Groundwater tracing:Breathing new life into a practical approach to testing aquifersFREDERIC COSME, PRINCIPAL HYDROGEOLOGIST

OUTLINE Introduction 01

Applied Tracers 02

Environmental Tracers 03

Questions 04

INTRODUCTION

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Applied Tracers

• Voluntarily introduced in groundwater• Known quantity• More controlled

Examples: Bromide, fluorescein

INTRODUCTIOND I F F E R E N C E S B E T W E E N A P P L I E D A N D E N V I R O N M E N TA L T R A C E R S

Environmental Tracers

• Already present in groundwater• Unknown quantity• Less controlled

Examples: Temperature, major ions, contaminants, isotopes

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INTRODUCTIONAT W H AT S C A L E D O Y O U N E E D T O W O R K ?

10-1 m 1 m 10 m 102 m 103 m

Catchment

Site

PlumeLocalised Zone

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• Costs• Site constraints• Aquifer conditions• Detection limits• Laboratory or field analysis (Sampling method)• Background concentrations• Quality assurance/quality control (QA/QC)• Likely spatial and temporal distribution

Begin with the end in mind!Come up with hypotheses to design your data collection

INTRODUCTIONO T H E R K E Y C O N S I D E R AT I O N S

APPLIED TRACERS

Key Principles 01

Protection Zone 02

Groundwater Recharge 03

Groundwater Flux 04

Conclusions 05

Future Development 06

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APPLIED TRACERSK E Y P R I N C I P L E S

BASIC IDEA

• Dissolve a known quantity of tracer in water

• Introduce the solution into an aquifer via:• Injection well• Sinkhole, subsurface vault, pond, dam, etc.

• Monitor changes in tracer concentrations

Obtain breakthrough curves

IN PRACTICE

• Seems easy but tracer test methodology can be sophisticated

• Results can be highly dependent upon adopted methodology

S O U R C E :   B A T L L E ‐ A G U I L A R ,   2 0 0 9

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S A LT S

• Analysis is conventional

• Higher detection limit (10 – 100 g/L)

• Background can be high

• Toxicity

F L U O R E S C E N T D Y E S N A N O T R A C E R S

APPLIED TRACERS

• Very low detection limit (0.001 g/L)

• Background, interferences

• Innocuous (USEPA, German EPA)

(Amino-G acid excited by UV)

• Analysis is unconventional

• Specificity

• Requires specific risk assessment

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T Y P I C A L D E T E C T I O N L I M I T S

A N A LY S I S T Y P E - F L U O R E S C E I N

INSTRUMENTATION LIMITS FOR FLUORESCENT DYES

Fluorescenttracer

Limit of detection(g/L)

Fluorescein 0.002

Sulforhodamine B 0.006

Eosine 0.01

Tinopal 0.01

Amino G acid 0.02

Pyranine 0.02

Naphthionate 0.05

Photine 1

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• Many EU countries rely heavily on groundwater for their potable water supply

• Some areas are densely populated and there is a need to define protection zones inside which activities are regulated or prohibited

• When an accident occurs, there is also a need to predict contaminant migration and support logistics of intervention

• In most EU countries, protection zones are typically defined using fluorescent dye tracers due to their ability to quantify effective porosity

PROTECTION ZONESC O N T E X T

OPPOSITE TO GQRUZ

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• Alluvial gravel layer is about 7 m thick

• T ranges from 1.10-4 m2/s to 2.10-1 m2/s with average being 3.10-2 m2/s

• Average storage coefficient (Sy) is 0.10

PROTECTION ZONESA P P L I C AT I O N S O U R C E :   D E R O U A N E A N D   D A S S A R G U E S ,   1 9 9 8

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PROTECTION ZONESA P P L I C AT I O N - R A D I A L LY C O N V E R G I N G F L O W S O U R C E :   D E R O U A N E A N D   D A S S A R G U E S ,   1 9 9 8

Distance (m)

Tracer EffectivePorosity

ne (%)

27 KI 4.8

49 KI 7.2

78 Naphthionate 5.6

88 LiCl 8.2

91 Fluorescein 5.8

115 Rhodamine WT 4.7

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• Effective porosity is lower than the Specific Yield (Sy) up to a factor of two

• Transfer time can be underestimated if relying on Syderived from pumping test

• The distribution in effective porosity is variable, reflecting the aquifer heterogeneities

• Lower effective porosities reflect that contamination will follow the “path of least resistance” (i.e. via advectivezones) while Sy is more a bulk parameter

• This is even more pronounced in fractured rock aquifers. For example, effective porosities as low as 0.03 % have been measured in limestone.

PROTECTION ZONESO U T C O M E S

S O U R C E   :   S U T H E R S A N ,   2 0 1 6

3 D   D E P I C T I O N   O F   A L L U V I A L   A Q U I F E R

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• Limestone is a dual porosity medium (fracture and matrix) that is used extensively as an aquifer for potable water supply in the UK and Northwest EU

• A key factor of vulnerability is migration of nitrogen and pesticides resulting from agricultural activities through the unsaturated zone

• There is a need to better predict the recharge mechanisms and integrate these into the vulnerability

UNSATURATED ZONEC O N T E X T

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UNSATURATED ZONEA P P L I C AT I O N S O U R C E :   B R O U Y E R E ,   2 0 0 4

Loess

SilexConglo-merate

Weathered Limestone

Fresh Limestone

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0,0E+00

5,0E-03

1,0E-02

1,5E-02

2,0E-02

2,5E-02

0,0 100,0 200,0 300,0 400,0 500,0 600,0 700,0Temps d'arrivée (j)

Con

cent

ratio

n (p

pm/k

g)

0,00

0,02

0,04

0,06

0,08

0,10

0,12

0,14

0,0 30,0 60,0 90,0 120,0 150,0Temps d'arrivée (h)

Con

cent

ratio

n (p

pm/k

g) chlorure

potassium

UNSATURATED ZONEA P P L I C AT I O N S O U R C E :   B R O U Y E R E ,   2 0 0 4

~5h

~11h

Transfer Time (h)

~1 year

Peak ?

Transfer Time (day)

FIR

ST

TE

ST

SE

CO

ND

TE

ST

Key Parameters

First Test

Second Test

Vertical Distance

10 m 10 m

Tracer KCl KI

Mass injected 100 kg 10 kg

Volume injected ~ 300 L 30 L

Chaser 300 L/h 0 L/h

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LIMESTONE MATRIX

• High porosity: nm ~ 30 – 40 %

• Microporosity (~ 1 m) very high capillary tension

• Low hydr. conductivity: Ks,M << 10-9 to 10-8 m/s

LIMESTONE FRACTURES

• Low porosity: nf < 1%

• Larger openings lower capillary tension

• High hydr. conductivity: Ks,F >> 10-3 m/s

First test shows long tail in breakthrough curve, reflective of strong back diffusion of tracer into fractures

UNSATURATED ZONEO U T C O M E S S O U R C E :   B R O U Y E R E ,   2 0 0 4

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• Most decisions regarding contaminated groundwater are driven by contaminant concentrations.

• However, exceeding concentration criteria does not necessarily mean that the groundwater contamination poses an unacceptable risk

• Making decisions regarding contaminated groundwater can be improved by also considering the contaminant mass flux:

GROUNDWATER FLUXC O N T E X T

S O U R C E   :   I T R C ,   2 0 1 0

S O U R C E :   I T R C ,   2 0 1 0

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GROUNDWATER FLUXF I N I T E V O L U M E P O I N T D I L U T I O N M E T H O D

time

Q1t

Q1t< Q2

t

Monitoring during tracer injection Monitoring after tracer injection

Dilution >> when Qt >>Cinj

Cw

S O U R C E :   B R O U Y E R E ,   2 0 0 8

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• Groundwater flux measurement depends on: • Detection limit of tracer (0.01 g/L to

1 g/L)• Control on tracer injection and sampling

flow rates (< 0.1 L/min)

Basis of accuracy

• Real-time measurement

GROUNDWATER FLUXA P P L I C AT I O N – F I N I T E V O L U M E P O I N T D I L U T I O N M E T H O D

Particularly suited to dynamic environments (e.g. tidal zones, discharge to surface water, active remediation)

S O U R C E :   T H I E L E ,   2 0 1 7

Groundwater level

River level

Darcy Flux

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CONCLUSION

• Another “toolbox” to test aquifers • Versatile - Nearly infinite number of approaches• Importance of developing a hypothesis to be tested• Design applied tracer test to verify this hypothesis• Key design considerations include – Injection approach, tracer

choice, tracer monitoring, QA/QC

A P P L I E D T R A C E R S

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FUTURE DEVELOPMENT“ S M A R T ” A P P L I E D T R A C E R SS O U R C E :   K N A P P ,   2 0 1 7

ENVIRONMENTAL TRACERS

Key Principles 01

Groundwater Discharge 02

Contaminant Degradation 03

Groundwater Discharge 04

Conclusions 05

Future Development 06

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BASIC IDEA

• Use parameters that are “freely” available in the environment

• Monitor spatial or temporal distribution of parameters

IN PRACTICE

• Can accommodate for large scale and slow groundwater movement

• Sampling and analysis can require stringent conditions (e.g. lab turnaround time for some tracer can be in the order of 3 to 6 months)

• Australia is a global leader in this!

ENVIRONMENTAL TRACERSK E Y P R I N C I P L E S

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F I E L D PA R A M E T E R S , M A J O R I O N S , I S O T O P E S

• Relatively low to moderate cost

• Typically used to assess mixing processes

C O M P O U N D S P E C I F I C I S O P O T O P E A N A LY S I S

A G E D AT I N G A N D R A D I O A C T I V E T R A C E R

ENVIRONMENTAL TRACERS

• Moderate cost

• Typically used to assess degradation processes

• Moderate to high cost

• Connectivity and flowpaths

Background and QA/QC!!!

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• Measuring the rate of groundwater discharge is key to aquatic ecology studies

• The groundwater – surface water interface is a dynamic zone with a number of mixing processes involved

• This interface is also subject to strong redox gradients, resulting in biological activity

GROUNDWATER DISCHARGEC O N T E X T

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• Surface water is enriched in δ2H and δ18O due to evaporation

• Terrestrial groundwater is depleted in δ2H and δ18O

Mixing proportion can be estimated using mixing line between the two end members

• Seepage water (i.e. water actually discharging) is dominated by river water (~ 90 %)

Indicates significant mixing before discharge in the river

GROUNDWATER DISCHARGEH E AV Y I S O T O P E D ATA I N WAT E R S O U R C E :   D U R A N ,   2 0 1 2

Terrestrial Groundwater

Surface WaterSeepage

Water

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• Contrast in isotopic signature between plant, groundwater, hyporheic zone and surface water

Enables an understanding of different contributors in nitrogen

• Enrichment in heavy isotope from the deep part to the shallow part of the hyporheic zone

Indicates significant nitrogen removal rate (up to 80% removal)

GROUNDWATER DISCHARGEC O M P O U N D S P E C I F I C I S O T O P E A N A LY S I S S O U R C E :   L A M O N T A G N E ,   2 0 1 8

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• Assessing contaminant degradation is key to risk assessment or remedial design

• Enhanced bioremediation is one of the most cost-effective remediation techniques over other in-situ techniques (ISCO, thermal, surfactant)

• Sometimes monitored natural attenuation can be the most practical remediation option

• When organic contaminants degrade, there is an enrichment of heavy isotopes in the remaining contaminant pools (Environmental forensics)

• Compound specific isotope analysis can:• Support an assessment of spatial and temporal

trends in biodegradation• Form a basis to derive degradation rates

CONTAMINANT DEGRADATIONC O N T E X T – I S O T O P I C F R A C T I O N AT I O N S O U R C E :   U S E P A ,   2 0 0 9

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CONTAMINANT DEGRADATIONS O U R C E :   P A L A U ,   2 0 1 51 , 1 , 1 - T C A I N F R A C T U R E D L I M E S T O N E

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• Fractionation results for reduction and oxidation obtained via batch testing (laboratory)

• Field data indicate that 1,1,1-TCA tends to degrade following abiotic reaction

• Abiotic degradation is slow and difficult to monitor using more conventional analysis

• Provides possible perspective on remedial approach:

• Enhanced biodegradation – limestone aquifer with long plume, amendment delivery and zone of influence

• Monitored natural attenuation – slow degradation rate

CONTAMINANT DEGRADATIONR E S U LT S A N D O U T C O M E S O U R C E :   P A L A U ,   2 0 1 5

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• Groundwater is “ageing” along the flowpath, with surface water being the youngest

• The following environmental tracers can be used to “date” groundwater:

• Noble gases (e.g. He)• Natural radionuclides (e.g. radon-222)• Radionuclides with both natural and

anthropogenic sources (e.g. 3H) • Anthropogenic tracers (e.g. CFCs)

• Age dating can be used to evaluate:• Connectivity with geological formations• Aquitard leakage• Aquifer recharge rates• Groundwater – surface water interaction

GROUNDWATER RECHARGEC O N T E X T S O U R C E :   S U C K O W ,   2 0 1 4

A groundwater sample never has a unique “Age” but an Age Distribution

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• 14C expressed in pmC (percent modern carbon)

Higher value indicative of younger groundwater

• 3H expressed in TU (tritium units)

Higher values indicative of younger groundwater

• 4He expressed in cm3 STP g-1 (standard temperature and pressure)

Higher values indicative of older groundwater

Losing stream, influenced by recent pumping activities

GROUNDWATER RECHARGEG R O U N D WAT E R – S U R FA C E WAT E R I N T E R A C T I O N S O U R C E :   L A M O N T A G N E ,   2 0 1 5

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CONCLUSION

• Toolbox is complementary to “Applied Tracers”• Also versatile - Nearly infinite number of approaches• Multiple lines of evidence• Importance of involving practitioners for scoping, sample collection,

laboratory analysis and data interpretation (Don’t try to replicate ten years worth of research)

E N V I R O N M E N TA L T R A C E R S

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FUTURE DEVELOPMENTI N T E G R AT E D L A B O R AT O R Y A N D R E S E A R C H FA C I L I T Y

• Increase accessibility to 34S analysisUseful in geochemical analysis

(MAR/ASR, acid mine drainage, etc)

• Development of noble gases analysisAlternative to overcome anthropogenic

influence in age dating assessment

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QUESTIONS?

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Batlle-Aguilar J., Brouyere S., Dassargues A., Morasch B., Hunkleler D., Hohener P., Diels L, Vanbroekhoven K, Seuntjens P and Halen H, 2009. Benzene dispersion and natural attenuation in an alluvial aquifer with strong interactions with surface water. Journal of Hydrology, 369, 305-317.

Derouane J. and Dassargues A, 1998. Delineation of groundwater protection zones based on tracer tests and transport modelling in alluvial sediments. Environmental Geology 36 (1-2). Springer-Verlag. November 1998.

Suthersan S.S., Potter S.T., Schnobrich M., Quinnan J., Welty N. and Fewless T., 2016. Rethinking site conceptual models in groundwater remediation. Groundwater Monitoring & Remediation, 36, no. 4. Fall 2016.

Brouyere S., Dassargues A. and Hallet V., 2004. Migration of contaminants through the unsaturated zone overlying the Hesbaye chalky aquifer in Belgium: a field investigation. Journal of Contaminant Hydrology 72 (2004) 135-164.

ITRC, 2010. Use and measurement of mass flux and mass discharge. Prepared by Interstate Technology and Regulatory Council. August 2010.

Brouyere S., Batlle-Aguilar J., Goderniaux P. and Dassargues A, 2008. A new tracer technique for monitoring groundwater fluxes: The finite volume point dilution method. Journal of Contaminant Hydrology 95 (2008) 121 – 140.

ReferencesI N O R D E R O F A P P E A R A N C E

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Thiele Z., Cosme F., De Greene K., Jamin P., Savaglia A., Boothe A., O’Halloran R., Tyler J., Orban P. and Brouyere S, 2017. Evaluation of groundwater and contaminant mass flux to a marine environment using fluorescent dye tracer test. Proceedings of the 7th International Contaminated Site Remediation Conference CleanUp 2017, September 2017. Melbourne.

Knapp J., Gonzalez-Pinzon R., Drummond J., Larsen L., Cirpka O. and Harvey J., 2017. Tracer-based characterization of hyporheic exchange and benthic biolayers in streams. Water Resources Research 53, 1575-1594. American Geophysical Union.

Duran J., Edwards M. and Laase A., 2012. Contaminated sediment and groundwater discharge to an estuarine river and implications for regulatory compliance. Proceedings of the 8th International Conference on the Remediation of Chlorinated and Recalcitrant Compounds. Monterey, California, May 2012.

Lamontagne S., Cosme F., Minard A. and Holloway A, 2018. Nitrogen attenuation, dilution and recycling at the groundwater – surface water interface of a subtropical estuary inferred from the stable isotope composition of nitrate and water. Hydrology and Earth System Sciences (Under review). European Geosciences Union.

References (Cont’ed)I N O R D E R O F A P P E A R A N C E

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USEPA, 2009. A guide for assessing biodegradation and source identification of organic ground water contaminants using compound specific isotope analysis (CSIA). United States Environmental Protection Agency.

Palau J., Jamin P., Badin A., Vanhecke N., Haerens B., Brouyere S. and Hunkeler D, 2016. Use of dual carbon-chlorine isotope analysis to assess the degradation pathways of 1,1,1-trichloroethane in groundwater. Water Research 92 (2016) 235-243.

Suckow A, 2014. The age of groundwater - Definitions, models and why we do need this term. Applied Geochemistry, Vol No 50, 222-230.

References (Cont’ed)I N O R D E R O F A P P E A R A N C E