Persistent Groundwater Contaminant Plumes: Processes, Characterization,

and Case Studies

UA-SRP & USEPA Seminar Series- Webinar February 24, 2014

Mark L. Brusseau

School of Earth & Environmental Sciences University of Arizona

1

Constrained Mass Removal & Plume Persistence

“significant limitations with currently available remedial technologies persist that make achievement of MCLs throughout the aquifer unlikely at most complex groundwater sites in a time frame of 50-100 years.”*

“Complex” groundwater sites are defined as those that have DNAPL present (e.g., chlorinated solvents) and that have substantial subsurface heterogeneity, including the presence of extensive lower-permeability units or fractured media.

• Why does this situation exist?

• What options are available?

*National Research Council (NRC). 2013. Alternatives for Managing the Nation's Complex Contaminated Groundwater Sites. Wash., DC 2

Outline

• Chlorinated-solvent sites- prevalence and issues

• Constrained mass removal and plume persistence: Impact of DNAPL source zones

• Constrained mass removal and plume persistence: Impact of mass storage in lower-K zones & hydraulic factors

• Constrained mass removal and plume persistence: Impact of sorbed mass

• Summary

3

~1600 SUPERFUND Sites

~80% have Chlorinated-Solvent Contaminants

4

Arizona Sites

Chlorinated-Solvents Presence:

State: 31/35

Federal: 13/15

5

Groundwater Contamination Sites in Tucson

Chlorinated-Solvent Contaminants are Primary Concern 6

at all 9 Sites

Groundwater Remediation Standard Method = Pump and Treat

Very effective for plume containment

7

Impact of P&T on Water Resources

• Analysis for Tucson [Brusseau & Narter, 2013]- year 2010

• Compare aggregate volume of groundwater extracted for all P&T systems to total metropolitan groundwater withdrawal

• Total groundwater withdrawal for all P&T systems = 16.6 M m3

• This is ~20% of the total groundwater withdrawal in Tucson

• Treated water used primarily for potable water or re-injection

• Represents ~6% of total potable water supply

8

Three Chlorinated-Solvent Sites in Arizona

• TCE is Primary COC • Very Low Retardation (R<2) • No Measurable Transformation Processes • V. Low Biogeochemical Attenuation Capacity

Large Plumes (several km long)

11 KM

4.5 KM

9

9 KM

Pump & Treat CMD Data

Composite Measure: CMD = Q * C

- OU1 Q = pumping rateC = concentration

~90% Reduction Currently ~ 1 kg/d

Asymptotic conditions

~2 equivalent pore volumes displaced

10

Constrained Mass Removal & Plume Persistence

Potential Factors: • Uncontrolled DNAPL Sources

• Plume-scale Lower-K Zones and Mass Storage (diffusive mass transfer- “back diffusion”)

• Plume-scale Sorbed-phase Mass Storage (sorption/desorption processes)

• Hydraulic Factors (P&T well-field, etc)

• Low Attenuation Capacity

• Other (Institutional, Analytical, etc)

11

Constrained Mass Removal & Plume Persistence

Need to Determine Relative Significance of Each Factor, and Site-dependent Functionality

Long Known:

12

1989

Tucson International Airport Area Superfund

Site

• TCE/DCE Contamination Identified in 1981

• Site Placed on Superfund NPL in 1983

• Pump and Treat started in 1987 (south plume)

• Source-zone Remediation efforts [SVE, ISCO]

• UA Collaboration since 1993

13

Composite CMD: AFP44

1987

High-resolution Temporal Data set

Asymptotic conditions

Start Pump & Treat

14

Constrained Mass Removal & Plume Persistence

Question: What is the relative significance of each of the various Persistence/Attenuation factors for this site?

Conducted an integrated Laboratory, Field, and Modeling study

15

Plume-scale Modeling Effort

~50 km2

Known Inputs

Conduct series of scenario-testing sensitivity analyses

16

17

Impact of Transport Processes

K Variability & Diffusive Mass Transfer (back diffusion)

18

Impact of Transport Processes

Sorption-desorption (nonlinear, rate limited)

[Sims include physical heterogeneity] 19

Impact of Transport Processes Controlling Factor for Early Phase DNAPL in Source zones

20

Source-zone Architecture, DNAPL Dissolution, and Mass Removal

Multi-scale Investigations of Systems

21

APS

~6 mm ~10 cm ~2 m

Pore Core Intermediate

DNAPL Source Behavior Pore-scale Imaging: 10 um resolution

1 2 3 41

2 3

4

Desorption Control

NAPL Dissolution Control [1-4]: Non-uniform accessibility

No-NAPL Expt

2 3 4

2 3 4

Column Experiments

Rel

ativ

e C

once

ntra

tion

22

DNAPL Source Behavior

Flow-cell Experiments

DNAPL Sn Imaging

1

10

100

1000

10000

100000

0 20 40 60 80 100 120 140 160 180

Con

cent

ratio

n (m

g/L)

Pore Volume

Control- Homogeneous

Mixed Source

Heterogeneous

Heterogeneous-2

Laboratory Experiments - Known DNAPL distributions - Permeability variability - Measure DNAPL in situ

23

DNAPL Source Behavior

Variables:

• Domain size [20 vs 10,000 m2]

• Gradient & Q [natural vs induced]

• Initial DNAPL Mass

Field Data

0.0001

0.001

0.01

0.1

1

10

0 50 100 150 200

CM

D (K

g/d)

Time (month)

AFP44- 3

3 Hangers

Dover- Surf

24

Difficult to conduct comparative analysis

Data Analysis & Interpretation

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Frac

tiona

l Mas

s D

isch

arge

Red

uctio

n

Fractional Mass Reduction

1:1 (First order)

Minimal Reduction (efficient mass removal)

Maximal Reduction (inefficient mass removal)

0.001

0.01

0.1

1

0 5 10 15 20

Rel

ativ

e C

once

ntra

tion

or R

elat

ive

CM

D

Relative Time

1:1

Minimal Reduction

Maximal Reduction

- Employ contaminant mass discharge (CMD) metric

- Determine relationship between reduction in mass discharge and reduction in mass

- Enhances comparative analysis

25

DNAPL Source Behavior

Contaminant Mass Distribution [Accessibility] {source architecture, site age (mass removed)}

Field Data Flow-cell Experiments

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1

Frac

tion

Red

uctio

n in

CM

D

Fraction Reduction in Mass

TIAA-1

TIAA-2

Visualiz.

Dover-CSF

Dover-Surf

Borden-1

Borden-2

Increasing fraction of poorly accessible mass)

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1

Frac

tiona

l Red

uctio

n in

CM

D

Fractional Reduction in Mass

Control-homogeneous Mixed Source Heterogeneous-1 Heterogeneous-2

26

Post Source-zone Remediation

Persistence Factors:

• Residual DNAPL Sources (incomplete removal/containment)

• Plume-scale Lower-K Zones and Mass Storage (diffusive mass transfer- “back diffusion”)

• Plume-scale Sorbed-phase Mass Storage (sorption/desorption processes)

• Hydraulic Factors (P&T well-field, etc)

• Other (Institutional, Analytical, etc)

27

Composite CMD: AFP44

SVE Start

ISCO Start

1987

Impacts from Source Remediation efforts

Current CMD = 0.2 kg/d

Pre SZR CMD = 2 kg/d

~90% Reduction

ISCO End

SVE End

28

Plume Persistence after Source Remediation

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Con

tam

inan

t Mas

s D

isch

arge

(Kg/

d) Simulated-

Remediation Simulated- No Remediation Measured

Non-source Factors: *Plume-scale*

1. Mass in Lower-K Zones 2. Sorbed Mass 3. Hydraulic Factors (well field)

*Ideal case- all source mass removed

Predictions for AFP44 Site

0 2 4 6 8 10 12 14

Time (Y) 29

Lower-permeability Zones & Diffusion

0.001

0.01

0.1

1

10

100

0 5 10 15 20 25

Mas

s R

emai

ning

(%)

Relative Time

0 1 3.5 Modflow: Clay-Sand-Clay

Mass R

emoved (%

)

90

99

99.9

99.99

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1

Frac

tion

Red

uctio

n in

Mas

s D

isch

arge

Fraction Mass Reduction

Model Simulations

Stochastic (random K fields) vs.

Discrete (homogeneous, orthogonal) layers (MODFLOW)

30

0

1

3.5

Modflow: Clay-Sand-Clay

Variance of lnK

Well-field Configuration

0.001

0.01

0.1

1

0 5 10 15 20 25

Rel

ativ

e C

once

ntra

tion

Relative Time

3 longitudinal wells

3 downgradient (transverse) wells 9 uniform-dist wells

Natural gradient (equiv Q)

Model Simulations

3–Layer system (Clay-Sand-Clay) [MODFLOW]

31

Sorption-Desorption Processes

Extensive Elution Tailing

• Observed for all media

• Occurs with short contact times

• Need continuous-distribution domain model

Causative Mechanisms?

0.0000001

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

0 500 1000 1500 2000 2500 3000 3500 4000

Rel

ativ

e C

once

ntra

tion

Pore Volumes

Non-Linear, Rate-Limited Sorption

Linear, Rate-Limited Sorption

Non-Linear, Equilibrium Sorption

Measured

RLS >> NLS

Column Experiments

32

Sorption-Desorption Processes 1

Eustis 0.1

0.01

Progressive increase0.001

in resistance with increasing contact0.0001

time 0.00001

0.000001

0.0000001

2 PV

4 PV

8 PV

20 PV

100 PV

1000 PV

Aged 30 days

Aged 420 days

Aged 4 years

Interaction with Hard Carbon

[sorbate permeation within, and sorbate-induced deformation of,

the HC matrix]

1

0.1 Replication Exp 1

Exp 2

Exp 3

Rel

ativ

e C

once

ntra

tion

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Pore Volumes

98% quartz sand 2% clay (kaolinite- non-expanding) 0.38% organic carbon 0.14% hard carbon (kerogen, bc)

Rel

ativ

e C

once

ntra

tion Exp 4

0.01 Simulation

0.001

0.0001

0.00001

0.000001 Non-linear sorption Competitive sorption 0.0000001

0 500 1000 1500 2000 2500 3000 3500 4000

Pore Volumes 33

Sorption-Desorption Processes

98-80% quartz, feldspars 2-20% clay (montmorillonite- expanding) 0.03% organic carbon 0.02% hard carbon (kerogen, bc)

Non-linear sorption

Peak Shift = change in d-spacing

AFP 44 Sediment

XRD Analysis: several AFP44 samples and 2 (mont) specimen controls

Clay inter-layer d-spacing = ~0.3-0.6 nm TCE thickness = ~0.3 nm Increase in d-spacing for TCE treatment

= ~0.4 nm

TCE Intercalation [+ HCI]

No apparent aging effect

34

Summary: 3 Hanger Site at TIAA

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0 10 20 30 40 50 60

Con

tam

inan

t Mas

s D

isch

arge

(kg/

d)

Elapsed Time (month)

Hydraulic Source Control

Plume Reduction = ~50%

Identify Relevant Factors:

1. Low-K Zones and DMT 2. Source Residual 3. Well-field Configuration

[~2-3 pore volumes]

35

Measured Model Simulation

Summary: continued

• Source Zones- incomplete removal/containment of contamination, continuing source

• Large, Persistent Plumes- contributing factors

• Site “Architecture” and “Age” key factors – Subsurface properties (permeability field, flow field) – Contaminant distribution (phases, relative accessibility) – Change in contaminant distributions and accessibility as sites age

• Alternatives to P&T ?

• Long-term Site Management

36

Acknowledgements

• The many students and post-docs who have contributed to this research; our collaborators and partners with EPA, AECOM, US Air Force, CRA, Tucson Airport Authority, ADEQ.

• Financial support provided by the National Institute of Environmental Health Sciences Superfund Research Program (ES04940), the US Department of Defense Strategic Environmental Research and DevelopmentProgram (ER-1614), the US Air Force, and the Tucson Airport Authority

37

References • Brusseau, M.L.; Nelson, N.T.; Zhang, Z.; Blue, J.E.; Rohrer, J.; Allen, T. 2007. Source-Zone Characterization of a Chlorinated-Solvent Contaminated Superfund Site

in Tucson, AZ. J. Contam. Hydrol., 90:21-40.

• Brusseau, M.L., Hatton, J., and DiGuiseppi, W. 2011. Assessing the Impact of Source-Zone Remediation Efforts at the Contaminant-Plume Scale: Application to a Chlorinated-Solvent Site. J. Contam. Hydrol., 126:130-139.

• Brusseau, M.L., Carroll, K.C., Allen, T., Baker, J., DiGuiseppi, W., Hatton, J., Morrison, C., Russo, A., and Berkompas, J. 2011. The Impact of In-situ Chemical Oxidation on Contaminant Mass Discharge: Linking Source-zone and Plume-scale Characterizations of Remediation Performance. Environ. Sci. Technol., 45:5352-5358.

• Brusseau, M.L., Russo, A.E., and Schnaar, G. 2012. Nonideal Transport of Contaminants in Heterogeneous Porous Media: 9- Impact of Contact Time on Desorption and Elution Tailing. Chemosphere, 89:287-292.

• Brusseau, M.L. 2013. Use of Historical Pump-and-Treat Data to Enhance Site Characterization and Remediation Performance Assessment. Water Air Soil Poll., 224: article 1741.

• Brusseau, M.L. and Narter, M. 2013. Assessing the Impact of Chlorinated-Solvent Sites on Metropolitan Groundwater Resources. Groundwater, 51(6): 828-832.

• Brusseau, M.L.; Matthieu III, D.E.; Carroll, K.C.; Mainhagu, J.; Morrison, C.; McMillan, A.; Russo, A.; Plaschke, M. 2013. Characterizing Long-term Contaminant Mass Discharge and the Relationship Between Reductions in Discharge and Reductions in Mass for DNAPL Source Areas. J. Contam. Hydrol., 149: 1-12.

• Chorover, J. and Brusseau, M.L. 2008. Kinetics of Sorption-Desorption, pgs 109-149 in Kinetics of Water-Rock Interaction, S.L. Brantley, J. Kubicki, and A.F. White, Editors, Springer, New York, NY.

• DiFilippo, E.L. and Brusseau, M.L. 2008. Relationship Between Mass Flux Reduction and Source-zone Mass Removal: Analysis of Field Data. J. Contam. Hydrol., 98:22-35.

• DiFilippo, E.L., Carroll, K.C., and Brusseau, M.L. 2010. Impact of Organic-Liquid Distribution and Flow-Field Heterogeneity on Reductions in Mass Flux. J. Contam. Hydrol., 115:14-25.

• Johnson, G.R., Norris, D.K., and Brusseau, M.L. 2009. Mass Removal and Low-concentration Tailing of Trichloroethene in Freshly-amended, Synthetically-aged, and Field-contaminated Aquifer Material. Chemosphere, 75:542–548.

• Matthieu III, D.E., Brusseau, M.L., Johnson, G.R., Artiola, J.L., Bowden, M.L., Curry, J.E. 2013. Intercalation of Trichloroethene by Sediment-Associated Clay Minerals. Chemosphere, 90:459-463.

• Russo, A., Johnson, G.R., Schnaar, G., and Brusseau, M.L. 2010. Nonideal Transport of Contaminants in Heterogeneous Porous Media: 8. Characterizing and Modeling Asymptotic Contaminant-Elution Tailing for Several Soils and Aquifer Sediments. Chemosphere, 81:366-371.

• Schnaar, G. and Brusseau, M.L. 2006. Characterizing pore-scale dissolution of organic immiscible liquid in natural porous media using synchrotron X-ray microtomography. Environ. Sci. Technol., 40:6622-6629.

• Zhang, Z. and Brusseau, M.L. 1999. Nonideal Transport of Reactive Solutes in Heterogeneous Porous Media: 5. Simulating Regional-Scale Behavior of a Trichloroethene Plume During Pump-and-Treat Remediation. Water Resour. Res., 35: 2921-2935. 38