engineering site inspection to evaluate the structural and hydraulic integrity of the existing embankment and spillway;

A prefeasibility-level geotechnical investigation of the RWD in November and December 2012, which included drilling of eight boreholes in the RWD area;

A laboratory testing program to characterize the geotechnical properties of the embankment materials;

Update of foundation and tailings material properties used in embankment design based on the results of the field investigation and laboratory testing program;

Geotechnical analyses including a steady-state seepage analysis and slope stability for static and pseudo-static conditions;

Hydrologic analysis of the RWD drainage basin for 100-year, 500-year and probable maximum flood (PMF) events;

Hydraulic analysis and design of the proposed spillway.

In addition to the above engineering studies, a PFS level estimate of initial and sustaining capital expenses for the RWD Raise was also prepared. All costs associated with the RWD Raise are assumed to be capital costs, so no operating costs were included. The estimated capital costs for the RWD Raise are summarized in Table ES-1.

Table ES-1: RWD Raise Capital Cost Estimate Summary


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Vista Gold Corp. – Mt. Todd Project

June, 2013

Cost Category Cost

(Thousands AUD)

Site and Foundation Preparation 222

Embankment Construction 890

Outlet Works Relocation 11

Spillway Construction 277

Other Construction Costs 224

Engineering Procurement 176

Construction Management 70

Temporary Construction Facilities 54

Contingency (15%) 289

Total 2,213


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I N T R O D U C T I O N 1.0

1 . 1 G E N E R A L

The Mt. Todd Gold Project located in Australia’s Northern Territory (NT) is currently owned by Vista Gold Corp. (Vista Gold). Tetra Tech Inc. (Tt) was retained by Vista Gold to contribute to a Canadian National Instrument (NI) 43-101 compliant Prefeasibility Study (PFS) in 2011 for the proposed gold mining operations at the site. The 2011 PFS did not require increased storage in the Raw Water Dam (RWD) reservoir. Tt was tasked with creating this prefeasibility-level RWD Raise report required under the current 50,000 tpd mining scenario.

When the Mt. Todd mine was active in the 1990’s, a water dam was constructed to the east of the mine to satisfy demand for a steady supply of fresh water. Figure 1 in Attachment A displays the location of site facilities. Vista Gold’s proposed 50,000 tpd mine plan requires more fresh water than the historic operations. In order to increase the capacity of the reservoir, a raise to the existing embankment has been proposed. This report, Appendix J to the PFS, presents the RWD Raise designed by Tetra Tech.

The following activities are proposed to facilitate the RWD Raise:

Excavate and raise existing embankment, by downstream methods, to 140.0 meters above mean sea level (masl);

Excavate and raise the existing spillway to 136.5 masl;

Extension of the outlet pipe and relocation of the downstream outlet works valve;

Construction of two saddle dams in areas of low relief near the reservoir;

Breaching of the Morris Dam, a small historic embankment which would be partially inundated by the proposed reservoir.

Upon closure of the Mt. Todd Mine, ownership of the Raw Water Dam will be transferred to the Jawoyn people, a local aboriginal Australian tribe. The design has considered this intended extension of the life of the facility beyond the intended life of the mine.

1 . 2 S I T E L O C A T I O N

The Mt. Todd Project is located 56 kilometers (km) by road northwest of Katherine and approximately 250 km southeast of Darwin in NT, Australia. Access to the property is via high quality, two-lane paved roads from the Stuart Highway, the main arterial highway within the territory. The general site location is shown in Figure 1 (see Attachment A).

1 . 3 P R E V I O U S S T U D I E S

The preliminary design of the existing RWD at the site was issued by Bateman Kinhill Kilborn in July of 1995, when Mt. Todd was under the ownership of Zapopan N.L. The design specifications are discussed in a report titled “Mt. Todd Gold Mine Phase II Vol. II: Project Specifications”.


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The drawings produced to accompany the Bateman Kinhill Kilborn report are the only set of design drawings Tetra Tech has been provided and many discrepancies exist between the drawings and existing conditions. For instance, the existing RWD crest is higher than the drawings show, the existing spillway invert is higher than shown, the outlet works were constructed on the north side of the channel bottom instead of the south, as shown, and the spillway channel follows a different path than that shown in the drawings. In addition, these drawings have stamps of both, ‘PRELIMINARY – NOT FOR CONSTRUCTION’, and ‘ISSUED FOR CONSTRUCTION’. Since these are the only designs available, the engineering completed for this report assumed that construction followed the specifications presented therein except in cases where existing conditions have been verified or corrected by field measurements and investigations.


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S I T E C O N D I T I O N S 2.0

2 . 1 G E N E R A L

The existing RWD is immediately north of Mt. Todd. The embankment measures approximately 120 meters (m) long and 13 m tall at its highest point. The crest is at about 136.5 masl and is approximately 5 m wide with slopes extending down at 3H:1V (Horizontal to Vertical slope ratio). The embankment is composed of a low-permeability clay core, ‘Zone A’, surrounded by a drain/filter material, ‘Zone B’, covered by run-of-mine waste material, ‘Zone C’. The embankment shows no obvious signs of seepage. The dam’s south abutment lies on Mt. Todd and the north abuts a small hill, which separates the spillway and the embankment.

The spillway lies about 100 m north of the dam and is approximately 36 m long. The elevation of the spillway invert is approximately 134.75 masl. The current spillway is a 1.5 m high cantilever concrete wall keyed about 1 m into the foundation soil and bedrock of the abutments. The existing spillway shows signs of uncontrolled seepage through the abutment, and possibly foundation materials; water is seen flowing through the north abutment (about 1 liter/minute) and pools in the rock downstream are full year-round. The energy of flowing water has created differential erosion of the exposed rock downstream of the spillway, making the surface uneven and not trafficable in any way other than by foot.

The reservoir collects and stores water to the east of the embankment from an unnamed tributary of Horseshoe Creek. Annual inflows generally exceed annual evaporation and seepage losses which causes overflow into Horseshoe Creek. The capacity of the existing RWD reservoir is roughly 4.8 million cubic meters (m3).

The proposed raise to the Raw Water Dam (to 140.0 masl) would cause water to spill from the reservoir at two additional saddle points around the reservoir; see Figure 2 for locations. The raise to the RWD requires the construction of small (~1 m high) saddle dams to achieve the required freeboard. The saddle dam areas are currently undisturbed.

Miners in the Mt. Todd vicinity during the early 20th century constructed Morris Dam, a small water retention dam, southeast of the RWD reservoir. The construction methods and materials used are unknown.

Vegetation in the area of the project site consists of eucalypt woodland with tropical grass (Vista Gold, 2011).

2 . 2 C L I M A T E A N D H Y D R O L O G Y

The project site is in a sub-tropical climate with a defined wet season (December to April) and dry season (May to November) (MWH, 2006). The wet season occurs approximately from November to April and dry season occurs from May to October. Mt. Todd receives most of its rainfall during the heavy wet season between January and early March. Average annual rainfall in the project area is between 973 millimeters (mm) and 1146 mm, as recorded at Pine Creek and Katherine, respectively (NSR, 1992).


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The temperature at the project site ranges between 10o to 40o C (50o to 104o F) (Gustavson, 2006). The climate data used in engineering analyses were developed from a combination of on-site data and data recorded by the nearby Katherine Council monitoring station (Tetra Tech, 2010).

The average humidity is 82% and humidity is highest during the wet season, reaching a maximum in February and dropping to a minimum in August and September (NSR, 1992).

The average annual pan evaporation rate at Katherine is 2566 mm, reaching to highest in October and November. Evaporation is higher than rainfall for every month except for January and February, which produces an average annual deficit of about 1600 mm (NSR, 1992).

Wind velocity varies with season. Winds are generally light during the wet season and are mostly from the west and northwest; however, they are generally stronger during the dry season and are from the south, southeast and east. Wind gusts of up to 70 kilometers/hour can be produced by severe afternoon and evening thunderstorms during the wet season once every two to three years (NSR, 1992).

Mt. Todd is located north of the Edith River in the Daly River Catchment Basin. Locally, surface water runoff not intercepted directly by Edith River generally collects in three ephemeral streams through the project site: Batman creek, Horseshoe creek, and Stow creek, which all ultimately drain into the Edith River. In addition, the locally dubbed “West Creek” gully, located on the eastern side of Pond RP1, collects runoff from the Yinberrie hills as well as water from the RP1 spillway (Vista Gold, 2011).

There are no water supply dams downstream of the project site and there are no streamflow records for Horseshoe Creek or Stow Creek; but, there is a gaging station on the Edith River downstream of the junction with Stow Creek, which was operated from 1962 to 1985. The streams in the vicinity of the project site flow at intervals during the wet season and dry up rapidly when the dry season begins, from June to August (NSR, 1992). The groundwater is contained in fractured, fissile bedrock with static water levels varying from 5 to 60 m below ground surface depending on surface topography. The overall groundwater flow direction is southerly. There is no known groundwater usage within a 10 km radius of the project site (NSR, 1992).

2 . 3 G E O L O G Y

The Mt. Todd Gold Project is situated within the Pine Creek Orogen (PCO), which encompasses three domains: the Litchfield Province, Central Doman, and Nimbuwah Domain (Ahmad et al., 2009). Mt. Todd is located within the Central Domain, which is characterized by greenschist-facies metasedimentary rocks and simple structures dominated by upright northwest- and northtrending folds. Low–grade metamorphism and upright deformation occurred in the Central Domain after approximately 1860 million years ago (Ma). Between 1835-1800 Ma, a major period of igneous activity, minor deformation, and rift-related sedimentation occurred (described as the Cullen Event). The Central Domain contains the majority of the gold, base metal, and tin deposits in the PCO.

Under and near the dam, a brown sandy silt topsoil between 0.3 m and 1.0 m thick overlies red and brown very weak completely weathered bedrock. This siltstone and/or greywacke bedrock gradually increases with strength and weathering decreases with depth. Generally, at 5 m below existing ground surface, the rock is weak and moderately weathered. The Burrel Creek Formation of the Finniss River Group, represented by the greywacke and siltstone, are the most common rock types in the area of the RWD. The Burrel Creek Formation is unconformably overlain by variable contact metamorphosed sediments and tuffs of the Tollis Formation, which forms part of the El Sherana Group. The principal


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deposit mineralization occurs in contact metamorphosed graywackes of the Tollis Formation (NSR, 1992).

2 . 4 S I T E S E I S M I C I T Y

The NT province, where the project is located, is considered to have a relatively low level of seismic activity. According to the United States Geological Survey (USGS) database (USGS, 2009); the Peak Ground Acceleration (PGA) for the area with a 10% probability of exceedance in 50 years is 0.08 times the acceleration of gravity (g). This value corresponds to a return period of 475 years.

2 . 5 G E O L O G I C H A Z A R D S

While faults have been identified in the area, occurrence of any young and potentially active faults (i.e., Quaternary age, less than 1.8 million years since last movement) within the area has not been confirmed. A site-specific seismic hazard assessment was not performed for this study, but the Northern Territory is generally characterized by low seismic risk as noted in Section 2.4, and strong ground motions are not anticipated to pose a credible risk to the Mt. Todd Project. Risks associated with natural slope instabilities may be possible in the vicinity of Mt. Todd, though this potential risk has not been fully assessed.

The subsurface materials observed in the vicinity of Mt. Todd indicate some possible age relationship inconsistencies between material intervals. There are a few possible explanations for these observations, including fault-related shearing at this location, or possibly historic slope movement. However, no scarps were observed on Mt. Todd, and currently there is inconclusive evidence to definitively characterize the nature of the materials observed. Further characterization of this area is recommended prior to final design of the RWD Raise. At this time, based on the lack of apparent scarps, slope movement on Mt. Todd is not expected to pose a significant risk to the project. In addition, risks associated with ground subsidence, rapid soil erosion, abandoned mine workings, or other potential geological hazards are not known to pose a credible risk to the proposed project.


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S I T E I N V E S T I G A T I O N S 3.0

3 . 1 2 0 1 2 G E O T E C H N I C A L I N V E S T I G A T I O N

A prefeasibility-level geotechnical investigation of the Raw Water Dam was performed during November-December of 2012. In addition to other concurrent site investigations, Tetra Tech personnel supervised drilling of eight (8) geotechnical boreholes in the RWD area. Four boreholes were drilled in the abutments and footprint of the proposed RWD Raise and four were drilled in the abutments of the spillway. Table 3-1 displays the locations, dates, quantity and type of downhole tests completed. Borehole logs are included in Attachment B

Table 3-1: 2012 Mt. Todd Geotechnical Investigation Borehole Location, Depth, Date and Testing


June, 2013

Borehole ID Easting (GDA94)

Northing (GDA94)

Elevation (m)

Total Depth (m)

Date Completed

Downhole Tests Completed (Depth (m))

TTBH-12-08 190264 8436648 139 24.6 11/30/2012 1 Single Packer Test (19.3 – 21.6)

TTBH-12-09 190261 8436598 138 26.9 11/28/2012 2 Single Packer Tests (11.4 - 12.4, 22.0 - 24.0)

TTBH-12-10 190251 8436739 146 30.55 12/2/2012 2 Single Packer Tests (3.95 – 6.55, 27.55 – 30.55)






Boreholes were augered to refusal then advanced using HQ coring techniques (when additional depth was desired). Standard Penetration Tests (SPTs) were collected at 1.5 m depth intervals while augering.

All samples were photographed and shipped to SGS Australia’s Sydney laboratory for testing. The results of laboratory testing are displayed in Table 3-2.


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Table 3-2: 2012 Mt. Todd Geotechnical Investigation Laboratory Testing Results


June, 2013

Borehole ID Sample Number Depth

Sam

ple

Type

USC

S C

lass

Fine

/ Coa

rse

AS

1289

3.1

.1,

3.2.

1, 3

.3.1

Hyd

rom

eter

A

S 12

89 3

.1.1

, 3.

2.1,

3.3

.1

Atte

rber

g Li

mits

A

S 12

89 3

.1.1

, 3.

2.1,

3.3

.1

Moi

stur

e A

S 12

89 2

.1.1

Dry

Den

sity

A

S 12

89 2

.1.1

Classification

m Gravel Sand Silt Clay LL PL PI % t/m3

TTBH-12-08 03 2.5 SPT 13 13 44 30 35 14 21 15.2 1.91

TTBH-12-08 07 8.5 SPT 0 33 44 23 22 12 10 12.8 1.92

TTBH-12-08 10 13 SPT 4 31 44 21 24 12 12 14.8 1.9

Borehole logs and laboratory test results are included as Attachment B.

3 . 2 S U R F A C E A N D S U B S U R F A C E C O N D I T I O N S

A profile of the subsurface conditions encountered in the dam and spillway abutments is described as follows: topsoil, where present, is brown sandy silt with some gravel and clay, low plasticity, well graded and 0.0 m to 3.5 m thick. Underlying any topsoil is red interbedded siltstone and greywacke, very weak and completely weathered, becoming stronger and less weathered at approximately 10 m below ground surface. The strength of the interbedded siltstone and greywacke increases with depth, becoming very strong between 22.6 m and 26.7 m below natural ground surface. Topsoil on the south abutment, which is the north slope of Mt. Todd, is very thin and contains a high percentage of cobbles and gravel.

Alluvial silts, sands and gravels are expected in the valley bottom near the stream channel at a depth of up to 3.5 m. Underlying the alluvial materials is red interbedded siltstone and graywacke, very weak and completely weathered, becoming stronger and less weathered with increasing depth.

Groundwater at the site varies with the season and the level of the Raw Water reservoir, but generally is expected to be less than 1 m below natural ground surface during the wet season and up to 5 m below ground surface during the dry season.


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E X I S T I N G D A M 4.0

4 . 1 O R I G I N A L D E S I G N A N D E X I S T I N G C O N D I T I O N S

The Raw Water Dam was constructed in November 1995 to provide fresh water for the Mt. Todd Gold Mine. The original storage capacity of the RWD was approximately 4.25 million m3. Bateman Kinhill Kilborn (1995) predicted that the RWD would recharge to full capacity each year.

The drawings produced to accompany the Bateman Kinhill Kilborn (BKK) report (1995) are the only set of design drawings Tetra Tech has been provided and there are many discrepancies between the designs and existing conditions. When field observation could not confirm the BKK drawings, the structures are assumed to follow the drawings.

The existing RWD was designed to a crest height of 136.5 masl. The crest was designed to be 6 m wide, and the existing crest is rounded with about 5 m of width. The spillway design called for an invert at 133.5 masl, which would provide 3 m of freeboard. The existing spillway invert is at approximately 134.75 masl, providing a freeboard of about 2 m.

The embankment was designed with a symmetrical tapered low-permeability core (Zone A) covered by a symmetrical tapered transition material (Zone B). The dam shell is run-of-mine waste (Zone C). The foundation was designed to be excavated 5 m into existing ground in the creek bed and 2 m through the rest of the foundation. A key trench extending below the core was designed to be at least 4 m wide and at least 1 m into the ‘siltstone horizon of slightly weathered to fresh rock’. Tetra Tech has not found slightly weathered to fresh rock any shallower than 22.6 m below ground surface in the vicinity (see Section 3.2), therefore this key trench is unlikely to have been constructed in accordance with the design intent.

The designed spillway was a 0.5 m tall concrete weir placed above a grout curtain on 2 m centers. The top of the weir was specified to be 133.5 masl. The existing spillway’s invert is at 134.75 masl; 1.25 m higher than designed. Construction of the grout curtain has not been verified.

The intake structure was specified to be a tree of 2, possibly 3, ‘cactus arm’ screened intakes. The design drawings do not show a shutoff valve on the upstream side of the embankment. The construction of the intake structure has not been verified.

The outlet design calls for poured-in-place concrete to surround the pipework under the embankment. A shutoff valve is installed in the outlet pipe immediately downstream of the embankment. A valve-controlled bypass pipe is located approximately 50 m downstream of the pipe’s outlet from the dam.

The designs show the outlet works on the south side of the unnamed creek, but the existing outlet works were constructed on the north side.

4 . 2 P E R F O R M A N C E A S S E S S M E N T

During the field investigations, no signs of focused seepage or slope instabilities around the embankment were witnessed with the reservoir level about 1 m below the spillway invert. Tetra Tech is unaware of any historic seepage or stability issues and has no reports of the embankment performing in


11


any way other than intended. Trees are allowed to grow on the embankment, which could cause uncontrolled seepage along root paths.

The existing spillway shows signs of uncontrolled seepage through the abutment, and possibly foundation materials; water is seen flowing through the north abutment (about 1 liter/minute) and pools in the rock downstream are full year-round. Weathering of exposed bedrock in the channel bottom and the energy of spilling water have created differential erosion of the exposed rock downstream of the spillway, making the surface uneven and passable only by foot.


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R A W W A T E R D A M R A I S E 5.0

5 . 1 G E N E R A L

The existing embankment is proposed to be raised to 140.0 masl elevation, a nominal 3.5 m raise. To tie together the existing and new core zones, the top of the existing dam will be excavated prior to construction of the downstream raise. The downstream extent of the footprint of the raise should be excavated to bedrock, similar to the design of the existing dam.

The core and transition zones will run horizontally downstream before the zones are elevated (see Figure 5 in Attachment A). This design allows construction to advance faster while achieving minimal seepage and slope stability required for such a structure.

The upstream face of final embankment should be covered with rip rap to protect the embankment material from erosion; the downstream face should be seeded with appropriate grasses.

5 . 2 D E S I G N C R I T E R I A

According to design parameters for embankment dams presented by ANCOLD (2010), the embankment raise should have freeboard sufficient to provide containment of the probable maximum flood (PMF).

The design and material selection should inhibit internal erosion; filter compatibility between materials should be checked as per NRCS, 1994.

Slope stability design requirements are included in Table 5-1, per ANCOLD’s design parameters.

Table 5-1: RWD Minimum Factors of Safety for Design


June, 2013

Loading Condition Minimum Factor of Safety Steady state seepage with maximum storage pool 1.5

Seismic evaluation 1.0

5 . 3 E M B A N K M E N T C O N S T R U C T I O N

This section details the expected steps for construction of the designed embankment raise.

5.3.1 EXCAVATION AND FOUNDATION PREPARATION

Before excavation and foundation preparation can begin, the existing spillway must be breached to maintain required freeboard at all times, and the reservoir drained to the required level.

Strip all vegetation and backfill and compact all root cavities which may allow uncontrolled seepage. Excavate crest of existing embankment down to 134 masl to expose material of Zone A, B and C. To allow adequate blending of Zone C material on the downstream face, all slope protection should be


13


removed from the downstream slope face. Existing ground in the proposed raise’s abutments and downstream footprint should be excavated to bedrock.

5.3.2 EMBANKMENT RAISE

Construct new downstream Zone C material to 134 masl, then construct downstream filter (Zone B), core (Zone A), upstream filter (Zone B) and surrounding fill (Zone C) as specified in final design to be based upon Figure 5. The interface between existing zones and new construction should be well-mixed and provide continuous filter, drain and permeability properties.

5.3.3 SLOPE PROTECTION

Upstream, downstream and crest material should be covered with rip rap to prevent erosion. During operation, vegetation should be prevented from growing on the RWD.

5 . 4 E N G I N E E R I N G A N A L Y S E S

5.4.1 GENERAL

The engineering analyses conducted for the proposed RWD Raise are discussed in this section. Geotechnical seepage and slope stability analyses and an evaluation of liquefaction potential were completed.

5.4.2 FILTER COMPATIBILITY

The gradation limits for material zones set forth by Bateman Kinhill Kilborn (1995) were compared to standards for filter compatibility presented in NRCS (1994). The NRCS standards provide a means to specify a material gradation which will both allow drainage of water and prevent migration of fine grained particles (internal erosion). The material specifications used by Bateman Kinhill Kilborn were found to be sufficient and are recommended by Tetra Tech.

5.4.3 SEEPAGE ANALYSIS

Seepage analyses were conducted to estimate the steady state phreatic surface within the embankment to allow more accurate stability analyses. Steady state seepage analyses were conducted with the finite element based SEEP/W module of the GeoStudio 2007 geotechnical software suite (GEO-SLOPE, 2007).

Water levels measured in the RWD during the 2012 geotechnical investigation were interpreted to assist in SEEP/W model calibration. The calibration of the model was performed by varying material properties until the model output matched encountered field conditions and engineering expectations.

The material properties used in the seepage analysis were produced from a combination of values derived from the original report by Knight Piésold (1995) (surficial soils and bedrock) and values established based on recent laboratory and in-situ field testing (Zone A and the bedrock) and engineering experience with similar materials. The material properties used in the seepage analysis are presented in Table 5-2.


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Table 5-2: RWD Material Properties for Seepage Analysis


June, 2013

Material Hydraulic Conductivity

Ratio (Kv/Kh)

Hydraulic Conductivity, Kh

(m/day) (cm/sec)

#1 - Surficial Soils 1.0 8.6 x 10-3 1 x 10-5 #2 - Bedrock 1.0 6.1 x 10-3 7 x 10-6

#3 - Transition Zone 1.0 4.3 x 10-1 5 x 10-4 #4 - Zone A 0.1 2.0 x 10-4 2 x 10-7 #5 - Zone B 1.0 9.0 x 10-2 1 x 10-4 #6 - Zone C 1.0 4.3 x 10-1 5 x 10-4

The predicted piezometric surface was used for the slope stability models, and is shown in Attachment D.

5.4.4 SLOPE STABILITY ANALYSES

Slope stability analyses were conducted on the maximum section of the RWD to assess the slope stability of the proposed design. The location and cross section used in the analyses is the same as shown in Figures 4 and 5 in Attachment A.

Stability analyses were conducted using the SLOPE/W component of GeoStudio 2007 (v. 7.21, build 5051) by GEO-SLOPE International, Ltd. SLOPE/W was used to conduct limit equilibrium analyses using the general limit equilibrium (GLE) method, which satisfies both moment and force equilibrium. The SLOPE/W program incorporates a search routine to locate the failure surfaces with the lowest factor of safety within user-defined search limits. Trial failure surfaces were defined with “entry and exit” parameters. This option defines a range of possible slip surface entry and exit locations within which the most critical (lowest factor of safety) may be found.

Due to the model geometry and various material transitions, a perfectly circular failure surface did not appear to accurately represent the most likely potential failure surface. To optimize the shape of the slip surface, the most critical failure surfaces in each analysis were subjected to an optimization tool in SLOPE/W. This tool analyzes each point along the slip surface, systematically adjusting an individual point’s position until the lowest factor of safety is reached. Frequently, the result is a failure surface which appears to be more realistic and produces a lower factor of safety.

Two different stability conditions were analyzed: static and pseudo-static. The static analyses were used to evaluate the slope stability of the facility under normal operating conditions while the pseudo-static conditions were performed to evaluate the stability of the facility under seismic loading conditions.

The pseudo-static stability analysis model incorporates the effects of seismic loads by subjecting the two-dimensional sliding mass to a horizontal acceleration equal to a seismic coefficient based on the Peak Ground Acceleration (PGA). Data provided by the USGS for the project site indicate a PGA of 0.08g may be anticipated for the site. This PGA corresponds to a 10 percent probability of exceedance in 50 years, equivalent to a return period of 475 years. According to recommendations provided by the U.S. Army Corps of Engineers (USACE) miscellaneous paper GL-84-13 (Hynes-Griffin and Franklin, 1984), a


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seismic coefficient equal to one-half the PGA is typically used for a pseudo-static analysis, which in this case would be 0.04g, and the shear strength properties of materials which may experience an increase in pore water pressure during cyclic loading are reduced by 20%. For conservatism, a PGA of 0.08g was used in the slope stability analyses. Material shear strength properties were not reduced by 20% because the materials found on site and used in construction are not believed to experience an increase in pore water pressure during cyclic loading.

The material properties used in the stability analyses are a combination of values derived from the original report by Knight Piésold (1995) (surficial soils and bedrock) and values established based on recent laboratory and in-situ field testing (Zone A and the bedrock) and engineering experience with similar materials.

The Zone A material properties derived from the 2012 laboratory testing program exhibited an angle of internal friction (Ø') of 33° and no cohesion (c’=0 kilopascals (kPa)). As the bedrock is composed of interbedded siltstone and graywacke, no distinction between the two materials was made in the stability models. Table 5-3 presents the material properties used in the slope stability analyses.

Table 5-3: RWD Material Properties for Slope Stability Analyses


June, 2013

Material Strength Model Unit Weight (kN/m3)

c’ (kPa)

Ø' (degrees)

#1 - Surficial Soils Mohr-Coulomb 19 5 28 #2 - Bedrock Mohr-Coulomb 24 1000 25

#3 - Transition Zone Mohr-Coulomb 16 0 28 #4 - Zone A Mohr-Coulomb 21 0 33 #5 - Zone B Mohr-Coulomb 20 0 34 #6 - Zone C Mohr-Coulomb 20 0 38

The lowest modeled factor of safety (FoS) for the static and pseudo-static conditions was 1.85 and 1.48 respectively. Both of these FoS are above the acceptable value as described in Section 5.2. The slope stability results are included in Attachment D.


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S P I L L W A Y 6.0

6 . 1 G E N E R A L

A detailed survey of the existing Raw Water Dam spillway area by Earl James & Associates (EJA) in November 2012 indicated that the crest of the existing spillway is at about 134.75 masl. The existing RWD spillway has developed some cracks. The downstream spillway channel has experienced significant erosion due to weathering caused by wet/dry weather cycles and overtopping flows during severe storm events.

The RWD spillway area will be improved to stabilize the existing spillway and increase the storage capacity of the RWD, providing the desired water storage in the RWD reservoir. The improvements to the RWD spillway area will include constructing a cascading set of three spillway walls and channel armoring between each spillway walls. The existing spillway will be replaced by a new concrete wall, the middle of the three new spillways, maintaining the existing crest elevation of 134.75 masl. There will be a spillway approximately 31 m upstream of the existing spillway with a crest elevation of 136.5 masl and the third about 34 m downstream of the existing spillway with a crest elevation of 132.5 masl.

6 . 2 H Y D R O L O G I C A N D H Y D R A U L I C A N A L Y S I S

The drainage basin contributing to the RWD is approximately 28.6 km2 and was delineated based on a combination of the most recent topographic survey map, the USGS Quad Map of the area and Google aerial map. An overview of the drainage basin along with its parameters is shown in the Drainage Basin Map, Figure 6 of Attachment A.

The Natural Resources Conservation Service (NRCS) curve number approach was used for the hydrologic analysis. The NRCS method was performed using the HEC-HMS 3.5 model, which was developed by the U.S. Army Corps of Engineers. The precipitation values were calculated by frequency analysis of approximately 139 years of historic precipitation data obtained near the project site. The NRCS Type II storm distribution was selected for the site. The Type II distribution is characterized as intense short duration rainfall, which is similar to the intense rainfall events at the project site.

A curve number (CN) of 77 representing a Type B Hydrologic Soil Group for a natural desert landscape was selected as a conservative representation of the drainage basin’s runoff potential. Lag time for the drainage basin is approximately equal to 0.6 times the time of concentration. Time of concentration was calculated for the longest basin flow path using the NRCS TR-55 methodology and results are included in Attachment C. Table 6-1 provides a summary of the HEC-HMS model input parameters for the RWD drainage basin.


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Table 6-1: HEC-HMS Model Input Parameters for RWD Drainage Basin


June, 2013

Basin ID Basin Area (km2)

Curve Number

Lag Time (Minutes)

24-hour Duration Precipitation Depth (mm)

100-yr 500-yr PMP

RWD_Basin 28.6 77 181 68 108 340

Stage-storage data for the RWD, which are provided in Table 6-2, were developed by Tetra Tech using the “RWD Stage-Volume-Area Relationships” graph in Appendix B of the MWH Water Management Report (2006) up to elevation 134.5 m (see Attachment C) combined with LIDAR data and an image file with 5 m contour intervals provided by Vista Gold in 2008. Storage volumes at elevation 135 and 140 masl were calculated by applying the average area method for consecutive elevations with known surface areas. A third order polynomial was fitted to the known stage storage data and volumes at elevations 134.75, 136, 137, 138 and 139 masl were estimated using the third order polynomial curve. The stage-storage data in Table 6-2 were input into the HEC-HMS model to route the inflow through the RWD spillway.

Table 6-2: RWD Stage-Storage Data


June, 2013

Stage (m) Storage (m3) Stage (m) Storage (m3)

125.0 0 134.0 3615671 126.0 11194 134.5 4287313 127.0 78358 134.75 4755158 128.0 145522 135.0 5104412 129.0 313432 136.0 7184291 130.0 593283 137.0 9667527 131.0 996268 138.0 12689403 132.0 1634328 139.0 16304106 133.0 2496268 140.0 20584168

HEC-HMS model results are included in Attachment C. Table 6-3 summarizes the peak flows (listed in cubic meters per second, m3/s) and runoff volumes from the 100-year, 500-year, and PMF (Probable Maximum Flood), 24-hour duration storm events calculated by the HEC-HMS model.


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Table 6-3: Summary of HEC-HMS Model Results for RWD


June, 2013

Point of Analysis

(POA)

Peak Outflow Discharge (m3/s) Runoff Volume (1000 m3)

100-yr 500-yr PMF 100-yr 500-yr PMF

RWD 17.9 51.0 315.6 612.5 1452.1 7519.9

The upstream spillway was first roughly sized using the HEC-HMS model to estimate the peak outflow discharges with the assumption that the water surface elevation (WSEL) produced by the PMF in the RWD reservoir must be at least 0.5 m below the proposed RWD crest elevation of 140 masl to account for RWD reservoir wave run-up. The US Army Corps of Engineers’ HEC-RAS 4.1 model was used to calculate final spillway sizes and to estimate the water surface profile through the proposed spillways, which is shown in the Spillway Plan & Profile, Figure 7, in Attachment A. The HEC-RAS model was run with a steady flow analysis option, considering a mixed flow regime. Both upstream and downstream boundary conditions were used to run the HEC-RAS model in mixed flow regime. Downstream boundary conditions were set to the known water surfaces that correspond to the RWD access road culvert and ford crossing, which was designed by Tetra Tech in November 2012, headwater elevations for each design storm. The headwater elevations were calculated using the Bentley’s FlowMaster program, results of which are located in Attachment C. The upstream boundary conditions were evaluated based on the HEC-HMS model results for each design storm (see Attachment C). The results of the HEC-RAS model are presented in Attachment C. Table 6-4 below provides a summary of the proposed RWD spillway parameters:

Table 6-4: Proposed RWD Spillway Sizing Parameters


June, 2013

Spillway ID Width (m) Crest Elevation (m)

WSEL over Spillway (m)

100-yr 500-yr PMF* Upstream 37.0 136.5 136.8 137.1 138.4

Middle 36.0 134.75 135.1 135.3 136.7 Downstream 26.1 132.5 132.9 133.2 135.0

6 . 3 S P I L L W A Y D E S I G N

The raised spillway is designed to increase the reservoir level by about two meters and reduce further weathering and erosion of the bedrock in the spillway channel. The design provides a cascade flow over three spillway weir walls. This design creates two stilling pools below the upper and middle walls to assist in dissipating energy and provide a consistent water pool protecting the bedrock from wet/dry weathering. The spillway will be designed to minimize damage during the 500 year flood. Floods up to


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the PMF will overtop the spillway by up to nearly two meters, but should not cause failure of any of the three walls.

The existing spillway will be replaced with a design similar to the existing wall design, using the foundation slab and grouting that was placed at the time of construction. The downstream wall will have a similar design consisting of a cantilever wall on a spread footing founded on bedrock about 0.5 m below existing grade. A grout curtain will be injected beneath the wall footing to reduce underseepage.

The upstream wall is considerably higher than the middle and downstream walls, involving much higher overturning and sliding loads and material stresses. This wall will be designed as a gravity concrete wall founded on bedrock about 0.5 m below existing grade. A grout curtain will be injected beneath the wall to reduce underseepage.

Abutment protection will be designed for the 500 year flood using shotcrete and grouted riprap. The protection will also include embedment into the bedrock, providing a keyway interlock to improve longevity. The channel sections between the spillway walls are composed of erodible rock material. To protect them against erosion, these sections will be covered and armored with shotcrete.

The wall and footing designs will use conventional cantilever and gravity wall design methods. Reinforcing steel will be designed to meet stress requirements according to standard practice. The foundation grouting will extend about three to five meters into the bedrock beneath the wall footings and will extend up the wall abutments.

6 . 4 E X I S T I N G S P I L L W A Y R E M O V A L

The existing spillway will be removed down to the existing ground surface elevation of roughly 133 masl, which corresponds to removal of roughly top 1.75 m of the spillway wall. This is necessary because the RWD embankment will be excavated to elevation 134 masl. Removing the spillway will help prevent the routing of flood waters over the RWD embankment during severe storm events.


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O U T L E T W O R K S 7.0

7 . 1 G E N E R A L

The Bateman Kinhill Kilborn (1995) drawings show the current outlet works configuration consists of a multiple-level intake tower, a 375 mm diameter cement-lined ductile iron pipe outlet conduit through the base of the dam embankment, and a control valve at the downstream dam toe. The outlet conduit has no closure at the upstream end, and is pressurized to the reservoir stage through the embankment. The raw water supply pipeline is directly connected to the valve and extends to the processing plant. A tee section and valve are located downstream of the dam to discharge water directly to the stream, bypassing the raw water supply pipeline.

Evaluation of the Bateman Kinhill Kilborn (1995) design indicates that the existing outlet tower and pipeline can withstand the dam raise loading from the additional embankment and reservoir head. However, the record drawings show the outlet alignment to be a location different from the current location. In addition, the intake tower is entirely below the reservoir surface during the seasonal operating level and has not been inspected. Therefore, additional evaluation of the outlet works components and condition should be made prior to final design.

As currently planned, the outlet will remain in place throughout the construction and will be used for the raised dam. The downstream valve will be removed and the pipeline will be extended to the location of the new dam toe. At the raised dam toe, a new valve vault will be constructed and the existing valve will be located in the vault and connected to the raw water supply pipeline.

The outlet works can be used to lower and maintain the reservoir level during spillway and dam construction; however, it will need to be plugged to construct the outlet pipe extension, relocate the valve and re-attach the raw water supply pipeline. Reservoir water diversion will be considered in final design.


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S A D D L E D A M S 8.0

8 . 1 G E N E R A L

If water levels reach 140 masl, water could flow from the reservoir at 3 points: the RWD spillway, a topographic saddle about 50 m north of the spillway and a topographic saddle on the south side of Mt. Todd. To prevent uncontrolled spilling over the saddle points, small embankments will be constructed along the saddles. See Figure 4 for saddle dam locations.

The reservoir will be operated so that the water level remains at or below the spillway level, 136.5 masl, during all but flood conditions. As such, the saddle dams have been designed under the assumption that they will not store water for any significant length of time. These embankments are freeboard dams and they are only designed to store temporary flood waters.

8 . 2 S A D D L E D A M D E S I G N

The saddle dams are constructed of homogenous, compacted Zone A material. The slopes of saddle dams will be 3H:1V and the crest must be at least 1 m wide. The construction contractor may opt to ease construction efforts by constructing a wider crest. The total expected alignment length of required saddle dams is approximately 350 m.

All topsoil and vegetation should be removed and underlying material compacted. After approved foundation preparation, construction of the embankments can proceed in compacted lifts to ultimate elevation of 140 masl.


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M O R R I S D A M R E M O V A L 9.0

9 . 1 G E N E R A L

Morris dam is located along the east side of the RWD reservoir. The structure is a 5 m high embankment dam used to store water for mining operations prior the 1990s. No design drawings or construction records were available for review. It appears that there is no operating outlet, within the dam. A notch is located on the right abutment, near the dam crest, to provide a spillway.

The composition of the embankment is unknown and the upstream and downstream side slopes are relatively steep. The downstream toe is currently inundated at full reservoir level and would be further inundated with the raised reservoir levels. Evaluation of the dam, its storage capacity, and location suggest the dam should be removed from service for the RWD raise. A breach of the dam has been developed to be implemented during construction of the RWD raise.

The breach has an estimated bottom elevation of 133.0 m, which should be re-evaluated during final design. The bottom should be at or below the bottom of the reservoir to provide complete release of water stored behind Morris Dam. The breach side slopes should be 3H:1V and should be vegetated to minimize erosion. Excavated material may be useable in the raised dam construction.


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C O N S T R U C T I O N C O N S I D E R A T I O N S 10.0

1 0 . 1 B O R R O W

The dam raise consists of three zones, each with a specific material for meeting engineering design criteria. The record drawings and engineering report indicate that borrow materials for the original dam zones were obtained from the reservoir or imported to the dam site. Borrow material investigations for reclamation of the project indicate clays are available for the dam core, Zone A and the dam shell, Zone C. Materials suitable for the dam drain, Zone B, are assumed to not occur naturally on the project site. These materials can be processed from onsite alluvial soils, or imported from offsite aggregate pits or quarries.

1 0 . 2 W A T E R C O N T R O L

The RWD reservoir will need to be lowered up to 3 m to construct the new upstream spillway weir wall and dam raise. Construction could be simplified by completely draining the reservoir, which should be considered. If the loss of the raw water supply during the construction period is not possible, operation controls will be required to reduce the risk of damage to the dam during construction of the raise.

The reservoir can be lowered by operation of the outlet and removal of a section of the existing spillway wall. The outlet will not be operable during construction of the outlet pipe extension and reinstallation of the valve. During this time, all intake structure openings need to be plugged to dewater the outlet conduit.

Impact of reservoir lowering and outlet unwatering will be further evaluated during final design.

1 0 . 3 C O N S T R U C T I O N S C H E D U L E

An initial construction schedule has been developed to assist in construction planning. This schedule indicates that the raise construction, including the dam raise, outlet extension, and spillway modifications can be completed in six to eight months with proper scheduling of activities and sufficient equipment and labor availability. Considering the climate of the area, the construction could be completed in one dry season with little impact from wet season weather. This would require contractor mobilization in February of the year of construction.


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C O S T E S T I M A T E B A S I S 11.0

1 1 . 1 G E N E R A L

The design basis assumptions and unit rate sources for the construction costs for the proposed RWD Raise are discussed in the following sections. It is assumed that the RWD will remain operational after mining has ended and the mine and facilities sites are reclaimed. All costs presented and discussed in this section are in Australian Dollars (AUD).

1 1 . 2 Q U A N T I T Y E S T I M A T E S

Quantity estimates for the items used in the cost estimate were developed from the project drawings using CAD and Civil 3D methods, as well as graphical measurements. The estimates included volumes for excavation and fill materials, lengths for pipeline quantities, and volumes for concrete quantities. It was assumed that the existing outlet intake, pipeline, and valve will be used in the raised dam.

1 1 . 3 C O N S T R U C T I O N C O S T E S T I M A T E S

The construction costs associated with the RWD Raise include the following direct and indirect cost items:

Direct Construction Costs: Raw Water Dam Raise: excavation, Zones A, B, and C;

Spillway modifications: excavation, concrete, grout, and riprap;

Outlet extension: excavate toe and salvage valve, pipe extension, valve box and valve replacement;

Saddle dam construction: excavation and Zone A;

Morris Dam removal: excavation and reclamation.

Indirect Capital Costs:

Operation Cost;

Engineering Procurement;

Construction Management.

Table ES-1 displays cost associated with each sub-section listed above.

All unit costs derived from the Rawlinson’s Australian Construction Handbook 2012 (Rawlinson’s Handbook) for the PFS cost estimate were based on base prices reported for Adelaide and scaled up for Katherine using the factors provided in the Handbook.


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11.3.1 RAW WATER DAM RAISE, SADDLE DAMS AND MORRIS DAM BREACH: SITE AND FOUNDATION PREPARATION

The excavation for construction of the raise includes stripping and grubbing of vegetation, removal of the top of the existing dam to elevation 134 masl and excavation of surficial materials within the footprint of the embankment. This activity also includes the removal of unsuitable soils within the construction limits as well as hauling and stockpiling of excavated surficial soils.

The excavation for construction of the two saddle dams includes stripping and grubbing of vegetation, and excavation of surficial materials within the footprint of the embankments.

The excavation for the breach of Morris dam embankment included clearing and grubbing of the embankment and hauling of the excavated material to waste disposal within 1 km of Morris Dam. The reclamation included preparation of the excavated surface and vegetation with a seed mix and cover. It was assumed that a contractor performed this work.

Unit costs for stripping, grubbing and excavation were derived from the Rawlinson’s Handbook. Unit costs for excavation, hauling and stockpiling of shallow surficial soils was based on cost estimates provided by Proteus EPCM Engineers (Proteus) of Australia (A Tetra Tech Company).

11.3.2 RAW WATER DAM RAISE: EMBANKMENT ZONES A, B, AND C CONSTRUCTION

Materials for Zones A and C of the main dam and two saddle dams were assumed to be sourced from borrow sites within the project area and Zone B (sand and gravel drain) were imported from a local source within 20 km of the site. Mine rock was not used for Zones A, B, or C. The embankment construction costs include hauling, spreading and compaction of placed fill using an earthwork contractor.

The unit costs were derived from the Rawlinson’s Handbook (2012).

11.3.3 OUTLET WORKS EXTENSION: EXCAVATE TOE AND SALVAGE VALVE, PIPE EXTENSION, VALVE BOX AND VALVE REPLACEMENT

Excavation costs of the outlet extension included excavation of the dam toe to expose the outlet pipe and of the alignment for the pipe extension and new valve vault, removal of the valve and valve vault. The installation costs included purchase and installation of the pipe extension, placement of concrete for pipe bedding and the valve vault and placement of pipe backfill in the area of the raised dam toe. The existing pipe modifications are included in the estimated price.

The work will be performed by a contractor and prices were based on the Rawlinson’s Handbook and estimated for miscellaneous items that were not in the handbook. Riprap was assumed to be hauled from on-site Non-Acid Generating (NAG) sources, using mining equipment, and placed using contractor’s equipment. Unit costs for excavation, hauling and stockpiling of soils was based on cost estimates provided by Proteus EPCM Engineers (Proteus) of Australia (A Tetra Tech Company).

11.3.4 SPILLWAY CONSTRUCTION: EXCAVATION, CONCRETE, GROUT, AND RIPRAP

Construction costs of the spillway excavation for the three weir walls, placement of wall concrete and grouting of wall foundations were based on the Rawlinson’s Handbook. Riprap was assumed to be hauled from on-site NAG sources, using mining equipment, and placed using contractor’s equipment. Unit costs for excavation, hauling and stockpiling of soils was based on cost estimates provided by Proteus EPCM Engineers (Proteus) of Australia (A Tetra Tech Company).


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11.3.5 OTHER CONSTRUCTION

Contractor Mobilization cost was estimated using a percent of the direct construction costs. This estimate includes: contract developed, bonds acquisition, mobilization and demobilization of equipment, materials, and labor, and other indirect costs incurred by the contractor.

Water Control will be required for construction of the dam and the spillway to manage the reservoir level and to dewater excavations. It was assumed that the construction of the RWD dam raise project can be completed in one construction season, during the dry portion of the year. The reservoir was assumed to be lowered sufficiently to enable construction of the dam raise (including removal of the top of the existing dam) and the spillway wall in the dry season. The reservoir level during construction will be managed to provide a safe freeboard level to store a frequent storm event. These levels will be developed during final design.

The cost of water control was based on percentage of direct construction cost.

11.3.6 ENGINEERING AND DESIGN SERVICES

Engineering for final design and preparation of plans, specifications, and construction contract documents will be performed based on the concepts presented in this report. The engineering services will involve additional site investigations including surveying, borrow and foundation evaluations, engineering analyses, preparation of final designs, and preparation of the design report. The services will include construction permitting with the appropriate agencies.

The engineering and design costs are based on a percent of total construction cost at this stage of design.

11.3.7 CONSTRUCTION MANAGEMENT

Construction procedures will be observed and quality control and quality assurance will be performed and documented during construction. Engineering support will be provided during construction to assist in successful construction completion and to evaluate changed conditions.

The construction management costs are based on a percent of total construction cost at this stage of design.

11.3.8 TEMPORARY CONSTRUCTION FACILITIES

The contractor will require temporary facilities for job site office, material laydown, and equipment maintenance. Contractor housing is not included in the cost item. The costs were developed from Rawlinson’s Handbook.


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C O N C L U S I O N S A N D R E C O M M E N D A T I O N S 12.0

1 2 . 1 C O N C L U S I O N S

The scope of the RWD Raise design and plans for the current PFS involves excavation and raise of existing embankment and spillway, relocation of the downstream outlet works valves, construction of two saddle dams and breaching of the Morris Dam. The purpose of the RWD Raise design and plans is to increase the capacity of the reservoir and upgrade the existing spillway, which has developed some cracks and experienced significant erosion in downstream areas, with a cascading set of three spillway walls and channel armoring.

The existing RWD embankment is proposed to be raised to elevation 140.0 masl. Also, the elevation of the upstream spillway crest is proposed to be 136.5 masl to provide the desired water storage in the RWD reservoir. For construction of the proposed embankment, the existing spillway must be removed and the existing embankment must be excavated to elevation 134.0 masl for foundation preparation and in order to maintain required freeboard during construction.

Slope stability analyses were performed on the most critical section of the RWD using the SLOPE/W component of GeoStudio 2007. Seepage analyses were also conducted using SEEP/W module of the GeoStudio 2007 to estimate the steady state phreatic surface within the embankment to allow more accurate stability analyses. These analyses produced results indicating acceptable factors of safety for the proposed RWD Raise.

The proposed RWD spillway was designed based on the hydrologic and hydraulic analyses using the HEC-HMS, HEC-RAS and FlowMaster programs. The proposed RWD spillway is composed of cascading set of three spillway walls with crest elevations of 136.5, 134.75 and 132.5 masl from upstream to downstream. The existing spillway will be rebuilt, maintaining the existing crest elevation, and there will be two new spillway walls approximately 31 meters upstream and 34 meters downstream of the existing spillway. The sections between each spillway wall will be armored with shotcrete to decelerate erosion.

Saddle dams will be constructed at two locations to prevent uncontrolled overflow of the reservoir during flood conditions. The Morris Dam along the east side of the RWD reservoir will be breached to mitigate potential slope instabilities, allow more storage volume in the RWD reservoir and possibly provide material for saddle dam construction.

The RWD outlet structure will remain in place, but the outlet valve at the downstream toe of the existing dam will be moved to the proposed downstream toe. A new valve vault will be constructed at the proposed dam toe and connected to the raw water supply pipeline.

1 2 . 2 R E C O M M E N D A T I O N S

Additional geotechnical drilling and laboratory testing are needed to better define the subsurface conditions for the final design of the RWD Raise. The hills surrounding the reservoir and dam should be investigated for potential slope instabilities. An accurate survey of the proposed dam inundation area along with a bathymetric survey of the existing reservoir must be performed to create an accurate stage-storage relationship for a more precise hydrologic analysis and water balance modeling. Moreover, a detailed survey of the spillway channel is necessary for the final design of spillway weir


28


walls. The existing inlet and outlet works should be surveyed for more accurate design of relocation procedure.


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R E F E R E N C E S 13.0

Ahmad M, Wygralak AS and Ferenczi PA, 2009. Gold deposits of the Northern Territory (Second Edition). Northern Territory Geological Survey, Report 11 (Second Edition update by Wygralak AS and Scrimgeour IR).

Australian National Committee on Large Dams (2010) Guidelines on Planning, Design, Construction, Operation and Closure of Tailings Dams, 66.

Bateman Kinhill Kilborn. Jul 1995. Mt Todd Gold Mine Phase II Specifications and Plans, Vol. II Sections 7, 8. 98 p.

GEO-SLOPE International, Ltd. (GEO-SLOPE), 2007. SEEP/W (software and manual), SLOPE/W (software and manual). GEO-SLOPE International Ltd.: Calgary, Alberta, Canada.

Gustavson Associates. December 2006. Preliminary Economic Assessment, Mt. Todd Gold Project, Northern Territory, Australia. Prepared for Vista Gold Corp.

Hynes-Griffin, M.E. and Franklin, A.G. (1984) “Rationalizing the Seismic Coefficient Method”. Miscellaneous Paper GL-84-13, U.S. Department of the Army. Waterways Experiment Station. U.S. Army Corps of Engineers (USACE), Vicksburg, MS.

Knight Piesold Pty. Limited. Jul 1995. Water Dam Geotechnical Investigation, Mt Todd Gold Project. 86 p.

MWH (2006) Mt. Todd Environmental Management Services TSF Scoping Study. Report dated December, 2006.

NSR Environmental Consultants Pty Ltd. October 1992. Mt Todd Gold Project Draft Environmental Impact Statement.

NRCS (1994) Gradation Design of Sand and Gravel Filters. Chapter 26, Part 633 National Engineering Handbook, National Resources Conservation Service, United States Department of Agriculture.

Rawlinsons Australian Construction Handbook. (2012), Edition 30. Rawlinsons Publishing, Perth. 952pp.

Tetra Tech (2010) Mt. Todd Gold Project, Existing Tailing Storage Facility Raise. Report dated September, 2010.

United States Geological Survey (USGS), Department of the Interior. Australia Seismic Hazard Map. http://earthquake.usgs.gov/earthquakes/world/australia/gshap.php. Accessed September, 2009.

Vista Gold Australia Pty Ltd. (2011) Mining Management Plan for Mt. Todd Operation. Report dated August, 2011.

ATTACHMENT A FIGURES

GOLF PIT

TOLLIS PIT

RAW WATER DAM

RAW WATER

SUPPLY RESERVOIR

RETURN WATER POND

WATER POLISHING POND

HEAP LEACH PAD

BATMAN PIT

LOW GRADE ORE STOCKPILE

RUN OF MINE PAD

WASTE ROCK DUMP

WASTE ROCK DUMP

RETENTION POND (RP1)

MT. TODD ROAD (FROM STUART HIGHWAY

TAKE JATBULA ROAD TO MT. TODD ROAD)

EXISTING PROCCESS PLANT

NORTH TAILINGS

STORAGE FACILITY

(TSF1)

PROPSOED POWER PLANT

MT. TODD GOLD PROJECT

PRE-FEASIBILITY - APPENDIX J

RAW WATER DAM RAISE

NORTHERN TERRITORY, AUSTRALIA

SITE LOCATION MAP & MAJOR FACILITY ORIENTATION

SCALE: NOT TO SCALE

REGIONAL MAP

SCALE: NOT TO SCALE

GENERAL NOTES:

UNLESS OTHERWISE INDICATED ON THE DRAWINGS, THE FOLLOWING GENERAL NOTES SHALL

APPLY:

1. ALL DIMENSIONING, STATIONING AND SCALES ARE IN SI METRIC SYSTEM. STATIONING IS

MEASURED HORIZONTALLY, NOT ALONG THE SLOPE.

2. GROUND SURFACE CONTOURS SHOWN ON THESE DRAWINGS REFLECT EXISTING

(PRE-CONSTRUCTION) CONDITIONS UNLESS OTHERWISE NOTED.

3. DRAWINGS ARE FOR PRE-FEASIBILITY STUDY ONLY AND ARE NOT TO BE USED FOR

CONSTRUCTION.

PREPARED SUBGRADE

COMPACTED RESIDUAL SOIL (ZONE A)

FILTER COMPATIBLE FILL (ZONE B)

CONCRETE

EXISTING WATER LEVEL

DRAIN FILL (ZONE C)

Issued by:Issued for:

REVISION

SHEET

OF

Project no.:

Date:Location:

Project:

Scale:

Approved by:

Drawn by:

Designed by:

Checked by:

TETRA TECH350 Indiana Street, Suite 500

Golden, Colorado 80401

(303) 217-5700 (303) 217-5705 fax

THE CONTENT OF THIS DOCUMENT IS NOT INTENDED FOR THE USE OF, NOR IS

IT INTENDED TO BE RELIED UPON BY ANY PERSON, FIRM OR CORPORATION

OTHER THAN THE CLIENT AND TETRA TECH. TETRA TECH DENIES ANY LIABILITY

WHATSOEVER TO OTHER PARTIES FOR DAMAGES OR INJURY SUFFERED BY

SUCH THIRD PARTY ARISING FROM THE USE OF THIS DOCUMENT BY THEM,

WITHOUT THE EXPRESSED WRITTEN AUTHORITY OF TETRA TECH AND OUR

CLIENT. THIS DOCUMENT IS SUBJECT TO FURTHER RESTRICTIONS IMPOSED BY

THE CONTRACT BETWEEN THE CLIENT AND TETRA TECH AND THESE PARTIES

PERMISSION MUST BE SOUGHT REGARDING THIS DOCUMENT IN ALL OTHER

CIRCUMSTANCES.

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COVER

SHEET

A

FIGURE 1

1 8

JUNE, 2013

TM

DEN

JJ

DJ

AS SHOWN

RAW WATER

DAM RAISE


114-311285

A

0201

DRAWING INDEX

SHEET TITLE

FIGURE 1 COVER SHEET

FIGURE 2 PROPOSED SITE FACILITIES

FIGURE 3 GEOTECHNICAL BOREHOLE LOCATIONS

FIGURE 4 PROPOSED EMBANKMENT PLAN

FIGURE 5 PROPOSED RAW WATER PROFILE AND SECTION

FIGURE 6 DRAINAGE MAP

FIGURE 7 SPILLWAY P&P

FIGURE 8 SPILLWAY SECTIONS

NOT FOR

CONSTRUCTION

RESIDUAL SOIL

BEDROCK

PROPOSED WEST

SADDLE DAM

EXISTING/PROPOSED

SPILLWAY

EXISTING/PROPOSED RAW

WATER DAM

PROPOSED RAW WATER

RESERVOIR LIMITS

PROPOSED SOUTH

SADDLE DAM

MT. TODD

EXISTING TSF1

PROPOSED TSF

ACCESS ROAD

RAW WATER RESERVOIR


REVISION

SHEET

OF

Project no.:

Date:Location:

Project:

Scale:

Approved by:

Drawn by:

Designed by:

Checked by:



(303) 217-5700 (303) 217-5705 fax










CIRCUMSTANCES.

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PROPOSED

SITE FACILITIES

A

FIGURE 2

2 8

JUNE, 2013

TM

DEN

JJ

DJ

AS SHOWN

RAW WATER

DAM RAISE


114-311285

METER

50 50 100

1:50

1500

NOT FOR

CONSTRUCTION

RAW WATER RESERVOIR

PROPOSED RAW

WATER DAM

EXISTING RAW

WATER DAM

125

130

135

135

140

140

TTBH-12-08

TTBH-12-09

TTBH-12-10

TTBH-12-11

TTBH-12-12

TTBH-12-13

TTBH-12-14

TTBH-12-15

KPWD1

KPWD2

KPWD3

WDTP5

WDTP6

WDTP4

WDTP1

WDTP2

WDTP3

EXISTING/PROPOSED

SPILLWAY

2012 GEOTECHNICAL INVESTIGATION

I.D.

TTBH-12-08

TTBH-12-09

TTBH-12-10

TTBH-12-11

TTBH-12-12

TTBH-12-13

TTBH-12-14

TTBH-12-15

Northing(m)

8436648

8436598

8436739

8436654

8436809

8436790

8436854

8436839

Easting(m)

190264

190261

190251

190229

190265

190291

190290

190314

Elevation(m)

139

138

146

135

144

147

144

140

1995 GEOTECHNICAL INVESTIGATION

I.D.

KPWD1

KPWD2

KPWD3

WDTP1

WDTP2

WDTP3

WDTP4

WDTP5

WDTP6

WDTP7

WDTP8

WDTP9

WDTP10

WDTP11

WDTP12

WDTP13

WDTP14

WDTP15

WDTP16

WDTP17

Northing(m)

8436606

8436635

8436678

8436603

8436633

8436678

8436643

8436633

8436593

8436673

8436663

8436693

8436693

8437303

8436993

8436893

8436743

8436543

8436593

8436653

Easting(m)

190259

190243

190264

190259

190269

190259

190239

190309

190339

190399

190479

190639

190559

190809

190869

190829

190779

190729

190459

190549

Elevation(m)

129

126

131

129

126

131

124

124

124

127

125

129

129

133

128

125

125

131

125

127

LEGEND:

EXISTING CONTOURS

PROPOSED CONTOURS

EXISTING ROADS

EXISTING DRAINAGE

EXISTING WATER LEVEL

BOREHOLE (2012 GEOTECHNICAL

INVESTIGATION)

BORE HOLE (1995

GEOTECHNICAL INVESTIGATION)

TEST PIT (1995 GEOTECHNICAL

INVESTIGATION)


REVISION

SHEET

OF

Project no.:

Date:Location:

Project:

Scale:

Approved by:

Drawn by:

Designed by:

Checked by:



(303) 217-5700 (303) 217-5705 fax










CIRCUMSTANCES.

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GEOTECHNICAL

BOREHOLE

LOCATIONS

A

FIGURE 3

3 8

JUNE, 2013

TM

JA

JJ

DJ

AS SHOWN

RAW WATER

DAM RAISE


114-311285

METER

5 5 10

1:5

150

NOT FOR

CONSTRUCTION

RAW WATER RESERVOIR

PROPOSED RAW

WATER DAM

125

130

135

135

140

140

PROPOSED RAW WATER

RESERVOIR LIMITS

ELEV = 136.5m


REVISION

SHEET

OF

Project no.:

Date:Location:

Project:

Scale:

Approved by:

Drawn by:

Designed by:

Checked by:



(303) 217-5700 (303) 217-5705 fax










CIRCUMSTANCES.

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PROPOSED

EMBANKMENT

PLAN

A

FIGURE 4

4 8

JUNE, 2013

TM

JA

JJ

DJ

AS SHOWN

RAW WATER

DAM RAISE


114-311285

METER

3 3 6

1:3

90

A

05

04

B

05

04

NOT FOR

CONSTRUCTION

125

130

135

140

145

150

125

130

135

140

145

150

0+000 0+010 0+020 0+030 0+040 0+050 0+060 0+070 0+080 0+090 0+100 0+110 0+120 0+130 0+140 0+150 0+160 0+170 0+180 0+185

PROPOSED RAW WATER

DAM CREST, 140m

(PROJECTED)

ORIGINAL GROUND SURFACE

(ESTIMATED)

EXISTING RAW

WATER DAM CREST, 136.5m

(PROJECTED)

1

0.25

1

2.5

1

2.5

1

ZONE A

PROPOSED DAM

ZONE B

ZONE B

PROPOSED DAM ELEV = 140m

COMPETENT BEDROCK

ZONE C

ZONE C

0.4

0.25

1

0.4

1

2

1

1.5

1

1

1.5

RESIDUAL SOIL/COMPLETELY

WEATHERED BEDROCK

2m (MIN.)

EXISTING DAM ELEV = 136.5m

EXISTING DAM

EXISTING GROUND

RESIDUAL SOIL/COMPLETELY

WEATHERED BEDROCK

2m4m2m

0.25m

0.25m

9m

6m (EXISTING CREST)

1m

1m


REVISION

SHEET

OF

Project no.:

Date:Location:

Project:

Scale:

Approved by:

Drawn by:

Designed by:

Checked by:



(303) 217-5700 (303) 217-5705 fax










CIRCUMSTANCES.

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PROPOSED RAW

WATER DAM

PROFILE AND SECTION

A

FIGURE 5

5 8

JUNE, 2013

DJ

DEN

TM

DJ

AS SHOWN

RAW WATER

DAM RAISE


114-311285

SCALE:

SECTION B-B

1:1.5

B

05 04

SCALE:

SECTION A-A

1:2.5

A

05 04

NOT FOR

CONSTRUCTION

RWD

28.6km2

AREA DELINEATED APPROXIMATELY

BASED ON GOOGLE AERIAL MAP

RAW WATER RESERVOIR

RAW WATER DAM

BASIN BOUNDARY


REVISION

SHEET

OF

Project no.:

Date:Location:

Project:

Scale:

Approved by:

Drawn by:

Designed by:

Checked by:



(303) 217-5700 (303) 217-5705 fax










CIRCUMSTANCES.

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DRAINAGE

MAP

A

FIGURE 6

6 8

JUNE, 2013

SA

SA

JJ

DJ

AS SHOWN

RAW WATER

DAM RAISE


114-311285

METER

200 200 400

1:200

6000

PROPOSED CONTOUR MAJOR

PROPOSED CONTOUR MINOR

EXISTING CONTOUR MAJOR

EXISTING CONTOUR MINOR

3870

3870

LONGEST DRAINAGE PATH

SURFACE FLOW DIRECTION

DRAINAGE BASINS

DISCHARGE POINT OF ANALYSIS

DRAINAGE BASIN ID

DRAINAGE BASIN AREA

NOT FOR

CONSTRUCTION

CHANNEL FLOWLINE

PROPOSED DOWNSTREAM

SPILLWAY WEIR

MIDDLE SPILLWAY WEIR

PROPOSED UPSTREAM

SPILLWAY WEIR

120

125

130

135

140

120

125

130

135

140

0+000 0+010 0+020 0+030 0+040 0+050 0+060 0+070 0+080 0+090 0+100 0+110 0+120 0+130

EXISTING GROUNDEXISTING SPILLWAY

WEIR WALL

PROPOSED UPPER

SPILLWAY WEIR

PROPOSED LOWER

SPILLWAY WEIR

C

0

7

0

7


REVISION

SHEET

OF

Project no.:

Date:Location:

Project:

Scale:

Approved by:

Drawn by:

Designed by:

Checked by:



(303) 217-5700 (303) 217-5705 fax










CIRCUMSTANCES.

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SPILLWAY

PLAN AND PROFILE

A

FIGURE 7

7 8

JUNE, 2013

DJ

DEN

JJ

DJ

AS SHOWN

RAW WATER

DAM RAISE


114-311285

METER

5 5 10

1:5

150

SCALE:

SECTION C-C

1:25

C

07 07

D

0807

E

0807

F

0807

NOT FOR

CONSTRUCTION

125

130

135

140

145

125

130

135

140

145

0+000 0+010 0+020 0+030 0+040 0+050

EXISTING GROUND

37m

ELEV=136.5m

ELEV=137m

ELEV=137m

ELEV=133m

CONCRETE WEIR

125

130

135

140

145

125

130

135

140

145

0+000 0+010 0+020 0+030 0+040 0+050

EXISTING GROUND

ELEV=132m

ELEV=134.75m

36m

1m 1m

ELEV=135m

CONCRETE WEIR

120

125

130

135

140

120

125

130

135

140

0+000 0+010 0+020 0+030 0+040 0+050

EXISTING GROUND

ELEV=130m

ELEV=132.5m

ELEV=133m

26.2m

ELEV=133m

1

1

1

1

CONCRETE WEIR


REVISION

SHEET

OF

Project no.:

Date:Location:

Project:

Scale:

Approved by:

Drawn by:

Designed by:

Checked by:



(303) 217-5700 (303) 217-5705 fax










CIRCUMSTANCES.

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SPILLWAY

SECTIONS

AND DETAILS

A

FIGURE 8

8 8

JUNE, 2013

DJ

DEN

JJ

DJ

AS SHOWN

RAW WATER

DAM RAISE


114-311285

SCALE:

SECTION D-D (UPSTREAM SPILLWAY WEIR)

1:2

D

07 08

SCALE:

SECTION E-E (MIDDLE SPILLWAY WEIR)

1:2

E

07 08

SCALE:

SECTION F-F (DOWNSTREAM SPILLWAY WEIR)

1:2

F

07 08

ATTACHMENT B 2012 INVESTIGATION BOREHOLE LOGS AND

LABORATORY TEST RESULTS

56

89

89

100

56

89

89

89

100

100

100

0100[0]

83[8]

66[14]

97[63]

12-10-9(19)

7-8-11(19)

4-5-4(9)

3-3-7(10)

5-10-7(17)

6-7-11(18)

4-9-11(20)

6-10-15(25)

5-6-8(14)

5-7-8(15)

6-8-12(20)

50/6cm

0.20.9

3.5

5.3

11.0

14.7

16.5

21.8

22.6

23.8

24.6

GM Red and tan SANDY GRAVEL with silt, moist, dense, well graded. [Zone C]

MH Red and gray GRAVELLY SILT with sand, dry, stiff, high plasticity silts, gravels composed ofweak highly weathered siltstone and graywacke. [Zone B]

CH Red GRAVELLY CLAY with silt, moist, stiff, high plasticity, gravels composed of completelyweathered siltstone. [Zone A]

Same as above but less gravel. [Zone A]

Same as above but Tan and red SANDY CLAY with silt and gravel, fine grained sands. [Zone A]

Same as above but GRAVELLY CLAY with silt and sand. [Zone A]

INTERBEDDED SILTSTONE AND GRAYWACKE Red and gray fine grained INTERBEDDEDSILTSTONE AND GRAYWACKE, very weak, completely weathered, moist, thinly bedded,fracturing indistinct.

Same as above but moderately strong to extremely weak, highly to completely weathered, veryclosely spaced fractures filled with gouge and red CH, fractures open up to 50mm. - 16.5 Auger refusal, switched to HQ core.

Same as above but very weak, completely weathered.

Same as above but very strong, moderately weathered, closely spaced fractures open up to 10mmfilled with red CH or quartz veins, little staining.

Same as above but slightly weathered, closely spaced fractures open up to 2mm filled with quartzveins or very little red CH.

Borehole terminated at 24.6 m depth.

Drilling Contractor: Macquarie Drilling

Logged By: Tony Monasterio

Ground Elev. (m): 139

Drill Rig Type: Hydrapower Scout

Northing (m): 8436648 Easting (m): 190264

Operator: Ben

Location: RWD

Water: Not Measured

Hammer Weight/Drop: 140/30Drilling Type: 8" HSA/HQ Core

Dates(s) Drilled: Nov. 29 - Nov. 30, 2012

DE

PT

H(m

)

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

SA

MP

LE

PAGE 1 OF 1BOREHOLE ID: TTBH-12-08

PROJECT LOCATION Northern Territory, AustraliaPROJECT NUMBER 114-311285

CLIENT Vista Gold PROJECT Mt. Todd Prefeasibility Geotechnical Investigation

BO

RE

HO

LE T

ET

RA

TE

CH

MT

. TO

DD

TM

062

513.

GP

J M

TT

OD

D.G

DT

6/2

7/1

3

RE

CO

VE

RY

(%

)[R

QD

(%)]

BLO

WC

OU

NT

S(N

VA

LUE

, bpf

)

GR

AP

HIC

LOG

MATERIAL FIELD DESCRIPTION

78

78

89

67

94[10]

95[38]

95[37]

95[11]

62[8]

47[8]

100[54]

100[13]

100[14]

6-8-7(15)

4-6-8(14)

2-2-4(6)

1-1-1(2)

0.21.1

2.1

3.5

5.6

6.5

11.5

12.5

23.724.1

25.4

26.726.9

GC Red and tan SANDY GRAVEL with silt, dry, dense, well graded. [Zone C]

MH Red and tan GRAVELLY SILT with sand, dry, stiff, high plasticity silts. [Zone B]

CH Red and brown GRAVELLY CLAY with silt, dry, stiff, high plasticity. [Zone A]

Same as above but Red, less gravel, moist. [Zone A]

Same as above but SILTY CLAY trace gravel. [Zone A]

Same as above but saturated. [Zone A] - 5.6 Water table.

INTERBEDDED SILTSTONE AND GRAYWACKE Red and gray INTERBEDDED SILTSTONEAND GRAYWACKE, weak, highly weathered, closely spaced fractures filled with red CH, closelyinterbedded. Overall rockmass weak due to fractures. - 6.5 Auger refusal, switched to HQ core.

Same as above but medium spaced fractures moderately filled with red CH, staining alongfractures.

Same as above but staining penetrates rockmass.

- 13.6 10cm thick gouge material.

- 18.5 to 18.9 Highly stained zone.

Same as above but moderately strong.

Same as above but moderately weathered, staining along fractures.

Same as above but strong, moderately spaced fractures filled with gouge, red CH and weatheredquartz, staining throughout. Overall rockmass strong.

Same as above but very strong.







Operator: Ben

Location: RWD

Water: Not Measured


Dates(s) Drilled: Nov. 25 - Nov. 28, 2012

DE

PT

H(m

)

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

SA

MP

LE




BO

RE

HO

LE T

ET

RA

TE

CH

MT

. TO

DD

TM

062

513.

GP

J M

TT

OD

D.G

DT

6/2

7/1

3

RE

CO

VE

RY

(%

)[R

QD

(%)]

BLO

WC

OU

NT

S(N

VA

LUE

, bpf

)

GR

AP

HIC

LOG


48[0]

100[38]

89[36]

87[7]

99[63]

58[39]

49[30]

49[15]

43[0]

100[68]

100[59]

100[33]

2.1

9.5

14.0

15.6

17.0

21.5

27.127.2

INTERBEDDED SILTSTONE AND GRAYWACKE Red and gray fine grained INTERBEDDED SILTSTONEAND GRAYWACKE, extremely weak to very weak, completely weathered to extremely weathered, closelyspaced fractures filled with red CH and gouge open up to 30mm. Siltstone is nearly saprolite.

GRAYWACKE Red to gray very fine grained GRAYWACKE, weak to strong, highly weathered, closely spacedfractures filled with gouge and red CH open up to 10mm, highly stained throughout. Overall rockmass is weak.

Same as above but fracture spacing is wide, overall rockmass is moderately strong.

SILTSTONE Gray and tan SILTSTONE, extremely weak, completely weathered, closely fractured, very poorrecovery. Core expressed as fragments of rock in a MH matrix.

GRAYWACKE Gray and tan very fine grained GRAYWACKE, very weak, highly weathered, fracturingindistinct due to poor core recovery.

SILTSTONE Same as above SILTSTONE.

INTERBEDDED GRAYWACKE AND SILTSTONE Tan and gray very fine grained INTERBEDDEDGRAYWACKE AND SILTSTONE, very weak, highly weathered, closely spaced fractures filled with red CH orquartz open up to 1mm.

Same as above but weak.

Same as above but Gray and tan, strong, moderately weathered, staining up to 10mm into rock from fractures.Fractures in the harder rock yield a weaker rockmass strength due to brittle fracturing. Overall rockmass isstrong.






Operator: Ben

Location: RWD

Water: Not Measured


Dates(s) Drilled: Dec. 01 - Dec. 02, 2012

(Continued Next Page)

DE

PT

H(m

)

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

SA

MP

LE




BO

RE

HO

LE T

ET

RA

TE

CH

MT

. TO

DD

TM

062

513.

GP

J M

TT

OD

D.G

DT

6/2

7/1

3

RE

CO

VE

RY

(%

)[R

QD

(%)]

GR

AP

HIC

LOG


30.6


DE

PT

H(m

)

30

SA

MP

LE




BO

RE

HO

LE T

ET

RA

TE

CH

MT

. TO

DD

TM

062

513.

GP

J M

TT

OD

D.G

DT

6/2

7/1

3

RE

CO

VE

RY

(%

)[R

QD

(%)]

GR

AP

HIC

LOG


100

16[0]

33[0]

70[12]

18[0]

99[67]

78[45]

10-23-27/11cm

3.5

4.5

10.0

13.0

15.5

GW Brown and red SANDY GRAVEL with clay, moist, moderately dense, high plasticity clays, wellgraded, gravels and cobbles composed of subangular moderately strong highly to slightly weatheredsiltstone and graywacke. [Fill]

SW Red coarse grained SAND with gravel, moist, loose, well graded, subrounded sand grains, anyfines have been washed away. [Stream Channel]

INTERBEDDED SILTSTONE AND GRAYWACKE Red to gray fine grained INTERBEDDEDSILTSTONE AND GRAYWACKE, extremely weak to moderately strong, completely to highlyweathered, closely spaced fractures filled with red CH and weathered quartz, bedding indistinct.

Same as above but weak to moderately strong, highly weathered, fractures open up to 10mm.

Same as above but Gray, slightly weathered, moderately spaced fractures filled with gray CH orquartz open up to 1mm.







Operator: Rob

Location: RWD

Water: Not Measured



DE

PT

H(m

)

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

SA

MP

LE




BO

RE

HO

LE T

ET

RA

TE

CH

MT

. TO

DD

TM

062

513.

GP

J M

TT

OD

D.G

DT

6/2

7/1

3

RE

CO

VE

RY

(%

)[R

QD

(%)]

BLO

WC

OU

NT

S(N

VA

LUE

, bpf

)

GR

AP

HIC

LOG


78

100

7388[36]

69[11]

53[16]

7-9-15(24)

19-41-9/5cm

50/11cm

0.2

2.1

6.0

9.7

GC Red and gray CLAYEY GRAVEL with sand, dry, loose, high plasticity clays, fine to coarsegrained sands, gravels composed of subangular weak completely weathered siltstone andgraywacke.

INTERBEDDED SILTSTONE AND GRAYWACKE Red and tan very fine grained INTERBEDDEDSILTSTONE AND GRAYWACKE, extremely weak, completely weathered, fractures and beddingunknown. (Could be considered CH)

Same as above but weak, highly weathered, closely spaced fractures filled with red CH andweathered quartz open up to 1mm, red staining along fractures.- 2.5 Auger refusal, switched to HQ core.

Same as above but Tan, extremely weak, completely weathered, fracture spacing indistinct,fractures filled with red CH, red staining along fractures. Very poor recovery due to materialweakness.







Operator: Rob

Location: RWD Spillway

Water: Not Measured


Dates(s) Drilled: Dec. 06, 2012

DE

PT

H(m

)

0

1

2

3

4

5

6

7

8

9

SA

MP

LE




BO

RE

HO

LE T

ET

RA

TE

CH

MT

. TO

DD

TM

062

513.

GP

J M

TT

OD

D.G

DT

6/2

7/1

3

RE

CO

VE

RY

(%

)[R

QD

(%)]

BLO

WC

OU

NT

S(N

VA

LUE

, bpf

)

GR

AP

HIC

LOG


78

100

94[0]

42[0]

58[23]

63[11]

35[9]

23[0]

5-15-18(33)

12-30-20/5cm

0.20.4

1.5

2.0

18.4

GC Red and tan CLAYEY GRAVEL with sand, dry, loose, high plasticity clays, sands fine to coarsegrained, gravels composed of subangular weak completely weathered siltstone and graywacke.(Could be considered CH)

INTERBEDDED SILTSTONE AND GRAYWACKE Tan and red very fine grained INTERBEDDEDSILTSTONE AND GRAYWACKE, very weak, completely weathered, fractures and beddingindistinct. (Could be considered CH)

Same as above but Red and gray. - 1.0 Auger refusal, switched to HQ core.

Same as above but weak, highly weathered, closely spaced fractures filled with red CH andweathered quartz open up to 10mm.

Same as above but weak to moderately strong, overall rockmass is weak due to fractures.







Operator: Rob


Water: Not Measured



DE

PT

H(m

)

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

SA

MP

LE




BO

RE

HO

LE T

ET

RA

TE

CH

MT

. TO

DD

TM

062

513.

GP

J M

TT

OD

D.G

DT

6/2

7/1

3

RE

CO

VE

RY

(%

)[R

QD

(%)]

BLO

WC

OU

NT

S(N

VA

LUE

, bpf

)

GR

AP

HIC

LOG


96

76

65[5]

72[16]

36[11]

17-17-13(30)

21-45-5/3cm

0.4

2.5

9.9

GC Red and tan CLAYEY GRAVEL with sand, dry loose, high plasticity clays, gravels composed ofsubangular weak completely weathered siltstone and graywacke.

CH Tan and red GRAVELLY CLAY, moderately stiff, high plasticity, gravels composed same asabove. [Saprolite] - 1.0 Auger refusal, switched to HQ core.

INTERBEDDED SILTSTONE AND GRAYWACKE Red and tan very fine grained INTERBEDDEDSILTSTONE AND GRAYWACKE, very weak to weak, highly weathered, closely spaced fracturesfilled with red CH or gouge open up to 15mm, staining penetrates rock completely.







Operator: Rob


Water: Not Measured



DE

PT

H(m

)

0

1

2

3

4

5

6

7

8

9

SA

MP

LE




BO

RE

HO

LE T

ET

RA

TE

CH

MT

. TO

DD

TM

062

513.

GP

J M

TT

OD

D.G

DT

6/2

7/1

3

RE

CO

VE

RY

(%

)[R

QD

(%)]

BLO

WC

OU

NT

S(N

VA

LUE

, bpf

)

GR

AP

HIC

LOG


67

78

100

42[7]

93[0]

59[8]

7-5-5(10)

8-18-18(36)

31-50/5cm

0.8

3.2

9.9

GC Red and gray CLAYEY GRAVEL with sand, dry loose, high plasticity clays, gravels composedof subangular weak completely weathered siltstone and graywacke.

INTERBEDDED SILTSTONE AND GRAYWACKE Red and tan very fine grained INTERBEDDEDSILTSTONE AND GRAYWACKE, very weak to weak, completely weathered, fractures and beddingunknown.

Same as above but Red and gray, highly weathered, very closely spaced fractures filled with red CHand gouge open up to 10mm, staining penetrates rock completely, some highly altered zones arestrong. - 3.5 Auger refusal, switched to HQ core.







Operator: Rob


Water: Not Measured



DE

PT

H(m

)

0

1

2

3

4

5

6

7

8

9

SA

MP

LE




BO

RE

HO

LE T

ET

RA

TE

CH

MT

. TO

DD

TM

062

513.

GP

J M

TT

OD

D.G

DT

6/2

7/1

3

RE

CO

VE

RY

(%

)[R

QD

(%)]

BLO

WC

OU

NT

S(N

VA

LUE

, bpf

)

GR

AP

HIC

LOG


TEST CERTIFICATE

CLIENT:

PROJECT:

LOCATION:

Lab Sample Description Moisture Dry Liquid Plastic Preparation Linear

Number Content Density Limit Index & Shrink.

(%) (t/m3) History (%)

1 2 3 4 5

13-AC-255 15.2 1.91 35 21 DS -

AD

1 AS 1289 2.1.1

2 AS 1289 3.1.1

3 AS 1289 3.2.1, 3.3.1

4 DS = Dry Sieved

WS = Wet Sieved

N = Natural State With No Sieving

AD = Air Dried

OD = Oven Dried at 50oC

N = Natural State As Received

5 AS 1289 3.4.1

Approved Signatory: Aaron Lacey Date: 22/01/2013

TTBH-12-08

03

CLAY: red-brown.

Mt. Todd (114-311285)

Suite 500, 350 Indiana Street Golden CO 80401

Tetra Tech

SOIL CLASSIFICATION TEST DATA

2.5m

Sample

Source

NOTES TO TESTING

24.01.13

13-32-20

Client

Date Tested:

Job Number:

Sampled By:

Test Method:

Sample History:

Test Method:

Preparation:

Test Method:

Test Method:

This document is issued in accordance with NATA’s accreditation requirements

Accreditation No. 2418

SGS Australia Pty Ltd

Unit 15, 33 Maddox Street

(PO Box 6432)

Alexandria NSW 2015

Australia

This document is issued by the Company subject to its General Conditions of Service (www.sgs.com/terms_and_conditions.htm). Attention is drawn to the limitations of liability, indemnification and jurisdictional issues established therein.

This document is to be treated as an original within the meaning of UCP 600. Any holder of this document is advised that information contained hereon reflects the Company's findings at the time of its intervention only and within the limits of client's

instructions, if any. The company's sole responsibility it to its client and this document does not exonerate parties to a transaction from exercising all their rights and obligations under the transaction documents. Any unauthorized alteration, forgery or

falsification of the content or appearance of this document is unlawful and offenders may be prosecuted to the fullest extent of the law.

ABN 44 000 964 278

ph: +61 (0)2 8594 0481

fax: +61 (0)2 8594 0499

PF-(AU)-[IND(MTE)]-(GEN)-RPT-607.VER1.09.02.2011 – Page 1 of 1

TEST CERTIFICATE

Lab Number:

Date Tested:

Checked By:

Sample Description:

Sieve Size (mm) % Passing Sieve Size (mm) % Passing

Approved Signatory: Chris Lloyd Date:

0.01089

24/01/2013

None

None

Remarks:

Loss on Pretreatment:

150.0 1.18

0.150

0.02089

19.0

0.600

2.36

6.7

30

89

0.002

0.005

4.75

86

86

85

82

93 67

57

Dispersant Type:

40

88

Hydrometer Type:

9.5

Pretreatment:

13.2

100

63.0 0.425

0.300

100 0.075 74

10037.5

0.050

26.5

53.0

10075.0

Sodium Hexametaphosphate

ASTM 152H

100

48

87

Address:

Project:

Sample Source:

Sampled By:

100

Location:

Client

AS 1289 3.6.1 / 3

13-32-20Job Number:

Test Method:

CLAY: red-brown.

86

Tetra Tech


Mt. Todd (114-311285)

Client:

PARTICLE SIZE DISTRIBUTION

13-AC-255

23/01/2013

JL

TTBH-12-08 03 2.5m





(PO Box 6432)

Alexandria NSW 2015

Australia


This document is to be treated as an original within the meaning of UCP 600. Any holder of this document is advised that information contained hereon reflects the Company's findings at the time of its intervention only and within the limits of

client's instructions, if any. The company's sole responsibility it to its client and this document does not exonerate parties to a transaction from exercising all their rights and obligations under the transaction documents. Any unauthorized

alteration, forgery or falsification of the content or appearance of this document is unlawful and offenders may be prosecuted to the fullest extent of the law.

ABN 44 000 964 278

ph: +61 (0)2 8594 0481

fax: +61 (0)2 8594 0499

0

10

20

30

40

50

60

70

80

90

100

0.001 0.010 0.100 1.000 10.000 100.000

sieve aperture mm

% p

assi

ng

Clay Silt Sand Gravel


TEST CERTIFICATE

CLIENT:

PROJECT:

LOCATION:




1 2 3 4 5

13-AC-256 12.8 1.92 22 10 DS -

AD

1 AS 1289 2.1.1

2 AS 1289 3.1.1

3 AS 1289 3.2.1, 3.3.1

4 DS = Dry Sieved

WS = Wet Sieved


AD = Air Dried



5 AS 1289 3.4.1


Test Method:

Preparation:

Test Method:

Test Method:

Test Method:

Sample History:

NOTES TO TESTING

25.01.13

13-32-20

Client

Date Tested:

Job Number:

Sampled By:

Sample

Source

8.5m

Mt. Todd (114-311285)


Tetra Tech


TTBH-12-08

07

SANDY CLAY: orange-brown.





(PO Box 6432)

Alexandria NSW 2015

Australia





ABN 44 000 964 278

ph: +61 (0)2 8594 0481

fax: +61 (0)2 8594 0499


TEST CERTIFICATE

Lab Number:

Date Tested:

Checked By:

Sample Description:


Approved Signatory: Date: 23/01/2013

9.5

4.75

0.010100

None

None

Remarks:


150.0 1.18

0.150

Chris Lloyd

0.020100

19.0

0.600

6.7

23

100

0.002

0.005

98

98

96

84

60

51

Dispersant Type:

31

100

2.36

Hydrometer Type:

Pretreatment:

13.2

63.0 0.425

0.300

0.075 67

37.5

0.050

26.5

53.0

75.0


ASTM 152H

40

100

Address:

Project:

Sample Source:

Sampled By:

Location:

Client

AS 1289 3.6.1 / 3

13-32-20Job Number:

Test Method:


99

Tetra Tech


Mt. Todd (114-311285)

Client:


13-AC-256

22/01/2013

JL

TTBH-12-08 07 8.5m





(PO Box 6432)

Alexandria NSW 2015

Australia





ABN 44 000 964 278

ph: +61 (0)2 8594 0481

fax: +61 (0)2 8594 0499

0

10

20

30

40

50

60

70

80

90

100

0.001 0.010 0.100 1.000 10.000 100.000

sieve aperture mm

% p

assi

ng



TEST CERTIFICATE

CLIENT:

PROJECT:

LOCATION:




1 2 3 4 5

13-AC-257 14.8 1.90 24 12 DS -

AD

1 AS 1289 2.1.1

2 AS 1289 3.1.1

3 AS 1289 3.2.1, 3.3.1

4 DS = Dry Sieved

WS = Wet Sieved


AD = Air Dried



5 AS 1289 3.4.1


Test Method:

Preparation:

Test Method:

Test Method:

Test Method:

Sample History:

NOTES TO TESTING

24.01.13

13-32-20

Client

Date Tested:

Job Number:

Sampled By:

Sample

Source

13m

Mt. Todd (114-311285)


Tetra Tech


TTBH-12-08

10






(PO Box 6432)

Alexandria NSW 2015

Australia





ABN 44 000 964 278

ph: +61 (0)2 8594 0481

fax: +61 (0)2 8594 0499


TEST CERTIFICATE

Lab Number:

Date Tested:

Checked By:

Sample Description:


Approved Signatory: Date: 23/01/2013

9.5

4.75

0.010100

None

None

Remarks:


150.0 1.18

0.150

Chris Lloyd

0.020100

19.0

0.600

6.7

21

99

0.002

0.005

94

93

91

79

60

49

Dispersant Type:

30

97

2.36

Hydrometer Type:

Pretreatment:

13.2

63.0 0.425

0.300

0.075 65

37.5

0.050

26.5

53.0

75.0


ASTM 152H

39

96

Address:

Project:

Sample Source:

Sampled By:

Location:

Client

AS 1289 3.6.1 / 3

13-32-20Job Number:

Test Method:


94

Tetra Tech


Mt. Todd (114-311285)

Client:


13-AC-257

22/01/2013

JL

TTBH-12-08 10 13m





(PO Box 6432)

Alexandria NSW 2015

Australia





ABN 44 000 964 278

ph: +61 (0)2 8594 0481

fax: +61 (0)2 8594 0499

0

10

20

30

40

50

60

70

80

90

100

0.001 0.010 0.100 1.000 10.000 100.000

sieve aperture mm

% p

assi

ng



ATTACHMENT C HYDROLOGIC AND HYDRAULIC ANALYSES

Are

a (m

2)

Vol

ume

(m3)

Vol

ume

(m3)

Are

a (m

2)

Are

a (m

2)

Vol

ume

(m3)

Vol

ume

(m3)

Are

a (m

2)

L (m) L (ft) s (ft/ft) n P2 Tt (hr) L (m) L (ft) s (ft/ft) V (ft/s) Tt (hr)RWD 28.600 5.028 301.684 181.0 100.0 328.1 0.124 0.13 6.7 0.1254 9683.2 31769.2 0.013 1.80 4.9026

Time of Concentration and Lag Time Calculations using NRCS TR-55 Methodology

Sheet Flow Shallow Concentrated FlowBasin ID Area (km2) Tc (hr) Tc (min) Lag (min)

Note 1: Minimum lag time is 10 minutes

Project: RWD_Spillway Simulation Run: 100-yr

Start of Run: 21Dec2012, 00:00 Basin Model: RWD_SpillwayEnd of Run: 23Dec2012, 00:00 Meteorologic Model: 100-yrCompute Time: 24Jun2013, 09:44:31 Control Specifications: Control 1

HydrologicElement

Drainage Area(KM2)

Peak Discharge(M3/S)

Time of Peak Volume(1000 M3)

RWD_Basin 28.6 26.1 21Dec2012, 15:20 620.1RWD 28.6 17.9 21Dec2012, 17:20 612.5RWD_Outfall 28.6 17.9 21Dec2012, 17:20 612.5

Project: RWD_Spillway Simulation Run: 500-yr

Start of Run: 21Dec2012, 00:00 Basin Model: RWD_SpillwayEnd of Run: 23Dec2012, 00:00 Meteorologic Model: 500-yrCompute Time: 24Jun2013, 09:45:48 Control Specifications: Control 1

HydrologicElement

Drainage Area(KM2)




Project: RWD_Spillway Simulation Run: PMF

Start of Run: 21Dec2012, 00:00 Basin Model: RWD_SpillwayEnd of Run: 23Dec2012, 00:00 Meteorologic Model: PMPCompute Time: 24Jun2013, 09:46:32 Control Specifications: Control 1

HydrologicElement

Drainage Area(KM2)




Project Description

Solve For Headwater Elevation

Input Data

Discharge 14.60 m³/s

Crest Elevation 126.20 m

Tailwater Elevation 126.20 m

Crest Surface Type Paved

Crest Breadth 4.60 m

Crest Length 20.00 m

Results

Headwater Elevation 126.77 m

Headwater Height Above Crest 0.57 m

Tailwater Height Above Crest 0.00 m

Weir Coefficient 1.68 SI

Submergence Factor 1.00

Adjusted Weir Coefficient 1.68 SI

Flow Area 11.48 m²

Velocity 1.27 m/s

Wetted Perimeter 21.15 m

Top Width 20.00 m

Messages

Notes

Design flow is 50% of the 100-year storm flow.

Worksheet for 50%-100yrFlow-RWD-Culvert

6/24/2013 9:55:50 AMBentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03]

27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 1of1Page

Project Description


Input Data







Results







Flow Area 21.71 m²

Velocity 1.77 m/s


Top Width 20.00 m

Messages

Notes


Worksheet for 500yrFlow-RWD-Culvert



Project Description


Input Data







Results







Flow Area 86.41 m²

Velocity 3.54 m/s


Top Width 20.00 m

Messages

Notes


Worksheet for PMF-Flow-RWD-Culvert



0 50 100 150 200 250 300124

126

128

130

132

134

136

138

140

RWD Spillway Channel Plan: RWD Spillway Channel Proposed Cond 6/24/2013

Main Channel Distance (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

9....

30 50 75 100

125

150

171

187

199.

5

214.

83

227.

8323

3.94

250

264.

5

280

RWD_SpillwayChan MAIN

0 20 40 60 80 100 120133

134

135

136

137

138

139

140

141

142


RS = 280

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Ineff

Bank Sta

.035

0 20 40 60 80 100 120133

134

135

136

137

138

139

140

141

142


RS = 265.5

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Ineff

Bank Sta

.035

0 20 40 60 80 100 120136

137

138

139

140

141

142


RS = 265 Upstream Spillway Wall

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Bank Sta

.035 .013 .035

0 20 40 60 80 100 120133

134

135

136

137

138

139

140

141

142


RS = 264.5

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Ineff

Bank Sta

.035

7

0 20 40 60 80 100133

134

135

136

137

138

139

140

141


RS = 250

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Ineff

Bank Sta

.035

0 20 40 60 80 100134

135

136

137

138

139

140

141


RS = 237.38

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Ineff

Bank Sta

.035

0 20 40 60 80 100134

135

136

137

138

139

140

141


RS = 234.4 Middle Spillway Wall

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Bank Sta

.035 .013 .035

0 20 40 60 80 100133

134

135

136

137

138

139

140

141


RS = 233.94

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Bank Sta

.035

8

0 20 40 60 80 100 120130

132

134

136

138

140

142


RS = 227.83

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Ineff

Bank Sta

.035

0 20 40 60 80 100130

132

134

136

138

140


RS = 214.83

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Ineff

Bank Sta

.035

0 20 40 60 80 100130

131

132

133

134

135

136

137


RS = 200.5

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Ineff

Bank Sta

.035

0 20 40 60 80 100132.5

133.0

133.5

134.0

134.5

135.0

135.5

136.0

136.5


RS = 200 Downstream Spillway Wall

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Bank Sta

.035 .013 .035

9

0 20 40 60 80 100130

131

132

133

134

135

136

137


RS = 199.5

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Bank Sta

.035

0 20 40 60 80 100130

131

132

133

134

135

136

137


RS = 187

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Levee

Bank Sta

.035

0 20 40 60 80 100130

131

132

133

134

135

136

137


RS = 175

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Bank Sta

.035

0 20 40 60 80 100130

131

132

133

134

135

136


RS = 171

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Bank Sta

.035

10

0 20 40 60 80 100129

130

131

132

133

134

135

136

137


RS = 150

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Bank Sta

.035

0 20 40 60 80 100128

129

130

131

132

133

134

135


RS = 125

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Bank Sta

.035

0 20 40 60 80 100127

128

129

130

131

132

133

134


RS = 100

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Bank Sta

.035

0 20 40 60 80 100127

128

129

130

131

132

133


RS = 75

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Bank Sta

.035

11

0 20 40 60 80 100126

127

128

129

130

131


RS = 50

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Bank Sta

.035

0 20 40 60 80 100125

126

127

128

129

130

131


RS = 30

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Bank Sta

.035

0 20 40 60 80 100124

125

126

127

128

129

130

131


RS = 9.74

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Bank Sta

.035

0 20 40 60 80 100124

125

126

127

128

129

130

131


RS = 0

Station (m)

Elev

atio

n (m

)

Legend

WS PMF

WS 500-yr

WS 100-yr

Ground

Bank Sta

.035

12

HEC-RAS Plan: RWDspillwayPR River: RWD_SpillwayChan Reach: MAINReach River Sta Profile Q Total Min Ch El W.S. Elev Crit W.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude # Chl

(m3/s) (m) (m) (m) (m) (m/m) (m/s) (m2) (m)MAIN 280 100-yr 17.90 133.98 136.98 136.77 137.02 0.002981 0.89 20.02 44.68 0.43MAIN 280 500-yr 51.00 133.98 137.37 137.04 137.46 0.003191 1.31 38.88 51.58 0.48MAIN 280 PMF 315.60 133.98 139.16 138.19 139.37 0.002192 2.01 157.01 83.50 0.47

MAIN 265.5 100-yr 17.90 133.98 136.82 136.79 136.94 0.013046 1.48 12.11 37.88 0.83MAIN 265.5 500-yr 51.00 133.98 137.18 137.08 137.38 0.009294 1.95 26.19 42.05 0.79MAIN 265.5 PMF 315.60 133.98 139.05 139.32 0.003085 2.31 136.56 75.48 0.55

MAIN 265 100-yr 17.90 136.50 136.79 136.79 136.93 0.002539 1.69 10.71 37.77 1.00MAIN 265 500-yr 51.00 136.50 137.08 137.08 137.37 0.002002 2.38 21.83 39.91 1.00MAIN 265 PMF 315.60 136.50 138.41 138.41 139.26 0.001255 4.20 92.21 64.29 0.97

MAIN 264.5 100-yr 17.90 133.98 134.84 135.06 136.75 1.174734 6.13 2.92 32.72 6.55MAIN 264.5 500-yr 51.00 133.98 134.99 135.37 137.17 0.373296 6.55 7.79 33.34 4.33MAIN 264.5 PMF 315.60 133.98 135.93 136.81 139.04 0.065955 7.81 40.43 35.60 2.34


MAIN 237.38 100-yr 17.90 134.00 135.13 135.22 0.007442 1.27 14.14 37.33 0.66MAIN 237.38 500-yr 51.00 134.00 135.47 135.33 135.65 0.007396 1.90 26.79 37.86 0.72MAIN 237.38 PMF 315.60 134.00 137.16 136.68 137.71 0.005915 3.31 95.26 48.88 0.76









MAIN 175 100-yr 17.90 130.66 131.36 131.39 131.60 0.021862 2.17 8.24 22.14 1.14MAIN 175 500-yr 51.00 130.66 132.03 131.80 132.20 0.005551 1.79 28.53 36.69 0.65MAIN 175 PMF 315.60 130.66 134.52 134.71 0.001483 1.93 163.81 69.74 0.40

MAIN 171 100-yr 17.90 130.43 131.25 131.27 131.52 0.018602 2.29 7.80 17.12 1.08MAIN 171 500-yr 51.00 130.43 131.91 132.16 0.008422 2.20 23.14 29.44 0.79MAIN 171 PMF 315.60 130.43 134.48 134.70 0.001907 2.10 150.28 67.71 0.45




MAIN 75 100-yr 17.90 127.03 128.02 128.16 128.57 0.026777 3.27 5.48 9.07 1.34

HEC-RAS Plan: RWDspillwayPR River: RWD_SpillwayChan Reach: MAIN (Continued)Reach River Sta Profile Q Total Min Ch El W.S. Elev Crit W.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude # Chl

(m3/s) (m) (m) (m) (m) (m/m) (m/s) (m2) (m)MAIN 75 500-yr 51.00 127.03 128.71 128.87 129.40 0.022568 3.67 13.88 17.00 1.30MAIN 75 PMF 315.60 127.03 130.40 131.14 132.34 0.030425 6.18 51.10 35.78 1.65



MAIN 9.74 100-yr 17.90 124.40 126.79 125.49 126.81 0.000576 0.66 27.01 27.16 0.21MAIN 9.74 500-yr 51.00 124.40 127.27 126.32 127.32 0.001963 1.05 48.72 63.38 0.38MAIN 9.74 PMF 315.60 124.40 130.48 130.54 0.000275 1.05 299.38 83.61 0.18


ATTACHMENT D SEEPAGE AND SLOPE STABILITY ANALYSES

Name: #1 Surficial SoilsModel: Saturated / UnsaturatedK-Function: Surficial Soil, Ksat = 1.0e-07 m/sVol. WC. Function: SurficialK-Ratio: 1K-Direction: 0 °Name: #2 BedrockModel: Saturated / UnsaturatedK-Function: Siltstone, Ksat = 7.0e-08 m/sVol. WC. Function: Sandy Silty ClayK-Ratio: 1K-Direction: 0 °Name: #3 Transition ZoneModel: Saturated / UnsaturatedK-Function: Transition Zone, Ksat = 5.0e-06 m/sVol. WC. Function: Silty Clay (Fine Tailings)K-Ratio: 1K-Direction: 0 °

Vista Gold Corp.Mt. Todd MineRaw Water DamMaximum Proposed Section

#1

#2

#3 #4#5

#6

Directory: T:\Mining\Projects\VistaGold_MtTodd_114-311285\114-311285\300_Raw Water Dam\Technical\Geotechnical\GeoStudio\VG_MT_RWD_TM_062413.gsz

Name: #4 Zone AModel: Saturated / UnsaturatedK-Function: Zone A=2.0e-09 m/sVol. WC. Function: Clay/SiltK-Ratio: 0.1K-Direction: 0 °Name: #5 Zone BModel: Saturated / UnsaturatedK-Function: Zone B=1.0e-06 m/sVol. WC. Function: Zone BK-Ratio: 1K-Direction: 0 °Name: #6 Zone CModel: Saturated / UnsaturatedK-Function: Fine sand, Ksat=5e-06m/sVol. WC. Function: Fine sandK-Ratio: 1K-Direction: 0 °

0.045

723m

³/day

s0.0

0311

32m³

/days

0.049

357m

³/day

s

Distance (m)0 25 50 75 100 125 150

Ele

vatio

n(m

)

100

110

120

130

140

150

1.85

Name: #1 Surficial SoilsModel: Mohr-CoulombUnit Weight: 19 kN/m³Cohesion: 5 kPaPhi: Multiple Trial: 28 °Name: #2 BedrockModel: Mohr-CoulombUnit Weight: 24 kN/m³Cohesion: 1000 kPaPhi: 25 °Name: #3 Transition ZoneModel: Mohr-CoulombUnit Weight: 16 kN/m³Cohesion: 0 kPaPhi: Multiple Trial: 28 °

Slope Stability AnalysisMethod: GLESlip Surface Option: Entry and ExitHorz Seismic Load: 0


#1

#2

#3 #4#5

#6


Name: #4 Zone AModel: Mohr-CoulombUnit Weight: 21 kN/m³Cohesion: 0 kPaPhi: 33 °Name: #5 Zone BModel: Mohr-CoulombUnit Weight: 20 kN/m³Cohesion: 0 kPaPhi: Multiple Trial: 34 °Name: #6 Zone CModel: Mohr-CoulombUnit Weight: 20 kN/m³Cohesion: 0 kPaPhi: Multiple Trial: 38 °

Distance (m)0 25 50 75 100 125 150

Ele

vatio

n(m

)

100

110

120

130

140

150

1.48

Name: #1 Surficial SoilsModel: Mohr-CoulombUnit Weight: 19 kN/m³Cohesion: 5 kPaPhi: Multiple Trial: 28 °Name: #2 BedrockModel: Mohr-CoulombUnit Weight: 24 kN/m³Cohesion: 1000 kPaPhi: 25 °Name: #3 Transition ZoneModel: Mohr-CoulombUnit Weight: 16 kN/m³Cohesion: 0 kPaPhi: Multiple Trial: 28 °

Slope Stability AnalysisMethod: GLESlip Surface Option: Entry and ExitHorz Seismic Load: 0.08


#1

#2

#3 #4#5

#6


Name: #4 Zone AModel: Mohr-CoulombUnit Weight: 21 kN/m³Cohesion: 0 kPaPhi: 33 °Name: #5 Zone BModel: Mohr-CoulombUnit Weight: 20 kN/m³Cohesion: 0 kPaPhi: Multiple Trial: 34 °Name: #6 Zone CModel: Mohr-CoulombUnit Weight: 20 kN/m³Cohesion: 0 kPaPhi: Multiple Trial: 38 °

Distance (m)0 25 50 75 100 125 150

Ele

vatio

n(m

)

100

110

120

130

140

150

Documents

NI 43-101 Technical Report – Mt. Todd Gold Project 50,000 ... VI_Appendix... · 3.2 Surface and Subsurface Conditions ... RWD Raw Water Dam . SPT Standard Penetration Test