Permeable Reactive Zones for Groundwater Remediation

Permeable Reactive Zones for
Groundwater Remediation
Richard T. Wilkin * , Ph.D.
waste
PRB
treated
water
Office of Research and Development
*National Risk Management Research Laboratory, Ground Water and Ecosystems Restoration Division, Ada, OK
July 2008
NARPM

Outline of Topics
•Technology Background
•Field Case Examples – focus on COCs
‣Zerovalent Iron (Cr, TCE, As)
‣Organic Carbon (NO 3 , Pb, pH)
‣Mechanisms
•Summary Remarks
1

Permeable
Reactive
Zones
GROUNDWATER REMEDIATION
Zerovalent
Iron: Solvents,
Inorganics
Advantages
• Subsurface Treatment
• Plume capture complete
• Passive treatment
• Lower costs/P&T
• Adaptable
• Focused monitoring
Limitations
• Greater capital investment
• Longevity concerns
‣Treatment performance
‣Hydraulic performance
Cr, TCE
As?
2

Depth of PRZ Installations
Number of Installations
16
14
12
10
8
6
4
2
0
0-9 10-19 20-29 30-39 40-49 50-59 60-69 70-79 >80
Depth of PRB Installation, ft bgs
3

• Long-term performance evaluations at full-
scale zero-valent iron and organic carbon-based
based
reactive barriers
- Geochemical-Hydrologic
Hydrologic-Microbiological
-
• Pilot demonstrations to examine new
applications of the technology ( (e.g. e.g., , Arsenic, Lead)
• Laboratory studies that explore fundamental
geochemical processes important in PRBs
• Technical Assistance
PRB Research at EPA
4

Iron/Water/Contaminant
Interactions
• Increase in pH (~10), Decrease in Eh ( FeOOH, , adsorption
- Precipitate metal hydroxides
- Metal plating reactions (Hg)
- Precipitate Ca and Fe carbonates
- Microbiology: Sulfate-reducers
Precipitate Fe sulfides, Me sulfides
- Fe 0 => Green Rust => Magnetite
5

Role of Secondary
Precipitates
a
Fe
10 um
Pore infilling – hydraulics
Coat ZVI surfaces – reactivity
Creates secondary reactivity
Govern long-term performance
Control degradation
mechanisms
Qtz
20 um
Can be predicted!
Qtz
Fe
SEM/TEM
6
b
Fe

Total
Dissolved
Solids
Longevity
TDS
7

ZVI Examples
Elizabeth City, NC
Cr and TCE
Full scale installed in 1996
150 ft length, 2 ft wide, 25 ft deep
Trencher
East Helana, MT
As
pilot-scale installed 2005
30 ft length, 6 ft wide,
45 ft deep
Long-arm excavator
8

Chromium – Elizabeth City
-3.0
-3.5
PRB
location
1997
1998
2001
2003
Ground-water flow
2005
2007
Depth, meters below ground surface
-4.0
-4.5
-5.0
-5.5
-6.0
-6.5
-7.0
-0.1000
0.2125
0.5250
0.8375
1.150
1.462
1.775
2.087
2.400
Chromium mg/liter
9
0 1 2 3 0 1 2 3 0 1 2 3 0 1 2 3 0 1 2 3 0 1 2 3
Distance, meters
Transect 2
~40 wells

TCE – Elizabeth City
Depth, meters below ground surface
-3.0
-3.5
-4.0
-4.5
-5.0
-5.5
-6.0
-6.5
-7.0
PRB
location
2002
2003
2004
2005
Ground-water flow
2006
2007
TCE ug/liter
0
100.0
200.0
300.0
400.0
500.0
600.0
700.0
800.0
900.0
1000
>1000
10
0 1 2 3 0 1 2 3 0 1 2 3 1 2 3
Distance, meters
0 1 2 3 0 1 2 3

TCE – Downgradient of PRB
40
Frequency of TCE detects in downgradient
transect
30
Frequency
20
10
0
0 25 50 75 100 125 150 175 200 225 250
TCE, ug/L
2002-2007
11

East Helena SF site
East Helena SF site
12
N
300 m

PRB
Source
Isolation
GW
flow
13

Arsenic Concentrations
5
4
Upgradient Concentration
25 mg/L
Wells in PRB
Arsenic, mg/L
3
2
1
n=24
n=19 n=25
0
14
0 5 10 15 20 25 30
Months of Operation

Arsenic Flux
• Discrete interval
sampling, concentrations
• Discrete interval
hydraulic conductivity
determinations
• Continuous
water levels/gradient,
3-point problem
Base of
PRB
15

East Helena
Conclusions
• Zerovalent iron is effective for arsenic
• Arsenic removal mechanisms are
complex
• Finite uptake capacity requires detailed
site assessments
• Source control measures are desirable to
reduce subsurface arsenic flux and
maximize PRB lifetime
16

PRB Research:
Carbon-Based Reactive Media
o Arsenic: Columbia Nitrogen Superfund Site,
Charleston, SC (Compost + Limestone + Iron)
o Lead: Delatte Superfund Site, Ponchatoula, LA
(Cow Manure; Wood Chips, Limestone)
o Nitrate: Cimarron Pork hog farm, Stillwater, OK
(Haystraw)
o TCE: Altus AFB, OK (Cotton Burr)
17

Mechanisms in Carbon
Systems
Media options
(Cost vs. Longevity vs. Reversibility)
• Metals:
Sulfate reduction
Precipitation of CdS, ZnS, , and PbS
Co-ppt
ppt/adsorption with FeS
Interactions with OC
• Degradation of nitrate/perchlorate
• Organics:
Abiotic pathways, iron sulfides
Biotic pathways
18

Background - Cimarron Pork
• Concentrated Animal Feeding Operation site located in OK
• Facility in operation for approx. 7 y, closed in 1999; ground-water
impact from leaking lagoon
• Ground water remediation strategy developed for separate
ammonia and nitrate plumes
• Remedies implemented in late 2002 (site owner, OK Dept.
Agriculture, EPA Region 6)
• EPA ORD began monitoring of
Nitrate PRB in 2003
‣ Performance evaluation
‣ Longevity issues
19

Contaminant Plumes
MW6
MW9
MW10
MW7
MW3
MW13A
MW13B
MW8
MW31
MW34
MW35
MW11
NH 4 -N
Old
Lagoon
MW17
NO 3 -N 100
75
MW12
MW14
50
300
MW5
200
100
150
MW4
MW2
MW30
50
MW16
MW15
MW1
25
MW18
20
MW29
200 ft

Site Remediation Plan
MW6
NORTH
MW31
MW17
MW7
MW10
MW34
MW35
MW11
MW3
MW13A
MW13B
MW5
MW9
Old
Lagoon
MW8
Evaporation
Basin
MW23
MW32
MW30
MW29
MW14
MW16
MW15
MW12
MW2
MW4
MW18
MW1
MW21
MW22
MW26
MW20
MW33
MW28
MW19
MW27
MW24
MW25
Observation Well Locations
Pumping Well Locations
Access Well Locations
Nitrate Reactive Barrier
Ammonia Remediation Trench
21

22
PRB Installation

80
Nitrate
Nitrate-N, mg/L
Nitrate-N, mg/L
Nitrate-N, mg/L
60
40
20
0
80
60
40
20
0
80
60
40
20
T2A
T1A
T2E
T1E
upgradient
0 10 20 30 40 50 60
T2av
T1av
PRB
0 10 20 30 40 50 60
downgradient
‣ Average % removal
ranges from 10 (T1) to
99 (T2), based on
influent & effluent
‣ Nitrate removal within
PRB is 92 – 100%,

Denitrification
2NO 3
-
2NO 2
-
2NO N 2 O N 2
Nitrate ions
(+5)
Nitrite ions
(+3)
2NH 4
+
Nitric oxide
(+2)
Nitrous oxide
(+1)
Dissimilatory
Nitrate reduction
to ammonia
(under low electron acceptor conditions,
i.e., C>>>NO 3 - )
Dinitrogen
gas (0)
24

Heterotrophic Denitrification
5CH 2 O + 4NO 3- = CO 2 + 2N 2 + 3H 2 O + 4HCO 3
-
4000
3500
Mean DOC values in transect wells
DOC, mg/L
3000
2500
2000
1500
Mean DOC values in cluster
Wells, n = 14
Decrease in
capacity from
~2200 to 38 mg/L
Nitrate-N
To N 2,
based on reaction
stoichiometry
1000
~40 mg/L
500
0
25
0 5 10 15 20 25 30 35 40
Months of Operation

Downgradient Response
MW34 – center location
20
15
Potassium source from haystraw
K, mg/L
10
5
56 ft travel
in
510 days
0
Nitrate-N, mg/L
36
30
24
18
12
6
0
0 5 10 15 20 25 30 35 40
~ 0.11 ft/day
Seepage velocity
0 5 10 15 20 25 30 35 40
Months of Operation
26

27
0
1
2
3
4
5
6
7
8
TEPA
1-A
TEPA
1-B
TEPA
1-C
TEPA
1-D
TEPA
1-E
TEPA
1-G
TEPA
1-H
Apr-04
Oct-04
Jun-05
Apr-06
Apr-07
Apr-08
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
20.0
TEPA
1-A
TEPA
1-B
TEPA
1-C
TEPA
1-D
TEPA
1-E
TEPA
1-G
TEPA
1-H
Apr-04
Oct-04
Jun-05
Apr-06
Apr-07
Apr-08
pH
Pb,
ug/L
upgradient PRB downgradient
Delatte
Delatte Metals PRB
Metals PRB

Dissolved Organic Carbon - Performance
upgradient
downgradient
100
90
DOC,
mg/L
80
70
60
50
40
30
20
Apr-04
Oct-04
Jun-05
Apr-06
Apr-07
Apr-08
10
0
TEPA
1-A
TEPA
1-B
TEPA
1-C
TEPA
1-D
TEPA
1-E
TEPA
1-G
TEPA
1-H
28

Summary Remarks
• Many case studies show consistent degradation of
contaminants over years
• Need for coupling PRZs with source control measures
• Reactive medium options
• Design for highest concentrations – flux based evaluations
• Site Characterization!
– ZVI (ground water chemistry/hydrology)
– Organic Carbon (DOC concentrations)
– Flux based
• More information: wilkin.rick@epa.gov
– (http://www.epa.gov/ada/publications/html)
29

Acknowledgements
• EPA – Cindy Paul, Steve Hutchins, Ralph Ludwig,
Robert Puls, John Wilson, Tony Lee, Steve Acree,
Randall Ross
• Sam Lien, Tom He, Doug Beak (post-docs)
• EPA Regions 8, 6, 4
• U. S. Coast Guard
• Shaw Environmental
• Asarco, Inc.
• Argonne National Laboratory
30

Technical Assistance
• Ground Water Technical Support Center
• Dr. David S. Burden,
Director(burden.david@epa.gov
burden.david@epa.gov)
580-436
436-8606
QUESTIONS ????
31