Marathon Palladium Project (CIAR File No. 54755) Prepared on November 2, 2021 Generation PGM Response to the Joint Review Panel’s Request for Information #5 Received August 20, 2021

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IR5-4 Hare Lake Modelling - CORMIX

References:

EIS Addendum, Section 6.2.3, Section 6.2.3.6.4 (CIAR# 727)

EIS Addendum, Section 8.0 (CIAR# 727)

EIS Guidelines, Section 2.7.2.3.2 (CIAR# 150)

Supporting Information Document #6 – Water Quality and COPC Fate Modeling for the Marathon PGM-

Cu Project (CIAR# 234)

Additional Information Request #19 (CIAR# 612)

Related comments:

Ministry of the Environment Conservation and Parks- MECP (CIAR# 906)

Ministry of Northern Development, Mines, Natural Resources and Forestry - MNDMNRF (CIAR# 886)

Health Canada (CIAR# 905)

Rationale:

Several aspects of the Project have changed since the 2012 EIS, including the mine discharge

component, the inputs to the receiver and the effluent discharge window. Surplus water from the Mine

Rock Storage Area (MSRA) is now proposed to be discharged to the Process Solids Management Facility

(PSMF) then to Water Management Pond (WMP) from where it goes from treatment and discharge to

Hare Lake as opposed to being directed to the Pic River. The maximum discharge rate to Hare Lake will

increase due to the flow from the MRSA. The proposed discharge period has changed from spring freshet

and fall discharge windows under higher flows, to an April through to November discharge window. These

changes to the project require that the CORMIX mixing zone modeling be updated since the discharge

will now occur when Hare Lake is stratified.

Under stratified conditions, mixing in not as good as during spring and fall. The bottom layer of the Lake

becomes anoxic as it doesn’t receive oxygen from the atmosphere, and very few organisms can survive in

these conditions. This is crucial to cold-water fish as they frequent deeper colder waters, especially during

the warmer summer months. Hare Lake is a deep, oligotrophic, cold-water lake that supports cold-water

fish species. The anoxic condition in the Lake may eliminate adequate habitat for cold-water fish. Further,

there is concern about potential change to the thermal properties in Hare Lake due to the discharge of the

mine effluent. These concerns were addressed in the initial EIS (2012), but, with the changes to the

Project, they have not been re-evaluated. Water quality monitoring program dedicate to monitoring for the

onset and effects of meromixis (poor mixing conditions) on Hare Lake is crucial.

Section 2.7.2.3.2 of the EIS Guideline requires that, the proponent, in conducting the effect assessment

on surface water quality, refer to MECP’s document B-1-5 “Deriving Receiving-Water Based, Point

Source Effluent Requirements for Ontario Waters”. It is critical the CORMIX mixing zone modelling be

completed by following Guideline B-1-5, which is the reference document used to calculate receiving-

water based effluent criteria. The procedure in the guideline is based on developing a worst-case

scenario defined by a maximum effluent discharge rate at the proposed daily effluent limits, and low flows

in the receiving water.

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Information Request:

1. Update the CORMIX modeling taking into account the changes to the project. An assessment of the buoyancy of the plume is necessary to understand the project impacts based on (i) updated baseline water quality inputs, (ii) additional effluent components from the MRSA, and (iii) the discharge scenario. Evaluate a 10:1 mixing ratio and the buoyancy of the plume to determine feasibility in terms of effluent discharge. The updated modeling must also include an assessment of the effects of the lake stratification on the plume dispersion, along with vertical exchange during spring-fall turnovers;

2. Confirm that there are no drinking water intakes within the plume of the effluent discharge in Hare Lake;

3. Assess the potential for meromixis of Hare Lake as a result of the altered effluent components and discharge scenario, along with potential impacts to the thermal regime of the lake that may negatively impact aquatic life and critical habitat. This assessment should consider the potential for effluent sulphate and total dissolved solids levels to induce meromixis;

4. Identify potential changes to thermal properties of Hare Lake and Hare Creek that may result from increased and seasonal effluent amounts that will be discharged from April through to November. This assessment should also assess the potential effects on Hare Lake and Hare Creek ecological features and aquatic life as a result of potential changes to water temperatures;

5. Provide information on appropriate measures to mitigate potential thermal effects; and

6. Develop an ongoing water quality monitoring program dedicated to monitor the onset and effects of meromixis on Hare Lake and update the commitments in Table 8.1, EIS Addendum Chapter 8. At a minimum, the program should include the collection of: (i) temperature, dissolved oxygen and conductivity profiles; (ii) organic carbon; (iii) sulphate; and (iv) mitigation/contingency measures in case of onset of meromictic conditions in Hare Lake.

GenPGM Response:

1. Update the CORMIX modeling taking into account the changes to the project. An assessment of the buoyancy of the plume is necessary to understand the project impacts based on (i) updated baseline water quality inputs, (ii) additional effluent components from the MRSA, and (iii) the discharge scenario. Evaluate a 10:1 mixing ratio and the buoyancy of the plume to determine feasibility in terms of effluent discharge. The updated modeling must also include an assessment of the effects of the lake stratification on the plume dispersion, along with vertical exchange during spring-fall turnovers;

The proposed discharge of excess water from the water management pond to Hare Lake will be through

an engineered, offshore, submerged, multiport diffuser, designed to maximize the mixing potential and

reduce the spatial extent of the mixing zone.

The mathematical model referred to as CORMIX (Cornell Mixing Zone Expert System) was used to

predict the rate of mixing of the discharge with distance downstream from the diffuser (hence, the spatial

extent of the mixing zone). CORMIX was developed by Cornell University (Jirka et al, 1991), is supported

by the United States Environmental Protection Agency, and is a widely recognized model for the analysis

of mixing characteristics.

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The conceptual design for the diffuser used in the assessment of potential effects consisted of a diffuser

line with 10 evenly spaced nozzles with each nozzle approximately 0.051 m in diameter (approximately 2

inches). The diffuser line is located approximately 10 m offshore in approximately 3 m of water and

extends parallel to the shoreline due to the steep gradient of the nearshore bottom within its vicinity.

The exact design configuration will be optimized as required during the design and permitting phase to

ensure optimal performance of the diffuser specific to site conditions including consideration of the use of

“duck-billed” nozzles to account for variable discharge rates.

Sample model input and output files are provided as Figures 1 to 4, below. The files present an example

of one model scenario. The Sensitivity Analysis below provides results for a broader range of model runs

as part of the sensitivity analysis. Table 1 and the points below summarize the parameter values for this

example.

Table 1: Parameter Values for Sample Model Run

Run

Diffuser Length

Exit Velocity

Water Depth

Current Velocity

Discharge Rate

Discharge Density

M m/s m m/s m3/s kg/m3

Example 3 3.9 3 0.05 0.08 998.784

• Exit velocity refers to the speed at which the discharge water exits the individual nozzles along the

diffuser line. The magnitude is determined from the discharge rate, number of nozzles and diameter

of the nozzles. Typical engineering design may range from 3 to 8 m/s. High velocities may lead to

excessive pumping requirements, whereas low velocities (less than 0.5 m/s) may lead to undesirable

sediment accumulation. The target value used in this example was 3.9 m/s corresponding to the

discharge rate of 0.08 m3/s and proposed nozzle configuration (10 nozzles, each with 0.051 m

diameter).

• The current velocity refers to the speed (and direction) of the ambient flow in the vicinity of the

diffuser. A value of 0.05 m/s was used for this example. A broader range is provided in the sensitivity

analysis. This current speed corresponds to the maximum value recorded in Hare Lake over a 3 day

field program in October 2012. A total of 25 measurements were made using drogues. The

measured velocities ranged from 0.001 m/s to 0.05 m/s with a median of 0.01 m/s.

• The discharge rate refers to the release of water to Hare Lake. A value of 0.08 m3/s was used for this

example.

• The density of the discharge water was 998.784 kg/m3 for this example, corresponding to a TDS

concentration of 200 mg/L and temperature of 18°C. The density of the ambient water in the lake was

998.633 kg/m3, corresponding to a TDS concentration of 0 mg/L and temperature of 18°C. The

sensitivity analysis considered a broader range of densities relating to hypothetical conditions to

demonstrate the insensitivity of the diffuser performance to density.

Marathon Palladium Project (CIAR File No. 54755) Prepared on November 2, 2021 Generation PGM Response to the Joint Review Panel’s Request for Information #5 Received August 20, 2021

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Figure 1, Figure 2, and Figure 3 present the input files for the model runs, corresponding to effluent

characteristics, ambient characteristics and discharge characteristics. Figure 4 presents the output files

for the model run. The sub-model, CORMIX2, was used to assess mixing potential of all nozzles together.

For this example, the diffuser achieves a mixing potential of approximately 10:1 within approximately 0.9

m from the diffuser (measured in the offshore direction from the diffuser line) - referred to as the mixing

zone for the purpose of this discussion. At this point, the plume is approximately 1.6 m wide (based on a

half-width of approximately 0.8 m) and is approximately 1.8 m thick.

Figure 1: Sample Model Input File – Effluent Characteristics

Marathon Palladium Project (CIAR File No. 54755) Prepared on November 2, 2021 Generation PGM Response to the Joint Review Panel’s Request for Information #5 Received August 20, 2021

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Figure 2: Sample Model Input File – Ambient Environment

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Figure 3: Sample Model Input File – Discharge Configuration

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Figure 4: Sample Model Output – Mixing Potential Predicted Using CORMIX

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Sensitivity Analysis

The model prediction presented above represents one scenario based on the input data shown above.

The discussion below considers a broader range of conditions to help optimize the design of the diffuser,

assess the sensitivity of the model predictions to various parameter values, and determine the potential

effects of lake stratification on mixing zone size, and vice versa. The sensitivity analysis considered

parameters that characterize the diffuser, the ambient environment, and discharge water (see Table 2).

A total of 20 model runs are provided below for the scenario whereby the diffuser is located in the near

surface region of the lake, corresponding to the epilimnion when the lake has achieved thermal

stratification. Table 3 summarizes the parameter values used in each of the runs and Table 4

summarizes the results of each run. The first 10 runs were used to further optimize the diffuser

configuration, and the remaining 10 runs were used to test sensitivity to parameter values.

The model results presented in Table 4 show the configuration of the mixing zone as predicted using

CORMIX. The mixing zone is characterized by the alongshore and offshore distances from the diffuser to

the point at which 10:1 mixing potential is achieved, as per the IR 5.4 request. The height of the plume is

measured from the base of the diffuser and is centered within the plume thickness. The width of the

plume refers to the width measured normal to the trajectory of the plume at the edge of the mixing zone.

A small mixing zone is preferred, and achieving as small a mixing zone as practical is consistent with

provincial water quality policy.

Optimization of the diffuser considered the length of the diffuser line, the exit velocity of the discharge

water through the nozzles, and the water depth at the point of installation. The orientation of the

discharge was not assessed in this sensitivity analysis due to the physical characteristics and constraints

caused by the nearshore bottom (that is, steep bed slope, and irregular and rocky substrate).

In addition to investigating the mixing when the receiving ambient water has a concentration 0.0 mg/L

TDS (Table 4), we further investigated the scenario when the receiving water already has pre-existing

TDS concentration from prior discharge (Table 5). Results indicate that under the given conditions of

discharge, the mixing zone is relatively insensitive to the TDS induced density change of the ambient

water (minor changes are highlighted in red, see Table 5).

The following points summarize the findings of the mixing zone study:

• The recorded current measurements in Hare Lake range from 0.001 to 0.05 m/s with a median of

0.01 m/s. The model results show greater mixing potential at low currents as compared to high

currents. Both the alongshore and offshore distances to the edge of the mixing zone are relatively

insensitive for current velocities in the range of 0.001 to 0.05 m/s. However, for a current velocity of

0.1 m/s (which is larger than the maximum observed current velocity) there is an increase in both the

alongshore and offshore distances. The physical size of the mixing zone is predicted to remain within

approximately 1 m distance of the diffuser under the range of recorded current velocities with the

thickness of the plume not exceeding 2 m.

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• The discharge rate from the site is expected to remain within the range 0.01 to 0.1 m3/s. An upper-

bound condition of 0.15 m3/s (540 m3/h) is assumed and tested. The model results show potential for

a larger mixing zone under low discharge rates as compared to high discharge rates due to the

reduced exit velocity at the nozzles; though this can be overcome using a “duck-billed” type nozzle to

enhance initial hydrodynamic mixing.

• The density of the discharge water is estimated to be 998.784 kg/m3 during the summer based on a

predicted TDS concentration of 200 mg/L and temperature of 18°C. The sensitivity analysis

considered two hypothetical densities corresponding to TDS values of approximately 1,000 mg/L and

approximately 2,000 mg/L. Such levels are far beyond those that are expected based on

geochemical testing of mine wastes and expected water quality management needs), but were

assessed nonetheless to assess mixing zone sensitivity. Effluent with TDS in the 1,000 to 2,000

mg/L range would be expected at a site where treatment was required to manages acid mine

drainage, which is not the case for this Project, for example, where very high dosing rates of

treatment chemicals that have high TDS are needed. The model results show the 10:1 mixing

potential resulting from the diffuser to be insensitive to the density of the discharge water even at

these hypothetical extremes.

Discussion of Results

The aim of this mixing zone analysis was to assess the effects of the diffuser configuration on plume

dispersion and determine the effects of discharge effluent on the size of the mixing zone, as well as the

effects on stratification and thermal properties of Hare Lake.

As it concerns diffuser configuration, the characteristics of the diffuser were optimized towards creating

the smallest mixing zone that is reasonably possible. Under the conditions of the analysis, it was found

that a diffuser length of 3 m, exit velocity of 3.9 m/s, and discharge depth of 3 m would be optimal. Under

this configuration, the estimated plume size (to 10:1 mixing) corresponding to a discharge of 200 mg/L

TDS would extend approximately 1.0 m from the diffuser, and be as large as 18 m in consideration of the

high TDS effluent scenario.

In consideration of the analysis, it is apparent that the density of the discharged water will not be a driving

factor that will affect seasonal lake stratification processes, or would lead to the development of a

meromictic condition in Hare Lake. Rapid mixing of discharged waters is predicted with the preferred

discharge configuration that will limit incremental changes in water quality to a very small zone in the

immediate vicinity of the discharge location. At the expected discharge density of 998.784 kg/m3, the

effluent discharge is denser than the surrounding ambient water (998.663 kg/m3 at 18°C) and there will be

the potential for the discharged water to fall in the water column beyond the initial dynamic mixing area

where the discharge is jetted from the diffuser ports. Given the rapid mixing in this initial mixing zone, any

density difference relative to ambient is expected to be negligible and effluent sinking is unlikely. In any

event, when the lake is thermally stratified, the discharge is expected to be less dense than water in the

hypolimnion (expected 1000.00 kg/m3 at 4°C), and therefore the discharge would not sink beyond the

thermocline to reach the bottom of the lake. During the spring/fall turn over periods, the water

temperature in the epilimnion increases/decreases to 4°C and attains maximum density, causing the

overlying water to sink below the thermocline, through the region of the discharge plume, resulting in

mixing of the lake.

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In addition to potential discharge density related effects, there is no indication that a change of the

thermal properties of Hare Lake from the increase and seasonal effluents discharged from April through

to November would occur. During the months of discharge, site waters will be managed in a series of

water storage ponds, and related channels, and will be subject to similar environmental factors, including

wind, temperature, and precipitation, as Hare Lake. Therefore, it is anticipated that the temperature of the

discharge will be similar to that of the ambient water within the epilimnion of Hare Lake, leading to

minimal temperature gradients during mixing. Any small temperature differences that might be anticipated

between the discharge and Hare Lake would be dissipated within meters of the discharge location.

Overall, and in consideration of analysis presented above, it is not anticipated that effluent discharge to

Hare Lake will negatively impact the seasonal cycle of stratification and mixing within Hare Lake, nor are

meromictic conditions driven by effluent chemistry likely to develop. Based on the anticipated size of the

discharge plume, the influence of the discharge is expected to be localized around the location of the

diffuser.

Table 2: Sensitivity Analysis Parameters and Values

Diffuser Characteristics

Parameter

Base Case Sensitivity Analysis

Value Rationale Value Rationale

Diffuser Length 10 m First

assumption 3 - 20 m Realistic Range

Exit Velocity 3.9 m/s First

assumption 1.8 - 7.4 m/s Realistic Range

Water Depth 3 m Expected 2 - 5 m Realistic Range

Ambient and Discharge Water Characteristics

Parameter Base Case Sensitivity Analysis

Value Rationale Value Rationale

Current Velocity 0.01 m/s Median 0.001 - 0.1 m/s Extreme Range

Discharge Rate 0.08 m3/s Expected 0.01 - 0.15 m3/s Extreme Range

Discharge

Density 998.784 kg/m3

Expected

summer 999.47 - 1000.16 kg/m3 Unrealistic extreme

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Table 3: Sensitivity Analysis Simulation Run Configurations

Simulation Run Configurations

Run

Diffuser Length

Exit Velocity

Water Depth

Current Velocity

Discharge Rate

Discharge Density

m m/s m m/s m3/s kg/m3

(a) Optimization of the Diffuser Configuration

1 20 3.9 3 0.05 0.08 998.784

2 10 3.9 3 0.05 0.08 998.784

3 5 3.9 3 0.05 0.08 998.784

4 3 3.9 3 0.05 0.08 998.784

5 3 1.8 3 0.05 0.08 998.784

6 3 3.9 3 0.05 0.08 998.784

7 3 7.0 3 0.05 0.08 998.784

8 3 3.9 2 0.01 0.08 998.784

9 3 3.9 3 0.01 0.08 998.784

10 5 3.9 5 0.01 0.08 998.784

(b) Sensitivity of Parameter Values

11 3 3.9 3 0.001 0.08 998.784

12 3 3.9 3 0.01 0.08 998.784

13 3 3.9 3 0.05 0.08 998.784

14 3 3.9 3 0.1 0.08 998.784

15 3 0.5 3 0.01 0.01 998.784

16 3 3.9 3 0.01 0.08 998.784

17 3 7.4 3 0.01 0.15 998.784

18 3 3.9 3 0.01 0.08 998.784

19 3 3.9 3 0.01 0.08 999.47

20 3 3.9 3 0.01 0.08 1000.16

Note 1: For Runs 5, 6, and 7 the exit velocity was 1.8, 3.9 and 7.0 m/s at a discharge rate of 0.08 m3/s corresponding to a nozzle diameter of 0.076, 0.051 and 0.038 m (approximately 3, 2 and 1.5 inches).

Note 2: For Runs 15, 16, and 17 the exit velocity was 0.5, 3.9 and 7.4 m/s at a nozzle diameter of 0.051 m (approximately 2 inches) corresponding to a discharge rate of 0.01, 0.08 and 0.15 m3/s. A “duck-billed” type nozzle could be used to achieve a more consistent exit velocity under varying discharge rates.

Marathon Palladium Project (CIAR File No. 54755) Prepared on November 2, 2021 Generation PGM Response to the Joint Review Panel’s Request for Information #5 Received August 20, 2021

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Table 4: Simulation Results for Ambient Water with 0 mg/L TDS

Simulation Run Results

Run Notes

Configuration of the Mixing Zone (10:1)

Alongshore Distance

Offshore Distance

Height of

Plume

Thickness of plume

Width of

Plume

m m m m m

(a) Optimization of the Diffuser Configuration

1 Diffuser length = 20 m 4.7 6.6 0.8 0.9 13.4

2 Diffuser length = 10 m 4.5 6.3 0.9 0.9 9.8

3 Diffuser length = 5 m 6.0 8.4 0.8 1.2 6.2

4 Diffuser length = 3 m - optimum

length 0.0 0.9 1.0 1.8 1.7

5 Exit velocity = 1.8 m/s 33.7 9.4 0.6 1.2 12.8

6 Exit velocity = 3.9 m/s - preferred exit velocity

0.0 0.9 1.0 1.8 1.7

7 Exit velocity = 7.0 m/s 0.0 0.4 1.0 0.8 2.2

8 Water depth = 2 m* 0.0 1.0 1.5 1.3 2.6

9 Water depth = 3 m - target depth 0.0 0.6 1.0 1.4 1.9

10 Water depth = 5 m** 0.0 0.4 1.0 0.8 4.1

(b) Sensitivity Analysis

11 Current velocity = 0.001 m/s 0.0 0.6 1.0 1.3 1.9

12 Current velocity = 0.01 m/s 0.0 0.6 1.0 1.3 1.9

13 Current velocity = 0.05 m/s 0.0 0.9 1.0 1.8 1.7

14 Current velocity = 0.1 m/s 17.8 5.2 1.4 2.7 3.2

15 Discharge rate = 0.01 m3/s 12.8 6.9 0.6 2.6 3.5

16 Discharge rate = 0.08 m3/s 0.0 0.6 1.0 1.3 1.9

17 Discharge rate = 0.15 m3/s 0.0 0.6 1.0 1.3 1.9

18 Discharge density = 998.784 kg/m3 0.0 0.6 1.0 1.3 1.9

19 Discharge density = 999.47 kg/m3 0.0 0.6 1.0 1.3 1.9

20 Discharge density = 1000.16 kg/m3 0.0 0.6 1.0 1.3 1.9

Note 1: The height of the plume is measured from the base of the diffuser and is centered within the plume thickness

* Discharge height adjusted from 1 to 1.5 m to comply with model simulation assumptions

** Diffuser length changed from 3 to 5m to comply with model simulation assumptions

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Table 5: Simulation Results for Ambient Water with varying Concentration TDS

Simulation Run Results

Run Notes

Configuration of the Mixing Zone (10:1)

Alongshore Distance

Offshore Distance

Height of

Plume

Thickness of plume

Width of

Plume

m m m m m

(a) Optimization of the Diffuser Configuration

1 Diffuser length = 20 m 4.7 6.6 0.8 0.9 13.4

2 Diffuser length = 10 m 4.5 6.3 0.9 0.9 9.8

3 Diffuser length = 5 m 6.0 8.4 0.8 1.2 6.2

4 Diffuser length = 3 m - optimum length

0.0 0.9 1.0 1.8 1.7

5 Exit velocity = 1.8 m/s 49.0 9.4 1.1 2.2 7.2

6 Exit velocity = 3.9 m/s - preferred

exit velocity 0.0 0.9 1.0 1.8 1.7

7 Exit velocity = 7.0 m/s 0.0 0.4 1.0 0.8 2.2

8 Water depth = 2 m* 0.0 1.0 1.5 1.3 1.6

9 Water depth = 3 m - target depth 0.0 0.6 1.0 1.4 1.9

10 Water depth = 5 m** 0.0 0.4 1.0 0.8 4.1

(b) Sensitivity Analysis

11 Current velocity = 0.001 m/s 0.0 0.6 1.0 1.3 1.9

12 Current velocity = 0.01 m/s 0.0 0.6 1.0 1.3 1.9

13 Current velocity = 0.05 m/s 0.0 0.9 1.0 1.8 1.7

14 Current velocity = 0.1 m/s 17.5 5.2 1.5 3.0 2.7

15 Discharge rate = 0.01 m3/s 12.8 6.9 0.6 2.6 3.5

16 Discharge rate = 0.08 m3/s 0.0 0.6 1.0 1.3 1.9

17 Discharge rate = 0.15 m3/s 0.0 0.6 1.0 1.3 1.9

18 Discharge density = 998.784 kg/m3 0.0 0.6 1.0 1.3 1.9

19 Discharge density = 999.47 kg/m3 0.0 0.6 1.0 1.3 1.9

20 Discharge density = 1000.16 kg/m3 0.0 0.6 1.0 1.3 1.9

Note 1: The height of the plume is measured from the base of the diffuser and is centered within the plume thickness

Note 2: See Table 6 for updated ambient water densities, for different discharge rates and effluent densities

* Discharge height adjusted from 1 to 1.5 m to comply with model simulation assumptions

** Diffuser length changed from 3 to 5m to comply with model simulation assumptions

Marathon Palladium Project (CIAR File No. 54755) Prepared on November 2, 2021 Generation PGM Response to the Joint Review Panel’s Request for Information #5 Received August 20, 2021

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Table 6: Receiving Ambient Water TDS Concentrations and Density for Various Discharge Rates and Discharge Densities

Discharge Rate

(m3/s)

TDS Concentration

(mg/L)

Density

(kg/m3)

Based on Discharge of 200 mg/L TDS

0.01 20 998.678

0.08 165 998.78

0.15 310 998.899

Based on Discharge of 1000 mg/L TDS

0.08 823 999.289

Based on Discharge of 2000 mg/L TDS

0.08 1645 999.913

2. Confirm that there are no drinking water intakes within the plume of the effluent discharge in Hare Lake;

GenPGM confirms that there are no drinking water intakes at Hare Lake.

3. Assess the potential for meromixis of Hare Lake as a result of the altered effluent components and discharge scenario, along with potential impacts to the thermal regime of the lake that may negatively impact aquatic life and critical habitat. This assessment should consider the potential for effluent sulphate and total dissolved solids levels to induce meromixis;

As discussed above, the development of meromictic conditions in Hare Lake are not anticipated. The

difference in density, as driven by TDS levels, between the ambient water and discharge even under

unrealistic upper bound scenarios are not expected to create the conditions by which meromixis could

develop. The information request specifically identified sulphate in effluent as a potential issue as it

pertains to TDS. While it is true that sulphate would contribute to TDS, predicted sulphate levels in mine

drainage are relatively low. Mine wastes associated with the Project are not expected to generate

significant sulphate loadings (Type 1 materials) and/or management strategies have been put in place to

mitigate the possibility of such loadings (Type 2 materials).

The thermal regime of the lake will not be affected by meromixis as meromictic conditions are not

expected to occur as the result of the discharge to Hare Lake.

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4. Identify potential changes to thermal properties of Hare Lake and Hare Creek that may result from increased and seasonal effluent amounts that will be discharged from April through to November. This assessment should also assess the potential effects on Hare Lake and Hare Creek ecological features and aquatic life as a result of potential changes to water temperatures;

As discussed above, changes to the thermal properties of Hare Lake are not anticipated. The

temperature of the discharge will be similar to that of the ambient water within the epilimnion of Hare

Lake, leading to minimal temperature gradients during mixing. Any small temperature differences that

might be anticipated between the discharge and Hare Lake would be dissipated within metres of the

discharge location. The zone of influence of the discharge, based on delineation of the 10:1 mixing zone,

is limited to the immediate vicinity of the diffuser location. Within this context, no lake-wide effects on

ecological features and aquatic life in the lake would be expected, nor would such effects be expected

downstream in Hare Creek.

5. Provide information on appropriate measures to mitigate potential thermal effects; and

As explained above, no thermal effects, either as the direct result of discharge or through the

development of meromictic conditions that may change the thermal regime of the lake, are expected.

The conditions by which such effects would be manifested are not associated with the Project. The

provision of rapid mixing of effluent in the receiver through optimization of discharge design and

placement is the primary mitigation strategy associated with ensuring any incremental differences in the

properties of the effluent and receiver (e.g., TDS levels, temperature) are dissipated in the smallest areas

possible. As demonstrated by the analysis herein, the discharge design and placement proposed in Hare

Lake effectively provides 10:1 mixing within a few metres of discharge and any influence of the discharge

of effluent to Hare Lake, as it concerns TDS and temperature specifically, is very localized.

6. Develop an ongoing water quality monitoring program dedicated to monitor the onset and effects of meromixis on Hare Lake and update the commitments in Table 8.1, EIS Addendum Chapter 8. At a minimum, the program should include the collection of: (i) temperature, dissolved oxygen and conductivity profiles; (ii) organic carbon; (iii) sulphate; and (iv) mitigation/contingency measures in case of onset of meromictic conditions in Hare Lake.

As discussed above, the development of meromictic conditions in Hare Lake are not anticipated.

Nevertheless, monitoring in Hare Lake can be added to the overall Surface Water Monitoring Program to

demonstrate such is the case. Specific details for the monitoring program would be developed as part of

detailed permitting and would be part of the monitoring provisions included the provincial Environmental

Compliance Approval (ECA). In concept, the following is proposed:

• A sampling station mid-lake would be established, roughly corresponding to the deepest part of the

lake.

• Sampling would be conducted monthly during the ice-free season.

• In-field measurements of conductivity, temperature and dissolved oxygen would be taken.

Measurements would be taken as depth profiles at every metre in the water column from surface to

bottom.

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• Samples for laboratory analysis of a full suite of constituents including metals (total and dissolved),

anions (including sulphate), nutrients (phosphorus, nitrogen), organic carbon, alkalinity and hardness

would be collected at the top, middle and bottom of the water column.

• Data would be reported as part of annual water quality monitoring reporting subject to regulatory

provisions.

As it concerns contingency measures, a formal Contingency Plan will be developed as part of detailed

permitting. This plan will describe the means by which monitoring data would be analyzed to proactively

assess environmental change, identify Action Levels that would indicate when such change was beyond

a level at which further activity would be required, the nature of those further activities (e.g., investigation)

and, finally, the mechanism by which management actions would be implemented. Specific

considerations concerning the potential development of meromixis in Hare Lake would be detailed in the

Contingency Plan. While not to pre-empt that contingency planning, in the event that meromixis was to

develop in the lake, measures to identify the cause of the meromictic conditions and, subsequently, to

manage the conditions would be implemented. Specific management measures would be dependent on

the conditions prevailing in the lake at that time.

References

Jirka, G.H., Doneker, R.L. and T.O. Barnwell, "CORMIX: A Comprehensive Expert System for Mixing

Zone Analysis of Aqueous Pollutant Discharges", Water Science and Technology, 24, No. 6, 267-

274, 1991.