WATER TER QUALIT ALITY Y MODELLING ODELLING AND D EFFL FLUEN - - PowerPoint PPT Presentation

MVLWB Technical Session Snap Lake Mine Final Closure, and Water Licence and Land Permit Renewal July 16 to 18, 2019

WATER TER QUALIT ALITY Y MODELLING ODELLING AND D EFFL FLUEN UENT T QUALIT ALITY Y CRI RITERI TERIA

PUBLIC LIC PRESEN ENTATION ION

• Water Quality Models
• Site, Snap Lake, and Downstream
• Effluent Quality Criteria
• Model Sensitivities and Near-field Modelling

OUTL TLINE

WATER TER QU QUAL ALIT ITY Y MO MODELS ELS

L I N K E D M O D E L S

INTR TRODU ODUCTION CTION

Water Quantity Model Site Water Quality Model Snap Lake Water Quality Model Downstream Lakes Water Quality Model Effluent Quality Criteria Constructed Wetland Design

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M O D E L A S S U M P T I O N S

• Extended Care and Maintenance
• Modular water treatment plant (WTP)/reverse osmosis (RO) unit operational
• Closure
• Buildings decommissioned, North Pile covered, modular WTP/RO unit operational, passive treatment systems constructed

and functioning

• Post-closure
• The modular WTP/RO unit decommissioned, effluent from passive treatment systems meets effluent quality criteria (EQC)
• Passive treatment systems were not included in the Site model

INTR TRODU ODUCTION CTION CONTINUED TINUED

L I N K E D M O D E L S

SITE E MODEL DEL

Water Quantity Model el Site Water Quality Model Snap Lake Water Quality Model Downstream Lakes Water Quality Model Effluent Quality Criteria Constructed Wetland Design

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SITE E MODEL DEL CONCEPTU CEPTUAL DIAGR GRAMS AMS

E X T E N D E D C A R E & M A I N T E N A N C E A N D C L O S U R E P O S T - C L O S U R E

Pumping ing Runoff

• ff + Seepage

Seepage Outflo low (gravit ity)

Sump 1 Sump 2 Sump 3 Sump 4 Sump 5 Snap Lake North Pile Western Embankment Catchment Sump 1 Sump 2 Sump 3 Sump 4 Western Embankment Catchment Water Management Pond Sewage Treatment Plant Underground Mine Snap Lake Modular WTP + RO Unit North Pile Sump 5 I I I

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The North Pile sumps included inflows and outflows from: 1. Direct precipitation 2. Inflows/concentrations from the North Pile 3. Inflows/concentrations from sump catchment area 4. Inflows/concentrations from other sumps 5. Evaporation 6. Pumping to the water management pond/outflow

SITE E MODEL DEL INFL FLOWS & OUTFL TFLOWS

North th Pile e Sump mp Volum lume/ e/ Conc

1 2 3 5 6 4

SITE E MODEL DEL WATER ER QUALI ALITY SOURCE CE TERMS

Source Water er Quality lity Monit itor

• rin

ing Station tion Rib berm seepage SNP 02-02 Fine processed kimberlite runoff (before cover) SNP 02-02 Fine processed kimberlite runoff (after cover; May and June) SNP 02-05 Fine processed kimberlite runoff (after cover; July to April) SNP 02-02 Fine processed kimberlite draindown SNP 02-02 North Pile embankment seepage SNP 02-02 and SNP 02-05 Western embankment catchment area SNP 02-02 Natural catchment area Stream 1 Developed catchment area SNP 02-05 Sewage treatment plant SNP 02-16i Underground water quality SNP 02-01

SITE E MODEL DEL PREDICTED DICTED WATER ER MANAGEME GEMENT T POND D INFL FLOWS S AND OUTFL FLOWS

35,000 13,000 4,000 270,000 Catchment Runoff Precipitation Sewage Treatment Plant North Pile 154,000 5,000 150,000 5,000 Underground Evaporation Modular WTP + RO Unit Seepage to Snap Lake

A N N U A L I N F L O W S ( m 3) A N N U A L O U T F L O W S ( m 3)

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SITE E MODEL DEL PREDICTED DICTED DISCHAR SCHARGES S TO SNAP LAKE

Annual al Dischar scharge e to Snap Lake e (m3) Operations ECM and Closure Post-closure >18,000,000 300,000 270,000

50 100 150 200 250 2018 2020 2022 2024 2026 2028 2030 2032 2034 2036 2038 2040 2042 2044 2046 2048 Nitrate, as N (mg/L) Year

Sump 3

ECM Closure Post-closure

SITE E MODEL DEL PREDICTED DICTED NITRA TRATE TE CONCENT CENTRA RATION TIONS

Sump Sump Volu

• lumes (m3)

Closu

• sure

Post-closu losure 3 8,300 61,000 5 11,700 68,000

Reviewe wer comment nts:

• ECCC-08, MVLWB-55: discuss decreases in predicted sump concentrations
• In Closure, concentrations in Sump 3 are predicted to increase because Sump 3 receives a greater

proportion of North Pile runoff

• In Post-closure, concentrations in the sumps are predicted to decrease because of the assumption that the

sumps fill to their maximum volume before overflowing

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SITE E MODEL DEL ANNUAL AL NITRA TRATE TE LOAD D TO SNAP LAKE

ECM - Extended Care and Maintenance

Annual al Nitrate e Load ad to Snap ap Lake e (kg N/yr) Operations ECM and Closure Post-closure 90,000 5,000 <7,000

L I N K E D M O D E L S

SNAP LAKE MODEL EL

Water Quantity Model el Site Water Quality Model Snap Lake Water r Quality Model Downstream Lakes Water Quality Model Effluent Quality Criteria Constructed Wetland Design

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SNAP LAKE MODEL EL CONCEP EPTU TUAL AL DIAGRAMS GRAMS

E X T E N D E D C A R E & M A I N T E N A N C E A N D C L O S U R E P O S T - C L O S U R E

Pumping ing Runoff

• ff

Seepage Outflo low

Natural Runoff Site Runoff North Pile Water Management Pond Downstream Camp Use Underground Mine Modular WTP + RO Unit Sewage Treatment Plant Snap Lake Natural Runoff Site Runoff North Pile Downstream Sump 5 Outflow Snap Lake Sump 3 Outflow

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SNAP LAKE MODEL EL INPUT PUTS S FOR R EXTENDED ENDED CARE RE & MAINTEN TENANCE ANCE AND CLOSU SURE RE

Other Inflows/Outflows

• Precipitation
• Other Stream Inflows
• Evaporation
• Seepage from Underground Mine to Snap Lake

Modular WTP + RO Unit Discharge North Pile Seepage Site Runoff Water Management Pond Seepage Camp Use Outflow Stream 1

Reviewe wer comment nts:

• GNWT-89: Snap Lake volume, inflows and loading

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SNAP LAKE MODEL EL INPUT PUTS S FOR R POST-CLOSURE OSURE

Other Inflows/Outflows

• Precipitation
• Other Stream Inflows
• Evaporation

Stream 1 Outflow North Pile Seepage Site Runoff Sump 5 Outflow Sump 3 Outflow

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SNAP LAKE MODEL EL WATER TER QUAL ALITY SOURCE E TERMS

Input Water er Qualit lity Sour urce ce Ter erm Treated effluent discharge from the water treatment plant Monitoring data from SNP 02-17 and SNP 02-17b Treated effluent discharge from the modular water treatment plant + reverse osmosis unit ECM and Closure: Median from the Site model Water management pond pumping to Snap Lake (2003-2004) Monitoring data from SNP 02-14 Water management pond pumping to the underground mine ECM and Closure: Median in the water management pond from the Site model Water management pond seepage Calibration period: Monitoring data from SNP 02-14 ECM and Closure: Median in the water management pond from the Site model

SNAP LAKE MODEL EL WATER TER QUAL ALITY SOURCE E TERMS S CONTINUED TINUED

Input Water er Quality lity Source e Ter erm Site runoff Calibration period: Monitoring data from SNP 02-05 ECM, Closure and Post-closure: Median from Stream 1 Natural wetland Calibration period: Monitoring data from SNP 1735-11 Natural watershed runoff Calibration period: Monitoring data from Stream 1 ECM, Closure and Post-closure: Median from Stream 1 North Pile seepage Calibration period: Monitoring data from SNP 02-02 ECM, Closure and Post-closure: Median from SNP 02-02 Sump 3 outflo flow to Snap Lake Post-closu losure re: 95th

th percenti

tile le from

• m the Site

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Sump 5 outflo flow to Snap Lake Post-closu losure re: 95th

th percenti

tile le from

• m the Site

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• Water quality in Snap Lake is predicted to

improve due to:

• Decrease in effluent volume
• Treatment provided by the modular

water treatment plant (WTP)/reverse

• smosis (RO) unit during Extended

Care & Maintenance (ECM) and Closure

• Natural inflows
• Parameter concentrations are predicted to

remain below AEMP benchmarks

SNAP LAKE MODEL EL PREDI DICTED CTED NITRA TRATE TE CONCENT CENTRA RATION TIONS

EDGE E OF THE E MIXING ING ZONE NE IN THE E MAIN N BASIN IN OF SNAP AP LAKE

1 2 3 4 5 6 7 8 9 10 2018 2020 2022 2024 2026 2028 2030 2032 2034 2036 2038 2040 2042 2044 2046 2048 Nitrate, as N (mg/L) Year AEMP Benchmark Minus 25% NO3-N = 25 ECM Closure Post-closure

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L I N K E D M O D E L S

DOWNSTREAM TREAM LAKES MODEL EL

Water Quantity Model el Site Water Quality Model Snap Lake Water Quality Model Downstre ream Lakes es Water er Quality Model Effluent Quality Criteria Constructed Wetland Design

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Snap Lake

DSL1 DSL2 Lac Capot Blanc DSL4 & 5 DSL6 DSL7 DSL8 DSL9/ KING01 DSL10 King Lake King River MacKay Lake Embayment Node 22 Camsell Lake Northeast Lake MacKay Lake West North Lake

DOWNSTREAM TREAM LAKES MODEL EL CONCEP CEPTU TUAL AL DIAGRAM GRAM

DSL - Downstream lake

EXTEN ENDED DED CARE & MAINTENA ENANCE, CE, CLOSURE E AND POST-CL CLOS OSURE

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• Concentrations of total dissolved solids are predicted to peak:
• Lac Capot Blanc outlet in 2023
• Downstream Lake 8 in 2026
• KING01 in 2027
• King River in 2028
• Node 22 in 2028

DOWNSTREAM TREAM LAKES MODEL EL RESUL ULTS S

• At Node 22 in MacKay Lake:
• Measure 1(d) states that “No Total Dissolved Solids or its constituent ions from Snap Lake Mine

effluent will be detectable, relative to the range of natural variability, at the inlet to MacKay Lake, 44 km downstream of Snap Lake.”

• An Acceptable Limit was established in the Downstream Watercourses Special Study Report (Golder

2017) to assess conformity with Measure 1(d)

DOWNSTREAM TREAM LAKES MODEL EL RESUL ULTS S CONTINUED TINUED

PREDICT CTED ED TOTAL L DISSOL OLVED ED SOLIDS DS CONCENTR ENTRATION ONS S AT NODE 22 IN MACKAY Y LAKE

2 4 6 8 10 12 14 16 18 20 2015 2016 2017 2018 Total dissolved solids (mg/L) Year Model Monitoring Data Acceptable Limit 2 4 6 8 10 12 14 16 18 20 2015 2017 2019 2021 2023 2025 2027 2029 2031 2033 2035 2037 2039 2041 2043 2045 2047 Total dissolved solids (mg/L) Year Model Monitoring Data Acceptable Limit

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EF EFFL FLUENT ENT QU QUALIT LITY CRIT RITERIA RIA

L I N K E D M O D E L S

DOWNSTREAM TREAM LAKES MODEL EL

Water Quantity Model Site Water Quality Model Snap Lake Water Quality Model Downstream Lakes Water Quality Model Effluent Quality Criter eria Constructed Wetland Design

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TERMINOL OLOG OGY

Effluen luent t Quality Criteri ria (EQC)

• Apply at end-of-pipe
• Typically higher than in-lake AEMP

benchmarks due to mixing

• Regulated under the Water Licence
• Operational control (i.e., managed by the

Project)

• Enforce

ceable AEMP Benchmarks ks

• Apply in-lake
• From scientific literature
• Refers to generic water quality guidelines,

criteria published by national, provincial, territorial government agencies

• May include site-specific water quality
• bjectives (SSWQOs), which are based on

local conditions and biota

PROPO POSE SED D AEMP BENCHMARK CHMARKS

Param amet eter er AEMP P Benchmark ark SNP 02 02-20e and SNP 02 02-20f 20f (Near ar Existing ing Diffus fuser) er) Propos

• sed

ed SNP 02 02-20h h and SNP 02 02-20i 20i (Near ar Future re East Wetland land) Propos

• sed

ed SNP 02 02-20j j and SNP 02 02-20k k (Near ar Future re West Wetland) land) Chloride* (mg/L) 216 – 263 120 – 236 127 – 227 Fluoride (mg/L) 1.5 1.5 1.5 Sulphate* (mg/L) 309 – 429 128 – 309 128 – 309 Nitrate*, as N (mg/L) 9.3 – 10 10 2.93 – 10 10 3.2 – 10 10 Nitrite, As N (mg/L) 0.2 0.2 0.2 Total ammonia, as N (mg/L) 1.52 1.52 1.52 Total phosphorus, as P (mg/L) 0.011 0.011 0.011 Aluminum (mg/L) 0.1 0.1 0.1 Antimony* (mg/L) 0.006 0.006 0.006 Arsenic (mg/L) 0.005 0.005 0.005 BC ENV CCME CCME + SSWQO CCME + SSWQO + Health th Canada da Health th Canada da

PROPO POSE SED D AEMP BENCHMARK CHMARKS

Param amet eter er AEMP P Benchmark ark SNP 02 02-20e and SNP 02 02-20f (Near ar Existing ing Diffus fuser) er) Propos

• sed

ed SNP 02 02-20h h and SNP 02 02-20i 20i (Near ar Future re East Wetland land) Propos

• sed

ed SNP 02 02-20j j and SNP 02 02-20k k (Near ar Future re West Wetland) land) Barium* (mg/L) 1 1 1 Boron (mg/L) 1.5 1.5 1.5 Chromium* (mg/L) 0.005 and 0.0089 0.005 and 0.0089 0.005 and 0.0089 Cobalt* (mg/L) 0.001 – 0.0013 0.0008 – 0.0011 0.0008 – 0.001 Copper (mg/L) 0.0043 – 0.0083 0.002 – 0.0 .0054 0.002 – 0.0 .0048 Iron (mg/L) 0.3 0.3 0.3 Lead (mg/L) 0.0027 – 0.007 0.001 – 0.0038 0.001 – 0.0032 Mercury (mg/L) 0.000026 0.000026 0.000026 Molybdenum (mg/L) 0.073 0.073 0.073 Nickel (mg/L) 0.087 – 0.15 0.025 – 0.106 0.025 – 0.097 SSWQO CCME CCME + ECCC Health th Canada da ECCC

PROPO POSE SED D AEMP BENCHMARK CHMARKS

Param amet eter er AEMP P Benchmark ark SNP 02 02-20e and SNP 02 02-20f (Near ar Existing ing Diffus fuser) er) Propos

• sed

ed SNP 02 02-20h h and SNP 02 02-20i 20i (Near ar Future re East Wetland land) Propos

• sed

ed SNP 02 02-20j j and SNP 02 02-20k k (Near r Future re West Wetla land nd) Nickel (mg/L) 0.087 – 0.15 0.025 – 0.106 0.025 – 0.097 Selenium (mg/L) 0.001 0.001 0.001 Silver (mg/L) 0.00025 0.00025 0.00025 Strontium (mg/L) 10.7 .7 10.7 .7 10.7 .7 Thallium (mg/L) 0.0008 0.0008 0.0008 Uranium (mg/L) 0.015 0.015 0.015 Vanadium* (mg/L) 0.12 12 0.12 12 0.12 12 Dissolved cadmium* (mg/L) 0.00019 – 0.00034 0.00008 – 0.00023 0.00008 – 0.00021 Dissolved manganese* (mg/L) 0.44 – 0.54 0.32 – 0.47 0.32 – 0.47 Dissolved zinc* (mg/L) 0.019 – 0.0394 0.0059 – 0.0244 0.0066 – 0.0218 SSWQO CCME BC ENV ECCC

PARAME AMETER TER-DEP DEPENDEN ENDENT T AEMP P BENCH CHMARK ARKS

50 100 150 200 250 300 350 2018 2020 2022 2024 2026 2028 2030 2032 2034 2036 2038 2040 2042 2044 2046 2048 Hardness (mg/L as CaCO3) Year ECM Closure Post-closure 50 100 150 200 250 300 350 400 450 500 2018 2020 2022 2024 2026 2028 2030 2032 2034 2036 2038 2040 2042 2044 2046 2048 Sulphate AEMP Benchmark (mg/L) Year ECM Closure Post-closure

Pred edict icted ed Hardnes ness s Conc ncentr tratio ions s in Snap p Lake Predict edicted ed Sulphat hate e AEMP MP Benchma mark in Snap Lake

Hardnes ess (mg/L L as CaCO3) Sulphat ate e Benchm hmark ark (mg/L) <=30 128 <=75 218 <=180 309 181 - 250 429

Reviewe wer comment nts:

• GNWT-ENR-82, GNWT-ENR-97, GNWT-ENR-102, MVLWB-10, MVLWB-20, MVLWB-62, MVLWB-63, SLEMA-6: AEMP benchmarks

EFFLUENT UENT QUALITY CRI RITERI TERIA A FOR CLOSUR SURE AND POST-CLOSUR OSURE

• 3. Are Predic

icted ed 95th

th P WMP/Sump Concen

entra trati tions

• ns >

Normal al Range e in Snap Lake? e?

• 4. Are Predic

icted ed 95th

th P WMP/Sump Concen

entra trati tions

• ns >

AEMP P Benchmarks arks?

• 5. Are Predic

icted ed 95th

th P Concen

entr trations ations at the Mixing g Zone e > 75% % of the AEMP P Benchmark? ark?

• 6. Water Qualit

ity-Bas ased ed POPC Not

• t a POPC -

EQC not

• t

Neces essary

YES YES YES NO NO NO NO NO NO

1.

• 1. Initial

tial List of Parameter ers (MVLWB et al. 2017)

• 2. Pre-screen

reening ing

• 8. Develo

elop EQC (Calc lcula ulate e water qualit ality-based ed EQC, propos

• se

e technolog nology-bas ased ed EQC)

• 7. Review Water Qualit

ity-bas ased ed POPC and Ident ntify ify POPC that should ld have e EQC

SCREENING FOR PARAMETERS OF POTENTIAL CONCERN (POPC)

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EFFLUENT UENT QUALITY CRI RITERI TERIA A FOR CLOSUR SURE AND POST-CLOSUR OSURE CONTI TINUED ED

Parame ameter ers s of Pot

• ten

entia ial Concern Post-Clo Closure re Effluen ent Quality lity Crit iter eria ia Maximu imum m Aver erage age Concentr tratio ion Maximu imum m Grab ab Concen entr tratio ation Nitrate, as N (mg/L) 25 50 Total suspended solids (mg/L) 15 25 pH 6.5 to 9.0 Parame ameter ers s of Pot

• ten

entia ial Concern Closu

• sure

e Effluent luent Quality lity Criter eria ia Maximu imum m Aver erage age Concentr tratio ion Maximu imum m Grab ab Concen entr tratio ation Nitrate, as N (mg/L) 25 50 Total suspended solids (mg/L) 15 25 Faecal coliforms (CFU/100 mL) 10 20 pH 6.5 to 9.0

MO MODEL EL SEN ENSITIVITIES SITIVITIES AND ND NE NEAR AR-FIELD FIELD MO MODEL ELLING LING

SITE E MODEL DEL SENSITIVITIE TIES

Scen enar ario io Descr script iptio ion Annual al Prec ecipitat ipitatio ion Statist tistic ic Prec ecipitat ipitatio ion Year ear Annual al Preci ecipitat itatio ion Depth th (mm) Dry 10th percentile 1970–1971 235 Average Average 1995–1996 372 Wet 90th percentile 1964–1965 470 P R E C I P I TAT I O N Input JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Median 153 130 119 168 67 55 106 93 78 108 107 103 75th %tile 155 133 122 186 70 55 119 108 90 111 116 111 95th %tile 158 135 124 200 72 56 130 120 100 114 123 117 N O R T H P I L E I N P U T C O N C E N T R AT I O N S - N I T R AT E , a s N ( m g / L )

SITE E MODEL DEL PRECIPIT CIPITATION TION SENSITI SITIVITY RESUL ULTS TS

• Monthly rainfall and snowfall

rates based on the average precipitation year resulted in the highest predicted parameter concentrations in Sump 3 and Sump 5 during the Extended Care and Maintenance and Closure periods

• The dry, average, and wet

precipitation scenarios resulted in similar predicted parameter concentrations in Sump 3 and Sump 5 during Post-closure

50 100 150 200 250 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 Nitrate, as N (mg/L) Year Sump 3 10th Percentile Precipitation Average Precipitation 90th Percentile Precipitation ECM Closure Post-Closure

Review iewer er concern cern:

• GNWT-ENR-141

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SITE E MODEL DEL NORTH TH PILE INPUT UT CONCENT CENTRATI TION ON SENSITIV TIVITY RESUL ULTS

• Applying the 95th percentile

SNP 02-02 parameter concentrations to the North Pile runoff and seepage resulted in the highest predicted parameter concentrations in Sump 3 and Sump 5

• The results from this scenario

would not change the proposed list of parameters of potential concern that require effluent quality criteria in the Water Licence in Post-closure

50 100 150 200 250 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 Nitrate, as N (mg/L) Year Sump 3 Median 75th Percentile 95th Percentile ECM Closure Post-Closure

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NEAR-FI FIELD D MODEL EL

GNWT-ENR-78, 79

• A near-field mixing model was used to predict dilution factors at 50 m, 100 m, and 150 m

from the approximate locations where the Sump 3 outflow and the Sump 5 outflow will enter Snap Lake

• The predicted dilution factors were used to calculate parameter concentrations in Snap Lake

at 50 m, 100 m, and 150 m from the outfall locations

• Parameter concentrations were compared to proposed Aquatic Effects Monitoring Program

benchmarks

NEAR-FI FIELD D MODEL EL INPUTS UTS

Outflo low Proper

• pertie

ies Outflo low Desig sign Ambi bient t Proper ertie ies Mixing ing Zone e Infor

• rmation

mation

• Type of outflow
• Density
• Discharge rate
• Orientation relative to

ambient current and shoreline

• Channel depth
• Channel width
• Current
• Density
• Roughness coefficient
• Depth
• Wind speed
• Specified spatial region
• ver which mixing, and

plume characteristics are modelled

𝐷X = 𝐷𝑃𝑣𝑢𝑔𝑚𝑝𝑥 − 𝐷𝑇𝑜𝑏𝑞 𝑀𝑏𝑙𝑓 𝐸𝐺X + 𝐷𝑇𝑜𝑏𝑞 𝑀𝑏𝑙𝑓

NEAR-FI FIELD D MODEL EL DILUTION UTION FACT CTORS ORS

Month Sump 3 Dilution ution Factor

• rs

50 50 m from Outfall fall 100 m from Outfall fall 150 150 m from Outfall fall May 61 78 90 June 18 24 28 July 107 127 146 August 143 170 192 September 122 146 168 Month Sump 5 Dilution ution Factor

• rs

50 50 m from Outfall fall 100 m from Outfall fall 150 150 m from Outfall fall May 14 18 21 June 17 20 23 July 128 152 175 August 112 180 236 September 149 250 276

• Using modelled sump nitrate concentrations (without passive treatment)
• Predicted parameter concentrations at 50 m were below 75% of the AEMP benchmarks, except for nitrate and total

phosphorus

• Predicted parameter concentrations at 100 m and 150 m were below 75% of the AEMP benchmarks, except for nitrate
• All other parameters were below 75% of the AEMP benchmarks at 50 m
• Using sump nitrate concentrations with passive treatment (i.e., maximum average concentration EQC of

25 mg-N/L)

• Predicted nitrate concentrations at 50 m, 100 m and 150 m were below 75% of the AEMP benchmark
• All other parameters were below 75% of the AEMP benchmarks at 50 m, except for total phosphorus
• Based on the results above (i.e., total phosphorus concentrations were predicted to exceed 75% of the

AEMP benchmark at 50 m) and that CORMIX results are generally accurate to within ±50%, the mixing zone boundary in Snap Lake is recommended to be set to no smaller than 100 m

NEAR-FI FIELD D MODEL EL PREDIC DICTED D CONCENT CENTRA RATION TIONS