FINAL Beal Leach Pad Investigation Report.pdf

United States Department of Agriculture Forest Service Northern Region preliminary leach pad investigation beal mountain mine Beaverhead-Deerlodge National Forest

Silver Bow County, Montana

February 2010

Final Report

TETRA TECH

Final Report Preliminary Leach Pad Investigation Beal Mountain Mine

Beaverhead-Deerlodge National Forest Silver Bow County, Montana

Prepared for:

USDA – Forest Service, Northern Region

PO Box 7669 Missoula, Montana 59807

(406) 329-3036

Prepared by:

Tetra Tech

851 Bridger Drive, Suite 6 Bozeman, Montana 59715

(406) 582-8780 Tetra Tech Project No. 1158561667B

February 2010

Beal Mountain Mine Leach Pad Investigation Final Report USDA-Forest Service, Region 1

Tetra Tech February 2010 i

TABLE OF CONTENTS

1.0 INTRODUCTION

1.1 Leach Pad Investigation

1.2 Report Organization

2.0 BACKGROUND

2.1 History

2.2 Leach Pad Description

2.3 Observations and Investigations of Water Accumulation on the Pad

3.0 LEACH PAD INVESTIGATION AND PRELIMINARY RESULTS

3.1 Consolidation of Existing Information and Leach Pad Cross-Sections

3.1.1 Methods of Study

3.1.2 Plan Maps and Cross Sections

3.1.3 Results

3.2 Water Balance

3.2.1 Methods of Study

3.2.2 Direct Infiltration to the Leach Pad

3.2.3 Lateral Groundwater Flow

3.2.4 Combined Direct Infiltration and Lateral Groundwater Flow

3.2.5 Potential Winter Leach Pad Drain Down

3.2.6 Water Balance Conclusions

3.3 Monitoring Well Installation Investigation

3.3.1 Methods of Study

3.3.2 Data

3.3.3 Results

3.4 Leach Pad Cover/Liner Investigation

3.4.1 Methods of Studyl

3.4.2 Data

3.4.3 Results

4.0 CONCLUSIONS

4.1 Possible Solutions to Observed Problems

4.2 Additional Work

5.0 REFERENCES

LIST OF TABLES

Table 1. Rate of solution accumulation on the leach pad by month Table 2. Normalized Annual Site Precipitation data Table 3. Annual rate of water accumulation on the leach pad 2006-2008 Table 4. Potential contribution by direct infiltration of meteoric water to leach pad volumes Table 5. Potential contribution of lateral upgradient flow of groundwater to leach pad volumes.28

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Table 6. Combined contribution of direct infiltration and lateral upgradient flow of groundwater to leach pad volumes Table 7. Assumed initial moisture content and resulting drain-down volumes Table 8. Monitoring Location Justification Table 9. Location Data for new Monitoring wells and Piezometers

LIST OF FIGURES

Figure 1. Location Map Figure 2. Site Map Figure 3. Leach Pad Investigation Plan View Map Figure 4. Leach Pad Solution Volume Change Over Time Figure 5. Leach Pad Solution Volume Change vs. Precipitation Figure 6. Groundwater Influence on Leach Pad Solution Volume Figure 7. Groundwater and Leach Pad Liner Elevations Figure 8. Water Treatment Drawdown Scenarios for the Heap Leach Pad Figure 9. 1992 Pegasus Map of Leach Pad Clay Liner Depths and Locations Figure 10. Leach Pad Liner Investigation Section Views A through C Figure 11. Leach Pad Liner Investigation Section Views D through F Figure 12. Potentiometric Map Figure 13. Leach Pad Trench Cross Sections

LIST OF APPENDICES

Appendix A. Direct Infiltration Calculations Appendix B: Potential Groundwater Contribution Calculations Appendix C: Drain Down Calculations Appendix D: Leach Pad Monitor Well Lithologic and Completion Logs Appendix E: Test Pit Logs

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1.0 INTRODUCTION

Tetra Tech, Inc. is completing technical studies, an engineering evaluation and cost analysis (EE/CA), and is conducting active water treatment of leach pad solution in conjunction with a reclamation and restoration project under contract GS-10F-0268K / AG-0356-D-08 with the USDA Forest Service, Region 1 for the Beal Mountain Mine property. The Beal Mountain Mine is located approximately 16 miles west-southwest of Butte, in Silver Bow County, Montana (Figure 1). The Mine occurs within the Beaverhead-Deerlodge National Forest near the headwaters of German Gulch.

1.1 Leach Pad Investigation

This report describes the investigative program and presents the preliminary results for modification (#005) which is an addition to the larger Beal Mountain Mine contract that includes an overall plan and outline of tasks associated with investigating the potential source(s) of water to the Beal Mountain Mine Heap Leach Pad. It is the intent of this proposed modification to investigate the elevation of the top of the leach pad liner along the containment dike, and evaluate the relationships among groundwater elevations, leach pad bottom liner elevation, and leach pad solution elevation in an attempt to identify the potential source(s) of continued accumulation of solution within the leach pad containment.

Modification #005 defined four major areas of investigations:

1. Compilation of existing information on leach pad design, as-built construction, reclamation and closure in order to produce accurate plan maps and cross-sections of the leach pad;

2. Water balance modeling of the leach pad and environs to identify and evaluate potential sources of water accumulating on the pad;

3. Installation of six (6) monitor wells and three (3) piezometers to determine groundwater elevations and flow direction outside of the pad in relation to the elevation of the bottom liner and cover; and

4. Leach pad cover and liner excavations to observe construction characteristics, relations between the cover and liner, and effectiveness of the design to exclude water.

Tetra Tech, Inc. has completed the preliminary field aspect portions of this work on the Beal Heap Leach Pad Investigation and some preliminary results are available. Monitoring of water levels in wells will continue throughout the coming year.

1.2 Report Organization

This report is subdivided into five (5) sections plus attached appendices. Following this Introductory section, a discussion of the history of the Beal Mountain Mine, relevant historical reports, and observations and historical investigations concerning rates of accumulation of water on the leach pad are briefly summarized in the Background section (Section 2.0). Section

3.0 presents data pertinent to the consolidation of existing information and development of cross sections and water balance, monitor well installation investigation, and leach pad liner investigation. Section 4.0 is a conclusion section and section 5.0 contains references cited.

Figures and tables are incorporated into the text of the report. Appendices are attached at the end of the report.

Butte

SITE

N 0 Miles

This Drawing, in the form transmitted, is the original work product of TETRA TECH. This drawing cannot be altered, revised or reproduced without the prior written consent of TETRA TECH. An original will be retained by TETRA TECH as the "record copy" for purposes of this project. TETRA TECH does not approve of or warrant these documents if any alteration or modification is made without TETRA TECH's written approval.

Location Map Beal Mountain Mine

Silver Bow County, Montana

FIGURE 1

Job Number

Project Location

Tetra Tech February 2010 3

2.0 BACKGROUND

This section presents a brief summary of the history of the Beal Mountain Mine, describes the heap leach pad, and presents observations and the results of previous investigations concerned with the quality and amount of water accumulating on the pad.

2.1 History

The Beal Mountain Mine is located in the headwaters of German Gulch in the Pioneer Mountains, Silver Bow County, Montana (Figure 1), about 16 miles west southwest of Butte and 10 miles southwest of Fairmont (Gregson) Hot Springs. The mine is primarily situated on land managed or controlled by the United States Department of Agriculture, Forest Service (USDA- FS), Beaverhead-Deerlodge National Forest (B-DNF) (Figure 1).

The Beal Mountain Mine produced gold and silver from two open pit mining operations beginning in 1988. Mining operations were completed in 1997 and gold recovery from the mine’s heap leach pad was completed in 1999. Active reclamation and closure activities were initiated in 1998 and are ongoing. With a filing of bankruptcy in 1998, and subsequent exhaustion of bonding funds to complete reclamation, the USDA-FS, in cooperation with the Montana Department of Environmental Quality (MDEQ), became the lead agency responsible for final mine closure. As the land management agency, the USDA-FS placed the mine closure under its CERCLA (Comprehensive Environmental Responsibility, Compensation, and Liability Act) authority, and determined that the non-time-critical removal action process would be followed for mine closure.

The Beal Mountain mineral deposits (Beal Mountain and South Beal) occur in the headwaters area of German Gulch (Figure 2). The main Beal Mountain deposit is located on the south flank of a prominent northeast–southwest trending ridge (Beals Hill) that is located between two creeks, German Gulch on the southeast and Minnesota Gulch to the northwest. Both creeks are tributaries of Silver Bow Creek and the Clark Fork River (Figure 1). An outlying deposit, South Beal, occurs about 1,500 feet south of the main Beal Mountain deposit on a steep north-facing valley side-slope and across German Gulch. Elevation in the vicinity of the mine ranges from about 6,500 feet in German Gulch to 7,863 feet at the top of Beals Hill. The mining permit boundary (Figure 2) contains about 1,475 acres, with about 90% of the permit area in German Gulch and 10% in Minnesota Gulch. Topography consists of broad, gently to moderately sloping ridge tops and steep V-shaped valleys (Figure 1). Ridge tops and south facing slopes are typically open, and north-facing slopes are tree covered.

As part of the closure process, the USDA-FS contracted with Tetra Tech (previously Maxim Technologies, Inc.) to develop both an Existing Conditions Report (Maxim, 2004a) and an Engineering Evaluation/Cost Analysis (EE/CA) (Tetra Tech 2009) that would evaluate final closure options for the Beal Mountain Mine. The Existing Conditions Report describes in some detail the geology, hydrology, water quality, aquatics, and fisheries conditions at and near the mine. The Existing Conditions Report also characterizes the source, nature, and extent of contamination and the risks of potential contaminant release related to various mine facilities at the Beal Mountain Mine.

LAD Area B

LAD Area A LAD Area D

LAD

Area C

N

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An agency revised draft EE/CA was prepared and released in September of 2005 (Maxim 2005). In February of 2009, the USDA-FS contracted with Tetra Tech, Inc. (Tetra Tech) to revise and update the 2005 Draft EE/CA to a final document. Updating of the document was required because water quality monitoring and various other types of data collected to fill identified data gaps continued to be collected following the release of the 2005 report.

The USDA-FS goal for the site is to close the mine and allow the area to return to its multiple use state. Although portions of the mine property were reclaimed, there are several on-going operational, maintenance, and reclamation requirements that need to be met for specific facilities before final closure is complete. There are also several significant and outstanding issues that potentially impact the environment that need to be addressed. These issues include the long-term geochemical reactivity of mine wastes (including both acidity and the release of selenium to the environment from several potential mine sources), geotechnical stability of the pit high-wall and leach pad containment dike, public safety issues related to the pit high-wall, infiltration of precipitation and groundwater into the leach pad, treatment and disposal of heap leach solution, mitigation of impacts to surface water in German Gulch and other nearby drainages, and impacts to seeps and springs in the vicinity of the Beal Mountain Mine area.

2.2 Leach Pad Description

The Beal Mountain Mine heap leach pad straddles the topographic divide between German and Minnesota Gulches. The leach pad was constructed in three stages in 1988 (Stage I), 1990 Stage II), and 1992 (Stage III). The heap leach pad (Figure 2 and Figure 3) covers approximately 77 acres, stores an estimated 14,807,100 tons of spent ore, and has a capacity to hold about 106,000,000 gallons of solution. The foundation is constructed on unconsolidated and discontinuous glacial till overlying weathered bedrock. A constructed containment dike or embankment surrounds about 60% of the leach pad perimeter. The dike was constructed from approximately 3,000,000 tons of waste rock from portions of the first three years of mining from the main Beal Mountain pit. Along the southern side of the leach pad, the preexisting topography was a steep south-facing hill slope. Because of this topography, the dike along the south side was constructed to stabilize and hold ore on the side-hill pad construction site, and to act as a surface upon which to lay out the bottom composite liner. This southern portion of the dike is about 70 feet wide across its crest and about 350 feet wide at the base. It is also about 175 feet high and over 2,400 feet in length. Containment around the northern and northeastern portion of the leach pad was created by excavating glacial and weathered bedrock materials out of the containment basin.

On top of the foundation materials and beneath the base liner, a series of under-drains were installed to remove shallow groundwater and to provide a leak detection system (see Figure 12, in Tetra Tech 2009). The under-drain system drains to both the north and south as the topographic divide between German and Minnesota gulches occurs beneath the pad. The under-drains are a dendritic system of pipes that connect rock-filled basins (blanket collection drains or BCD) in the subsurface, with two ponds (BCD and BCD-A; Figure 2 and Figure 3).

The leach pad base constructed on top of the BCD under-drain is a composite liner that consists of two six- to nine-inch lifts of compacted clay as a bottom liner overlain by a 40-mil PVC geomembrane liner. Depth of spent ore on the pad is approximately 200 feet with the thickest section located in the southern part of the facility. Six sumps were constructed for recovering leachate solution from the heap leach pad (Figure 2 and Figure 3).

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The heap leach pad was reclaimed during 2002 and 2003. Work completed for reclaiming the pad included reclamation of the containment dike, drawing down solution contained within the pad, regrading the spent ore to a more stable configuration (perimeter ore slopes are 3H:1V or lower), and constructing a low permeability cap. A composite cap for the leach pad was constructed using various low permeability geosynthetic and soil covers. A 30-mil PVC geomembrane was installed over most of the leach pad, and variations in cover construction include the use of Geosynthetic Clay Liner (GCL) covers and geogrid drainage layers over other portions of the pad. Figure 3 shows the geometry and materials used in construction of the cover over various portions of the leach pad. The existing conditions report (Maxim 2004) describes in some detail and illustrates the various geosynthetic composite covers used in the cover. Following placement of the geocomposite covers, an 18-inch thick layer of clayey and weathered quartzite South Beal waste and Beal shear zone material were placed as subsoil.

An 18-inch soil cover was placed over the reclaimed pad and the containment dike. The soil was seeded with an approved seed mixture.

2.3 Observations and Investigations of Water Accumulation on the Pad In October 2003, the draw down and biological treatment of the leach pad solution associated with mine closure was completed and the water treatment plant was mothballed and closed for the season. Depth of solution above the base liner in the vicinity of the sumps was approximately 17 feet. At that time, the pad was estimated to contain approximately 3,100,000 gallons of solution. As the pad solution levels rose to 25 million gallons (the maximum calculated threshold for geotechnical stability of the containment dike) in December of 2004, it was decided to re-commission the biological water treatment plant for operation during the summer of 2005 to remove excess water from the pad. By June 30th of 2005, leach pad solution volume increased to about 35,800,000 gallons. The biological water treatment plant was again operated through the summer and fall of 2005 and was capable of decreasing the volume of solution on the pad to about three to five million gallons. In all, approximately 182 million gallons of water was treated and discharged from leach pad to Land Application Disposal LAD systems from 2002 to 2005. The biological water treatment plant was again mothballed at the end of the 2005 summer season and later taken apart for sale at auction by the Department of Environmental Quality (DEQ) in 2008. In 2006, a pilot scale design for a reverse osmosis water treatment plant was completed and field tested by Tetra Tech personnel. A decision was made in 2007 to contract with Tetra Tech for a full scale RO treatment system for delivery and operation in 2008. Between the cessation of treatment in October of 2005 and June 2008, the leach pad solution volume increased to approximately 90 million gallons.

In August of 2008, full-scale water treatment by reverse osmosis began, and a measured 12 million gallons of pad solution was treated and discharged via LAD by mid-October 2008. In October of 2008, the pad solution volume was estimated at 75 million gallons. This volume of water was well above the 25 million gallon maximum that should be allowed on the pad to minimize the risk of failure by weight loading to the geotechnical instability.

5+00 10+00

15+00

28+00

20+00 25+00

0+00

5+00 10+00

15+00

27+00

20+00 25+00

0+00

5+00 10+00

27+00

15+00 20+00

25+00

0+00

5+

+0

+0

+0

+0

+0

0+00

0+00

5+

+0

15+00

20+00

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40+00 42+00

7375740074257450

742574507475

0+00

5+

+0

+0

+0

+0

+0

SUMP-3A

SUMP-1

SUMP-2

SBB-87-06

SBB-87-07

SBB-91-30

SBB-91-29

SBB-88-25SBB-88-26

SBB-88-20

SBB-87-12

SBB-87-13

SUMP-3

SUMP-4

SUMP-2A LPMW-5

LPMW-6

LPPZ-1

LPPZ-2

LPPZ-3

LPMW-4

LP-TP5

LPMW-3

LPMW-2

LPMW-1

LP-TP2

LP-TP3

LP-TP1

LP-TP4

TRENCH 1 TRENCH 2

BLANKET

COLLECTION

DRAIN POND (BCD)

BARREN POND

FRESH

WATER

PONDBLANKET

COLLECTION

DRAIN POND

(BCD-A)

DETOX

POND

N 0 Feet

This Drawing, in the form transmitted, is the original work product of TETRA TECH. This drawing cannot be altered, revised or reproduced without the prior written consent of TETRA TECH. An original will be retained by TETRA TECH as the "record copy" for purposes of this project. TETRA TECH does not approve of or warrant these documents if any alteration or modification is made without TETRA TECH's written approval.

Beal Mountain Mine Leach Pad Investigation

Plan View Silver Bow County, Montana

FIGURE 3

November, 2009

Jo b

N um be r

SURFACE WATER

DIVERSION TRENCH

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Figure 4 shows the rate of increase of solution on the pad over time along with the incremental increase in volume. A review of the rate of accumulation of water on the pad based on the last three periods of dewatering (2003, 2005 and 2008) suggests an average annual additional accumulation of water on the pad of about 28-34 million gallons per year. A breakdown of estimated accumulation by month on the pad is presented in Table 1 .

Table 1. Rate of solution accumulation on the leach pad by month.

Months of the Year Millions of Gallons per Month

April 2.0 to 2.5 May and June 6.0 to 8.0 July and August 2.5 to 3.0 September through March 1.4

Total 28.8 to 34.3

Figure 5 shows the relationship between precipitation and solution volume using daily recorded precipitation data from the Natural Resource Conservation Service SNOTEL site at Basin Creek, which is located about 20 miles to the southeast of the site at an elevation of about 7,100 feet above sea level. Figure 5 also shows a positive correlation between an incremental increase in solution volume and timing of precipitation, therefore indicating a leak in the leach pad cover was thought to be potentially responsible for the increased solution volume.

Water balance modeling completed during the existing conditions report (Maxim, 2004), estimated that following construction of the soil cover at the heap and completion of residual drain down from the heap leach material, the long-term percolation rate through the cover into the heap leach material would be on the order of 0.75 inches per year (3.5% of annual precipitation). This equates to a flow rate of approximately 3.0 gallons per minute (gpm) or approximately 1.6 million gallons per year and is based on an assumption that the cover components were installed with minimal construction defects. The resultant estimate of infiltration through the cover equivalent to 3.5% of annual precipitation is based on previous experience designing and evaluating cover performance in a variety of different environments.

This appears to be a reasonable estimate of performance given the inclusion of geosynthetic components in the cover. Assuming this scenario estimate is low; the worst case scenario modeled in the 2004 evaluation (a closure cover incorporating PVC on 5:1 (H:V) slope), the resultant net infiltration only increased to 8.6% of annual precipitation, or 3.8 million gallons per year. However, this value is still approximately an order of magnitude less than the recharge that is currently being observed at the Beal Mountain Heap Leach Facility.

Based on the direct infiltration calculations in 2006, the amount of direct precipitation is capable of providing all solution volume gains observed, if 100% of the precipitation infiltrates. The 100% infiltration volume matches the actual accumulated volume very well. While it is unlikely that 100% of all precipitation that directly falls on the leach pad infiltrates, the amount of evapotranspiration that occurs over the 77 acres is likely offset by the snow drifts that accumulate at various locations on top of and along the north flank of the leach pad. If the composite (geomembrane/GCL/soil) cover system is functioning to some degree as designed, this amount of infiltration is unlikely and another source, potentially groundwater infiltration onto the pad, may account for some portion of the observed annual accumulations.

To investigate the potential that groundwater is a contributor to the increasing solution in the leach pad, depth to groundwater was monitored continuously in November 2005 through November 2006 and again in June 2008 through March 2009 (MBMG 2007 and 2009). Figure

Tetra Tech February 2010 9

6 presents groundwater elevation data for two monitoring wells (SBB-88-25 and SBB-88-26) near the north leach pad embankment, solution elevations in Sump 3A, and cumulative monthly precipitation. Elevated levels in Sump 3A during the August through October 2008 monitoring period are due to injection of the RO treatment system reject water. Sump Levels in 3A decreased dramatically upon shutdown of the RO system on October 20, 2008. Groundwater elevation peaked in monitoring wells SBB-88-25and SBB-88-26 during October 2008. This peak corresponds with switching the RO LAD system from the hillside south of LAD area A to the hillside south of LAD areas B and D (located upgradient of the leach pad) and a significant precipitation event. Groundwater elevations in this area appear to be highly responsive to precipitation events and possibly LAD activities. Figure 6 indicates a positive correlation between an incremental increase in groundwater elevation, timing of precipitation, and solution volume increases. This suggests a likely potential for groundwater to contribute to the leach pad volume. Additionally, the graph indicates periods in which groundwater elevations along the north leach pad embankment are higher than embankment and the top of the bottom leach pad liner. This scenario could allow groundwater to spill over the embankment and into the leach pad. Unfortunately, the elevation of the leach pad liner at various locations along the north embankment was unknown at the time of this analysis as were groundwater elevations along much of the north embankment. Figure 7 depicts the relations described on Figure 6 using a plan map and two cross sections of the heap leach pad in relation to the water levels in the nearby monitoring wells described above.

As outlined in the Beal Mountain Mine Draft Final Engineering Evaluation/Cost Analysis (EE/CA) (Rev 4) (Tetra Tech, 2009), the existing groundwater elevations along the north and northeast edges of the heap leach pad are locally above the adjacent crest of the heap leach pad containment dike and top edge of the bottom leach pad liner (Figure 7). Two wells (SBB-88-25 and SBB-88-26; Figure 7) exist adjacent to the north edge of the leach pad, west of the highpoint near the process water pond and adjacent to the maintenance/shop pad. Measured water levels in these wells indicate that groundwater periodically exceeds the crest elevation of the heap leach pad bottom liner (Figure 7). Recorded measurements indicate high groundwater levels occur seasonally during snowmelt periods and possibly later in the year during periods of high land application disposal (LAD) during water treatment of the heap leach pad solution and/or precipitation events. Therefore, a potential exists for groundwater to enter the heap leach pad above the elevation of the crest of the embankment (top of the bottom liner) and below the cap elevation, where existing groundwater is locally and seasonally above the embankment crest elevation.

During the winter periods shown in the graphs, a declining incremental change in volume is likely related to the long-term drain-down of water that is retained in the spent ore under the leach pad cover but above the water table on the pad. Potential ranges of drain-down water volumes are recalculated based on recent dewatering and recharge events, and on leach pad material properties in the water balance section 3.2.5, below.

To attempt to corroborate the correlation between increasing solution in the leach pad and infiltrating precipitation, samples of rainfall, snow, and snowmelt were collected at the Beal Mountain site beginning in spring 2004 through spring 2005. These precipitation samples were stored in a refrigerator until the samples were shipped to an analytical laboratory for analysis of the ratio between Oxygen-18 and Oxygen-16 isotopes, along with deuterium content.

Theoretically, oxygen isotope analyses are ideal tracers of water sources and movement because they are integral constituents of water molecules and not something that is dissolved in water like other tracers that are commonly used in hydrologic analyses. Using a simple mixing model and known volume changes in the leach pad sump, at least half of the change in oxygen

Tetra Tech February 2010 10 isotope ratio and the majority of the hydrogen isotope ratios in the pad solution in June 2005 can be attributed to rain and snowmelt that occurred between April and June 2005 (Maxim, 2005). Unfortunately, the isotope data was unable to distinguish between precipitation directly infiltrating through the leach pad cover, and precipitation that has infiltrated through the adjacent groundwater system.

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Beal Leach Pad Sump 1 - Solution Elevation and Volume

6/28/03

12/25/03

6/22/04

12/19/04

6/17/05

12/14/05

6/12/06

12/9/06

6/7/07 12/4/07

6/1/08 11/28/08

So lu tio n

El ev at io n (fe et

So lu tio n

Vo lu m e

(M g al lo ns

Solution Elevation Solution Volume

South Dike Crest Elevation - 7504.1' (107.8 million gallons)

27.5 million gallons

7478.0' - 27.5 million gallons

R O s ys te m o ff

~3 w ks

R O s ys te m o n

Figure 4. Leach Pad Solution Volume Change Over Time.

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10/6/2003

4/3/2 004

9/30/2004

3/29/2005

9/25/2005

3/24/2006

9/20/2006

3/19/2007

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3/13/2008

9/9/2 008

M on th ly

P re ci pi ta tio n (in ch es

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0.35

0.40 Volum

e C hange (M gal/m onth)

Monthly Precipitation (Basin Creek Snotel) Sump Volume Change

Figure 5. Leach Pad Solution Volume Change vs. Precipitation.

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6/28/2003

12/25/2003

6/22/2004

12/19/2004

6/17/2005

12/14/2005

6/12/2006

12/9/2006

6/7/2007

12/4/2007

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11/28/2008

5/27/2009

El ev at io n (fe et

To ta l M on th ly

P re ci pi ta tio n (in ch es

SBB-88-25 SBB-88-26 Sump 3A Sump 1 Precipitation

Approximate North Containment Dike Elevation

RO System Extract Sump 1 Inject Sump 3A

RO LAD areas B/D

Figure 6. Groundwater Influence on Leach Pad Solution Volume.

0 Feet

This Drawing, in the form transmitted, is the original work product of TETRA TECH. This drawing cannot be altered, revised or reproduced without the prior written consent of TETRA TECH. An original will be retained by TETRA TECH as the "record copy" for purposes of this project. TETRA TECH does not approve of or warrant these documents if any alteration or modification is made without TETRA TECH's written approval.

Beal Mountain Mine Leach Pad Liner Investigation

Silver Bow County, Montana

FIGURE 7

April 2009

0 Feet 200

Tetra Tech February 2010 15

Leach pad solution levels measured in December of 2008 indicated that approximately 80 million gallons of solution were stored on the pad. Given anticipated seasonal additions of solution to the pad over the months of January through June of approximately additional 18 to 23 million gallons (Table 1), the total volume of water on the pad by the end of June of 2009 would potentially be as much as 98 to 103 million gallons. The maximum volume of water believed to be able to be stored on the pad based on a previous discharge event that occurred in 1999, is 106 million gallons. Therefore the leach pad was very close to maximum capacity prior to the startup of RO water treatment in the spring/early summer of 2009. In addition, this volume of solution was greatly in excess of the recommended maximum volume of 25 million gallons, below which the water level should be maintained to minimize the risk of a failure of the containment dike resulting from solution weight loading to the geotechnical instability.

Because water quality in the heap leach pad is not suitable for discharge to either surface water or groundwater, water must be treated before it can be discharged. Based on the geotechnical stability analysis, a total accumulation of 25 million gallons appears to be the critical volume that could destabilize the heap leach pad without active dewatering of the down-gradient slide area and cause a potential for the solution to be released. HELP modeling suggests that if the leak through the cover is repaired and any groundwater inflows are stemmed, then long-term infiltration through the cap on the leach pad should be reduced to about three gpm, but could be as high as six gpm under conditions of reduced evapotranspiration (Maxim, 2004a).

Heap Leach Pad De-watering Prediction

As of December 2008, the heap leach pad contained approximately 80 million gallons of solution. The maximum estimated capacity of the heap leach pad is 106 million gallons with the estimated annual inflow to the heap leach pad at approximately 25 million gallons. Figure 8 below shows four operating scenarios for de-watering of the heap leach pad as follows: 1) Optimal treatment conditions during a 4.5 month operational season from June 1st to October 15th; 2) Optimal treatment over an extended operational season from May 1st to December 1st;

3) Inflow reduced by ½ with an optimal 4.5 month treatment season; and, 4) Inflow reduced by ½ with an optimal 7 month treatment season. For all of these scenarios it was assumed that the water on the pad could not be reduced below 10 million gallons with the RO Plant. Based on these various scenarios, dewatering of the heap leach pad with no reduction in the rate of water accumulating on the pad could take from 3.75 years (scenario 1) to 9 years (scenario 2) depending on the length of the treatment system year. With a 50% rate of reduction of water accumulating on the pad, dewatering of the pad down to some finite volume could take from 2.8 (scenario 3) to 2 years (scenario 4), again depending on the length of the treatment year.

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Heap Leach Pad Drawdown Predictions

2009 2010 2011 2012 2013 2014 2015 2016 2017 2018

Year

Vo lu m e

(m ill io n ga llo ns

Scenario1 Scenario 2 Scenario 3 Senario 4

Figure 8. Water Treatment Drawdown Scenarios for the Heap Leach Pad.

Tetra Tech February 2010 17

3.0 LEACH PAD INVESTIGATION AND PRELIMINARY RESULTS

This section of the report describes investigations focused on identifying and quantifying potential source(s) of water to the Beal Mountain Mine Heap Leach Pad. Areas of investigation included: consolidation of existing construction and reclamation information/drawings, and the preparation of plan maps and cross-sections of the leach pad; a re-examination of the water balance model for the leach pad; monitor well installation and instrumentation; and leach pad cover and bottom liner test pits and trenches excavated to observe construction relations between the cover and liner, and effectiveness of the design to exclude water from the leach pad. Preliminary results of the investigations are reported where available.

3.1 Consolidation of Existing Information and Leach Pad Cross-Sections This sub-task of the Beal Mountain Mine leach pad investigation required a review of the available pre-mining, operational and post-mining topographic maps and other designs, as-built drawings and figures to assess the potential liner/cap interface configuration, its location, and elevation in order to assist with the identification of potential water sources to the leach pad.

This sub-task also required the preparation of a plan map, and five north-south and one east-west cross-sections of the leach pad.

3.1.1 Methods of Study

Forest Service, Montana (DEQ) and MBOMG files and archives were searched for all relevant reports and maps concerning the construction and reclamation of the Beal Mountain leach pad.

Data from the following reports and maps were considered most relevant and used in the preparation of the plan map and cross sections, and to clarify actual methods, practices and designs used construction and reclamation of the Beal Mountain Mine heap leach pad.

Beal Mountain Mining. (1988) – Application for a Hard-Rock Mining Permit. Hydrometrics, Inc.

Beal Mountain Mining. (1988) Construction Drawings for: Heap Leach Pad & Related Facilities, Beal Mountain Mining. (1988) Technical Specifications for Construction of Heap Leach Pad and Related Facilities

Beal Mountain Mining. (1988), Heap Leach Pad & Related Facilities.

Beal Mountain Mining. (1990), Stage III Leach Pad Construction Reports. Klohn–Leonoff.

Beal Mountain Mining. (1991), Construction Quality Assurance Final Report. Vector

Engineering.

Beal Mountain Mining. (1992) – Construction Quality Assurance Final Report 1992 Leach

Pad Expansion. Vector Engineering.

Pegasus Gold Corp. (1992) 1992 Leach Pad Clay Liner Depths and Locations Beal Mountain Mining. (1994) Design Review of Slope Stability and Liner Puncture resistance, Stage III Leach Pad Ore Raising. Klohn–Leonoff.

In addition to obtaining and studying these reports and maps, pre-mining, construction and post heap leach pad reclamation topographic contour maps were digitized for use in preparation of the plan maps and cross-sections presented below.

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3.1.2 Plan Maps and Cross Sections

This section presents the plan maps and cross sections prepared for the Beal Mountain heap leach pad investigation. Figure 9 is a copy of a Pegasus Gold Corporation map entitled “1992 Leach Pad Clay Liner Depths and Locations”. This figure illustrates the final Stage III post-construction topographic contours on the top of the clay liner at the bottom of the leach pad (upon which the bottom 40 mill PVC leach pad liner was subsequently placed). Therefore, this figure provides final elevations on the containment dike or leach pad embankment and illustrates the regraded topography and the top of the clay liner at final construction of the Stage III leach pad.

Figure 3 is a Plan map prepared for this report of the Beal Mountain Heap Leach Pad with post closure topographic contours. This map shows the following features:

• Post reclamation topography,

• Six lines of section across the leach pad presented on Figures 10 and Figure 11,

• Location of select existing monitoring wells,

• Location of currently assessable leach pad sumps,

• Location of new leach pad investigation wells,

• Location of new leach pad piezometer wells,

• Location of new leach pad cover investigation test pits (with N-S, E-W sampling grid),

• Location of new leach pad cover/bottom liner investigation trenches,

• Cap / cover construction material configurations,

• Stage 1 leach pad grading and liner extents,

• Stage III leach pad grading and liner extents,

• Projected pool or zone of saturation on the leach pad assuming an elevation of 7500’

(the lowest elevation of the leach pad containment dike, occurring along the south edge of the pad), and

• Zones of potential inflow of surface and groundwater onto the leach pad (blue line).

Figure 10 presents leach pad investigation cross-sections A through C and Figure 11 cross-sections D through F, respectively. These cross sections were prepared for this report and illustrate the following features:

• Distance and elevation along the lines of section,

• Pre-mining topography (pre-stage I leach pad),

• Post leach pad reclamation topography,

• Select monitor well locations,

• Sump locations,

• Stage 1 leach pad grading and liner extents,

• Stage III leach pad grading and liner extents, and

• Projected pool or zone of saturation on the leach pad assuming an elevation of 7500’

(the lowest elevation of the leach pad containment dike, occurring along the south edge of the pad).

3.1.3 Results

The plan maps and sections presented above illustrate the location and/or character of physical features (monitor wells, piezometers, sumps test pits, trenches, cover material construction designs, grading and liner extents, and the projected zone of saturation of spent ore on the leach pad) that are referenced in subsequent discussions. In addition, plan maps and cross-section also clearly present the final Stage III post-construction topographic contours on the top of the clay liner along the base of the leach pad (Figure 9) and post reclamation topography of the leach pad (Figure 3).

0 Feet

This Drawing, in the form transmitted, is the original work product of TETRA TECH. This drawing cannot be altered, revised or reproduced without the prior written consent of TETRA TECH. An original will be retained by TETRA TECH as the "record copy" for purposes of this project. TETRA TECH does not approve of or warrant these documents if any alteration or modification is made without TETRA TECH's written approval.

1992 Leach Pad Clay Liner Depths & Locations Beal Mountain Mine

Silver Bow County, Montana

FIGURE 9

B

0+00 5+00 10+00 15+00 20+00 25+00 28+00

0+00 5+00 10+00 15+00 20+00 25+00 27+00

0+00 5+00 10+00 15+00 20+00 25+00 27+00

SBB-88-25

(OFFSET 18FT)

SUMP-3A

SBB-88-26

(OFFSET 8FT)

GROUND SURFACE (CURRENT)

GROUND SURFACE (PRE STAGE 1)

STAGE 1 GRADING

STAGE 1 LINER

LEGEND

Well Max GWE Min GWE Period of Record

SBB-88-25 7519.68 7497.04 10/21/1988 - 03/25/2009

SBB-88-26 7515.37 7493.61 10/21/1988 - 03/25/2009

SBB-87-06 7429.10 7418.48 09/02/1988 - 06/28/2005

SBB-87-07 7431.43 7422.46 11/19/1987 - 06/28/2005

SUMP-3A 7512.23 7490.90 08/04/2003 - 09/28/2008

STAGE 3 GRADING

STAGE 3 LINER

STAGE 3 FULL POOL

This Drawing, in the form transmitted, is the original work product of TETRA TECH. This drawing cannot be altered, revised or reproduced without the prior written consent of TETRA TECH. An original will be retained by TETRA TECH as the "record copy" for purposes of this project. TETRA TECH does not approve of or warrant these documents if any alteration or modification is made without TETRA TECH's written approval.

Beal Mountain Mine Leach Pad Investigation

Section Views A-C Silver Bow County, Montana

FIGURE 10

November, 2009

Jo b

N um be r

0 Feet

Vert. Exaggeration: 2

0+00 5+00 10+00 15+00 20+00 25+00

0+00 5+00 10+00 15+00 20+00 25+00 30+00 35+00 40+00 42+00

0+00 5+00 10+00 15+00 20+00 25+00 30+00

GROUND SURFACE (CURRENT)

GROUND SURFACE (PRE STAGE 1)

STAGE 1 GRADING

STAGE 1 LINER

LEGEND

Well Max GWE Min GWE Period of Record

SBB-88-25 7519.68 7497.04 10/21/1988 - 03/25/2009

SBB-88-26 7515.37 7493.61 10/21/1988 - 03/25/2009

SBB-87-06 7429.10 7418.48 09/02/1988 - 06/28/2005

SBB-87-07 7431.43 7422.46 11/19/1987 - 06/28/2005

SUMP-3A 7512.23 7490.90 08/04/2003 - 09/28/2008

STAGE 3 GRADING

STAGE 3 LINER

STAGE 3 FULL POOL

This Drawing, in the form transmitted, is the original work product of TETRA TECH. This drawing cannot be altered, revised or reproduced without the prior written consent of TETRA TECH. An original will be retained by TETRA TECH as the "record copy" for purposes of this project. TETRA TECH does not approve of or warrant these documents if any alteration or modification is made without TETRA TECH's written approval.

Beal Mountain Mine Leach Pad Investigation

Section Views D-F Silver Bow County, Montana

FIGURE 11

November, 2009

Jo b

N um be r

0 Feet

Vert. Exaggeration: 2

Tetra Tech February 2010 22

3.2 Water Balance

The leach pad covers an area of approximately 77 acres, has approximately a 20% vegetation cover (grasses), and is located at an elevation between 7,450 to 7,630 feet. The solution capacity of the pad is thought to be about 106 million gallons based on a discharge event that took place in December of 1999 in the final stage of active leach pad operations. A review of the rate of accumulation of water on the pad based on the last three periods of dewatering (2003, 2005 and 2008) suggests an average annual accumulation of water on the pad of about 28-34 million gallons per year. Water is currently treated in a Reverse Osmosis (RO) treatment system to prevent the leach pad from over-flowing and discharging to groundwater off of the pad. The RO treatment system pumps leach pad solutions from sump #1 (Figure 3) at a rate of about 400 gpm, and reject water from the RO treatment system is returned at a rate of about 200 gpm to the leach pad by discharging to sump #3A (Figure 3). Assuming a 30% porosity for spent ore on the pad, the pool volume calculated in the vicinity of Sump-3A up to the elevation of the internal divide spill point is approximately 1,696,000 gallons. However, this volume is presumably already at capacity and any reject water from the treatment system produces a mounding effect in the vicinity of Sump-3A. The injection mound is controlled by the transmissivity of the ore material as solution moves over the internal divide into the Sump-1 pool or alternatively exits the leach pad over the north embankment. Treated water from the RO system is either directly discharged to a surface water diversion/discharge ditch or discharged through a Land Application Disposal (LAD) system. The LAD system includes two main areas;

one south of historic LAD area A and east of the process plant, and one northwest of the process plant in the northeast portion of historic LAD area D. Both areas exhibit moderate to steep grassy slopes.

Site-specific precipitation and evaporation data have been collected by Beal Mountain Mining, Inc. (BMMI). Data from the Beal Mountain station is available for the period of April 1988 through September 1988 and January 1989 through April 2005 (Table 2). Based on this data, about half of the average annual precipitation occurs during the period from April to July. June has the highest average monthly precipitation (2.39 inches; 18% of total annual precipitation) and February has the lowest average monthly precipitation (0.66 inch; 4% of total annual precipitation).

3.2.1 Methods of Study

Conceptually, the volume of solution on the leach pad is the result of the water balance between inputs minus withdrawals. Probable contributions or inputs of new water onto the pad are the result of either direct infiltration of meteoric water (precipitation and snowmelt), lateral flow from groundwater, or a combination of both. Withdrawals include leakage, volume removed by pumping, and evapotranspiration.

Based on laboratory water quality data for water samples collected from the blanket collection drain system constructed below the bottom leach pad liner, it is assumed there is no significant leakage into or out of the leach pad through the bottom liner.

Two possible sources of water entering the leach pad containment area were examined in conjunction with the water balance model to identify the potential source(s) of overall solution volume change on the leach pad. These sources include:

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A) Direct infiltration of meteoric water;

B) Lateral flow from groundwater;

C) Combination of A and B above could be responsible for the solution volume change.

Investigation of these potential sources with respect to the overall water balance on the leach pad, required the evaluation of the following parameters: the area of influence, precipitation, evapotranspiration, groundwater elevations, groundwater flow directions and leach pad volume.

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Table 2. Normalized Annual Site Precipitation data.

Beal Site Basin Creek Percent

Basin Creek>Beal Site

Percent Beal Site < Basin

Creek 1989 17.080 23.8 39.34 28.24 1990 13.580 20.7 52.43 34.40 1991 17.730 21.9 23.52 19.04 1992 13.350 18.2 36.33 26.65 1993 21.520 31.0 44.05 30.58 1994 15.570 24.5 57.35 36.45 1995 19.495 29.5 51.32 33.92 1996 14.755 22.6 53.17 34.71 1997 18.630 28.0 50.30 33.46 1998 19.113 26.0 36.03 26.49 1999 10.340 20.4 97.29 49.31 2000 13.150 20.6 56.65 36.17 2001 15.790 21.7 37.43 27.24 2002 16.710 21.2 26.87 21.18 2003 12.260 22.8 85.97 46.23 2004 14.470 23.3 61.02 37.90 2005 18.80 1 27.9 2006 16.98 1 25.2 Average annual percent difference 2007 19.28 1 28.6 50.57 32.62 2008 17.19 1 25.5 2009 -- --

1989-2004 Average 15.85 23.51 48.38

(i.e. Beal Site + 48.38% = Basin Creek or Basin Creek

- 32.60% = Beal Site

1989-2008 Average 24.17

1989-2008 est average 16.29

1 Estimated Beal Site precipitation based on 1989 - 2004 Average percent difference

Tetra Tech February 2010 25

3.2.2 Direct Infiltration to the Leach Pad

Contributing Area Based on available documentation and measurements from maps (Figure 3), the leach pad area is approximately 77 acres.

Precipitation During mine operations, a climate monitoring station was maintained at the mine to record site specific precipitation. Upon mine closure, the station was removed. 2004 is the most recent year in which a full year of site precipitation data is available. The nearest automated climate monitoring station is the Natural Resource Conservation Service SNOTEL station at Basin Creek, which is located about 20 miles to the southeast of the site at an elevation of about 7,100 feet above sea level. Comparison of historic (1989 through 2004) mine site climate data and the Basin Creek station data indicates the Basin Creek station generally receives approximately 32.6% more precipitation than Beal Mountain.

Since the Basin Creek station receives more precipitation than Beal Mountain and site data is unavailable for the period of 2005 to present (period since most recent leach pad draw down) Basin Creek data was normalized to represent the Beal Mountain site (Table 2). Therefore, Basin Creek data for 2005 to present was reduced by 32.60% to estimate Beal Mountain site precipitation conditions. The resulting average annual (calendar year) precipitation at the Beal Mountain site for the period of 1989 through 2008 is approximately 16.29 inches.

Evapotranspiration Unfortunately, only two complete months (July and September 1988) and two partial months (June and August 1988) of site specific pan evaporation data could be found in the project record. Other documentation has mentioned a site evaporation potential of 37.9 inches. The first mention of this value identified during this review was in a 1998 water balance completed by Klohn Leonoff Consulting Engineers to model the leach pad during active mining operations.

Further review of that document indicates the evaporation data used originates from the Canyon Ferry Cooperative weather station located approximately 80 miles northeast of the site. The Canyon Ferry station is located at an elevation of approximately 3,800 feet; almost 4,000 feet lower elevation than the Beal Mountain site. Based on the distance to the Canyon Ferry station and the elevation difference, it is Tetra Techs opinion that the Canyon Ferry station evaporation data is not representative of Beal Mountain conditions. No evaporation or evapotranspiration data from a comparable setting (elevation and terrain) could be identified during this review. In the absence of comparable data potential evapotranspiration was estimated using the published Blaney-Criddle method. An online calculator using this method is available at http://onlinehydro.sdsu.edu/onlineblaneycriddle.php. Results of this method suggest approximately 42% (6.74 inches) of the annual precipitation is evapotranspired. However, this estimation is likely an over approximation since the closest groundcover available within the method to that present on site, is a “small grain” crop.

Currently the reclaimed leach pad site is sparsely vegetated with a native grass mix providing approximately 20% ground cover which Tetra Tech estimates to be approximately half of a small grain crop. Additionally, the surface soil is relatively coarse with several large flat areas.

Considering the published evapotranspiration estimation method results, site wind conditions, actual site vegetation cover, and site soil types, Tetra Tech estimates 20% of leach pad precipitation may be evapotranspired.

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Leach Pad Accumulation Leach pad solution elevations have been continuously monitored since August 2003. Solution elevations in Sump 1 are converted to volume based on an empirical relationship developed during draw down periods.

To simplify the water balance, the periods of 2006 and 2007 were…