LEPANTO CONSOLIDATED MINING COMPANY LEPANTO MINE DIVISION

D. R. JAVIER Department Manager , Civil Engineering Services

MANAGING A GOLD MINE TAILINGS DAM

PHILIPPINES

Lepanto Mines

Mankayan, Benguet

Manila

Sea

China

Bontoc

La Union Poro Point

Baguio City

Dagupan City

Tailings Dam 5A

Outline of presentation

Design Construction Operation

VICINITY MAP

Lepanto Airstrip

TD 5A

Designer : • Energosystems and Geosciences

Incorporated Consultants :

• Knight Piesold Consulting Engineers • Woodward-Clyde (URS of Australia)

SECTION OF THE DAM

Random Fill

Sand & Gravel Filter

Boulder Toe

Zoned Earthfill Embankment

Design Height – 132 meters

Length/Width of Crest – 345 meters/10 meters

Spillway – Designed to handle probable

maximum flood

TUNNEL AND DECANT TOWER

Diversion Tunnel

Tunnel #1 3.0m wide x 3.0m high and 183m long

Tunnel #2 4.0 m wide x 5.0 m high and 550 m long

Decant Tower 1 & 2

3 inlets each at 2.0m wide x 4.0m high

PERMEABILITIES OF EMBANKMENT MATERIAL

Silty Clay 1 x 10-6 to 1 x 10-7 cm/s

Random Fill 1 x 10-5 cm/s

Sand Filter 1 x 10-3 to 1 x 10-4 cm/s

Gravel Filter 1 x 10-1 to 1 x 10-2 cm/s

Rock Toe 1 x 10 to 1 x 10-1 cm/s

SEISMIC CONSIDERATIONS

Operating Basis Earthquake (OBE) = 0.15g

Maximum Credible Earthquake (MCE) = 0.25g

FACTOR OF SAFETY

Factor of Safety vs Failure

(under static loading) = 1.2

Factor of Safety vs Maximum Probable Earthquake Loading Conditions

= 0.98-1.5

FREEBOARD REQUIREMENT

Minimum freeboard requirement is 500 year flood event compared to DMO requirement of 100 .

EMBANKMENT SLOPE

Upstream = 2 horizontal is to 1 vertical

Downstream = 2.5 horizontal is to 1

vertical

•Impounding Capacity – 50 million cubic meters • Catchment Area – 18.50 square kilometers • Reservoir Area - 103 hectares

DATE STARTED – January 1992

COMMISSIONING DATE – September 1993

The Twin Decant Tower has reached elevation 694.0m

• Driving of DiversionTunnel to divert Mankayan river before the start of embankment construction.

• Steel rib supports are used in very heavy ground where rockbolting and shotcrete is not applicable. Steel Rib Support

Decant Tower # 1

Decant Tower # 2

DIVERSION TUNNEL & DECANT TOWER

EMBANKMENT CONSTRUCTION

Stripping of the river bed is done for the dam foundation. All the boulders from the stripping activity are hauled and moved to the rock toe drain area.

A core trench 6m deep X 6m wide with 1:1 slope is excavated out of the dam foundation near the central section of the core axis to provide additional stability against sliding.

Hauling and aligning of sand/gravel filter. The sand filter was screened to produce a clean well graded fine to coarse sand while the gravel filter was crushed and screened to a uniform minus 19 mm size.

3m sand filter

3m gravel filter

piezometers

QUALITY CONTROL

A material testing laboratory on site was provided to test the following: concrete (21 Mpa), aggregates and soil materials (abrasion , permeabilities, etc).

Field density test is done to ensure that compaction is not less than 90% of the proctor density. Minimum moisture content is 13%.

Water jetting

Slush grouting

Clearing

The left and right abutments are cleaned and slush grouting is maintained over the core and filter zones. Abutment slopes are being maintained at no greater than 1:1. Water jetting, dental concreting and slush grouting are implemented for the abutment treatment.

ABUTMENTS PREPARATION

A fan pattern of grout holes are drilled at the embankment surface to intercept possible cracks and filled with a cement grout.

GROUTING

Lime Slaking Plant

Detoxification Plant

The influent is treated with lime and sodium metabisulfite to ensure the effluent is compliant to government regulatory standards.

Upstream Backfilling

Downstream Backfilling

The upstream section of the embankment has been raised to elev. 691.30m

The downstream embankment for the current backfilling operation has reached elev. 669.0m.

A once a month drain cleaning is done to control the rise of phreatic surface within the dam.

Weekly drain flow monitoring : - Dry season = 20 liters/sec - Wet season = 45 liters/sec

DIS

CH

AR

GE

, g

pm

RA

INF

AL

L,

mm

MONTH

UNDERDRAIN FLOW MONITORING

Rainfall

Discharge

Vibrating wire piezometers (VWPs) are installed along the centerline of TD5A to check on the performance of the dam especially its stability and its seepage defensive design features.

VWPs are being monitored weekly

SAND & G

RAVEL FILTER

VWP 6 VWP-15

VWP-14

VWP-10ARANDOM FILL

720 EL.

700 EL.

680 EL.

660 EL.

640 EL.

620 EL.

600 EL.

LONGITUDINAL SECTION OF T.D. # 5-A

PHREATIC SURFACE

Copyright LCMCo/agc

River

Dra

in

Rock Toe

Drain

RANDOM FILL

0 40 100

VWP = Vibrating Wire Piezometer

ROCK TOE WEIR: Q = 517 gpm

Bottom Elev. Ref. Elev. Water Depth Water Elev. Pressure (psi)

603.0606.0602.0613.5601.0600.0

691.30689.50667.00682.50677.00667.00

CREST LEVEL

WATER LEVEL

VWP 9C

PIEZOMETER LOCATIONS

Bottom Elev. Ref. Elev. Water Depth Water Elev. Pressure (psi)

VWP-6 603.00 691.30 72.50 618.80 22.50

VWP-9c 606.00 689.50 73.70 615.80 14.00

VWP-10a 602.00 667.00 62.20 604.80 3.90

VWP-14 613.50 682.50 51.40 631.10 25.00

VWP-15 601.00 677.00 62.60 614.40 19.00

VWP-16a 600.00 667.00 58.90 608.10 11.50

VWP- Vibrating Wire Piezometer

MONTHLY PIEZOMETER READING OF TD5A

0.0

100.0

200.0

300.0

400.0

500.0

600.0

700.0

800.0

900.0Jan,

2000

May

Sept

Jan,

2001

May

Sept

Jan,

2002

May

Sept

Jan,

2003

May

Sept

Jan,

2004

May

Sept

Jan,

2005

May

Sept

Jan,

2006

May

Sept

Jan.

2007

May

Sept

Jan,

2008

May

Sept

Jan.

2009

May

Sept

Jan,

2010

May

MONTH

RA

INF

AL

L,m

m

560.00

580.00

600.00

620.00

640.00

660.00

680.00

700.00

EL

EV

AT

ION

,m

Rainfall mm

Pond WaterLevel m

PZ1

PZ2

VWP6

VWP6A

PZ7

VWP8

PZ9

PZ9A

VWP9C

VWP9B

VWP10A

PZ10

PZ11

VWP14

VWP15

VWP16

VWP16A

Diversion Tunnel Regular monitoring: Ocular - for any signs of cracks, scouring of the invert, vandalism, etc . Extensometer – for tunnel movement

Regular inspection of the Decant Tower for any cracks and scouring of invert .

SUMMARY

The Lepanto TD5A has been in operation for the past 17 years. In October last year when we had the highest rainfall in the dam’s life, there were no significant movements of the structures in the dam.

To assure us of the continuous integrity of the dam, Lepanto Mine Division has engaged the services of a reputable international consulting firm to conduct annual review and evaluation of the on-going construction and performance of the dam.

Panoramic view of upstream and downstream of TD5A

Then Now

Then Now

Migratory birds have made our tailings pond their permanent habitat.

EMERGENCY MEASURES MAJOR TYPHOON

INSTALL TEMPORARY STOPLOGS - 3m TEMPORARY RAISE OF EMBANKMENT

- 3m Freeboard, 12m Berm LAST RESORT TO OVERTOPPING OF DAM

- Cut 1m deep x 12m wide Fuse Type Plug Spillway

CONDITIONS o Elevated Pore Pressures o Seepage at Random Fill Shell o Sustained Turbidity of River Drain

ACTIONS

o Inform Dam Experts (EGI, KPP, URS)/Management o If investigation confirms any of the three conditions, install

second line of defensive features

CONTINGENCY MEASURES EMBANKMENT PROBLEMS

LEPANTO MINE DIVISION

CENTRAL SAFETY RESPONSE ORGANIZATION

CHAIRMAN CONSULTANTS

CENTRAL COORDINATORS

GROUP MANAGERS PRO

FIELD COORDINATORS

SUPERINTENDENTS

COMMUNITY PNP PERSONNEL BRGY OFFICIALS

CAMP/AREA/ORGANIZATION MUNICIPAL OFFICERS

OTHER OUTSIDE CONCERN

COMMUNICATION

DISCOVERY

MONITORING TEAM (3 SHIFTS)

ON SHIFT SECURITY SUPERVISOR ON SHIFT SAFETY SUPERVISOR ON SHIFT DAM SUPERVISOR

NO

TIFI

CA

TIO

N

TAILINGS DAM FIRE TYPHOON FLOOD EARTHQUAKE, ETC.

TRIGGER

POINTS

FIRE SERVICES RESCUE &

RECOVERY

MEDICAL TEAM TRANSPORT

SERVICES

EVACUATION

TEAM

RELIEF TEAM UTILITY CONTOL

TEAM

SECURITY TEAM

CENTRAL CONTROL BASE

GENERAL OFFICE

SIGNALS/COUNTERSIGNALS

CONTINUOUS SHORT BLAST OF

SIREN

TAILINGS DAM 5A MAJOR DISASTER

DISCOVERY

NOTIFICATION OF IMMEDIATE MEN IN THE VICINITY THEN CALL THE CENTRAL

TELEPHONE OPERATOR

DISASTER CONTROLLABLE

TELEPHONE OPERATOR MUST DO -REPORT TO ALL CONCERNED -NOTIFY POWER PLANT TO SIGNAL ALARM (5 SHORT SIREN BLAST)

CONTROL DISASTER

NOTIFY OFFICIALS

RM/CES MGR (RESPONSIBLE STAFF) CENTRAL CONTROL OPERATION

CENTRAL

-DEFINE & PINPOINT LOCATION -ASSEMBLE & ORGANIZE RESCUERS - PREP. & ASSEMBLY OF RESCUE APPARATUS

CENTRAL

TD MEN RETREAT TO GATHERING POINTS

THEN COMMUNICATE WITH TD4 FIELD OFFICE

RETREAT TO TD4 FIELD OFFICE

RETREAT TO TD4 FIELD OFFICE

STAY AND AWAIT INSTRUCTION

RM/CES MGR (RESPONSIBLE STAFF) CENTRAL CONTROL OPERATION

CENTRAL

-DEFINE & PINPOINT LOCATION -ASSEMBLE & ORGANIZE RESCUERS - PREP. & ASSEMBLY OF RESCUE APPARATUS

CENTRAL

RECON TEAM TO DISASTER SCENE

ASSESS SOURCE & EXTENT OF DISASTER;

INFORM CONSULTANTS

NOTIFY SURFACE BASE

RESCUER & EQUIPMENT TO DISASTER SCENE

PERFORM RESCUE & CONTROL OPERATION

PERFORM RESCUE & CONTROL OPERATION

GAS ANALYSIS/SAMPLING

SEALING

RESCUE TEAM & EQUIPMENT

APPLY SURFACECONTROL OPERATION

RESCUE & RECOVERY CONTROL DISASTER

Date: June 2010

DATE pH Pb TOTAL DISSOLVED TOTAL SUSPENDED pH

(ppm) SOLIDS(ppm) SOLIDS(ppm)

Outlet Outlet Outlet Outlet Outlet A Outlet B Decant Decant

June

1 7.47 0.075 1031 28 0.0057 0.0066 0.529 8.30

2 7.11 0.100 1167 38 0.0188 0.0203 0.764 8.51

3 7.40 0.050 1236 29 0.0224 0.0237 1.110 8.43

4 7.32 0.100 1136 21 0.0132 0.0128 0.695 8.36

5 7.68 0.040 1154 23 0.0065 0.0055 0.989 8.95

8 - 0.050 1086 27 0.0017 0.0122 1.070 -

9 7.20 0.056 1217 23 0.0130 0.0017 1.060 8.15

10 7.44 0.050 1249 21 0.0096 0.0108 0.933 8.03

11 6.99 0.070 712 12 0.0032 0.0034 0.328 7.96

12 6.96 0.093 1043 38 0.0170 0.0168 0.673 8.62

15 6.98 0.038 983 30 0.0176 0.0109 0.316 8.58

16 7.15 0.046 798 31 0.0066 0.0071 0.232 7.85

17 7.09 0.020 763 24 0.0068 0.0081 0.653 7.80

18 6.71 0.028 922 18 0.0083 0.0090 0.861 8.05

19 6.72 0.070 986 34 0.0093 0.0063 0.687 8.17

20 6.84 0.059 1042 13 0.0353 0.0234 0.810 8.16

22 6.88 0.076 910 18 0.0223 0.0197 0.854 8.45

23 7.14 0.040 861 18 0.0106 0.0086 0.895 8.98

24 7.19 0.025 899 16 0.0122 0.0104 0.874 8.01

25 7.21 0.027 785 20 0.0120 0.0121 1.040 8.69

26 7.29 0.030 886 24 0.0087 0.0067 0.321 8.36

28 7.06 0.030 843 21 0.0163 0.0174 0.466 8.21

29 6.87 0.020 775 26 0.0248 0.0266 0.3580 8.00

Next Review Date:

Revision No.: 00

CN (ISE)

(ppm)

( Environment )

Page 1 of 1

LEPANTO CONSOLIDATED MINING COMPANY

Lepanto Mine Division

REC-ASY-022

Date Effective:

INTEGRATED MANAGEMENT SYSTEM

TITLE: ASSAY RESULTS OF TD5A EFFLUENT

Migratory birds have made our pond their permanent habitat.

Panoramic view of upstream and downstream of TD5A

Then Now

Then Now

Concrete sealing of newly installed stoplogs

Installation of stoplogs

Outlet view

Lime Slaking Plant

Detoxification Plant

Borrow area

Abutment Clearing