New Prosperity Gold-Copper Mine Project

Topic Specific Hearings: Geology & Hydrogeology

Williams Lake, British Columbia

July 26-27, 2013

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Outline

1. Context for NRCan’s Participation in the Federal Review Panel Process (Jessica Coulson, Team Leader)

2. Hydrogeology (Alexandre Desbarats, Research Scientist)

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NRCan is participating as a federal authority: providing specialist and expert information and knowledge within the meaning of s.20 of the Canadian Environmental Assessment Act, 2012

Regulatory role under the Explosives Act Technical review:

• Hydrogeology (induced seepage from Fish Lake, seepage from the Tailings Storage Facility)

• Geochemistry (Acid Rock Drainage and Metal Leaching) • Geotechnical (Pit slope stability, slope stability) • Seismicity

Context for NRCan’s Participation in the Federal Review Panel Process

Hydrogeology

A.J. Desbarats, Ph.D. P.Eng. P.Geo.

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NRCan’s technical review has focused on two overarching groundwater-related issues where the mine project could cause adverse environmental effects on water quantity and water quality in Fish Lake and other surface water bodies: Effects of pit dewatering on groundwater seepage

from Fish Lake: water levels in Fish Lake Seepage of pore-water from the Tailings Storage

Facility (TSF): water quality in Fish Lake, Wasp Lake, Big Onion Lake, Beece Creek

NRCan’s Review of the EIS: Hydrogeology

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NRCan’s Review of the EIS: Hydrogeology

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NRCan’s presentation will focus on one key issue raised in our submission and related issues identified in the submissions of other interveners: Hydrogeology Basics Seepage from the Tailings Storage Facility (TSF) Conclusions from NRCan’s review

Recommendations to the Federal Review Panel

NRCan’s Review of the EIS: Hydrogeology

Outline

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What is Hydrogeology and why is it important for these hearings?

Hydrogeology is the study of the movement of groundwater and its dissolved constituents through the pores and fractures of soils, sediments and rocks

Groundwater replenishes rivers and lakes and vice versa, and these exchanges could be interrupted

Seepage of tailings pore-water into the underlying groundwater may migrate to nearby lakes and creeks

Hydrogeology Basics

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Hydraulic Conductivity (Permeability)

It is the property that characterizes the ease with which groundwater can flow through a soil, sediment or rock

It is a very important property for calculations of groundwater flow and contaminant migration

In Nature, it is a highly variable property (14 orders of magnitude)

Broken waste rock is highly permeable Glacial till generally has low permeability

Hydrogeology Basics

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Hydrogeology Basics

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Example application of Darcy’s Law: Estimation of hypothetical seepage through the base of the TSF

K = 8.64 × 10-4 m/day ( 1 × 10-8 m/s) A = 12 × 106 m2

L = 42 m Head at surface of TSF = 1590 m Average head at base of TSF = 1580 m Head difference ΔH = 1590 – 1580 = 10 m Q = K A ΔH / L = 2468 m3/day (28 L/s)

Hydrogeology Basics

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What is a numerical groundwater flow model?

A computer program that solves the groundwater flow equation describing a problem of interest

The real-world subsurface is represented by discrete blocks of sediment or rock or tailings

A water balance equation is written for each block by applying Darcy’s law between adjacent blocks

The unknown variables are the head values for each block

The water balance equations for each block are solved simultaneously to determine the head values

Hydrogeology Basics

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Geological cross-section at main embankment of TSF

Hydrogeology Basics

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Model cross-section at main embankment of TSF

Hydrogeology Basics

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Seepage from the Tailings Storage Facility

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NRCan’s Review of the EIS: Hydrogeology

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NRCan’s Review of the EIS: Hydrogeology

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TSF Williams Lake (WL) Area ≈ 12 M m2

Volume ≈ 500 M m3

Supernatant Pond ≈ 54 M m3

Area ≈ 7 M m2 Volume ≈ 88 M m3

TSF = 5.7 x WL

Pond = 0.6 x WL = 12 x Fish Lake

NRCan’s Review of the EIS: Hydrogeology

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Why is it important? Dissolved metals leached from tailings are a long-term source

of potential contamination to surface receptors Where could tailings pore-water migrate to? Fish Lake Big Onion and Little Onion Lakes Wasp Lake / Beece Creek

NRCan’s Review of the EIS: Hydrogeology

Seepage of tailings pore-water from the base of the TSF

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Proponent Conclusions:

Using the 2D SEEP/W cross-section model, the proponent has estimated seepage beneath the TSF embankments (“embankment seepage”) at 55 L/s or 4752 m3/day

Using the 3D regional MODFLOW model, the proponent has

estimated seepage through the base of the TSF at 15 L/s or 1296 m3/day (year 17) – 9 L/s or 760 m3/day (year 21+)

Total TSF seepage is estimated at: 55 L/s + 15 L/s = 70 L/s

NRCan’s Review of the EIS: Hydrogeology

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Concerns:

The proponent’s methodology for calculating total seepage is inconsistent

Seepage fluxes are underestimated The proponent may not be able to maintain a

positive water balance in the TSF

NRCan’s Review of the EIS: Hydrogeology

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Seepage Flux Components

NRCan’s Review of the EIS: Hydrogeology

“Embankment seepage”: leaving footprint of TSF in shallow groundwater system

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NRCan has developed a steady-state numerical model of the TSF in order to independently verify the proponent’s TSF seepage estimates and to estimate seepage rates for different hydraulic conductivity assumptions and different boundary conditions:

A version with a constant-head boundary at the top of the impoundment (positive water balance)

A version with a recharge boundary at the top of the impoundment (climate-controlled water balance)

NRCan’s Review of the EIS: Hydrogeology

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NRCan’s TSF Model: Plan view

NRCan’s Review of the EIS: Hydrogeology

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NRCan’s TSF Model: North-South Section

NRCan’s Review of the EIS: Hydrogeology

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Constant-Head Boundary Condition: Water table in TSF is always at overflow level

NRCan’s Review of the EIS: Hydrogeology

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TSF seepage flux components

NRCan’s Review of the EIS: Hydrogeology

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Seepage from the TSF to the shallow groundwater zone

TASEKO

BENCHMK-BGC

BENCHMK-KP

KP-TAILINGS

DGWZ-K

BGC-TILL

BASE-CASE

CONSERVATIVE

0 4000 8000 12000TSF Seepage (m3/d)

NRCan’s Review of the EIS: Hydrogeology

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Seepage fluxes exiting the shallow groundwater zone via the main embankment, the south and west embankments and the deep groundwater zone

BENCHMK-BGC

BENCHMK-KP

KP-TAILINGS

DGWZ-K

BGC-TILL

BASE-CASE

CONSERVATIVE

0 4000 8000 12000Seepage (m3/d)

Deep Groundwater ZoneS & W EmbankmentsMain Embankment

NRCan’s Review of the EIS: Hydrogeology

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Recharge Boundary Condition: Water table in TSF depends on relative rates of recharge and seepage

NRCan’s Review of the EIS: Hydrogeology

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Modeling highlights (base-case conductivities – average climate)

Recharge rate ≈ 15652 m3/d (451 mm/year) Evaporation from supernatant pond ≈ 5601 m3/d Spillway overflow drainage ≈ 4803 m3/d Seepage from base of TSF ≈ 5594 m3/d Some tailings within the TSF are not submerged beneath

the water table

NRCan’s Review of the EIS: Hydrogeology

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Plan view of the TSF showing area of unsaturated tailings

NRCan’s Review of the EIS: Hydrogeology

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Cross-section of the TSF showing position of water table

NRCan’s Review of the EIS: Hydrogeology

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Cross-section of the TSF showing position of water table

NRCan’s Review of the EIS: Hydrogeology

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NRCan’s base-case post-closure TSF seepage estimate (100 L/s) is more than 11 times proponent’s 3D model estimate (9 L/s)

NRCan main “embankment” seepage of 59 L/s versus

proponent’s 2D estimate of 28 L/s (not reported for proponent’s 3D model – NRCan Benchmk-BGC: 3.3 L/s)

NRCan south and west “embankment” seepage of 29 L/s

versus proponent’s 2D estimate of 27 L/s (not reported for proponent’s 3D model – NRCan Benchmk-BGC: 2.6 L/s)

Conclusions:

NRCan’s Review of the EIS: Hydrogeology

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NRCan deep “basin” seepage of 20 L/s versus proponent’s 2D estimate of 0 L/s (not reported for proponent 3D model - NRCan’s Benchmk-BGC: 4.6 L/s )

Seepage estimates are sensitive to boundary conditions

applied to surface of the TSF, e.g. excess water supply versus climate controlled water supply

With recharge boundary condition (climate controlled water

supply to TSF), some tailings are exposed to oxidizing conditions above the water table

Conclusions (continued):

NRCan’s Review of the EIS: Hydrogeology

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Recommendations:

Disregard tailings seepage predictions based on the proponent’s 3D regional and TRM groundwater flow models, including studies of interception well requirements for the main embankment, and of tailings pore-water migration towards the Big Onion Lake catchment

Consider that the proponent’s 2D seepage model artificially precludes any deep seepage flow beneath the basalt layers underlying the TSF

Consider that the rate of seepage leaving the facility is likely to be in the range of 7000 to 10000 m3/d, depending on hydraulic properties, and when the water table throughout the TSF is maintained at the spillway overflow level

NRCan’s Review of the EIS: Hydrogeology

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Consider that rates of seepage from the facility will be generally lower and fluctuate when climatic variables such as precipitation and evaporation control the amount of water entering the facility

Consider that there is a strong likelihood that, for average

precipitation conditions and without mitigation measures, the proponent will not be able to maintain all tailings submerged beneath the water table thereby establishing local hydrogeological conditions favourable for the generation of acid mine drainage

NRCan’s Review of the EIS: Hydrogeology

Recommendations (continued):

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Supplementary Material

Till thickness Hydraulic conductivities used in TSF model Basalt heterogeneity 1994 Pump Test: Pumping well drawdown curve Geological map Boundary conditions: nesting of TSF model

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NRCan Groundwater Flow Model: Map of till thickness

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Test Pit TP09-19: Till profile

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Test Pit TP09-35: Till profile

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Hydraulic Conductivities

-11 -10 -9 -8 -7 -6 -5 -4 -3log K (m/s)

Argillite (n=5)

Lower Basalt (n=25)

Glaciofluvial sediments (n=15)

Upper Basalt (n=34)

Till (n=6)

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Basalt heterogeneity Averaging of hydraulic properties: measurement scale effects

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1994 Pump Test: Pumping well drawdown

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Borehole log: Pumping well 94-164

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