Hydrogeochemical Characterization to Evaluate the Potential for In Situ

Selenium Reduction

Erica Andrew, B.Sc.

Background

Characterization program conducted at Teck Coal Fording River Operations in British ColumbiaScope of work included:

Geophysics transectsInstallation of nested groundwater monitoring wellsHydraulic conductivity testsMonitoring and sampling of groundwater and surface water

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Selenium

Present in both inorganic and organic formsSolid, liquid and gas phasesIs an essential nutrient and is also a contaminant at higher concentrationsSelenium distribution and chemistry is complex and driven by redox conditions, biological activity, pH and sorptionDO and nitrate must be removed before significant selenium reduction can occurCCME guideline for selenium is 0.001 mg/L

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Selenium Chemistry

4 primary oxidation states +6 selenate (SeO4

-2)+4 selenite (HSeO3

-

and SeO32-)

elemental selenium Se0

-2 selenide Se-2

Driven byRedox conditionsBiological activitySorption processes

October 26, 2010 4 Higashi et al., Pp. 355-360 in: J.H. Lehr and J. Keeley (Eds.), Water Encyclopedia:Water Quality and Resource Development. Wiley, Hoboken, NJ. 717 pp. (May 2005).

Biological Treatment Primer

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BIOLOGICAL TREATMENT PRIMER Biological treatment relies on oxidation reduction reactionsThe processes that occur in natural environments are based on energetic favorability

Bacterial Cell

CO2

Organic Carbon

Electron Transfer

Electron Donor Electron Acceptor

H2O

O2

Biological Treatment Primer

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Bacterial Cell

CO2

Organic Carbon

Electron Transfer

Electron Donor Electron Acceptor

Decreasing Energy Yield

H2O

O2

N2

NO3 Fe3+

Fe2+ H2S

SO4

CH4

CO2

Se

SeO42-

Fording River Coal Mine

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STP

Kilmarnock

Geophysical Survey

Two 1 km transectsOne at the base of the STPSecond south of Kilmarnock settling pondsElectrical Resistivity Imaging and electromagnetic (EM31) surveys conductedUsed to select drilling locationsDelineated channel and non-channel depositsUsed with K-test results to estimate flux through valley

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South Tailings Pond Transect

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Kilmarnock Alluvium Transect

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Drilling Program

Barber RigFour sets of nested wellsGravel with varying amounts of sandBedrock encountered in STP wells

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South Tailings Pond

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South Tailings Pond

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Located on the fluvial sands, gravels and glacial till of the Fording River valleyCurrently used for ongoing tailings discharge from the process and wash plant operationsWater is also reclaimed and is re-used in the process plant

South Tailings Pond

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SEEPAGE ANALYSISMAIN EMBANKMENT- EL. 1633mMAXIMUM WATER HEAD

1633 masl

1606

160

8

1630

8 .67 56e -00 5 (m³/s ec)

DISTANCE, m-20 -10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170

ELEV

ATIO

N, m

(x 1

000)

1.580

1.585

1.590

1.595

1.600

1.605

1.610

1.615

1.620

1.625

1.630

1.635

1.640

1.645

1.650

Pond EL. 1632mEL.1633m

Golder Associates Ltd., Design Review South Tailings Pond Dam, Fording River Operations (April 2009).

Sampling Points at South Tailings Pond

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13 groundwater sample locations

Four installed by Golder in 2009Eight existing standpipes around the STPSeepage return well

8 surface water sample locations

Groundwater at STP

Groundwater levels vary in the nested wellsA downward gradient exists in the nested wellsSeepage from STP likely to the Kilmarnock alluvium to the south and the Fording River to the westGroundwater flow below and immediately adjacent to the STP likely comprises mostly or entirely STP seepage

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Water Chemistry for STP

Shows some indication of conditions suitable for selenium attenuation, specifically reductionReducing conditions are evident by:

Low DONegative Eh measurementsPresence of reduced redox species

Results indicate that the STP itself and seeps do not support selenium reduction

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Water Chemistry at STP

Groundwater wells on the west and main embankment, conditions are reducingThe nested wells and seepage return well show low DO, but relatively high positive EhThe Fording River shows oxidizing conditions

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09-03A 09-03B

Water Chemistry at STP

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1599.24

D. Selenium 0.0098 mg/LNitrate 0.709 mg/LDO 5.39 mg/LEh 249 mV

1600.97 1599.47

1593.78

D. Selenium 0.0185 mg/LNitrate 1.12 mg/LDO 0.09 mg/LEh 242 mV

Kilmarnock Alluvium

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Kilmarnock Alluvium

Average flow rate of 110,702 m3/dayTwo phases of settling pondsUnderlain by fluvial sands and gravelsDepth to groundwater ranges from 6.25 to 10.52 m bgs

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Sampling Points at Kilmarnock

Four groundwater sample locations installed by Golder in 2009Four to seven surface water sample locations depending on the time of year

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Water Chemistry for Kilmarnock Alluvium

Results indicate no reducing conditionsIncrease in NO3 and Se as compared to STPDO values near solubility levelsHigh positive Eh valuesAttenuation evaluated using two scenarios

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Scenario One

Groundwater represents only seepage from settling pondsGroundwater flow through upgradient areas is prohibitedGroundwater mounding is expected to be significantSelenium concentrations represent approximately 30% of pond inflow

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Scenario Two

Represents a mixing of groundwater flow through and pond rechargeAssumes STP nested wells represent upgradient groundwaterSimple mixing calculation for selenium75% of groundwater may be flow through from nearby STP25% represents pond recharge

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Conclusions

South Tailings Pond

Not conducive to selenium reductionLower selenium concentrations in STP seepage samples and nearby groundwater suggests some selenium attenuationWithin the underlying groundwater system, the groundwater is oxygenated within a short distance from STPSelenium added to the groundwater is expected to migrate downgradient with limited attenuation

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Conclusions

Kilmarnock Alluvium

Reducing conditions do not exist in the alluvium or settling pondsDO values are near solubility and high positive Eh valuesSimple mixing calculations suggest selenium attenuation for the settling ponds between 50% and 70%Further data and evaluation is needed

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Related Research

Active Pilot Treatment SystemPit Lake ProfilingPRB EvaluationPassive Treatment System

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Thank-you

Ron Jones, Teck CoalJohn Pumphrey, Teck CoalEnvironmental Group at TeckCoal Fording River OperationsTom Rutkowski, GolderMarc Bowles, Golder

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