United States
Environmental Protection
Agency
Office of Research and
Development
Washington, DC 20460
EPA/625/K-98/001
September 1998
&EPA
Seminars
Monitored Natural
Attenuation for
Ground Water
September 2-3, 1998Philadelphia, PA
September 14-15, 1998Denver, CO
September 16-17, 1998Chicago, IL
October 14-15, 1998Kansas City, MO
November 2-3, 1998Dallas, TX
November 16-17, 1998Atlanta, GA
December 2-3, 1998Seattle, WA
December 8-9, 1998Boston, MA
December 14-15, 1998San Francisco, CA
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EPA/625/K-98/001
September 1998
Seminars on
Monitored Natural Attenuation for
Ground Water
Office of Research and Development
U.S. Environmental Protection Agency
Washington, DC
Printed on recycled paper.
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Notice
Mention of trade names or commercial products does not constitute endorsement or recommendation
for use.
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Contents
Background on Monitored Natural Attenuation (MNA) 1-1
EPA Policy on Use of MNA for Site Remediation 1-3
Trends in the Use of MNA 1-7
Framework for Use of MNA 1-13
Biological and Geochemical Context for MNA 2-1
Biological Processes 2-3
Natural Attenuation of Petroleum Hydrocarbons in Ground Water 2-5
Natural Attenuation of Oxygenates in Ground Water 2-7
Natural Attenuation of Chlorinated Solvents in Ground Water 2-15
Natural Attenuation of Metals in Ground Water 2-17
Geochemical Processes 2-23
Geochemical Processes and Natural Attenuation 2-25
Redox Zonation and Biodegradation Efficiency 2-29
How Hydrogeology Affects the Efficiency of Natural Attenuation 3-1
Site Characterization and Data Interpretation for Evaluation of Natural Attenuation at
Hazardous Waste Sites 4-1
Estimating Biodegradation and Attenuation Rate Constants 5-1
Risk Management of MNA 6-1
Sampling, Analysis, and Monitoring to Evaluate MNA 7-1
Site Characterization 7-3
Verification and Long-term Monitoring 7-15
Criteria for Success 8-1
in
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Acknowledgements
This seminar series was funded by the U.S. Environmental Protection Agency's (USEPA's) Office of
Solid Waste and Emergency Response (OSWER). The seminar was developed and presented by
Drs. Francis Chapelle (U.S. Geological Survey [USGS]), Kelly Hurt (National Research Council),
Fran Kremer (USEPA's Office of Research and Development [ORD]), and John Wilson (ORD). Input on
the seminar was received from OSWER and the Regional Offices, including program efforts under the
Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), Resource
Conservation and Recovery Act (RCRA), and the Underground Storage Tank (UST) program.
Special thanks to Ken Lovelace, Guy Tomassoni, Hal White, and the Ground Water Forum for their
contributions. The series presentations represent a collaborative effort between USEPA and USGS.
Special thanks also to Herb Buxton of USGS for supporting this effort as well as the following
USGS staff for their time and effort in presenting portions of these seminars: Richard Dinicola,
Stephen Garabedian, James Landmeyer, Roger Lee, Peter McMahon, and John Schumacher. Thanks
to Joan Colson (ORD) for her assistance in coordinating these seminars and to the staff at Eastern
Research Group, Inc. (John Bergin, Mara Evans, Nick Kanaracus, Susan Brager Murphy,
Beth O'Connor, and Meg Vrablik) for all their help in providing the logistical support to implement
these seminars.
IV
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Sources of Information
Recent EPA Bioremediation Publications
http://www.epa.gov/ORD/WebPubs/biorem/
Bioremediation in the Field Search System: Database on national and some international field
applications
Version 2.1 EPA/540/R-95/508b (Revised)
Also on the Internet
Request to be on EPA's bioremediation mailing list or to request specific bioremediation documents
513-569-7562
NRMRL/SPRD Home Page
http://www.epa.gov/ada/kerrlab.html
OUST Home Page with links to OSWER Policy Directives
http://www.epa.gov/swerust1/directiv/index.htm
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Background on Monitored
Natural Attenuation
Seminar Series on Monitored Natural Attenuation for Ground Water
1-1
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EPA Policy On
Use of Monitored Natural
Attenuation For Site
Remediation
Background on Directive
EPA's Office of Solid Waste and Emergency Response
(OSWER) developed Policy Directive: Use of
Monitored Natural Attenuation at Superfund, RCRA
Corrective Action, and Underground Storage Tank Sites,
Directive 9200.4-17, December 1, 1997.
Clarifies EPA's position on use of monitored natural
attenuation (MNA) for remediating contaminated sites.
Not intended to be a detailed technical guidance.
Does not deal with legal or administrative issues (e.g.,
property transfer, NPL deletion).
How To Obtain Directive
EPA Definition
iRCRA, Superfund Hotline: 1-800-424-9346
iOUST Home Page
HVIore Information
>Policy Directive
> http://www.epa.goV/swerust1/d irectiv/9200_417. htm
Monitored Natural Attenuation (MNA):
... the use of natural attenuation processes
within the context of a carefully controlled and
monitored site cleanup approach that will reduce
contaminant concentrations to levels that are
protective of human health and the environment
within a reasonable time frame.
MNA Processes
MNA Processes
i Physical, chemical, or biological processes that
act without human intervention to reduce the
mass, toxicity, mobility, volume, or
concentration of contaminants.
i Includes biodegradation, dispersion, dilution,
sorption, volatilization, and chemical or
biological stabilization or destruction of
contaminants.
EPA prefers those processes that degrade
contaminants and expects that MNA will be
most appropriate where plumes are stable.
Some processes have undesirable results, such
as:
> Creation of toxic daughter products, or
> Transfer of contaminants to other media.
Seminar Series on Monitored Natural Attenuation for Ground Water
1-3
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Role of MNA in OSWER
Remediation Programs
iALL remedies must protect human health
and the environment.
i NOT a "walk away" or "do nothing" option.
i NOT a "default" or presumptive remedy.
Role of MNA in OSWER
Remediation Programs
Site-specific, risk-based decisions are
essential. MNA is an active choice although it is
a passive remediation technology.
Proponent must demonstrate that MNA is the
appropriate option, not the implementing
agency.
Demonstrating the Efficacy of MNA
Three types of site-specific information may
be required:
1. Historical ground water and/or soil chemistry data
demonstrates trend of declining contaminant
concentration.
2. Hydrogeologic and geochemical data that demonstrate
NA processes and rates.
3. Field or microcosm studies.
Unless #1 is of sufficient quality and duration,
#2 is generally required (regulatory decision).
Sites Where MNA May Be
Appropriate
i MNA is appropriate as remedial approach only
where it:
> Can be demonstrated to achieve remedial
objectives within reasonable time frame, and
> Meets the applicable remedy selection criteria for
the particular OSWER program.
Sites Where MNA May Be
Appropriate
i MNA will typically be used in conjunction with
active remediation measures (e.g., source
control) or as follow-up to such measures.
i MNA should not be used where such an
approach would result in significant
contaminant migration or unacceptable impacts
to receptors.
Reasonable Time Frame
Time frame should not be excessive compared
to that required for other remedies.
Reasonable time frame is a site-specific
decision.
Seminar Series on Monitored Natural Attenuation for Ground Water
1-4
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Reasonable Time Frame
Remediation of Sources
Some factors that impact "reasonableness" of
time frame include:
> Current and potential future uses of affected ground
water,
* Relative time frame in which aquifer may be needed,
* Public acceptance of extended time for remediation,
> Reliability of monitoring and institutional controls,
adequate funding overtime required to reach
cleanup objectives.
> Regional resource issues
i EPA expects that source control measures will be
evaluated for all sites and implemented at most
sites where practicable.
i Measures include removal, treatment or
containment of sources.
i Source control is especially important where MNA
is part of the remedy.
i Appropriate source control actions are high
priority and should be implemented sooner rather
than later in site response.
Performance Monitoring
Contingency Remedies
i Required to gauge effectiveness and protect
human health and the environment.
i Of even greater importance for MNA remedies
because longer cleanup time frames are generally
involved.
i Must demonstrate that NA is occurring as
expected, identify transformation products, detect
plume migration, and verify no impact to receptors.
i Required for as long as contamination levels
remain above cleanup goals.
A cleanup technology or approach that will
function as a "backup" in the event that MNA
fails to perform as anticipated.
Contingency measures are especially important
when MNA is selected based primarily on
predictive analysis (i.e., uncertainty is greater
than when based on historical data).
"Triggers" should be established which signal
unacceptable performance of the MNA remedy.
Summary
Summary
i MNA is appropriate at many but NOT all sites.
i NOT a "no action," "default" or "presumptive"
remedy.
i Should NOT result in significant contaminant
migration or unacceptable impacts to
receptors.
i Progress should be carefully monitored.
i Contingency measures should be included
when selection of MNA was based mostly on
predictive analysis.
i A cleanup is NOT completed until cleanup
objectives, set by the implementing Agency,
have been met.
Seminar Series on Monitored Natural Attenuation for Ground Water
1-5
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Where to Find the OSWER MNA
Directive and Technical Updates
ihttp://www.epa.gov/swerust1/directiv/9200_417.htm
i http://www.epa.gov/ORD/WebPubs/biorem
(case sensitive)
Seminar Series on Monitored Natural Attenuation for Ground Water
1-6
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Trends in the Use of Monitored
Natural Attenuation
Seminar Series on Monitored Natural Attenuation for Ground Water
1-7
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Trends in the Use of MNA
Fran Kremer
US EPA
Office of Research and Development
National Risk Management Research Lab
Cincinnati, OH
Programs that May Look at
Natural Attenuation in Cleanup
UST
CERCLA
RCRA
State Voluntary Cleanup Programs
Brownfields Sites
How Has Natural Attenuation
Been Used?
Variety of sites, including MLFs,
industrial LFs, refineries, recyclers,
etc.
At all but six sites, natural
attenuation used in combination with
active remedy components
Often have low exceedences of
cleanup levels
Contingencies for active measures
MNA Groundwater RODs
Contaminants Present at Sites for
which Natural Attenuation was
Specified
PCBs, Pesticides 1
PAHs, Phenols f
BTEX. MTBE
Solvents
1
Inoreanics
T]
p
|
, L
10 15 20 25 30
Number of Sites"
*Some sites have more than one contaminant
Contaminants Present at Sites for
which Natural Attenuation was
Specified
Coal Gassification
Fuel Storage
Junkyard
-
Metal Plating/Mining
Chemical/ Industrial Mfg.
Municipal Landfill
I
i
i
P
II
1
Seminar Series on Monitored Natural Attenuation for Ground Water
1-9
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LUST Groundwater Remediation
Technologies, FY97
Pump and Treat 8879
25%
Air Sparging 5577
16%
In Situ Bio 2971
8%
LBiosparging 1941
5%
Soil Remediation Technologies
at UST Sites, FY97
30
25-
20
15
10
;/
Office of Underground Storage Tanks, 1998
Occurrence of MTBE by
Geographical Area
Maximum MTBE Concentrations
Exceed 1 mg/L at:
-47% of 251 California sites
- 63% of 153 Texas sites
-81% of 41 Maryland sites
T. Buscheck, et al.
MTBE Occurrence at Northern
California Sites
D Operating (182 Sites) D Non-Operating (136 Sites)
35 35 -u
35
30
2*>
20
15
10
5
IV
L
6
3
r
r
n
|_
j2
_
=?
12
* It
t ra
ND <35 35-1000 1,000- >10,000
(detected) 10,000
Highest MTBE Concentration (ug/L)
T. Buscheck, et al.
MTBE Occurrence at Southern
California Sites
D Operating (182 Sites) D Non-Operating (136 Sites)
35
30
| 25
2 20
i 1S
10
5
16|
L
2n
'
4
C
^4
^=r
3f
^
32
i
2(1
I/
4
TJ
ND <35 35-1000 1,000- >10,000
(detected) 10,000
Highest MTBE Concentration (ug/L)
MTBE Occurrence at Texas
Sites
1 Operating (153 Sites) D Non-Operating (75 Sites)
35
30
J 25
1 2°
I 1S
° 10
5
0
ND <35 35-1000 1,000- >10,000
(detected) 10,000
Highest MTBE Concentration (ug/L)
T. Buscheck, et al.
T. Buscheck, et al.
Seminar Series on Monitored Natural Attenuation for Ground Water
1-10
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MTBE Occurrence at
Maryland Operating Sites
4Sf
40
35
= 20
* 15
10
5
O
D Operating (41 Sites)
44
-VI-
ND 35-1000 >10,000
Highest MTBE Concentration (ug/L)
MTBE Occurrence at Florida
Sites
D Operating (21 Sites) D Non-Operating (7 Sites)
45|
40
$ 35
X 30
ND <35 35-1000 1,000- >10,000
(detected) 10,000
Highest MTBE Concentration (ug/L)
T. Euscheck, et al.
T. Buscheck, et al.
Seminar Series on Monitored Natural Attenuation for Ground Water
1-11
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Framework for Use of Monitored
Natural Attenuation
Seminar Series on Monitored Natural Attenuation for Ground Water
1-13
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Framework for Use of MNA
Fran Kremer
US EPA
Office of Research and Development
National Risk Management Research Lab
Cincinnati, OH
Potential Advantages of MNA
Generation of lesser volume of
remediation wastes, reduced
potential for cross-media transfer of
contaminants, & reduced risk of
human exposure to contaminated
media
Less intrusion
Potential for application to all or part
of given site
Potential Advantages of MNA
Use in conjunction with, or as a
follow up to, other (active) remedial
measures
Lower overall remediation costs than
those associated with active
remediation
Potential Disadvantages of MNA
Longer time frame may be required
to achieve remediation objectives
Site characterization may be more
complex and costly
Toxicity of transformation products
may exceed that of the parent
compound
Long term monitoring
Potential Disadvantages of MNA
Institutional controls may be
necessary to ensure long-term
productiveness
Potential for contaminant migration
Possible renewed mobility of
previously stabilized contaminants
More extensive education and
outreach efforts
Two Basic Questions for
Bioremediation
When to start?
When to stop?
Seminar Series on Monitored Natural Attenuation for Ground Water
1-15
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When to Stop Active Remedial
Processes
When active treatment no longer
doing any good
When active treatment is no faster
than MNA
Contaminant Releases
> Migrate from source area
> Area of contamination expands until
equilibrium reached
> MNA equals source output
When/Where is Equilibrium
Reached?
Site factors- soil type, precipitation
influx
Contaminant factors- solubility,
concentration, carrier...
Equilibrium
> Eventually, MNA exceeds rate of
source output, and concentration of
contaminant(s) stabilizes or
decreases
> Importance of source control as the
primary remedial alternative
Source Control
"Source control actions should use
treatment to address "principal
threat" wastes (or products)
wherever practicable, and
engineering controls such as
containment for waste (or products)
that pose a relatively low long-term
threat or where treatment is
impracticable"
Monitoring Strategies
Three kinds of monitoring
-1. Site characterization to describe
disposition of contamination and
forecast its future behavior.
-2. Validation monitoring to determine
whether the predictions of site
characterization are accurate.
-3. Long-term monitoring to ensure that
the behavior of the contaminant plume
does not change
Seminar Series on Monitored Natural Attenuation for Ground Water
1-16
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Developing Conceptual Model
Determine nature and 3-D extent of
contamination
Determine site processes mobilizing
contaminants
Determine factors influencing
contaminant movement pathways
Determine changes in contaminant
location and concentration with time
Determine the point(s) of attainment
Determine Nature and 3-D
Extent of Contamination
Contaminants
Contaminant properties
- P/C-solubility, volatility, Henry's Law,
sorption coefficients, pH
-Bio-degradation potential, required
redox, electron acceptors/donors, by-
products
Determine Nature and 3D...(cont)
Contaminant location- where are
they, how far have they moved,
define in 3-D
Contaminant concentration
Contaminant form/phase-solid,
NAPL, vapor, adsorbed, dissolved
Determine Processes
Mobilizing Contaminants
Volatilization
Leaching
Mobile NAPL-gravity, water table
fluctuations, GW flow
Dissolution in GW
Determine Factors Influencing
Contaminant Movement Pathways
Lithology
Hydrogeology-flow rates, flow paths,
gradients
Determine Changes in
Contaminant Location and
Concentration with Time
Soil concentrations
NAPL movement
Changes in dissolved fraction
Seasonal fluctuations
Seminar Series on Monitored Natural Attenuation for Ground Water
1-17
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Points of Attainment
Predictive Models
> Given 3-D extent of contamination,
will natural attenuation be
protective?
> Develop model
Use of site specific data to predict
the fate and transport of solutes,
given the controlling physical,
chemical and biological processes
Results of the modeling only as good
as the data input
Several solute fate and transport
models available
How to Improve Understanding
& Implementation of MNA
Control/treat/remove sources
Thoroughly monitor plume and
downgradient areas
Include contingencies for other
measures if MNA fails to meet
desired goals
Involve regulatory agencies early in
process
How to Improve Understanding
& Implementation of MNA
Communicate that MNA is a responsible,
managed remediation approach(not a walk
away)
Present site-specific data and analysis
that demonstrate occurrence
Develop defensible conceptual model
supporting MNA
Build defensible predictive models, where
appropriate
Natural Attenuation
Burden of proof is on the proponent,
not the regulator
Not a default technology or
presumptive remedy
Not complete until goals of the
regulatory agency have been
reached to their satisfaction
Seminar Series on Monitored Natural Attenuation for Ground Water
1-18
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Biological and Geochemical
Context for Monitored Natural
Attenuation
Seminar Series on Monitored Natural Attenuation for Ground Water
2-1
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Biological Processes
Seminar Series on Monitored Natural Attenuation for Ground Water
2-3
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Natural Attenuation of Petroleum
Hydrocarbons in Ground Water
John T. Wilson
Office of Research and Development
National Risk Management Research Laboratory
U.S.Environmental Protection Agency
Cincinnati, Ohio
Patterns of Natural Bioremediation
Limited by supply of a soluble electron
acceptor
- Aerobic respiration
- Nitrate reduction
- Sulfate reduction
Controlled by mixing processes
(bioplume)
Patterns of Natural Attenuation
Patterns of Natural Attenuation
Limited by biological activity
- Iron reduction
- Methanogenesis
- Sulfate reduction
First-order kinetics
Lines of Evidence
Limited by supply of electron donor
Reductive dechlorination
Controlled by supply of electron donor
Documented Occurrence of
Natural Attenuation
Documented loss of contaminants at
the field scale
Use geochemical data to support natural
attenuation
Geochemical indicators
Laboratory microcosm studies,
accumulation of metabolic end-
products, volatile fatty acids, FAME
Trends during biodegradation (plume interior
vs. background concentrations)
- Dissolved oxygen concentrations below background
- Nitrate concentrations below background
- Iron (II) concentrations above background
- Sulfate concentrations below background
- Methane concentrations above background
Seminar Series on Monitored Natural Attenuation for Ground Water
2-5
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Total Assimilative Capacity
Calculation of BTEX destroyed from changes in
the concentrations of:
Oxygen
Nitrate
Iron II
Sulfate
Methane
Total Assimilative Capacity
Calculations are most appropriately used to
rationalize degradation of BTEX that appears to
have already happened in the field
Calculations are usually not appropriate to
predict future degradation of BTEX in existing
contamination
Total Assimilative Capacity
Calculations reveal:
Assimilative Capacity that was used
Not Assimilative Capacity remaining
Total Assimilative Capacity
Oxygen
Denitrification
Iron Reduction
Sulfate reduction
Methanogenesis
1,920ug/L
1,680ug/L
2,550 ug/L
21,OOOug/L
2,560 ug/L
Total Assimilative Capacity = 29,710 ug/L
Relative Importance of Biodegradation
Mechanisms at 25 Fuel Spill Sites
Denitrification
14%
Sulfate Reduction
29%
Methanogenesis
39%
Total Assimilative Capacity
Greatest sources of error:
Under-estimates contribution of iron reduction.
Assumes all the electron acceptor demand is
BTEX.
Native organic matter (TOC) may have an
important electron acceptor demand.
Seminar Series on Monitored Natural Attenuation for Ground Water
2-6
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Natural Attenuation of Oxygenates
in Ground Water
John T. Wilson
Office of Research and Development
National Risk Management Research Laboratory
U.S.Environmental Protection Agency
Cincinnati, Ohio
Natural Attenuation of
MTBE in Ground Water
Natural Attenuation of MTBE in Ground Water
under methanogenic conditions
Depletion of MTBE and Benzene down gradient
of the source area at the U.S. Coast Guard
Support Center at Elizabeth City, N.C.
The source is a spill of JP-4 jet fuel from an old
fuel farm in the flood plain of the Pasquotank
River. The source area is located on the
following map
GW Flow Direction Approximate Scale In F(
GW Flow Direct!
Elizabeth City, North Carolina
Elizabeth City, North Carolina
Seminar Series on Monitored Natural Attenuation for Ground Water
2-7
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Natural Attenuation of MTBE in Ground Water
under methanogenic conditions
Conditions in the source area (CPT-1)
GW Flow Direction Apt
Elizabeth City, North Carolina
- Water Table
Non Permeable Material
Permeable Material
Elevation
(feet)
0.01
0.02
0.03
0.04
Hydraulic Conductivity
(cm/sec)
Oil Lens
Ground water flow
Elevation
(feet)
-5- '
-10-
-15"
-20--
10000 20000 30000
TPH
(mg/kg)
Seminar Series on Monitored Natural Attenuation for Ground Water
2-8
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In many floodplain landscapes, the most
important transfer of contaminants from
LNAPL to ground water is through
diffusion from the LNAPL to transmissive
layers in the aquifer, rather than through
dissolution and direct advection.
This suggests an approach to estimate
the impact of spills of petroleum
hydrocarbons on ground water.
Oil Lens
Diffusion Gradient
Ground water flow
Elevation
(feet)
10
Elevation
(feet) .5
0.01
0.02
0.03
0.04
Hydraulic Conductivity (cm/sec)
0 5 10
MTBE
(mg/liter)
15
0 2 4 6 8 10 12 14 16
MTBE at Source Area CPT-1
(mg/liter)
Natural Attenuation of MTBE in Ground Water
under methanogenic conditions
Conditions down gradient of the source area,
beyond the edge of the LNAPL at ESM-14
GW Flow Direct!
Elizabeth City, North Carolina
Seminar Series on Monitored Natural Attenuation for Ground Water
2-9
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Hydraulic Conductivity (cm/sec)
0.01 0.02 0.03 0.04 0.05 0.06 0.07
-I 1 1 1 1 I-
MTBE (ug/L)
10
Elevation
(feet)
800
GW Flow Direction Approximate Scale In F(
Elizabeth City, North Carolina
Location MTBE Benzene
(mg/liter)
CPT-2 0.47
CPT-1 3.9
CPT-5 0.71
ESM-14 0.38
ESM-10 0.024
GP-1 0.001
Methane
0.033
2.3
1.6
0.39
0.47
0.015
0.57
6.1
10.6
9.2
8.5
2.3
Location DO
CPT-2 1 3
CPT-1 0.0
CPT-5 0.0
boM-14 U.I
ESM-10 1.1
GP-1 0.1
Sulfate Nitrate Iron II
35 3 <0 1 26
10.9 <0.1 22.8
<0.1 <0.1 47.3
<0.1 <0.1 68.8
<0 1 <0 1 91 5
<^~^ Oil Lens ^~T^^~
*_ _-
I I I I I
1 I 1 1 J
> Ground water flow
Seminar Series on Monitored Natural Attenuation for Ground Water
2-10
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Oil Lens
J 1 J
Aquifer
Natural Attenuation of MTBE in Ground Water
under methanogenic conditions
By the time ground water had moved entirely
underneath the LNAPL, soluble electron
acceptors were depleted, Methane and Iron II
were accumulating, and the ground water
contained high concentrations of MTBE and
BTEX.
Natural Attenuation of MTBE in Ground Water
under methanogenic conditions
The highest hydraulic conductivity and the
hydraulic gradient were used to estimate travel
time between monitoring locations along the
flow path.
A linear regression of the Natural Logarithm of
MTBE concentration against time of travel
predicts a first order rate in the field of
-3.0 per year.
1 1.5 2
Travel time (years)
Natural Attenuation of MTBE in Ground Water
under methanogenic conditions
Core material was acquired from the more
conductive depth intervals at location MW-14.
Microcosms were constructed with:
MTBE alone, and an autoclaved control
MTBE plus BTEX, and an autoclaved control
10000
=d 1000 --
100 --
-100 0 100 200 300 400 500
Time (Days)
Seminar Series on Monitored Natural Attenuation for Ground Water
2-11
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10000
1000--
100-
10
Controls
MTBE with BTEXTMB
-100 0 100 200 300 400 500
Time (Days)
Rate of Natural Biodegradation of MTBE under
methanogenic conditions in microcosms
Treatment
Rate
Upper
Q5%
Lower
Q5%
per year
MTBE alone -3.21 -3.72 -2.70
MTBE plus -2.62 -2.Q5 -2.30
BTEXXXTMB
Rates of removal in controls subtracted
Natural Attenuation of MTBE in Ground Water
under methanogenic conditions
The rate of attenuation in the field is in good
agreement with the rate in laboratory.
At this site, the rate of attenuation was rapid.
Elizabeth City, N.C., Old Fuel Farm
Exposure: Decades
Geochemistry Strongly Methanogenic
MTBE Degradation rate 2 to 3 per year
Elizabeth City, N.C. Fire Station Spill
A leak from a buried pipeline, about 1/2 mile
from the fuel farm site.
Exposure < 10 years
Geochemistry is Sulfate Reducing, no Methane
MTBE Degradation in Field 0.47 per year
East Patchhogue, NY
Glacial Sands on Long Island
Hydraulic Conductivity 0.05 to 0.10 cm/sec, or
40 to 80 feet/day
Release after 1979, tanks removed 1988
Geochemistry No Oxygen where MTBE is
present, little Methane
MTBE is persistent
Seminar Series on Monitored Natural Attenuation for Ground Water
2-12
-------
E. Patchogue, NY
Benzene ([jg/L)
E. Patchogue, NY
MTBE ([jg/L)
6000 5000 4000 3000 2000 1000 0
Distance (ft)
.000 5000 4000 3000 2000 1000
Distance (ft)
3
'3
i.
c
0>
0)
X
0
16 -i
14
12
10
8
6
4
2
n
1
Lak~~t . . .
1000 2000 3000 4000 5000 6000
MTBE (ug/Liter)
East Patchhogue, NY
Glacial Sands on Long Island
Where oxygen is present in the ground water
(>1.0 mg/L), MTBE is absent (<20 ug/Liter)
MTBE exists in a "shadow" of depleted oxygen,
down gradient from the spill.
No Oxygen, No Methane, No MTBE degradation
Location
CFB, Ontario
Location CFB, Ontario
Exposure A few years
Exposure A few more years
Geochemistry No Oxygen
No Nitrate
MTBE Degradation None apparent
Geochemistry Mixed in Oxygen
MTBE Degradation Gone?
Seminar Series on Monitored Natural Attenuation for Ground Water
2-13
-------
Location
CFB, Ontario
Exposure A few more years
MTBE Degradation at Field Scale
0.44 per year
MTBE Degradation in Aerobic
Microcosms
2.4 per year
Location Sampson Co, N.C.
Exposure Many years
Geochemistry Iron Reducing
No Methane
MTBE Degradation in Field
0.0, 0.3 and 0.4 per year
MTBE Degradation in Aerobic Microcosms
2.4 per year
Aerobic Degradation of MTBE in Microcosms is
much more Rapid than at Field Scale
Aerobic Degradation may be controlled by the
Kinetics of Re-oxygenation, not the Kinetics of
Biodegradation.
Kinetics of Aerobic Biodegradation may be
Specific to the Geochemistry and Geometry of
the MTBE plume.
Location Sampson Co, N.C.
Exposure Many years
Geochemistry Iron Reducing
No Methane
MTBE Degradation in Field
0.0, 0.3 and 0.4 per year
MTBE Degradation in Aerobic Microcosms
2.4 per year
Seminar Series on Monitored Natural Attenuation for Ground Water
2-14
-------
Natural Attenuation of Chlorinated
Solvents in Ground Water
John T. Wilson
Office of Research and Development
National Risk Management Research Laboratory
U.S.Environmental Protection Agency
Cincinnati, Ohio
Mechanism of Chloroethene
Biotransformation
cl
c
Cl
Cl Cl
= c > c
\ /
Cl H
_CI
= c *
\
Cl
cl
c
H
Cl
= c
\
H
C(
h C
H
H-
= C
\
Cl
s X
> C = C >
^ \
H H H
H
C = C
' \
H
Reductive dehalogenation:
Oxidation/reduction reaction where electrons are transferred
from donor to chlorinated hydrocarbon acceptor
Co-metabolic process:
Organisms growing on alternate carbon sources
Primary substrates:
Potential for natural (soil organic matter) and anthropogenic
sources
Alternate Pathways for
Chloroethene Biotransformation
DCE-
VC'
Oxidative biodegradation:
Vinyl chloride shown to biodegrade under aerobic conditions
Fe reducers may also oxidize vinyl chloride
Supporting evidence:
Transport properties (migration) of DCE and VC relative to
Aerobic biodegradation of vinyl chloride to CO,
demonstrated in microcosms
Native Biotransformations for
Chloroethenes
CO2
Ethane
Ethene
Requirements for Reductive
Dechlorination
Primary substrate
- Native organic carbon, BTEX, landfill
leachate, etc.
Strongly reducing conditions
- Generally need methanogenic
conditions
Seminar Series on Monitored Natural Attenuation for Ground Water
2-15
-------
Behavior of Chlorinated Solvent
Plumes
Type 1 Behavior
- Primary substrate is anthropogenic organic
carbon
- Solvent plume degrades
Type 2 Behavior
- Primary substrate is native organic carbon
- Solvent plume degrades
Type 3 Behavior
- Low native organic carbon concentrations
- Low anthropogenic organic carbon concentrations
- PCE, TCE and DCE? do not degrade
Type 1 Behavior
Primary substrate is anthropogenic organic carbon
- BTEX, landfill leachate, etc.
Anthropogenic organic carbon drives dechlorination
Questions
- Does electron acceptor supply exceed demand?
(i.e., is electron acceptor supply adequate?)
- Will plume strangle before it starves?
- What is role of competing electron acceptors?
- Do PCE, TCE and DCE dechlorinate?
- Is vinyl chloride oxidized?
- Is biodegradation rate adequate?
Type 2 Behavior
Primary substrate is native organic carbon
Type 3 Behavior
Low native organic carbon concentrations
Native organic carbon drives dechlorination
Low anthropogenic organic carbon concentrations
Questions
- Does electron acceptor supply exceed demand?
(i.e., is electron acceptor supply adequate?)
- Will plume strangle before it starves?
- What is role of competing electron acceptors?
- Do PCE, TCE and DCE dechlorinate?
- Is vinyl chloride oxidized?
- Is biodegradation rate adequate?
Dissolved oxyen (and nitrate) concentration(s) greater
than 1.0 mg/L (oxygenated system)
Reductive dechlorination will not occur
Highly halogenated compounds such as PCE and
TCE will not degrade
DCE (?) and VC may be oxidized
Seminar Series on Monitored Natural Attenuation for Ground Water
2-16
-------
Natural Attenuation of Metals in
Ground Water
Factors Affecting the Concentration of
Metals in Solution
John T. Wilson
Office of Research and Development
National Risk Management Research Laboratory
U.S.Environmental Protection Agency
Cincinnati, Ohio
ion exchange and adsorption
oxidation or reduction reactions
precipitation and dissolution of solids
acid-base reactions
complex formation
Factors Affecting the Concentration of
Metals in Solution
ion exchange and adsorption
Cadmium
Lead
Nickel
Copper
Mercury I and
Zinc
Factors Affecting the Concentration of
Metals in Solution
ion exchange and adsorption
relative order of sorption, in general
Lead > Copper > Zinc > Cadmium >Nickel
Sandy Aquifers are particularly vulnerable
to Cadmium and Nickel
Concentration of Metal in Solution
In the most simple form, described by
Distribution Coefficient
Kd = Concentration on Solids
Concentration in water
Cadmium and Nickel Distribution
Coefficients for Sandy Aquifer Materials
Christensen et al, Journal of
Contaminant Hydrology 24(1996):75-84
Sorption isotherms for Cadmium and
Nickel in 18 samples of sandy aquifer
material from 12 locations in Denmark, at
pH ranging from 4.9 to 8.9
Seminar Series on Monitored Natural Attenuation for Ground Water
2-17
-------
Concentration of Metals in Solution
Example sorption isotherm for Cadmium
in Sandy aquifer material from Denmark,
pH4.9
50
40
30
20
10-
Kd = 2.1 liter/kg
5 10 15 20
Cadmium in Water (ug/liter)
25
Factors Affecting the Concentration of
Metals in Solution
ion exchange and adsorption
Kd is sensitive to the pH of the Ground
Water
Effect of pH on Kd for Cadmium in core
material from 28 sandy aquifers in
Denmark
10000
1000
100
10
7
PH
10
Concentration of Metal in Solution
Kd = Concentration on Solids
Concentration in water
If bulk density =1.6 kg/liter
and water-filled porosity = 0.32
and Kd » 1.0 liter/kg;
Retardation = 5 (Kd)
7
PH
Seminar Series on Monitored Natural Attenuation for Ground Water
2-18
-------
100000
_ 10000 -
0)
^
i 1000 -
o
£ 100 -
^:
10 -
1
7
PH
10
3
-------
Factors Affecting the Concentration of
Metals in Solution
oxidation or reduction reactions
Factors Affecting the Concentration of
Metals in Solution
oxidation or reduction reactions
Arsenite and Mn+2 are more toxic than
Arsenate or Mn+4, are move soluble, and
more mobile in ground water.
Under aerobic conditions, Arsenic III
(AsO2~1 or Arsenite) and Manganese II
(Mn+2) may be oxidized back to Arsenic
V (AsO4-3 or Arsenate) and Manganese IV
by natural biological activity.
Factors Affecting the Concentration of
Metals in Solution
oxidation or reduction reactions
Chromium VI exists as an oxyanion, as
bichromate HCrO4- below pH 6.5
chromate CrO4'2 near pH 6.5
and dichromate Cr2O7~2 at concentrations
greater than 10 mM.
Factors Affecting the Concentration of
Metals in Solution
oxidation or reduction reactions
Chromium VI is mobile in ground water,
and is a greater health hazard than
Chromium III
Factors Affecting the Concentration of
Metals in Solution
oxidation or reduction reactions
Factors Affecting the Concentration of
Metals in Solution
oxidation or reduction reactions
Chromium III is a cation, that tends to
bind strongly to aquifer material
Dissolved Organic Matter in the ground
water will reduce Chromium VI to
Chromium III, making it effectively
immobile.
Seminar Series on Monitored Natural Attenuation for Ground Water
2-20
-------
Factors Affecting the Concentration of
Metals in Solution
oxidation or reduction reactions
Factors Affecting the Concentration of
Metals in Solution
oxidation or reduction reactions
Oxidized forms of Manganese in the
aquifer matrix material will oxidize
Chromium III back to Chromium VI
The equilibrium concentration of
Chromium VI, and therefore the natural
attenuation of chromium, is controlled
by the competition between the
oxidation and reduction reactions.
Factors Affecting the Concentration of
Metals in Solution
oxidation or reduction reactions
The natural attenuation of chromium, is
site specific, and must be confirmed by
monitoring
Seminar Series on Monitored Natural Attenuation for Ground Water
2-21
-------
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for printing purposes.
-------
Geochemical Processes
Seminar Series on Monitored Natural Attenuation for Ground Water
2-23
-------
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for printing purposes.
-------
Geochemical Processes and
Natural Attenuation
U.S. Geological Survey
Why is Geochemistry
Important to Natural
Attenuation ?
: Ground-water geochemistry is a
record of ongoing chemical,
physical, and microbial processes.
: Ergo: The efficiency of natural
attenuation can often be determined
from ground-water chemistry
information (redox conditions).
What is a redox process ?
: Electrons are transferred in chemical or
biochemical reactions.
: Benzene + O2 -
CO, +
In a redox reaction, one
compound donates an electron
and another compound accepts
an electron:
: Benzene + O, CO2 + e~ (Benzene is electron
DCE + Cl- (TCE is electron acceptor)
donor)
*e- +TCE
The flow of electrons from donors
to acceptors is capable of doing
work.
: Microorganisms (and everybody else)
uses the work done by flowing
electrons to sustain life functions.
Biodegradation of Petroleum
Hydrocarbons are electron-
donating processes.
: Benzene CO2 + e~ (benzene donates e~)
: 2e~ + O2 *2H2O (Oxygen accepts e~)
Electron
Acceptor
Seminar Series on Monitored Natural Attenuation for Ground Water
2-25
-------
Because the biodegradation of
petroleum hydrocarbons are
electron donating processes:
: The availability of electron acceptors
determines the rate and extent of
biodegradation.
Oxygen
Fe(III)
sulfate
CO2
Chlorinated solvents
Benzene Oxidation
Aerobic Respiration
7.5 02+ C6H6
6 CO2(g) + 3 H 2O
2G°r = - 3566 kJ/mole benzene
Mass Ratio of O2 to C6 H6 = 3.1:1
0.32 mg/L C6H6 degraded per mg/L O2 consumed
Biodegradation of Benzene
Consumes Dissolved Oxygen
: Low concentrations of dissolved oxygen
are associated with benzene
biodegradation coupled to oxygen
reduction.
Benzene Oxidation
Iron Reduction
60H+ + 30Fe(OH)3(a| + C6H6 -» 6CO2(g| + 30Fe2+ + 78H2O
2G°r = - 2343 kJ/mole benzene
Mass Ratio of Fe(OH)3 to C6H6 =41:1
Mass Ratio of Fe2+ produced to CgH^degraded = 15.7:1
0.06 mg/L C6H6 degraded per mg/L Fe2+ produced
Biodegradation of Benzene
Produces Dissolved Iron
: High concentrations of dissolved iron
are associated with benzene
biodegradation coupled to iron
reduction.
7.5H
Benzene Oxidation
Sulfate Reduction
+C6H6
3.75H2S + 3H20
2G°r = - 340 kJ/mole benzene
Mass Ratio of SO^ to C6 H6 = 4.6:1
0.22 mg/L C6 H6 degraded per mg/L SO^'consumed
Seminar Series on Monitored Natural Attenuation for Ground Water
2-26
-------
Biodegradation of Benzene
Consumes Sulfate
: Low concentrations of dissolved sulfate
are associated with benzene
biodegradation coupled to sulfate
reduction.
: High concentrations of H2S
Benzene Oxidation
Methanogenesis
4.5 H2O + C6H6
2.25 CO2(g) + 3.75 CH4
2G°r =-135.6 kJ/mole benzene
Mass Ratio of CH4 produced to C6H6 = 0.8:1
1.25 mg/L C6H6 degraded per mg/L CH4 produced
Biodegradation of Benzene
Produces Methane
: High concentrations of methane are
associated with benzene biodegradation
coupled to methanogenesis.
Total BTEXand Dissolved Oxygen
HILLAFB.JULY1994
Q 20,000 - 22,000 jig/L
88,000-20,000 ,^/L
4,000 - 8,000 ffl/L
Q 0-4,000 pgl\.
LINE OF EQUAL DISSOLVED OXYGEN
CONCENTRATION (mg/L)
J ENGINEERING SCIENCE, INC.
Total BTEX and Iron (II)
HILL AFB, JULY 1994
| | 20,000-22,000 |ig/L
B 8,000 -20,000 |ig/L
4,000 -8,000 |ig/L
I I 0 -4,000 |ig/L
I" I ENGINEERING SCIENCE, INC.
Total BTEX & Sulfate
HILL AFB, JULY 1994
20,000 -22,000 |ig/L
8,000 -20,000 |ig/L
4,000 -8,000 |ig/L
I I 0 -4,000 |ig/L
Line of Equal Sulfate
Concentration (mg/l)
Seminar Series on Monitored Natural Attenuation for Ground Water
2-27
-------
Total BTEX & Methane
HILL AFB, JULY 1994
| | 20,000-22,000
8,000-20,000 jig/L
4,000 -8,000 jig/L
0 -4,000 jig/L
of Equal Methane
Relative Importance of Biodegradation
Mechanisms at 25 Sites
Sulfate Reduction
29%
Denitrification
14%
Methanogenesis
39%
Geochemical Data Can Indicate:
: If biodegradation is occurring.
: If biodegradation has occurred in the
past.
: If electron acceptors are available to
support biodegradation in the future!
Seminar Series on Monitored Natural Attenuation for Ground Water
2-28
-------
Redox Zonation and
Biodegradation Efficiency
U.S. Geological Survey
In a redox reaction, one
compound donates an electron
and another compound accepts
an electron:
: Benzene + O, "CO2 + e~ (Benzene is electron
DCE + Cl~ (TCE is electron acceptor)
donor)
*e- +TCE
The flow of electrons from donors
to acceptors is capable of doing
work.
: Microorganisms (and everybody else)
uses the work done by flowing
electrons to sustain life functions.
Biodegradation of Chlorinated ethenes
can be electron-accepting processes
(ie., reductive dechlorination).
*TCE+ e--
cis-DCE +C1-
Biodegradation of chlorinated
ethenes can also be electron-
donating processes (oxidation).
* Vinyl Chloride CO2
* 2e- + O2 2H2O
-Cl
Because of this complexity,
chlorinated ethenes do not behave
uniformly in ground-water
systems
: Poly-Chlorinated ethenes will reduce
under reducing conditions.
: DCE and VC will oxidize under
oxidizing conditions.
Seminar Series on Monitored Natural Attenuation for Ground Water
2-29
-------
The Rate and Extent of
Biodegradation Processes at any
Given Site DependsUpon:
: Ambient Redox Conditions
: The Succession of Redox Conditions
EXAMPLE
Sequential
Reduction/Oxidation
TCE
H ,C1
C=C
vc
Hv ,H
C=C >
- N / \ '
Cl Cl cl H
Reduction Oxidation
[O .Fe(III)]
2CO + 3C1
Inefficient Natural Attenuation
Efficient NA leads to rapid
decrease of contaminants away
from source area.
Chlorinated
Ethenes
MCL
Distance from Source
Inefficient NA leads to gradual
decrease of contaminants away
from source area.
Chlorinated
Ethenes
MCL
Distance from Source
Seminar Series on Monitored Natural Attenuation for Ground Water
2-30
-------
How can we quickly screen water
chemistry data from a site in
order to determine if chlorinated
solvent biodegradation is
possible ?
Initial Screening Process
The screening process is designed to
recognize reductive dechlorination of
chlorinated solvents.
It presupposes that natural attenuation
of chlorinated solvents in most
plumes will be not be important
unless the solvents are initially
dechlorinated.
Analytical Parameters and Their
Weighting for Preliminary Screening
Analysis Condition
Value
Oxygen
Oxygen
Nitrate
Iron II
< 0.5 mg/L
> 1.0 mg/L
< 1 mg/L
> 1 mg/L
3
-3
2
3
Analytical Parameters and Their
Weighting for Preliminary Screening
Oxygen is toxic to the organisms that
carry out reductive dechlorination.
If it is present reductive
dechlorination cannot occur.
Analytical Parameters and Their
Weighting for Preliminary Screening
Analytical Parameters and Their
Weighting for Preliminary Screening
Analysis
Sulfate
Sulfide
Methane
Redox(Eh)
Condition Value
< 20 mg/L
> 1 mg/L
> 0.1 mg/L
> 1.0 mg/L
< +50 millivolts
< -100 millivolts
2
3
2
3
1
2
Analysis
DOC
Temp
C02
Alkalinity
Condition Value
> 20 mg/L
>20°C
> 2x background
> 2x background
2
1
1
1
Seminar Series on Monitored Natural Attenuation for Ground Water
2-31
-------
Analytical Parameters and Their
Weighting for Preliminary Screening
Analytical Parameters and Their
Weighting for Preliminary Screening
Analysis Condition Value
Chloride > 2x background 2
Hydrogen > 1 nanomolar 3
VFA > 0.1 mg/L 2
BTEX > 0.1 mg/L 2
Hypothetical Site #1
Analysis Condition Score
DO 0.1 mg/L 3
Nitrate 0.3 mg/L 2
Iron II 10 mg/L 3
Sulfate 2 mg/L 2
Hypothetical Site #1
Analysis Condition Score
PCE (spilled) 1,OOOug/L 0
TCE 1,200ug/L 2
(not spilled)
cis-DCE 500 I.ICJ/L 2
Vinyl chloride 50 ug/L 2
Analysis Condition
Reduced daughter products
TCE, DCE, vinyl chloride,
chloroethane, chlorobenzene
Ethene > 0.01 mg/L
> 0.1 mg/L
Hypothetical Site #1
Analysis Condition
Methane 5 mg/L
Redox -190 millivolts
Chloride 45 mg/L
Background 10 mg/L
Hypothetical Site #2
Analysis Condition
DO 3.0 mg/L
Nitrate 0.3 mg/L
Iron II Not Detected
Sulfate 10 mg/L
Value
2
2
3
Score
3
2
2
Score
0
2
0
2
Seminar Series on Monitored Natural Attenuation for Ground Water
2-32
-------
Hypothetical Site #2
Analysis
Methane
Redox
Condition Score
Not Detected 0
+100 millivolts 0
Chloride 15mg/L
Background 10mg/L
Hypothetical Site #2
Analysis
TCE (spilled)
cis-DCE
Vinyl chloride
Condition
1,200ug/L
< 1 ug/L
< 1 ug/L
Score
0
0
0
Interpretation of Results from
Preliminary Screening
Total Score
Interpretation
0 to 5 Inadequate evidence
6 to 15 Limited evidence
16 to 20 Adequate evidence
over 20 Strong evidence
Interpretation of Results from
Preliminary Screening
Hypothetical Site #1
23 total points - strong evidence
Hypothetical Site #2
4 total points - inadequate evidence
The Rate and Extent of
Chlorinated Ethene
Biodegradation Processes
Depends Upon:
: Ambient Redox Conditions
: The Succession of Redox Conditions
Seminar Series on Monitored Natural Attenuation for Ground Water
2-33
-------
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for printing purposes.
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How Hydrogeology Affects the
Efficiency of Natural Attenuation
Seminar Series on Monitored Natural Attenuation for Ground Water
3-1
-------
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for printing purposes.
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How Hydrogeology Affects
the Efficiency of Natural
Attenuation
U.S. Geological Survey
OSWER recognizes that Natural
Attenuation Processes include
physical, biological, and chemical
processes . These are:
: Physical (Dispersion, advection).
: Chemical transformations (sorption).
: Biological processes (reduction,
oxidation).
How can we take all of these
processes into account?
: To illustrate, let s do a mental
experiment.
Consider a contaminant spill that
reaches the water table. The size
of the contaminant plume that
develops is controlled by:
: Size of the spill.
: velocity of G.W. flow (v).
: Sorptive capacity of aquifer solids (s).
: Biodegradation (k).
Ifv is large compared to s and k,
the plume will be relatively large.
Conversely, ifv is small relative
to s and k, the plume will be
relatively small.
Seminar Series on Monitored Natural Attenuation for Ground Water
3-3
-------
Postulate: The efficiency of
natural attenuation is inversely
proportional to the distance of
contaminant migration
E~l/d
Therefore: The efficiency of natural
attenuation depends on:
: Velocity of ground water
: Sorptive capacity of aquifer
: Rates of biodegradation
This reasoning is useful because
it can be quantified:
OSWER recognizes that Natural
Attenuation Processes include
physical, biological, and chemical
processes . These are:
: Physical (Dispersion, advection).
: Chemical transformations (sorption).
: Biological processes (reduction,
oxidation).
This is saying mathematically, what the
OSWER Directive says in English.
The key to assessing natural
attenuation is to have:
: Hydrologic information (directions and
rates of GW flow).
: Geochemical information (sorptive
capacity of aquifer sediments).
: Microbiologic information (rates of
biodegradation).
Seminar Series on Monitored Natural Attenuation for Ground Water
3-4
-------
How do you get this information ?
: Hydrologic testing (hydraulic
conductivity, water-level maps)
: Geochemical testing (redox conditions,
sorptive capacity).
: Microbiologic testing (field and/or lab).
Direct Push
Technology
Ground
Surface
Water Table
1" Steel Pipe
1/4 inch PVC Tubing
30cm
45cm
Peristaltic
Pump
Application of the Electromagnetic
Borehole Flowmeter
Steven C. Young, Hank E. Julian,
Hubert S. Pearson, Fred J. Molz, and
Gerald K. Boman
EPA/600/SR-98/058
QR.
Apparatus and
Geometry
Associated
with a Borehole
Flowmeter Test
Pump
- To Logger (Q)
Borehole Flow
Meter
(Q = Discharge Rate)
Casing
Confining Layer
Elevation = Z
Data from a Borehole Flowmeter Test
Discharge Rate, Q
George Air 1 ssxs^.
Force Base,
California
Seminar Series on Monitored Natural Attenuation for Ground Water
3-5
-------
Hydraulic Conductivity - MW 27
Hydraulic Conductivity (cm/sec)
0.00 0.02 0.04 0.06 0.08 0.10 0.12
Qj S28
Hydraulic Conductivity - MW 29
Hydraulic Conductivity (cm/sec)
0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07
835.67
831.8
fg 830.00
£
Qj 828.11
826.22
82433
Hydraulic Conductivity - MW 31
Hydraulic Conductivity (cm/sec)
0.00 0.05 0.10 0.15 0.20 0.25 0.30
835
833
L
829
827 I
825 F
m
George AFB
Monitoring
Well
MW-27
MW-28
MW-29
MW-31
MW-45
MW-46
Average
Hydraulic
Conductivity
(cm/sec)
0.0074
0.0046
0.0028
0.013
0.0032
0.018
Hydraulic
Conductivity of
Most Transmissive
Interval (cm/sec)
0.11
0.022
0.062
0.26
0.0056
0.40
How do you get this information ?
: Hydrologic testing (hydraulic
conductivity, water-level maps)
: Geochemical testing (redox conditions,
sorptive capacity).
: Microbiologic testing (field and/or lab).
DISSOLVED CONCENTRATION (ppm)
Seminar Series on Monitored Natural Attenuation for Ground Water
3-6
-------
How do you get this information ?
: Hydrologic testing (hydraulic
conductivity, water-level maps)
: Geochemical testing (redox conditions,
sorptive capacity).
: Microbiologic testing (field and/or lab).
Total BTEXand Dissolved Oxygen
HILLAFB.JULY1994
^ 20,000 - 22,000 jig/L
88,000-20,000 ,^/L
4,000 - 8,000 ffl/L
Q 0-4,000 pgl\.
LINE OF EQUAL DISSOLVED OXYGEN
CONCENTRATION (mg/L)
J ENGINEERING SCIENCE, INC.
Total BTEX and Iron (II)
HILL AFB, JULY 1994
^ 20,000-22,000 |jg/L
B 8,000 -20,000 |ig/L
4,000 -8,000 |ig/L
I I 0 -4,000 |ig/L
I" I ENGINEERING SCIENCE, INC.
Seminar Series on Monitored Natural Attenuation for Ground Water
3-7
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Analytic or Digital Soulutions
can then be used to assess
Natural Attenuation:
Ifv is large compared to s and k,
the plume will be relatively large.
Conversely, ifv is small relative
to s and k, the plume will be
relatively small.
Example 1: Source Remains
in Place:Plume becomes stable.
20 y
Example 2: Source Removed:
Plume dissipates.
Conditions
at Time of
Source
Removal
Even with sophisticated models,
there is still uncertainty!
* Predictive models
must be tested
against historical
data.
* Modeling must be
verified with
monitoring data.
Seminar Series on Monitored Natural Attenuation for Ground Water
3-8
-------
Site Characterization and Data
Interpretation for Evaluation of
Natural Attenuation at Hazardous
Waste Sites
Seminar Series on Monitored Natural Attenuation for Ground Water
4-1
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for printing purposes.
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Site Characterization and
Data Interpretation for
Evaluation of Natural
Attenuation at
Hazardous Waste Sites
Kelly Hurt
National Research
Council
R.S. Kerr Environmental Research Center
Ada, OK
(580) 436-8987
hurt.kelly@epa.gov
The most common site
characterization
question.
How many wells are
enough?
The Two Most Common
Answers
As many as you can get.
It's site specific.
Review of the current
state of practice for site
characterization.
"State of the Practice"
Install monitoring wells to
determine ground-water flow
direction.
Install additional monitoring
wells downgradient of the
source area to define the
extent of contamination.
Seminar Series on Monitored Natural Attenuation for Ground Water
4-3
-------
"State of the Practice"
Determine whether the plume
is expanding, steady-state or
shrinking.
Determine whether the plume
has impacted or will impact
receptors.
A Typical Site
200" 400 600 BOO
Upgradient monitoring wells
were used to define
background conditions in the
aquifer.
Additional wells were
installed along the inferred
centerline of the plume.
Wells were placed on the
lateral and terminal edges of
the plume.
Typical Data
Presentation
Contour maps depict concentration
profiles of a variety of parameters.
These maps show the size and shape of
the contaminant plume and
distribution of geochemical
parameters.
Data are presented in terms of surface
area impacted.
PCE (ppb)
Deep PCE (|jg/L)
TCE (ppb)
Deep TCE (pg/L)
200 400 600 800
200 400 600 800
Seminar Series on Monitored Natural Attenuation for Ground Water
4-4
-------
cis-DCE (ppb)
Deep 1,2-cis-DCE ftjg/L)
Benzene (ppb)
Deep Benzene (ug/L)
Toluene (ppb)
Deep Toluene (ug/L)
200 400 600
Ethylbenzene (ppb)
Deep Ethylbenzene (yg/L)
200
400 600 800
Xylene (ppb)
Deep Total Xylenes (pg/LJ
Oxygen (mg/L)
Deep Field Measured Dissolved Oxygen (mg/L)
200 400 600 800
Seminar Series on Monitored Natural Attenuation for Ground Water
4-5
-------
Iron (II) (mg/L)
Deep Dissolved Iron (mg/L)
Rules of Thumb for Site
Investigations
Dissolved oxygen is directly
proportional to redox potential.
Dissolved oxygen concentrations
are inversely proportional to iron II
and alkalinity concentrations.
Rules of Thumb for Site
Investigations
Alkalinity concentrations are
directly proportional to iron II, but
iron II is not necesarrily directly
proportional to alkalinity.
Typical Site
Characterization
Designed to determine
absence or presence of
contamination.
Not designed to describe how
the plume is behaving.
Typical Site
Characterization
Typically uses permanent
monitoring wells to map the
contaminant plume.
Emphasizes concentrations of
contaminants of concern.
Typical Site
Characterization
Does not emphasize
hydrogeologic
characterization of the site.
At best, it uses slug testing to
estimate the transmissivity of
the screened interval.
Seminar Series on Monitored Natural Attenuation for Ground Water
4-6
-------
Typical Site
Characterization
Conceptualizes the plume as a
static object in 2-D space
There is a fundamental
difference in the requirements
for site characterization if
natural attenuation is to be
evaluated as a remedy.
Selection of natural attenuation
as a remedy demands a higher
level of understanding of
mechanisms acting on the
contaminant plume than
needed for other remediation
techniques. Therefore, more
importance is given to
collecting data from within the
plume.
Contour maps do not provide
information on the rate of
ground-water flow, the flux of
contamination being released
from the source area, the
quantity of contaminant in the
plume, or the flux of
contaminant to surface waters
or other receptor.
An Iterative Approach to
Fate and Transport
Typically uses push
technology to map the
contaminant plume.
Emphasizes the
concentrations of geochemical
indicators, as well as
contaminants.
An Iterative Approach to
Fate and Transport
Concentration data are also
organized to determine the
flux of contaminant in the
entire plume from the source,
along the flow path and to the
receptor.
Seminar Series on Monitored Natural Attenuation for Ground Water
4-7
-------
Calculation of
Contaminant Flux Along
the Flowpath
The reduction in the flux
along the flowpath is the best
estimate of natural
attenuation of the plume as a
whole.
Calculation of
Contaminant Flux Along
the Flowpath
The flux is the best estimate of
the amount of contaminant
leaving the source area. This
information would be needed
to scale active remedy if
necessary.
Calculation of
Contaminant Flux Along
the Flowpath
Flux estimate across the
boundary to a receptor is the
best estimate of loading to a
receptor.
An Iterative Approach to
Fate and Transport
Has a greater investment in
hydrogeological
characterization.
More conservative estimates
of transmissivity are
produced by conducting
pumping tests.
Benefits of an Iterative
Approach to Fate and
Transport
Higher resolution site characterization.
Optimization of well placement.
More representative data.
Better understanding of the fate and
transport of contaminants.
Thermo Chem Case
Study
Seminar Series on Monitored Natural Attenuation for Ground Water
4-8
-------
Purpose of the Case Study
Compares three levels of
characterization; (1)
Conventional wells widely
spaced, (2) Dense array of
conventional wells in
transects, (3) GeoProbe
transects.
Purpose of the Case Study
The dense array of
conventional wells arranged
in transects are assumed to
yield correct data.
Purpose of the Case Study
Results from the dense array
of conventional wells are
compared to a dense array of
GeoProbe samples to evaluate
the performance of push
techniques.
Purpose of the Case Study
Results from the dense array
of conventional wells are
compared to a conventional
array of monitoring wells to
determine the resolution of
conventional monitoring
strategies.
Benchmarking Direct-
Push Technology Against
Permanent Wells
Hydraulic Conductivity Tests
Contaminant Data
Geochemical Data
Hydraulic Conductivity
Tests
A GeoProbe unit was used to
estimate hydraulic
conductivity values at the
same depth intervals as
existing conventional
monitoring wells.
Seminar Series on Monitored Natural Attenuation for Ground Water
4-9
-------
Conventional
Well Xk,
_J
_
Screens at
1st, 2nd
and 3rd
intervals
K Tests
Single well pumping test
(Specific Capacity)
Measure discharge and
drawdown
K Tests
1.5' GeoProbe screens
Permanent monitoring well
screens ranged from 4 to 9 ft.
Comparison was conducted
over the same interval.
Distance between the push
probe and monitoring well
varied from 3 to 10 feet.
Data Analysis
Jacob's Solution (1946) to
the Theis Equation
Jacob's solution to the Theis
equation was used to estimate
transmissivity.
_
2641ogU2sJ
Seminar Series on Monitored Natural Attenuation for Ground Water
4-10
-------
Q = pumping rate, gpm
s = drawdown in the well, ft
T = transmissivity, gpd/ft
(assume 30,000 gpd/ft
initially, then revise with first
estimate from calculations)
t = time since pumping
started, days
r = radius of the well, ft
S = storativity, dimensionless
(.001 for a confined aquifer,
.075 for unconfined aquifers)
The known parameters
can be substituted into
the equation and
simplified for easier use.
For example, when using
a direct push well
T = 30,000 gpd/ft
t = 0.01 days
r = 0.04 ft
S = .075
The equation can be
simplified to
7=1550
For example, when using
a direct push well
T = 30,000 gpd/ft
t = 0.01 days
r = 0.16 ft
S = .075
Seminar Series on Monitored Natural Attenuation for Ground Water
4-11
-------
The equation can be
simplified to
7=1230
Q
Then substitute the
measured Q and
drawdown to get an
estimate of T.
Divide T by screen length
to get a relative estimate
of K for the interval
tested.
Assumptions
Borehole storage is negligible
Horizontal flow.
Late-time conditions are
reached quickly.
100% efficient wells.
Laminar flow exists
throughout the well and
aquifer.
Partial Penetration
Since the GeoProbe screens
are only partially penetrating,
estimates of K average
conductivities from above and
below the interval being
tested due to radial flow.
Partial Penetration of an Aquifer by a
GeoProbe Screen
Seminar Series on Monitored Natural Attenuation for Ground Water
4-12
-------
Late Time Conditions
Late Time Conditions
Early time data may be
invalid for use with the Jacob
Solution to the Theis
equation.
The Jacob equation largely
ignores the effect of time on
pumping yield. The
calculation of u, an evaluation
parameter, is necessary to
ensure that the asymptote has
been reached.
Late Time Conditions
Stabilization
Time
Late Time Conditions
If the calculated u is less than
0.05, then the assumption of
late time conditions is
justified.
Late Time Conditions
U =
1.87 r2 S
Tt
Late Time Conditions
For example, when r = 0.5 in.
(0.04 ft), S = 0.075, T = 5000
gpd/ft, and t = 20 min (0.01
days):
Seminar Series on Monitored Natural Attenuation for Ground Water
4-13
-------
Late Time Conditions
U =
\.%1(0.04)20.075
(5 000) (0.01)
Late Time Conditions
u = 0.000004
Laminar Flow
Q = VA
Q = maximum pumping rate
at which laminar flow exists
V = entrance velocity {can not
exceed 0.1 ft/sec (0.03 m/sec)}
A = open screen area
Laminar Flow
For example, when A = 0.0042 ft2
Q = 0.1 ft/sec (0.0042 ft2)
Q = 0.00042 ft3/sec or
approximately 700 mL/min
This calculation is necessary
because of the limited open
screen area in the GeoProbe
point. Exceeding the
maximum discharge will
result in well efficiency
concerns and invalid
estimates of K.
Results
Seminar Series on Monitored Natural Attenuation for Ground Water
4-14
-------
dl dl d I d I dl d I dl dl d I NORTHWEST
fe fe fe fe fe fe fe fe fe i--c«i
Thermo Chem'stte
K Values, GeoProbe (GP) vs. Conventional Wells (CW)
4567
Trial Number
'CW
'GP
In the glacial-outwash
sands at this site, the
GeoProbe test and
permanent monitoring
wells produced
comparable estimates of
hydraulic conductivity.
Range of Values
K values ranged from 0.00005
cm/s to 0.1 cm/s.
Certainly both methods had
enough sensitivity to
differentiate between low and
high flow zones during site
characterization.
However, some of the
assumptions associated with
this method of data analysis
are not met. Thus, the
GeoProbe method of
approximating K was used for
preliminary site analysis.
Comparing Push
Technology to Permanent
Wells
When the two estimates of K
differed, the estimate
acquired using the GeoProbe
was larger.
Seminar Series on Monitored Natural Attenuation for Ground Water
4-15
-------
K Values, GeoProbe (GP) vs. Conventional Wells (CW)
Contaminant Data
4567
Trial Number
'CW
'GP
Correlation Between PCE Concentrations Obtained
from Conventional Wells and GeoProbe Points
o
Z
z
z
z
* z
.Z y=1.0686x + 262.88
/ R2 = 0.7317
1000 2000 3000
Conventional Well
4000
Correlation Between TCE Concentrations Obtained
from Conventional Wells and GeoProbe Points
n j
/
/
Z
Z
Z
» / y = 0.8903X + 460.36
Z R2 = 0.9157
5000 10000 15000 20000
Conventional Well
Correlation Between Chloride Concentrations Obtained
from Conventional Wells and GeoProbe Points
Geochemical Data
* CO
0 40
n
y = 0.8445X + 3.4846
R2 = 0.8837
,^
y
/
:z
<*
0 20 40 60 80 100 120 140
Conventional Well
Seminar Series on Monitored Natural Attenuation for Ground Water
4-16
-------
Correlation Between Sulfate Concentrations Obtained
from Conventional Wells and GeoProbe Points
a. 30
0 25
% 20
o 15
n
»x»
, Z^
/.
* Z *
z
x; y = 0.8573X + 5.5508
R2 = 0.7103
10 20 30
Conventional Well
40
Calculation of
Contaminant Flux Along
the Flowpath
Contaminant Flux
Calculations
Flux = VAC
V = interstitial seepage
velocity
A = cross-sectional area
represented by the sample
C = concentration
Using push-technology it
is possible to see
contaminant flux and
geochemical distribution
with greater resolution.
Conventional
Well ^^
__?
I
|
GeoProbe
Screens at
1st, 2nd
and 3rd
intervals
PCE Flux (g/yr/m2), GeoProbe (GP)
vs. Conventional Wells (CW)
1.5-
3.0
4.5
6.0-
7.5
9.0
10.5
12.0
13.5
15.0
16.5
.
GF
350 700 1050 1400 1750 2100 2450 2800
PCE Flux (g/yr/m2)
Seminar Series on Monitored Natural Attenuation for Ground Water
4-17
-------
Fe ++ (mg/L), GeoProbe (GP) vs. Conventional Wells (CW)
1.5
3.0
4.5
6.0
7.5
9.0
10.5
12.0
13.5
15.0
16.5
18.0
IP
i
cw
0 2 4 6 8 10 12 14
Fe++ (mg/L)
Flux Estimates
Flux estimates from
permanent transect wells,
GeoProbe transect wells, and
a conventional array of wells
(located in same area as the
transect) were calculated.
Estimates of Flux Across
Transect (kg/yr)
PCE
TCE
cis-DCE
VC
Permanent GeoProbe Conventional
Transect Transect Well Array
55.1 45.9 1.5
182.5
311.7
26.7
224.2
918.0
53.0
8.9
19.0
0.05
Flux Estimates
Due to the wide spacing, the
conventional array of wells
fails to adequately
characterize contaminant
flux. The more densely
sampled transects yield much
more conservative estimates.
Data Use
By examining preliminary
contaminant flux and
geochemical data, judgements
can be made about the
heterogeneity of natural
attenuation before proceeding
further.
Location of the Plume
Seminar Series on Monitored Natural Attenuation for Ground Water
4-18
-------
Transect Location
Data presented are from
GeoProbes near well cluster 6.
This is the most heavily
impacted location along the
transect.
TCE Flux (g/yr/m2) Based on GeoProbe Data
cis-DCE Flux (g/yr/m2) Based on GeoProbe Data
E 1-5
0) 3.0
ra 4.5
>- 6.0
5 9.0
0 12.0
0) 13.5
15.0
£. 16.5
0> 18 0
T '
T I
=>
^
P
700 1050 1400 1750
TCE Flux (g/yr/m2)
E 1.5
Si 3.0
Q
ra 4.5
t 6.0
a 7.5
i 9-°
m R
Depth Below
co
-------
BTEX Concentrations (ppb) Based on GeoProbe Data
Fe ++ Concentrations (mg/L) Based on GeoProbe Data
m
m
f
1.5]
3.0
4.5
6.0
7.5
9 0
10.5
12.0
13.5
15.0
16.5
pj
a
ti
h "
\ "
'
^^
i
i »
'
5000 10000 15000 20000 25000 30000
1.5
3.0
4.5
6.0
7.5
9.0
10.5
12.0
13.5
15.0
16.5
BTEX (ppb)
Fe++ (mg/L)
Sulfate Concentrations (mg/L) Based on GeoProbe Data
1.5
3.0
6.0
7.5
9.0
10.5
12.0
13.5
15.0
16.5
18.0
D
"3
I)
D 5 10 15 20 25 30 3!
Sulfate (mg/L)
Lines of Evidence
Disappearance of contaminants -
Less flux of TCE is apparent in
some of the intervals (9 -16.5 ft).
Appearance of byproducts - At
this site, intervals that yield small
amounts of TCE yield large
amounts of cis-DCE.
Lines of Evidence
BTEX is present at the
appropriate interval to drive
reductive dechlorination.
Fe++ is being produced, and
sulfate is being removed in
the interval containing a
higher cis-DCE flux.
Interpretation
The contaminants in the
interval 9-16.5 feet below the
water table are undergoing
significant biological
transformation.
Seminar Series on Monitored Natural Attenuation for Ground Water
4-20
-------
Temporary Transects
The majority of the intervals
along the transect produce
evidence that biological
attenuation is occurring.
Temporary Transects
Natural attenuation may or
may not be protective of
potential receptors.
The preliminary data justifies
carrying out a complete
assessment of natural
attenuation.
Extent, Mass, and Duration
of Hydrocarbon Plumes
from Leaking Petroleum
Storage Tank Sites in Texas
Robert E. Mace, R. Stephen Fisher, David M.
Welch, and Sandra P. Parra
Bureau of Economic Geology
University of Texas at Austin
Austin, Texas 78713-8924
Average Depth to Water at 246 Sites
100
80
60
40
20
1 1
Mh -_ _
Site-Averaged Average Depth to Water (ft)
Construction of
Permanent Transects
A permanent transect
(designated by the
circles) was constructed
at the site to conduct long
term monitoring of
temporal trends in flux
and geochemical
parameters.
Seminar Series on Monitored Natural Attenuation for Ground Water
4-21
-------
SOUTHEAST
Geologic Cross-Section B-B'
Benefits of Constructing
Transects
Reveals the characteristics of
a cross section of the
contaminant plume.
Temporal comparisons can be
made on the same water with
the aid of a downgradient
transect.
More accurate flux and
degradation rate estimates
due to a more comprehensive
sampling of the plume.
Extent, Mass, and Duration
of Hydrocarbon Plumes
from Leaking Petroleum
Storage Tank Sites in Texas
Robert E. Mace, R. Stephen Fisher, David M.
Welch, and Sandra P. Parra
Bureau of Economic Geology
University of Texas at Austin
Austin, Texas 78713-8924
Seminar Series on Monitored Natural Attenuation for Ground Water
4-22
-------
Standard Deviation of the Direction
of Hydraulic Gradient (degrees)
/30
Percentage of 132
sites with at least
10 water-level
monitoring events
The previous cross
section reveals the
vertical placement of the
well screens within each
cluster along the transect.
Monitoring of the
Permanent Transect
Using the same methods as
with the site characterization,
flux and geochemical data can
be collected at any time.
Also, the spatial
relationships between
contaminants, electron
acceptors, and carbon
sources can be
demonstrated by
mapping the transect.
When viewing transect
maps remember that
ground-water flow is
from the viewer into the
screen.
Spatial Distribution of Hydraulic Conductivity Values along Northern Transect (cm/s), November 11
"
0 100 200 300 400 500 600 700
Location on Transect (feet)
0.000 0.002 0.004 0.006 0.008 0.010
Hydraulic Conductivity (cm/s)
Seminar Series on Monitored Natural Attenuation for Ground Water
4-23
-------
Spatial Distribution of PCE Flux along Northern Transect (g/yr), November 1997
Spatial Distribution of TCE Flux along Northern Transect (g/yr], November 1997
0 100 200 300 400 600 600 700
Location on Transect (feet)
0 100 200 300 400 500
Location on Transect (feet)
0 3000 6000 9000 12000 16000
Flux (g/yr)
0 1400028000420006600070000
Flux (g/yr)
ial Distribution of cis-OCE Flux along Northern Transect (g/yr), November 1997
Spatial Distribution of VC Flux along Northern Transect (g/yr), November 1997
0 100 200 300 400 500 600 700
Location on Transect (feet)
0 100 200 300 400 500
Location on Transect (feet)
0 20000 40000
Flux (g/yr)
0 5000 10000 15000
Flux (g/yr)
Spatial Distribution of BTEX Fiux along Northern Transect (g/yr), November 1997
0 100 200 300 400 500 600 700
Location on Transect (feet)
0 60000 100000150000200000
Flux (g/yr)
Hydrogen Data
Hydrogen data is an
important piece of evidence
used to demonstrate that
intrinsic bioremediation is
occurring at a significant rate.
Seminar Series on Monitored Natural Attenuation for Ground Water
4-24
-------
Spatial Distribution of Hydrogen along Northern Transect (nMIL), November 1997
Due to hydrogen production
during installation, direct-
push wells can not be used to
monitor dissolved hydrogen
gas concentrations. Thus, the
need for permanent wells.
0 100 200 300 400 500
Location on Transect (feet)
0 2 4 6 8 10
Concentration (nM/L)
Spatial Distribution of Fe++ along Northern Transect (mg/L) November 1997
Spatial Distribution of Sulfate along Northern Transect (mg/L) November 1997
100 200 300 400 500
Location on Transect (feet)
100 200 300 400 500
Location on Transect (feet)
0.0 1.0 2.0 3.0 4.0
Concentration (mg/L)
0 5 10 15 20 25 30 35 40
Concentration (mg/L)
Interpretation
Interpretation is the same as
with the temporary transect.
Use the transect maps to
differentiate between areas
that behave as is expected
when natural attenuation is
occurring and those that
don't.
Examples of Heterogeneity
At the 500 ft interval, PCE is
surrounded by TCE and both
are an in area that has high
hydrogen concentrations,
relatively high Fe++
concentrations, and low
sulfate concentrations.
Natural attenuation processes
are at work.
Seminar Series on Monitored Natural Attenuation for Ground Water
4-25
-------
Examples of Heterogeneity
Examples of Heterogeneity
The upper portion of the
aquifer is transmitting most
ofthecis-DCEandVC.
Therefore, this area has
undergone more reductive
dechlorination.
A less complete sampling
regime would fail to
demonstrate the complex
nature of fate and transport
mechanisms in the aquifer.
What About the
Geology?
Push technology can also be
used to take core samples of
aquifer material.
Core samples can be used to
verify trends seen in K
estimates.
Field Techniques to
Evaluate Sampling
Locations in Real Time
Field Test Kits
Test kits for Fe(II), alkalinity,
and in some cases
contaminants, can be used in
the field to map the plume
both laterally and vertically.
This allows the field scientist
to take the majority of
samples from contaminated
areas.
Trend Agreement Between BTEX and FE++
X
a
BTEX
Fe++
Seminar Series on Monitored Natural Attenuation for Ground Water
4-26
-------
Trend Agreement Between BTEX and Alkalinity
Relationship Between BTEX and Oxygen Measurements
'a
X
H
S
45
40
35
25
20
15
10
5'
\ /
\ /
\ /
\ /
\ f '
1
\ ,*
* ' «- "'^ '-. .
BTEX Oxygen
Oxygen (mg/L)
Correlation Between Field and Lab Determination of TCE Concentration in Water
7000
6000
5000'
4000
3000
2000
1000
0
R2 = 0.877
0 1000 2000 3000 4000 5000 6000 7000 8000 9000
Lab Method
Site Characterization
Recommendations
Use direct-push technology to
conduct site characterization,
preferably by constructing
temporary transects
Install monitoring well transects
based on the information provided
by the site characterization.
Site Characterization
Recommendations
Use monitoring well transects to
monitor temvoral trends.
GeoProbe Spacing on
Temporary Transect
Probe locations are
determined by starting at the
inferred center of the plume
and moving out in a stepwise
fashion at intervals of two
times the source area width.
Seminar Series on Monitored Natural Attenuation for Ground Water
4-27
-------
Spacing on Temporary
Transect
2nd sampling
location
2X source
width
Source
Area Plume
Boundary
1st sampling location
GeoProbe Spacing on
Temporary Transect
If the 2nd sampling location is
contaminated, then sample 2x
the source area width further
along the transect.
GeoProbe Spacing on
Temporary Transect
If the 2nd sampling location is
not contaminated, then
double the sampling location
density between the 1st and
2nd location until the plume is
delineated.
Spacing on Temporary
Transect
2nd sampling
location
3rd sampling
location
4th sampling location
Source
Area
Plume
Boundary
1st sampling location
Vertical Profiling
Follow the same logic as used
with lateral well placement.
Start at the water table,
especially if the contaminant
is a LNAPL, and proceed at
an interval appropriate for
the site.
Vertical Profiling
Aquifer thickness,
contaminant properties and
distance from the source area
must be considered when
determining the initial
sampling interval.
Seminar Series on Monitored Natural Attenuation for Ground Water
4-28
-------
Vertical Profiling
The goal of vertical profiling
is to ensure that variations in
physical and biological
systems are adequately
characterized.
Vertical Profiling
As site characterization
proceeds, then the sampling
intervals can be refined.
Typically, this will involve
increasing sampling density
until distinct patterns in
physical and geochemical
parameters are obvious.
Vertical Profiling
One of the most important
physical characteristics is
hydraulic conductivity. Use
the specific capacity test to
estimate relative differences
in flow of different intervals.
Vertical Profiling
Use field test kits such as
alkalinity, Fe II, sulfide, and
dissolved oxygen to detect
variations in biological
processes in the aquifer.
Vertical Profiling
If possible, conduct
continuous vertical profiling.
This will reduce the amount
of uncertainty in site
characterization.
Vertical Profiling
Seminar Series on Monitored Natural Attenuation for Ground Water
4-29
-------
Vertical Profiling
Vertical Profiling
Vertical Profiling
Vertical Profiling
Resource Allocation
At this site, 80 monitoring
wells were installed to
characterize and monitor the
site.
Twenty of the wells do not
contribute to the
interpretation of the site.
One conventional well cost as
much as three complete
temporary push locations.
That includes installation,
well development, and
sampling.
Seminar Series on Monitored Natural Attenuation for Ground Water
4-30
-------
So, 60 temporary push
locations (continuous vertical
sampling) could have been
completed for the same cost as
the 20 wells that didn't yield
any additional information.
At this site, as with many
sites, a more thorough site
characterization and
permanent transect
installation could have been
achieved for the same cost as
a conventional site
characterization and
monitoring network.
Take Home Points
It doesn't cost the PRP's
more.
Consultants don't lose money.
Regulators can make their
decisions easier.
Seminar Series on Monitored Natural Attenuation for Ground Water
4-31
-------
Estimating Biodegradation and
Attenuation Rate Constants
Seminar Series on Monitored Natural Attenuation for Ground Water
5-1
-------
This page has been left blank intentionally
for printing purposes.
-------
Estimating Biodegradation and
Attenuation Rate Constants
John T. Wilson
Office of Research and Development
National Risk Management Research Laboratory
U.S.Environmental Protection Agency
Cincinnati, Ohio
The Source ol
Contaminatioi
Groundwater Flow
Why Calculate Rate Constants?
Why Calculate Rate Constants?
1) Calculate concentrations at the point
of attainment of standards
2) Compare rates at the site to literature
to determine if the site is behaving
like other sites
3) Predict changes caused by changes
in flow velocity
4) To determine how rapidly the ground
water plume will clean up after the
source is controlled.
Attenuation
First order rate constants?
A first order rate of 1.0 per year equivalent to
2% a week or a half life of 8.3 months
First Order Rate Constants
0.5 year
-1
1.0 year
-1
12345
Years of Experience
Seminar Series on Monitored Natural Attenuation for Ground Water
5-3
-------
Literature Values for Natural Attenuation
in Ground Water
TCE Attenuation in Microcosms
TCE Attenuation in Field
Literature Values for Natural Attenuation
in Ground Water
Anaerobic Biodegradation of Organic Chemicals in
Groundwater: A Summary of Field and Laboratory
Studies (SRC TR-97-0223F)
Dallas Aronson
Philip Howard
Environmental Science Center, Syracuse Research
Corporation, 6225 Running Ridge Road, North Syracuse,
NY 13212-2509
Field Half-Lives for PCE as Reported in
Literature
Field Rate Constants for PCE as Reported in
Literature
10000
1000
100
10
In
1000
100 £
<*
10 I
I
1 §
o
£
0.1 S
0.01
Seminar Series on Monitored Natural Attenuation for Ground Water
5-4
-------
Field Half-Lives for TCE as Reported in
Literature
Field Rate Constants for TCE as Reported in
Literature
1UUUU
s=
ra
1
J
ill I I II I
100
10
"> I
0.01
Field Half-Lives for VC as Reported in
Literature
Field Rate Constants for VC as Reported in
Literature
1UUUU
s=
ra
fl
-,
£H
100
10
0.1
Field Data
Microcosm Studies
Analyte
PCE
TCE
cis-DCE
Vinyl chloride
Number
4
18
13
6
Rate
(per year)
4.0
1.1
1.6
1.3
Analyte
TCE
cis-DCE
Vinyl chloride
1,1,1-TCA
Number
7
3
Felll
02
3
Rate
(per year)
1.6
4.3
4.0
4.2
2.0
Seminar Series on Monitored Natural Attenuation for Ground Water
5-5
-------
St. Joseph, Michigan
St. Joseph Site
Case Study
Natural Attenuation of TCE
Extracting Rate Constants
St. Joseph Site
Vertical Transects
(TRANSECTOR)
Transects form logical units for studying sites
Data in this form can be displayed in
two-dimensions:
By representing the data as rectangles around
each measurement point
(chemical mass per unit thickness =
porosity x concentration x length x width)
St. Joseph Site
The transects provide much more spatial
resolution than is usually available. They
will be taken as ground truth to evaluate
other approaches.
Seminar Series on Monitored Natural Attenuation for Ground Water
5-6
-------
St. Joseph Site
ugfL
0.2500E+06 _
0.2500E+05
2500.
250.0
25.001
2.500
0.25001
0.2500E-011
St. Joseph Site
10ft.J
St. Joseph Site
Transect-Averaged Concentrations (MS/I-)
Dissolved Oxygen below 2.0 mg/L
Chemical Transect 2 Transect 4 Transect 5 Lake Transect
TCE
7411
c-DCE 9117
t-DCE
716
1,1-DCE 339
864
1453
34.4
24.3
30.1
281
5.39
2.99
1.4
(0.80)
1.1
nd
Transect-Averaged Concentrations
Dissolved Oxygen below 2.0 mg/L
Transect-Averaged Concentrations
Dissolved Oxygen below 2.0 mg/L
Chemical Transect 2 Transect 4 Transect 5 Lake Transect
TCE 7411 864 30.1 1.4
c-DCE 9117 1453 281 (0.80)
Vinyl 998 473 97.7 (0.16)
Chloride
Chemical Transect 2 Transect 4 Transect 5 Lake Transect
Ethene 480 297 24.2 no data
Sum of the 19100 3150 442 3.5
Ethenes
Chloride 65073 78505 92023 44418
Seminar Series on Monitored Natural Attenuation for Ground Water
5-7
-------
Apparent Loss Coefficients
In
CJM = average concentration at the down gradient transect
Cj = average concentration at the up gradient transect
A. = apparent loss coefficient from transect] toj+1
21 = travel time, determined from the seepage velocity,
retardation factor and the distance
St. Joseph Site
For TCE from transect 2 to 4
For TCE from transect 4 to 5
2t = 340 weeks
cj+1 = 5.04x10-4kg/m3
GJ = 6.70x10-3kg/m3
A, = -0.38/year
2t = 145 weeks
cj+1 = 1.44x10-5kg/m3
GJ = 5.04x10-4kg/m3
A, = -1.3/year
Transect
Pair
2 to 4
4 to 5
5 to Lake
TCE
Chloride
Apparent change (per year)
-0.38
-1.3
-0.94
-0.50
-0.83
-3.1
-0.18
-0.88
-2.2
Calculate Rate Constants
The next slides are a comparison of
reconstructed hypothetical wells
using data from the Keck Slotted
Hollow Stem Auger technique to
concentrations in real monitoring
wells with short screens.
The whole approach requires
properly constructed, properly
installed, and properly maintained
monitoring wells.
Seminar Series on Monitored Natural Attenuation for Ground Water
5-8
-------
Transect 2
Transect 1
Compound
TCE
cis-DCE
Vinyl Chloride
Chloride
Reconstructed from
slotted auger samples
T-2-5
Rl Permanent
Monitoring Well
OW-19
(mg/L)
12.1
33.7
2.3
89.7
1.64
4.63
2.4
84.6
Compound
TCE
cis-DCE
Vinyl Chloride
Chloride
Reconstructed from
slotted auger samples
T-1-4
Rl Permanent
Monitoring Well
OW-18
(mg/L)
3.4
11.2
3.7
78.6
0.201
0.413
0.922
84.6
Transect 4
Transect 5
Compound
TCE
cis-DCE
Vinyl Chloride
Chloride
Reconstructed
from
slotted
auger samples
T^l-2
Rl Permanent
Monitoring Well
OW-29
Rl Permanent
Monitoring Well
OW-31
(mg/L)
1.3
2.3
0.51
98.9
<0.001
0.312
0.423
31.1
<0.001
0.255
0.120
81.1
Compound
TCE
cis-DCE
Vinyl Chloride
Chloride
Reconstructed
from
slotted
auger samples
T-5-3
Rl Permanent
Monitoring Well
OW-32
Rl Permanent
Monitoring Well
OW-31
(mg/L)
0.035
0.22
0.063
63.6
0.0024
<0.001
<0.001
16.2
<0.001
0.255
0.120
81.1
Calculate Rate Constants
St. Joseph Site
The next figure compares the
screened intervals of the permanent
monitoring wells to the intervals
sampled by the Keck Slotted Auger
technique.
Seminar Series on Monitored Natural Attenuation for Ground Water
5-9
-------
Calculate Rate Constants
Methods to Calculate Rate Constants
The permanent wells may have been
screened above or below the
centerline "hot spot".
The permanent wells would have
overestimated natural attenuation
We will use reconstructed
concentrations from the Keck
survey instead of the permanent
monitoring wells.
1) Method of Buscheck and Alcantar
(1995)
2) Normalize to a conservative tracer
3) Calibrate a mathematical model
First-Order Decay Rate for a Steady
State Plume
St. Joseph Site
where:
A, =
vc =
ax
k/vx
first order biodegradation rate constant
(approximate)
retarded contaminant velocity in the x-direcion
dispersivity
slope of line formed by making a log-linear plot
of contaminant concentration vs. distance
downgradient along flow path
Sampling Locations Along Centerline
of Plume - St. Joseph
Method of Buscheck and Alcantar
(1995)
TCE
cis-DCE
Vinyl
chloride
Organic
chlorine
T-2-5
Oft
12.1
33.7
2.3
35.8
T-1-4
200ft
3.4
11.2
3.7
11.2
T-4-2
1000 ft
mg/L
1.3
2.3
0.51
3.0
T-5-3
1500 ft
0.035
0.22
0.063
0.23
55AE
2000 ft
0.022
0.42
0.070
0.37
Linear Regression of Ln cone. TCE
against distance along the flow path
Slope of the regression is k/Vx
Seminar Series on Monitored Natural Attenuation for Ground Water
5-10
-------
Method of Buscheck and Alcantar
(1995)
St. Joseph Site
Distance
(ft)
0
200
1000
1500
2000
TCE
(mg/L)
12.1
3.4
1.3
0.035
0.022
Ln cone. TCE
2.49
1.22
0.262
-3.35
-3.82
y = -0.0032X + 2.3589
R2 = 0.9252
2!
Ln [TCE] °
(mg/L) 'I.
0 .
A .
Ji
L
B*^
"...^^ g
^"""V,,^^
^^^^^
^^«S
I
>»,.
1 !
|
500 1000 1500 2000
Distance from Source (feet)
Method of Buscheck and Alcantar
(1995)
R = 1 + Koc foe p / 6
Koc = 120 mL/g
foe = 0.001
Porosity = 0.3
Bulk Density = 1.7g/cm3
Retardation = 1.7
Method of Buscheck and Alcantar
(1995)
Contaminant velocity (Vc) equals seepage
velocity divided by the retardation factor
Vc = 1.3 ft per day/1.7
= 0.76 ft per day
= 277 ft per year
Method of Buscheck and Alcantar
(1995)
When
Vc = 277 ft per year
a = 100 feet
x
k/Vx = -0.0032
Then
X = -0.00165 per day
= - 0.602 per year
Normalize to a Conservative Tracer
Will use the sum of chloride ion and
organic chlorine as a tracer
Seminar Series on Monitored Natural Attenuation for Ground Water
5-11
-------
Normalize to a Conservative Tracer
Multiply the concentration of chlorinated
organic analytes by their mass fraction
of chlorine
Sum the concentrations of chloride ion
and organic chlorine in each chlorinated
analyte
Mass Fraction Chlorine
Compound
PCE
TCE
DCE
Vinyl
chloride
Daltons
166
137.5
97
62.5
Daltons
Chlorine
142
106.5
71
35.5
Mass Fraction
Chlorine
0.855
0.810
0.732
0.568
Sampling Locations Along Centerline
of Plume - St. Joseph
Chloride
Organic
Chlorine
Total
Chlorine
& Chloride
T-2-5
Oft
89.7
35.8
125.5
T-1-4
200ft
78.6
11.2
89.8
T-4-2
1000 ft
mg/L
98.9
3.0
101.9
T-5-3
1500 ft
63.6
0.23
63.8
55AE
2000 ft
54.7
0.37
55.1
Normalize to a Conservative Tracer
Multiply the concentration of analyte
down gradient by the dilution of the
tracer to estimate the concentration
expected in the absence of dilution
Calculation of Corrected Concentration
Where flow of ground water is from point A to point B:
C (Chloride A /Chloride B)
B, Corr
B, Corr B
corrected concentration of contaminant at point B
measured concentration of contaminant at point B
Chloride A = measured concentration of tracer at point A
Chloride B = measured concentration of tracer at point B
Normalize to a Conservative Tracer
From T-2-5 to 55AE, for TCE
Corrected = 0^022 mg/L (125.5 mg/L)
Concentration
(55.1 mg/L)
= 0.050 mg/L
Seminar Series on Monitored Natural Attenuation for Ground Water
5-12
-------
First-Order Decay
C= C0eKt
where:
C = contaminant concentration at time t
CQ = initial contaminant concentration
k = first-order rate constant
Normalize to a Conservative Tracer
From T-2-5 to 55AE, for TCE
C = C ekt
(55AE) (T-2-5)
(0.050/12.1) = ekt
Normalize to a Conservative Tracer
ln(0.050/12.1) = kt
-5.49 = kt
k = -5.49/t
Normalize to a Conservative Tracer
The locations are 2,000 feet apart.
If the seepage velocity is 1.3 feet per day,
the retarded TCE velocity = 1.3/1.7 feet per day
= 0.76 feet per day
Normalize to a Conservative Tracer
Normalize to a Conservative Tracer
The travel time = 2,000 feet / 0.76 feet per day
= 2,631 days
k = - 5.49 / 2,631 days
= -0.00208/day
= -0.76/year
Seminar Series on Monitored Natural Attenuation for Ground Water
5-13
-------
Comparison of Rate Constants
Normalize to a conservative tracer
= -0.76 per year
Method of Buscheck and Alcantar
= -0.602 per year
Transect comparisons
= -0.94 per year
= -1.3 per year
= -0.38 per year
Calibrate BIOSCREEN
West Plume at St. Joseph, Michigan
Calibrate BIOSCREEN
Use the next figure to estimate the
hydraulic gradient
See following page for a full-size version of the slide.
St. Joseph Site
The average hydraulic
conductivity is 50 feet per
day or 0.02 cm per sec.
Seminar Series on Monitored Natural Attenuation for Ground Water
5-14
-------
Table is missing but will be added in the
near future.
Thank you for your patience.
-------
Hydraulic Conductivity at 55 AE
along the beach
U.U4 ~
S
I 0.03
o _
c u
50)
.2 0.02
= 1
|~ 0.01
n -
, n
PI
-
p.
n
6 12 18 24 30
Depth (feet)
1. HYDROGEOLOGY
Seepage Velocity*
or
Hydraulic Conductivity
Hydraulic Gradient
Porosity
2. DISPERSION
Longitudinal Dispersivity*
Transverse Dispersivity*
Vertical Dispersivity*
or
stimated Plume Length
Vs
4. BIODEGRADATION
1 st Order Decay Coeff*
or
Solute Half-Life
lambda
t-half
or Instantaneous Reaction Model
Delta Oxygen*
Delta Nitrate*
Observed Ferrous Iron*
Delta Sulfate*
Observed Methane*
DO
NO3
Fe2+
SO4
CH4
6.0E-1 (peryr)
/^ or
1.15 \(year)
0 (mg/L)
0 (mg/L)
0 (mg/L)
0 (mg/L)
0 (mg/L)
Calibrate BIOSCREEN
Use the next figure to estimate the
geometry of the plume.
The vertical scale bar in the upper
left corner represents 20 feet.
St. Joseph Site
5. GENERAL
Modeled Area Length*
Modeled Area Width*
Simulation Time*
2000
500
10
6. SOURCE DATA
Source Thickness in Sat. Zone*
(ft) f^^"
(yr) +
~80~\(ft)
Source Zones: ^__^~-
Width*(ft) I Cone. (mg/L)* V*~~~~~~~^
Verti
--Secti
for Zo
Seminar Series on Monitored Natural Attenuation for Ground Water
5-16
-------
Calibrate BIOSCREEN
Use the next figure to set up the
lanes in BIOSCREEN for TCE
attenuation.
St. Joseph Site
Sampling locations along upstream transect
T2-7 T2-2 T2-5 T2-1 T2-6 T2-4 T2-2
Distance from south end of transect, feet
0 125 155 185 230 275 350
Average cone. TCE, mg/liter
0.02 15.9 12.1 11.0 1.1 0.39 0.68
18
16
14
? 12
I «
£ 8
LU
O 6
4
2
0
100 200 300
Distance from South End (feet)
7. FIELD DATA FOR COIVPARISON
Concentration (mg/L)
Dist. from Source (ft)
Calibrate BIOSCREEN
Use the next table to set up field
data in BIOSCREEN for attenuation
of TCE.
Seminar Series on Monitored Natural Attenuation for Ground Water
5-17
-------
Sampling Locations Along Centerline
of Plume - St. Joseph
TCE
cis-DCE
Vinyl
chloride
T-2-5 T-1-4
0 ft 200 ft
12.1
33.7
2.3
3.4
11.2
3.7
T-4-2
1000 ft
T-5-3 55AE
1500 ft 2000 ft
mg/L --------------
1.3 0.035
2.3
0.51
0.22
0.063
0.022
0.42
0.070
7. FIELD DATA FOR COMPARISON
Concentration (mg/L)r
Dist. from Source (ft)B
8. CHOOSE TYPE OF OUTPUT TO SEE:
RUN ARRAY
:
RUN
CENTERLINE
View Output
View Output
Recalculate This
Sheet
Paste Example Datase
Restore Formulas for Vs,
Dispersivities, R, lambda, other
Calibrate BIOSCREEN
Results from RUN CENTERLINE
Calibrate BIOSCREEN
Results from RUN ARRAY
See following page(s) for a full-size version of the slide.
.TIONS IN HAJME (mg/L at Z=o
See following page(s) for a full-size version of the slide.
Seminar Series on Monitored Natural Attenuation for Ground Water
5-18
-------
Table is missing but will be added in the
near future.
Thank you for your patience.
-------
Table is missing but will be added in the
near future.
Thank you for your patience.
-------
Gallons Plume Mass if No Biodegradation| 5602.6 \(Kg)
- Actual Plume Massl 835.3 \(Kg)
- Plume Mass Remold by Biocleg|
S HELP f~
Return to Input
Calibrate BIOSCREEN
1.0 acre foot per year =
3.4 cubic meters per day
0.62 gallons per minute
Sources of information
100 acre feet per year =
0.09 million gallons per day
BIOSCREEN
BIOSCREEN and BIOPLUME III are
available on the NRMRL/SPRD Web
page:
http://www.epa.gov/ada/kerrlab.html
Information by Phone, FAX, or Mail
NCEPI
Order documents and databases with "EPA"
document numbers free of charge
FAX requests to 513-489-8695
Mail requests to NCEPI, PO Box 42419,
Cincinnati, OH 45242
NTIS
Purchase products with "PB" document numbers
Order by phone at 703-487-4650 or800-553-NTIS
(for rush service)
Seminar Series on Monitored Natural Attenuation for Ground Water
5-21
-------
TIO Information Online
Clean-up Information (CLU-IN) System
WWW site
- http://clu-in.com
- Go to "Publications and Software" area
to download publications and databases
Seminar Series on Monitored Natural Attenuation for Ground Water
5-22
-------
Risk Management of Monitored
Natural Attenuation
Seminar Series on Monitored Natural Attenuation for Ground Water
6-1
-------
This page has been left blank intentionally
for printing purposes.
-------
Risk Management of Monitored
Natural Attenuation
John T.Wilson
Office of Research and Development
National Risk Management Research Laboratory
U.S.Environmental Protection Agency
Cincinnati, Ohio
The Plume of
= Contaminated
Ground Water
, The Source of
Contamination
Groundwater Flow
Benefits of Source Control
Benefits of Source Control
Case study:
Characterization and Monitoring Before
and After Source Removal at a Former
Manufactured Gas Plant (MGP)
Disposal Site
EPRI TR-105921 Final Report Jan 1996
Source Area- 1/4 acre
Depth of Contamination- 0 to 20 feet
Volume of Contamination- 96,000 cubic yards
Water Table- 7 feet
Geology- 20 feet of sand over silty clay
Estimated Groundwater Naphthalene Plume and Groundwater
Contours Based on the 1983 Investigation
Benefits of Source Control
Costs for remedy $3,087,000
site work 37%
soil transportation 34%
soil treatment 24%
waste water disposal 5%
Seminar Series on Monitored Natural Attenuation for Ground Water
6-3
-------
Location of Downgradient Geological Cross Sections
Concentration (mg/L)
Centerline
Groundwater
Concentrations
Naphthalene Groundwater Plume in 1990 and 1991
Areal View
Pre - Source Removal - June 1990
B x, c
Concentration
|mg/L)
Sample Location
I >2.0 IM 1.0-2.0 SIS 0.5-1.0
s 0.1 -0.5 ma 0.01-0.1
Naphthalene Groundwater Plume in 1990 and 1991
Areal View (Cont'd)
Post Source Removal - November 1991
Concentration
(mg/L)
Sample Location
I >2.0 1.0-2.0 PS 0.5-1.0
SD 0.1 - 0.5 O 0.01 - 0.1
Naphthalene Groundwater Plume in 1992
Areal View
Post - Source Removal - May 1992
Naphthalene Groundwater Plume in 1993
Areal View
Post - Source Removal - April 1993
Sample Location
A A
Transect
Concentration
(mg/L)
I >2.0 1.0-2.0 M 0.5-1.0
B 0.1-0.5 EH 0.01-0.1
Sample Location
Concentration
(mg/L)
A A
Iransect
I >2.0 " 1.0-2.0 en 0.5-1.0
em 0.1 -0.5 a 0.01 -0.1
Seminar Series on Monitored Natural Attenuation for Ground Water
6-4
-------
Naphthalene Groundwater Plume in 1994
Areal View
Post - Source Removal - April 1994
Source A
Removal
Area
o Sample Location
I >2.0 u 1.0-2.0 m 0.5 -1.0
D 0.1 - 0.5 HO 0.01 - 0.1
Toluene Groundwater Plume
Areal View
Pre - Source Removal - June 1990
E r
0200
Scale (ft)
Sample
Location
A A
Transect
Concentration
(mg/L)
>2.0
H 1.0-2.0
n 0.6 - t.o
13 0.1 -0.5
Oil 0.01 -0.1
Toluene Groundwater Plume
Areal View (Cont'd)
Post - Source Removal - October 1992
Acenaphthylene Groundwater Plume
Areal View
Pre - Source Removal - June 1990
C D
200 Concentration
E
F Scale (ft)
\ = Sample
^m MiA Location
\ A A
\ Transect
(mg/L)
>2.0
a i.o - 2.0
H 0.5 - 1.0
^a 0.1 - 0.6
irrrg Q.01 - 0.1
Acenaphthylene Groundwater Plume
Areal View (Cont'd)
Post - Source Removal - October 1992
A A
Transect
\Concentration
(mg/U
>2-0
m 1.0 -2.0
£3 0.5-1.0
HI 0.1 - 0.5
BIES 0.01 -0.1
Phenanthrene Groundwater Plume
Areal View
Pre - Source Removal - June 1990
c
D
,
0 200
E F Scale (ft)
\° Sample
Location
A A
\ Transect
Concentration
(mg/L)
>2.0
B 1.0-2.0
n 0.5 - 1.0
^ 0.1 - as
E33 0.01 -0.1
Seminar Series on Monitored Natural Attenuation for Ground Water
6-5
-------
Phenanthrene Groundwater Plume
Areal View (Cont'd)
Post - Source Removal - October 1992
November 1994
o 200
Scale (ft)
Sample
Location
A A
Transect
\Concertration
(ma/L)
>2.0
B 1.0 - 2.0
n 0.5 -1.0
IS 0.1 - 0.5
go 0.01 -0.1
Naphthalene Groundwater Concentrations in 1990 and 1991
Cross-Sectional View
Pre - Source Removal - June 1990
Elevation (ft msl)
290 T-
Top or
Confining Layer
400
1000
1200
Concentration
(mg/L)
Distance From Source (ft)
I >2.0 1.0-2.0 0.5-1.0 H 0.1-0.5 EJ 0.01-0.1
Naphthalene Groundwater Concentrations in 1990 and 1991
Cross-Sectional View (Cont'd)
Post - Source Removal - November 1991
Top of
confining Layer '
Concentration
(mg/L)
10 400 EDO 800 1000 1200
Distance From Source (ft)
I >2.0 m 1.0-2.0 0.5-1.0 H 0.1-0.5 0.01-0.1
Naphthalene Groundwater Concentrations in 1994
Cross-Sectional View
November 1994
-V
1000 1200
Concentration
(mg/L)
Distance From Source (ft)
I >2.0 1.0-2.0 0.5-1.0 H 0.1-0.5 B 0.01-0.1
Measured and
MYGRT-Predicted
Naphthalene
Concentrations in
Groundwater
tepe^im Coefficient (Dx)
Dispersion Coefficient (Dz)
Seepage Velocity (V)
Penalralion Depth (Pd)
Saturated Depth of Aquifer (d
Decay Coefficient (k)
= 21,500.0 ftV
= 215.0 ttV
= 1150 ft/yr
131 ft
4.0
- 01 /yr
Distance from Source (ft)
-4 Measured concantral
MYGRT predicled CD
Measured and Predicted Naphthalene Concentrations
November 1994
Distance from Source (ft)
+ Naphthalene concentrations
MYGRT-predicted concentrations
Input Parameters:
Dispersion Coefficient (Dx) = 21,500.0 ft /yr
Dispersion Coefficient (Dz) = 215.02ft /yr
Seepage Velocity (V) = 115,0 ft/yr
Penetration Depth (Pd) = 120 fl
Saturated Depth of Aquifer (d)
Retardation Coefficient (Rd)
Decay Coefficient (k)
» 13.1 ft
= 4.0
= 0.1 /yr
Seminar Series on Monitored Natural Attenuation for Ground Water
6-6
-------
Benefits of Source Control
After source removal, the aquifer cleaned up
from the front end to the tail end.
The benefit moved faster than the average
seepage velocity. The whole plume cleaned
up, not just the front end.
Plume projected to reach NYDEC Drinking
Water Standard for Naphthalene by 2030.
Seminar Series on Monitored Natural Attenuation for Ground Water
6-7
-------
Large Chlorinated Solvent Plume
Natural Attenuation Model Study
Calibrated to Long Term Monitoring
Data
«*EPA _,._..
Basic Model Input Parameters
Hydraulic Conductivity = 280 ft/day
Thickness =190 feet including unconsolidated sand and
fractured bedrock aquifers
Effective porosity = 0.20
Retardation factor =1.0
Start time for model approximately 1940
Model domain x = 53,000 feet y = 30,000 feet
Pumping from recovery wells active for all simulations
according to published rates. Pump and treat began in
1989
SEPA.
Simulated Static Water Level
Simulated Water Level With
Active Recovery Wells
Flow Model Conclusion:
I Regional flow appears to be strongly
influenced by river navigation system
causing flow to converge southeast
I Recovery wells do no appear to modify
flow patterns significantly on a regional
scale
Initial Simulation:
No Source or Dissolved Decay
Source 1:
- Located: North half of site
- Active from beginning of model
Source 2:
- Located: South half of site
- Active from 1960
SEPA.
Seminar Series on Monitored Natural Attenuation for Ground Water
6-8
-------
No Decay Simulation
«*EPA _,._.,
SEPA ,
SEPA
Seminar Series on Monitored Natural Attenuation for Ground Water
6-9
-------
No Decay Simulation Conclusions
I Contaminants are predicted to reach the
river with no natural degradation or source
removal
I Time to reach river -34 years
I Steady state reached in -46 years
r/trH.^ *___
Addition of Source Decay
Location of Key Observation Wells
Observed TCE at Well 3u020
In Years Beginning 1987
h-
\
\
\
^v,
y = 10026e-°2668x
R
Vv<,
2 = 0.7853
*
'"*-
0246
Years After 1987
>
-J
3 10 12
0)
LU
° 600
c
Observed TCE at Well O3u821
In Years Beginning 1 987
, y = 1292.6e-°3559x
\ R2 = 0.9073
V
\
^v^.
* __
2 4 6 8 10 12
Years After 1987
D
Second Simulation:
Addition of Source Decay
I Source decay fit to actual decline in
concentrations in monitoring wells over
time
I Source decay added according to first order
kinetics with k = 0.25 per year
I Sources held constant till 1988 after which
decay was allowed
Seminar Series on Monitored Natural Attenuation for Ground Water
6-10
-------
Source Decay Simulation
«*EPA _,._.,
]000 25000 30000 35000 40000 45000 50000
Simulated TCE
Source Decay Only
After 1987
Simulated TCE
Source Decay Only
After 1987
5000 10000 15000 20000 25000 30000 35000 40000 45000 50000
Simulated TCE
Source Decay Only
After 1987
]00 30000 35000 40000
Simulated TCE
Source Decay Only
After 1987
ft
25000 30000 35000 40000 45000 50000
Simulated TCE
Source Decay Only
After 1987
SEPA ,
SEPA .
Seminar Series on Monitored Natural Attenuation for Ground Water
6-11
-------
Source Decay Simulation
Conclusion:
I Without dissolved phase natural attenuation,
TCE still would be predicted to reach the
river even though pumping and source
decay/removal are active
I Plume duration is ultimately controlled by
source discharge of TCE to the aquifer from
the source area
Third Simulation:
Addition of Intrinsic Bioremediation
I Bioremediation added at k = 0.35 per year
or half life = 2 years
I Rates applied throughout the time domain
of the simulation
I Pumping and source decay still active
Comparison of Simulation Results
14000 -
Obs
V
\
»
srved an
X
d Predic
in Years
><^
ted TCE
after 1£
B
" »
0 2 4 6 E
at Well
87
03U020
« Observed
Predicted
Expon
(Observed]
10 12
Predicted TCE Through Centerline of Plume
(Time = 1986)
|
1 25°°°
c
8
No Dissolved
4 Natural Attenuation
.
""_.
* Dissolved Phase " "
* ^ Natural Attenuation
* * *
0 10000 20000 30000 40000 50000
Distance from Source (Feet)
Go to Location Map
;-!-!'£ .
Relatvie TCE (Ct/Co)
Comparison of Relative TCE Concentrations at a
Well 3U020 With and Without Source Decay
'
'
i Source Decay
»
'
0 2 4 6 8 10 12
Time After 1987 (Years)
Go to Location Map
Source and Dissolved Phase
Decay Simulation
Seminar Series on Monitored Natural Attenuation for Ground Water
6-12
-------
r/trH.^ *___
n
SEPA.
n
SEPA
SEPA
Seminar Series on Monitored Natural Attenuation for Ground Water
6-13
-------
Source and Dissolved Phase
Decay Simulation Conclusions:
I Plume length and width reduced
I TCE is predicted to not reach the river at
concentrations greater than 5 ug/L
I Plume reaches steady state in 20 years
after release
I Concentrations of < 5 ug/L are reached
everywhere in the plume approximately
year 2022
Effect of Source Control
r/trH.^ *___
D
Pumping Assumptions
I Model assumes fully penetrating recovery
wells with completely mixed TCE solute
across the aquifer's saturated thickness
I Actual pumping may or may not recover
TCE as predicted due to the vertical
position of the well screen relative to
contaminant distribution
Simulated Total Control of TCE
by Pumping
I Total control of release of TCE was
simulated by eliminating the sources after
1988.
I Recovery well pumping rates were
maintained at the same level as all prior
simulations to simulate capture of the
existing plume.
Theoretical TCE Control by
Pumping
Seminar Series on Monitored Natural Attenuation for Ground Water
6-14
-------
r/trH.^ *___
D
D
SEPA.
SEPA
D
Conclusions
I Decreased concentrations along plume
length are due to dissolved phase
biotransformation (concentration v. distance
from the source)
I Decreased concentrations at a particular
monitoring location in the plume path are
due to source control (concentration v. time
of long-term monitoring)
£EPA
Seminar Series on Monitored Natural Attenuation for Ground Water
6-15
-------
Calculating Confidence Intervals
on Rate Constants
John T. Wilson
Back-of-the-Envelope Prediction of the
Rate of Remediation, using Simple
Regression Techniques
assume:
Stable contaminant plume
Contaminant plume contained within the foot print of
geochemlcal tracers
Contaminant attenuation follows a first-order rate law
Core of the Plume has been Identified
Monitoring wells available along the core center-line
St. Joseph Site
St. Joseph Site
1000
~ 100 -
I
10 -
c
o
I 1-
0)
C
o
<-> 0.1 -
0.01
Chloride Tracer
y = 11.332e
0246
Travel Time Down Gradient (years)
Distance
0
200
1000
1500
2000
Years
0
0.722022
3.610108
5.415162
7.220217
TCEug/L
12.1
4.7
1.6
0.07
0.051
LN TCE Cone.
2.493205453
1.547562509
0.470003629
-2.659260037
-2.975929646
Seminar Series on Monitored Natural Attenuation for Ground Water
6-16
-------
SUMMARY OUTPUT
Regression Statistics
Multiple R 0.96600234
R Square 0.93316052
Adjusted R Squart.910880694
Standard Error 0.73892431
Observations 5
ANOVA
2
Regression
Residual
Total
Intercept
X Variable 1
df
1
3
4
Coefficient
2.427631492
-0.78164541
SS
22.86885714
1.638027408
24.50688455
Standard Erro
0.526485602
0.120777909
Upper 95
4.103145223
-0.39727584
tower 95.0%
0.752117761
-1.166014981
100000 -<
10000 -
1000
100
10
1
First order rate of attenuation 0.40 per
. year
0 5 10 15 20 25
Time after source control (years)
Seminar Series on Monitored Natural Attenuation for Ground Water
6-17
-------
Sampling, Analysis, and
Monitoring to Evaluate Monitored
Natural Attenuation
Seminar Series on Monitored Natural Attenuation for Ground Water
7-1
-------
This page has been left blank intentionally
for printing purposes.
-------
Site Characterization
Seminar Series on Monitored Natural Attenuation for Ground Water
7-3
-------
This page has been left blank intentionally
for printing purposes.
-------
Monitoring the Effectiveness of
Natural Attenuation
U.S. Geological Survey
and
Barbara H. Wilson
Methods for Monitoring
Contaminants
^
Aromatic and
chlorinated
hydrocarbons
(BTEX,
trimethylbenzen
eisomers,
chlorinated
Method/Reference
SW8020 (sites with
petroleum
hydrocarbons only)
SW8260A (sites with
chlorinated solvents or
mixed
hydrocarbons)
Comments
Handbook method;
analysis may be
extended to higher
molecular weight
alkyl benzenes
Monitoring for Geochemical
Conditions
Analytical Parameter
Dissolved oxygen (DO)
Nitrate (NO3)
Nitrite (NQj)
Dissolved ferrous iron (Fe2*)
Sulfate (S04)
Hydrogen sulfide (ESS)
Dissolved Methane (CH,)
pH (units)
Hi (redox potential)
Dissolved Hydrogen (ft)
Field or laboratory parameter
field
laboratory
laboratory
field
laboratory
field
laboratory
field
field
field
Method of analysis
meter, field kit titration
Ion Chromatography
Ion Ctaniogr^hy
Hddkit.p.cta.photomd.r
Ion Chromatography
Field kit spectrophotometer
GCFID1
meter
meter
gas Chromatography2
When Hydrogen Analyses are
Useful
Some chlorinated solvents
plumes exhibit attenuation of
solvents without significant
accumulation of transformation
products.
If hydrogen concentrations
range from 1 nannomolar to 4
nannomolar, reductive
dechlorination will occur.
Molecular Hydrogen
(H2)drives Reductive
Dechlorination
Cl Cl
c=c
Cl, Cl
(Gosset and Zinder, 1996)
TCE Chloride
Steady-State Hydrogen
Concentrations Reflect
Redox Processes
Terminal Electron- Accepting Process
Derritrification
Fe(m) Reduction
Sulfate Reduction
Methano gene sis
Characteristic Hydrogen Concentration (nM)
0.1
0.2-0.8
1.0-4.0
>5.0
Seminar Series on Monitored Natural Attenuation for Ground Water
7-5
-------
Gas Sampling Port
60
50 -
40 -
30 -
20 -
Equilibrium hydrogen concentration in bubble
Hydroger
/ bubble
Hydrogen concentration in water 41 nMolar
Water flow rate 300 ml/minute.
Bubble volume 20 ml.
Bulb volume 250 ml.
0 5 10 15 20 25 30
Equlibration time (minutes)
Monitoring Strategies
There are three kinds of monitoring.
Monitoring Strategies
There are three kinds of monitoring.
1) Site characterization to describe disposition of
contamination and forecast its future behavior.
2) Validation monitoring to determine whether the
predictions of site characterizations are accurate.
3) Long-term monitoring to ensure that the
behavior of the contaminant plume does not
change.
1) Site characterization to describe disposition of
contamination and forecast its future behavior.
2) Validation monitoring to determine whether the
predictions of site characterizations are accurate.
3) Long-term monitoring to ensure that the
behavior of the contaminant plume does not
change.
Monitoring Wells Often Miss
the Plume (Plan View)
Until you have wells, you don't know
the direction of ground-water flow
18
Seminar Series on Monitored Natural Attenuation for Ground Water
7-6
-------
Monitoring Wells May Underestimate
Contaminant Concentrations
Example of Characterization
Monitoring
It's not nice to fool Mother Nature,
but she doesn't mind fooling you
Fate of MTBE relative to
benzene at a gasoline spill site
(1993-98)
By
James E. Landmever
U.S. Geological Survey
Battelle Conference, May 1998
Jwel996
Seminar Series on Monitored Natural Attenuation for Ground Water
7-7
-------
Jcnnyl998
Site Characterization
Distribution of contamination can be
mapped using:
Geoprobe samples
The Waterloo sampler
Hydropunch samples
other water sampling through a cone
penetrometer
extraction of core samples
soil gas sampling
Example: Characterization
Monitoring: Kings Bay, GA
Monitoring Wells
Geoprobe Source area delineation
Redox parameters
Chlorinated ethenes
Site Characterization
Each potentially transmissive
interval should be sampled
YOU OUGHT TO KNOW
WHERE THE WATER'S
GOING TO GO BEFORE YOU
PUT IN YOUR WELLS!!
Until you have wells, you don't know
the direction of ground-water flow
18
Seminar Series on Monitored Natural Attenuation for Ground Water
7-8
-------
Old Camden County Landfill,
Kings Bay, GA
Site Characterization
The density of sampling during
the site characterization must be
related to:
The geological complexity of the
site
Location of Source Areas and
Contamination Plume
Redox Zonation of
Kings Bay Site
Redox Zonation of
Kings Bay Site (Cont'd)
Concentrations of Changes of
Chlorinated Ethenes
Seminar Series on Monitored Natural Attenuation for Ground Water
7-9
-------
Natural Attenuation of
Chlorinated Solvents, Old
Camden County Landfill
Is relatively efficient.
Nevertheless, it is not efficient enough
to meet remediation goal.
NA was combined with source
removal.
CAP Specifies Source Area
removal, Plume is treated
with Natural Attenuation.
Example: Characterization
Monitoring: Albany, GA
Monitoring Wells
Redox parameters
Chlorinated ethenes
Marine Corps Logistics Base,
Albany, Georgia
Well ALB 12-lB-Redox
Conditions not favorable for
Reductive Dehalogenation
DO = 7.5mg/L
H2 = 0.05nM
CH4 < 0.02 mg/L
Benzene < 0.2 jig/L
TCE = 2,202 ng/L
cis DCE < 0.2
VC
Well 2218-MW2-Presence
of BTEX drives Reductive
Dehalogenation
DO = 2.0 mg/L
H2 = 7.3 mg/L
CH4 = 0.7 mg/L
Benzene =151
Hg/L
TCE = 168 ng/L
cis DCE = 568
Hg/L
VC = 236
Seminar Series on Monitored Natural Attenuation for Ground Water
7-10
-------
Well2218-MW-l- Water
Chemistry Records Past
Reductive Dehalogenation
DO = 5.0mg/L
CH4 < 0.02 mg/L
Benzene < 0.2
TCE = 201
cis DCE = 71
VC = 2.7
Redox Chemistry gives a
Snapshot in Time.
It may not reflect the historical
behavior of the contamination.
It may not predict future behavior of
the contamination.
Kings Bay is an Example of
Efficient NA~Albany is an
example of Inefficient NA
This illustrates why characterization
monitoring is so important for
assessing natural attenuation.
EVERY SITE IS DIFFERENT!!!
Site Characterization
Monitoring Should Consider
Multiple Lines of Evidence
Redox Conditions
Presently observed conditions
Distribution of Daughter Products
Record of past conditions
Hydrologic Framework
Prediction of future conditions
Seminar Series on Monitored Natural Attenuation for Ground Water
7-11
-------
This page has been left blank intentionally
for printing purposes.
-------
Verification and Long-term Monitoring
Seminar Series on Monitored Natural Attenuation for Ground Water
7-13
-------
This page has been left blank intentionally
for printing purposes.
-------
Monitoring the Effectiveness of
Natural Attenuation
U.S. Geological Survey
and
Barbara H. Wilson
Monitoring Strategies
There are three kinds of monitoring.
1) Site characterization to describe disposition of
contamination and forecast its future behavior.
2) Validation monitoring to determine whether the
predictions of site characterizations are accurate.
3) Long-term monitoring to ensure that the
behavior of the contaminant plume does not
change.
Validation Monitoring
Once a conceptual model has
been accepted, a period of
monitoring is required to verify
that the forecast of the
conceptual model is adequate
Monitoring Wells Often Miss
the Plume Vertically
Until you have wells, you don't know
the direction of ground-water flow
18
Monitoring Wells May Underestimate
Contaminant Concentrations
Seminar Series on Monitored Natural Attenuation for Ground Water
7-15
-------
The frequency of
validation monitoring
should be related to:
Example: Woodlawn NPL Site
Cecil County, Maryland
The natural variability in contaminant
concentrations
The distance and time of travel from the source to
the location where the acceptance criteria are
applied
The reduction in contaminant concentration
required to meet the acceptance criteria
Vinyl Chloride Plume in
Decomposed Rock (Saprolite)
and Fractured Bedrock.
VC at this site is from an industrial
source.
Woodlawn NPL Site
Cecil County, Maryland
Decomposed rock (saprolite)
Woodlawn NPL Site
Cecil County, Maryland
Occurrence of ground water in the Piedmont
Observed Water Levels
March 1996
Woodlawn NPL Site
Cecil County, Maryland
Saprolite
Generalized North/South Geologic Cross-Section
Woodlawn NPL Site
Cecil County, Maryland
Sandy silt
Saprolite
Generalized East/West Geologic
Cross-Section
Seminar Series on Monitored Natural Attenuation for Ground Water
7-16
-------
Woodlawn NPL Site
Cecil County, Maryland
Woodlawn NPL Site
Cecil County, Maryland
Saprolite
Hydraulic Conductivity
Hydraulic Gradient
Seepage Velocity
Plume Length
Half Life total plume
0.24 to 0.79 ft/d
0.06
87 ft/year
1,000 feet
-0.3 years
;erved Vinyl Chloride Concentration
in the Saprolite
November 1987
Woodlawn NPL Site
Cecil County, Maryland
Woodlawn NPL Site
Cecil County, Maryland
Observed Vinyl Chloride Concentration
in the Saprolite
March 1996
;erved Vinyl Chloride Concentration
in the Bedrock
November 1990
Woodlawn NPL Site
Cecil County, Maryland
Contaminant Transport
Contaminant plume appears to be
moving through fractured portions of the
bedrock.
Observed Vinyl Chloride Concentration
in the Bedrock
March 1996
Seminar Series on Monitored Natural Attenuation for Ground Water
7-17
-------
Woodlawn NPL Site
Cecil County, Maryland
VC degradation:
WHY IS IT HAPPENING?
Aerobic Oxidation (most rapid)
» 2O2 + CH2 = CHCI » 2CO2 + 3H+ + Cl
Anoxic Oxidation
10Fe3
CH2 = CHCI + 4H2O -> 2CO2
10Fe2+
Volatilization
Sorption (very low for vinyl chloride)
Cl
Location of Well F-6
Woodlawn NPL Site
Cecil County, Maryland
;erved Vinyl Chloride Concentration
in the Saprolite
November 1987
1400
1200
1000
800-
60°
- 400
200
0
Monitoring Well F-6 at Woodlawn Landfill
y = 1221.6ug/Le-°3057(xyears)
0 2 4 6 8 10
Time (years since 1/1987)
12
Monitoring Strategies
Long-term Monitoring
There are three kinds of monitoring.
1) Site characterization to describe disposition of
contamination and forecast its future behavior.
2) Validation monitoring to determine whether the
predictions of site characterizations are accurate.
3) Long-term monitoring to ensure that the
behavior of the contaminant plume does not
change.
If validation monitoring
documents that natural
attenuation will meet the
acceptance criteria, then a
program of long-term monitoring
should be implemented.
Seminar Series on Monitored Natural Attenuation for Ground Water
7-18
-------
Long-term Monitoring
The interval of sampling should
be related to the expected time
of travel of the contaminant
along the flow path from one
monitoring well to the next.
Example of Validation & Long-Term
Monitoring:Charleston MGP Site
Contaminants in Ground Water
Hydrogeology of MGP Site
Simulation of Plume Migration
See following page for an enlarged version of this slide.
Long-Term Monitoring Plan for
the MGP Site
Model indicates plume is stationary. Long
Term Monitoring designed to evaluate
changes in plume size.
GW time of travel is relatively slow (-40
ft/yr). Quarterly sampling is probably too
frequent; annual or biannual sampling is
more appropriate.
Seminar Series on Monitored Natural Attenuation for Ground Water
7-19
-------
Criteria for Success
Seminar Series on Monitored Natural Attenuation for Ground Water
8-1
-------
This page has been left blank intentionally
for printing purposes.
-------
Criteria for Sucess
Criteria for Success
Francis Chapelle
John T. Wilson
Fran Kremer
Kelly Hurt
* Understand how the plume is formed in the
first place
"Understand the rate of transport and the rate
of attenuation
"Understand the persistence of the
contaminant mass
Criteria for Success
Criteria for Success
* Understand how the plume was formed in the
first place
Understand the 3-dimensional distribution of
the original source of contamination
Understand the movement of water and vapor
through and from the original source
* Understand how the plume was formed in the
first place
Does existing ground water contamination
make sense based on what is known about the
original source material and the hydrogeology
of the site?
Criteria for Success
Criteria for Success
"Understand the rate of transport and the rate
of attenuation
What is the natural variation in ground water
flow velocity and flow direction?
What is the seepage velocity of the lithology
that actually carries the plume?
"Understand the rate of transport and the rate
of attenuation
What is the mass flux of contaminants?
Is it decreasing along the flow path?
Seminar Series on Monitored Natural Attenuation for Ground Water
8-3
-------
Criteria for Success
Criteria for Success
What is the relative importance in
understanding?
hydraulic conductivity
hydraulic gradient
dispersivity
rate of biodegradation
Uncertainty Analyses of Fuel Hydrocarbon
Biodegradation Signatures in Ground Water by
Probabilistic Modeling
W.W. McNab and B.P. Dooher
Ground Water 36(4):691-698 July August 1998
60
I 50
ss
V 40
u
c
re
te 30
| 20
o
| 1"
,9 o
Hydraulic Conductivity
Degradation Rate
50 100 150 200 250
Distance from Source (feet)
_ 60
I 50
I 40
U
I 3(H
o
I 10
Gradient
50 100 150 200 250
Distance from Source (feet)
300
Criteria for Success
Criteria for Success
"Understand the rate of transport and the rate
of attenuation
What is the confidence in the method used to
estimate hydraulic conductivity?
Is the resolution of the monitoring well system
defined and documented?
"Understand the rate of transport and the rate
of attenuation
Will the current rate of attenuation be
maintained?
Will an acceptable rate of attenuation be
maintained?
Seminar Series on Monitored Natural Attenuation for Ground Water
8-4
-------
Criteria for Success
Criteria for Success
"Understand the rate of transport and the rate
of attenuation
Is there a sufficient supply of electron
acceptors or donors to complete attenuation of
the contaminants in ground water?
The resolution of each well in the monitoring
well system is the product of:
Lateral distance between adjacent monitoring
wells in a transect
Vertical screen interval
Darcy velocity of ground water
Time between samples
Criteria for Success
Criteria for Success
The resolution of each well in the monitoring
well system has the units of volume.
Acre feet
Million gallons
Cubic feet.
When the resolution of the permanent
monitoring wells is predetermined, then the
monitoring system can designed and scaled to
meet that predetermined resolution.
Criteria for Success
Criteria for Success
Evaluate the resolution of monitoring wells
along with the concentrations of contaminants
and geochemical indicators.
"Understand the persistence of the
contaminant mass
Evaluate the effectiveness of source control
measures
Is a new plume forming?
Is the hot spot moving down gradient of
the former source area?
Seminar Series on Monitored Natural Attenuation for Ground Water
8-5
-------
Criteria for Success
Criteria for Success
"Understand the persistence of the
contaminant mass
Statistical estimate of the rate of attenuation of
the hot spot, after source control
How fast is the old plume going away?
How fast will other remedies approach
cleanup goals?
"Understand the persistence of the
contaminant mass
Required are a statistical comparison of two
rates of remediation, the rate of natural
attenuation, and the rate of active remedy.
Criteria for Success
"Understand the persistence of the
contaminant mass
The confidence in the comparison is limited by
the confidence in the estimate of the two rates.
If the comparison is not expressed with an
estimate of confidence, it is worthless.
100000
10000
I
"3>
3. 1000
c
I 100
0>
u
I 10
First order rate of attenuation 0.40 per year
5 10 15 20 25 30
Time after source control (years)
Seminar Series on Monitored Natural Attenuation for Ground Water
8-6
------- |