Evaluating Natural
Attenuation
Shu-Chi Chang, Ph.D., P.E., P.A.
Assistant Professor1 and Division Chief2
1Department of Environmental Engineering
2Division of Occupational Safety and Health,
Center for Environmental Protection and Occupational Safety and Health
National Chung Hsing University
May 2, 2007
Course plan
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5/2: Midterm and Evaluating NA
5/9: Evaluating NA and Biobarrier (4
hours)
5/16: Air sparging case study, GW and
soil sampling demonstration (4 hours)
5/23: Modeling natural attenuation or
guest speaker on NA (1 hour)
Course plan
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5/30: Modeling natural attenuation
6/6: Case study 1
6/13: Case study 2
6/20: Student presentation. Each group
will have 30 minutes.
6/27: Final examination
Outline
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Chemical and geochemical data
Lines of evidence
Documented loss of contaminant mass of plume
stabilization
Analytical data confirming intrinsic bioremediation
Microbiological data
Estimating biodegradation rates
Screening natural attenuation of PHCs
Screening natural attenuation of chlorinated solvents
Analytical data
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Several broad categories: source term and sorption
parameters, contaminants and daughter compounds,
electron acceptors, metabolic by-products, and
general quality parameters.
The analytes listed in the tables in next few pages
are useful for
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Estimating the composition and strength of a NAPL source
Showing that natural attenuation is occuring
Evaluating the relative importance of the various natural
attenuation mechanism
Soil-sediment analytical parameters
Data quality objectives
GW parameters useful for
evaluating natural attenuation (I)
GW parameters useful for
evaluating natural attenuation (II)
GW parameters useful for evaluating
natural attenuation (III)
GW analytical data quality
objectives (II)
GW analytical data quality
objectives (III)
Source term and sorption
parameters
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Continuing source: mobile or residual
NAPL, or contaminant sorbed to the
aquifer matrix
Degree of weathering of the NAPL, and
its composition and strength-> amount
of aqueous phase NAPL
TOC content is important to judge the
sorption and possible retardation
Contaminant and daughter
compounds
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Method 8020 can be used if site
contamination is limited to petroleum
hydrocarbons.
Method SW 8020a is used if only chlorinated
solvents of PHCs mixed with solvent are
found in the subsurface
The dissolved concentration of combined
BTEX and trimethylbenzene should not
exceed 30 mg/L for a JP-4 spill or about 135
mg/L for a gasoline spill.
Electron acceptors and
metabolic by-products
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Again, dissolved oxygen (DO), nitrate, Mn(IV),
Fe (III), sulfate, and CO2 (for
methanogenesis).
Again, observe from the reduced form: Fe(II),
Mn(II)
Readily measurable by-products: Fe(II), CO2,
H2S, CH4, C2H6, C2H4, alkalinity, lowered redox
potential, chloride, and hydrogen.
General water quality
parameters
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pH
Temperature: Q10 rule
Conductivity
Those values better to be measured
“fresh”
General groundwater sampling
consideration
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Type:
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Monitoring wells: most common
and versatile but may be biased
Monitoring points
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Geoprobe®
Drive by cone penetrometer,
hydraulic percussion, manually
powered equipment
Grab sampling locations
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Hydraulic punch, Geoprobe, cone
penetrometer, hand-driven
Geoprobe®
Cone penetrometer
technology (CPT)
Groundwater sampling
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Generic classification
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Grab: Bailer (most common)
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Suction lift: peristaltic pump
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Advantages: can be used at any depth
Disadvantages: aeration and agitation
Advantages: no cross contamination, no turbulence
(better DO and redox potential measurement)
Disadvantages: limited depth, offgassing
Positive displacement: submersible pump
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Advantages: Deep withdraw, high volume
Disadvantages: size limitation, rigorous decontamination
Bailer
Peristaltic pump
Submersible pump
Light drilling machine
Well-head measurement
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Flow-through cell
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Bailer
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<5% Height
If bubbles were observed,
slow down
If still has bubbles, replace
the tubing
Slowly immersing into water
Downhole measurement
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Care for decon
A few tips
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Sample should be collected directly
from the pump
Avoid aeration
No air in the container and sealed well
Lines of evidence used to
evaluate natural attenuation
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Historical trends in contaminant data showing
plume stabilization and/or loss of
contaminant mass overtime
Analytical data showing
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Depletion of electron acceptors and donors
Increasing metabolic by-product
Decreasing parent compounds
Increasing daughtor compounds
Microbiological data that support the
occurrence of biodegradation.
Documented loss of contaminant
mass or plume stabilization
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Visual tests of plume stabilization
Statistical tests of plume stabilization
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Mann-Whitney U test
Mann-Kendal test
Visual tests of plume
stabilization
Statistical tests of plume
stabilization
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Mann-Whitney U test
Statistical tests of plume
stabilization
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Mann-Kendall test
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Well data
Data comparison
Menn-Kendall statistic
Statistical tests of plume
stabilization
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Mann-Kendal test
Analytical data confirming
intrinsic bioremediation
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Electron acceptors
Daughter compounds
Metabolic by-products
Spatial distribution of e donors, e
acceptors, metabolic by-products, and
daughter compounds
Deducing the distribution of TEAPs in
GW
Electron acceptors, by-products,
and daughter compounds
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Electron acceptors
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By-products
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DO
Nitrate
Sulfate
Fe(II) and Mn(II)
H2S
CH4
CO2
Alkalinity
Redox potential
Dissolved hydrogen
Chloride
Daughter compounds
Spatial distribution of e donors, e
acceptors, metabolic by-products,
and daughter compounds
Microbiological data
Estimating biodegradation
rates
Screening for NA of PHCs
Screening of NA of chlorinated
solvents