Potassium Effluent Quality Criteria Amendment November 29, 2017 - - PowerPoint PPT Presentation

Potassium Effluent Quality Criteria Amendment

November 29, 2017

Presentation Overview

• Existing Potassium EQC
• Adaptive Management of Potassium

at the Ekati Diamond Mine

• Koala Watershed Water Quality

Model Update

• Request for Water Licence Amendment
• Summary

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Existing Potassium EQC

• Current EQC for potassium for the Ekati Diamond Mine were established during the

2012 Water Licence Renewal

• No generic potassium water quality guideline in existence
• Site-specific Water Quality Objective

(SSWQO) was developed

• Long-term exposure = 41 mg/L
• Short-term exposure = 112 mg/L

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Observed Trends in [K] Downstream of the LLCF

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Existing Potassium EQC

• Current EQC for potassium for the Ekati Diamond Mine were established during the

2012 Water Licence Renewal

• No generic potassium water quality guideline in existence
• Site-specific Water Quality Objective

(SSWQO) was developed

• Long-term exposure = 41 mg/L
• Short-term exposure = 112 mg/L
• EQC established for three

watersheds (Koala, King-Cujo, and Desperation-Carrie)

• Maximum average = 41 mg/L
• Maximum grab sample = 82 mg/L

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1616-43 (King-Cujo) 1616-47 (Desperation-Carrie)

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Existing Potassium EQC

• Supported by 2012 Water Quality Model (GoldSim)
• Peak potassium concentrations in Leslie and Moose lakes during the 2020 ice-covered season
• Stable potassium concentrations from 2010 to 2016 with no exceedances of benchmark

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Adaptive Management of Potassium

• Results from the Aquatic Effects Monitoring Program in 2013 and 2014
• differences between observed and predicted concentrations
• exceedances of SSWQO in the receiving environment
• Aquatic Response Framework under development, but not yet approved
• Dominion developed a Potassium Response Plan (Version 1.0, March 2015):

1) Re-examine potential for potassium toxicity 2) Re-examine 2012 Koala Watershed Water Quality Model

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Adaptive Management of Potassium

• Re-examination of potassium toxicity led to the development of an updated

SSWQO (July 2015; revised October 2015)

• Consistent with methods recommended by CCME for a Type A Water Quality Guideline
• Used a species sensitive distribution
• Based on surrogate or resident taxa present in all watersheds at the Ekati Diamond Mine
• Incorporated newly published and site-specific data
• Short- and Long-term SSWQO underwent extensive review alongside the

Potassium Response Plan (Version 1.0)

• Long-term SSWQO of 64 mg/L approved by WLWB for use in all watersheds at the

Ekati Diamond Mine in January 2016

• Short-term SSWQO of 103 mg/L
• < 2 X Long-term SSWQO

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Adaptive Management of Potassium

• Re-examination of the 2012 Koala Watershed Water Quality Model led to better

agreement between observations and predictions

• updated representation of Process Plant Discharge (PPD) concentrations
• changes to assumption of PPD water content
• improvements to water balance
• improved assumptions related to ice thickness and ice growth
• Updated potassium predictions provided in July 2015 and then with Versions 1.1

and 1.2 of the K Response Plan in mid and late 2016

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Adaptive Management of Potassium

• Inconsistencies between observed and predicted concentrations in the LLCF noted
• ver the last year
• Developed and implemented an operational water management model to optimize water

management in 2017

• Investigated and understood the source of elevated potassium
• Updated existing Koala Watershed Water Quality Model
• Potassium Response Plan (Version 1.3) submitted August 2017 (under review)

1) Water Quality Monitoring and Reporting (ongoing) 2) Investigation of Cause 3) Water Quality Modelling Update 4) Optimization of LLCF Discharge 5) Align EQC with SSWQO

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2017 Koala Watershed Water Quality Model

• Originally developed in 2004 and updated in 2012
• Water and Load Balance Model based on GoldSim modelling software
• Accounts for all inputs and outputs from LLCF
• Includes sub-models of Beartooth Pit, Panda and Koala pits, and downstream lakes
• Model updated in 2017 to include most recent flow, water level and water quality

data

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Model Schematic – the LLCF (Operations)

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Natural Watershed (local catchment) Flow through natural streams

Leslie Moose Nero Nema Martine Rennie Slipper

3.4 km2 780,000 m2 1,500,000 m3 440,000 m2 660,000 m3 1,400,000 m2 3,700,000 m3 1,000,000 m2 1,800,000 m3 940,000 m2 1,500,000 m3 1,900,000 m2 6,100,000 m3 39.5 km2 24.4 km2 7.1 km2 28.2 km2 25.5 km2 620,000 m2 1,400,000 m3 Lake Area Lake Volume

Discharge from LLCF Lac de Gras

Model Schematic – Downstream Lakes (Operations)

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IEMA-6

Ice Formation and Effects on Under-ice Concentrations

• Ice forming on lake surfaces is nearly 100% pure water
• During ice formation constituents (e.g., potassium) held in the freezing water is

excluded from the ice and remains in the ice-free water

• During winter, the volume of ice-free water decreases, but the load of constituent

remains the same, elevating concentrations

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IEMA-6

Ice Formation and Effects on Under-Ice Concentrations

• The magnitude of increase in concentration in under-ice depends on the relative

percent of total lake water volume that is held in ice

• Lake 1: Deeper waterbodies (e.g., Cell D) concentrations under-ice slightly

greater than open-water

• Lake 2: Shallow waterbodies (e.g., Leslie Lake) concentrations under-ice

much greater than open-water

Ice = 1.5-2 m Ice = 1.5-2 m

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Mine Plan Component Dates Koala, Panda, and Koala North open pits 2000 to 2008 Underground operations 2004 to 2020 Beartooth Pit 2005 to 2009 Pigeon Pit 2016 to 2021 Misery Pit 2002 to 2008 and 2014 to 2021 Fox Pit 2005 to 2017 Sable Pit 2019 to 2027 Lynx Pit 2018 to 2020 Jay Pit 2021 to 2034 Infilling of Beartooth Pit with minewater and FPK 2009 to 2020 Infilling of Koala and Panda pits with minewater and FPK 2020 to 2034 End of Operations 2034

Mine Plan

• Panda and Koala pits are

used for storage of Fine Processed Kimberlite (FPK) and minewater beginning 2020

• Lynx kimberlite processing

begins 2018

• Sable kimberlite processing

begins 2019

• Jay kimberlite processing

begins 2021

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PPD LLCF Sources Other

Sources of Potassium Loadings to LLCF

• Key source of Potassium Loadings is Process Plant Discharge (PPD)

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Potassium in Process Plant Discharge

• Elevated concentrations in period

2016 to present

• Previous elevated concentrations

were isolated and short-lived

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IEMA-3

Process Plant Discharge Geochemistry Potassium Study

Investigation of Cause/Source Mitigation

• Elevated concentrations of potassium in PPD
• No addition of potassium in Process Plant

Geochemical investigation to better understand properties of ore

• Laboratory testing program on FPK samples collected in Cell B of the LLCF, PPD

samples, and ore samples collected from Fox, Misery, and Pigeon open pits, and the Koala Underground

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Results

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K+ K+ K+ Ca2+ Ca2+ Ca2+ Solution

• re

Cation Exchange

Ca2+ Ca2+ K+

• re

K+

Na+ Na+

K+ K+ K+ K+

Na+ Na+

Process Plant Discharge Geochemistry Potassium Study

Ca2+ K+

Misery Ore - ↑ K Fox Ore - ↑ Na

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• 2018 – 2033: Misery will not be

primary feed

• Thus two options for predicting

potassium:

1) Geochemical predictive relationship between Ca and K, with model varying K based on predicted Ca 2) Set minimum calcium concentration based on calcite dissolution

• Base Case = Option 2, minimum

147mg/L potassium in PPD

• Greater than concentrations over most
• f history of PPD production
• Greater than concentrations predicted

using Option 1

• Uncertainty remains, but only relevant

for predictions from 2027 - 2039

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Observed PPD 147 mg/L Option 2 Option 1 (predictive relationship) Predicted PPD

Predicting Future Potassium in Process Plant Discharge

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Cell D Cell E

• Max. Avg. EQC = 41 mg/L

Calibration – Water Quality

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SSWQO = 64 mg/L SSWQO = 64 mg/L

Calibration – Water Quality

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SSWQO = 64 mg/L SSWQO = 64 mg/L

Calibration – Water Quality

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Cell D Cell E Proposed Max. Avg. EQC = 64 mg/L

• Max. Avg. EQC = 41 mg/L

ECCC-1

Future Predictions - LLCF

• Concentrations peak in winter 2020/2021
• Post 2021 concentrations fall as PPD is

deposited in Panda and Koala pits

• Concentrations rise from 2027/2028 as

water is decanted from Panda and Koala pits to LLCF

• Concentrations peak 2038/2039 when

decanting ends

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Future Predictions - LLCF

• Potassium in Cell E of the LLCF predicted to exceed 41 mg/L in the open-water

season in next two to three years

• Passage of loadings from recent PPD from Cell C to Cell E
• Operating level in LLCF does not allow storage of all inflows for period of

exceedance of 41 mg/L

• Predictions also show potential exceedance of 41 mg/L in 2030s
• Uncertainty associated with potassium concentrations in Sable, Lynx, and Jay ores
• Water from Panda and Koala pits will not be pumped to the LLCF until 2027

ECCC-1

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Leslie Lake Moose Lake Nema Lake Slipper Lake

SSWQO = 64 mg/L SSWQO = 64 mg/L SSWQO = 64 mg/L SSWQO = 64 mg/L

Future Predictions – Downstream Lakes

• Similar trends to predicted water quality

in LLCF

• Potential for potassium concentrations to exceed

64 mg/L in Leslie and Moose lakes under-ice in winter 2019/2020 and 2020/2021

• No exceedances predicted in 2030s

ECCC-2

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ECCC-2

2017 Koala Watershed Water Quality Model

• Updated modelling predicts open-water potassium concentrations in Cell E of the

LLCF will exceed 41 mg/L

• This cannot be avoided as loadings are passing through LLCF from Cell C

to Cell E, i.e., no source control mitigation is possible

• Updated modelling predicts brief exceedances of SSWQO (64 mg/L) in Leslie and

Moose Lakes under-ice

• Modelling suggests it may be possible to mitigate these exceedances with water

management

• Modelling suggests a risk of elevated potassium concentrations in 2030, but there

will be no discharge from Panda and Koala pits to LLCF until 2027

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Water Licence Amendment Application

• Dominion is requesting that potassium EQC at the Ekati Diamond Mine be aligned

with the approved SSWQO

• Maximum Average EQC = 64 mg/L
• Maximum Grab EQC = 103 mg/L
• SSWQO represents our best understanding of environmental risk associated with

potassium toxicity

• reflects current state of science including recently published and site-specific data
• Consistent with the WLWB’s Water and Effluent Quality Management Policy
• Direct link between receiving environment guildelines/objectives and EQC
• Facilitates clear and consistent interpretation and application of Licence requirements
• Consistent with process for establishing EQC at the Ekati Diamond Mine
• Provides consistency between Water Licence and the Potassium Response Plan

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Water Licence Amendment Application

• SSWQO is applicable in all watersheds at the Ekati Diamond Mine
• Updated SSWQO was derived using species that are representative of all watersheds at the

Ekati Diamond Mine

• Toxicity modifying factors have not been identified for potassium
• Short-term SSWQO
• Derived using the HC5 from a Species Sensitivity Distribution of species mean acute values for

relevant freshwater species

• Derivation followed CCME guidance, and included data for 16 species (3 fish and 13

invertebrate species)

• The most sensitive species was the amphipod, Hyalella azteca, which had a species mean

acute value of 182 mg/L

• Short-term SSWQO provides a suitable estimate of a concentration that would protect against

severe effects resulting from short-term exposure

• 103 mg/L is < 2X Long-term SSWQO and should replace existing max grab EQC

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(GNWT-ENR-3/ WLWB-2) (GNWT-ENR #4)

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Water Licence Amendment Application

• Dominion has met the three criteria set by the WLWB as reasons for not updating

the EQC to the SSWQO in 2016:

✓ Potential for discharge water quality to be greater than current EQC

• Most recent model (November 17th, 2017 submission) predicts average concentrations in the

Cell E of the LLCF will exceed 41 mg/L ✓ Requires formal submission

• Water Licence Amendment Application filed July 21, 2017

✓ Further understanding of the receiving environment

• AEMP monitoring and three-year re-evaluation
• Iterative updates to Koala Water Quality Model
• Potassium Response Plan and associated actions

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Summary

• Dominion Diamond has rapidly identified and responded to concerns over

potassium at the Ekati Diamond Mine and is committed to ongoing adaptive management

• Current EQC are not reasonably achievable
• Short- and Long-term SSWQO are protective of the receiving environment at the

Ekati Diamond Mine

• Updated SSWQO have been extensively reviewed
• Long-term SSWQO is already in use at the Ekati Diamond Mine
• Alignment between EQC and SSWQO is consistent with WLWB policy and with the

established process of setting EQC at the Ekati Diamond Mine

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Thank you. Do you have any questions?

MUG Technical Sessions 31