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Understanding the Fate ofGround Water Contaminants
Redefining Natural Attenuation
32 years ago
1975:Jamison, V. W., R. L. Raymond, and J. O.
Hudson. Biodegradation of high-octanegasoline in groundwater. Developments inIndustrial Microbiology 16.
1970s
• “Microbiologists reasoned that the concentration of organic nutrientsin ground water was too low to support life.”
• “Ground water was considered pure and wholesome because it wasprotected by the soil mantle.”
• PCB and chlorinated aliphatics (TCE) were not biodegradable.
• Benzene and toluene were not considered biodegradable in theabsence of oxygen.
25 years ago
1982:Suflita et al. Dehalogenation: a novel pathwayfor the anaerobic biodegradation ofhaloaromatic compounds. Science 218:1115-1117
1984:Reinhard, et al. Occurrence and distributionof organic chemicals in two landfill leachateplumes. EST 18:953-961.
20 years ago
1985:Kleopfer, R. et al. Anaerobic degradation of trichloroethylene insoil. EST 19:277-280.
1986:Wilson, B. et al. Biotransformation of selected alkylbenzenesand halogenated aliphatic hydrocarbons in methanogenicaquifer material: a microcosm study. EST 20:997-1002.
1987:Brown, J. et al. Polychlorinated biphenyl dechlorination inaquatic sediments. Science 236:709-712.
Aerobic(oxidized)
Anaerobic(reduced)
Eh (mV)
1000
0
- 500
O2
CO2
SO4-2
Fe+3
Mn+4
NO3-
H20
N2
Mn+2
Fe+2
SH2
CH4
1994 (from Bouwer)
Cl2C=CCl2
CHCl=CCl2 + Cl-
C=C
Cl
H
Cl
H
PCE
TCE
CH2=CHClCH2=CH2 + Cl-
Vinyl chlorideEthene
cis-DCE + Cl-
+ Cl-
10 years ago
1995:Technical Protocol for Implementing Intrinsic
Remediation with Long-Term Monitoring for NaturalAttenuation of Fuel Contamination Dissolved inGroundwater. Air Force Center for EnvironmentalExcellence
1998:Technical Protocol for Evaluating Natural Attenuation
of Chlorinated Solvents in Ground Water. U.S. EPA
2002:Lee, W., and B. Batchelor. Abiotic
reductive dechlorination of chlorinatedethylenes by iron-bearing soil minerals. 1.Pyrite and magnetite. EST 36:5147-5154.
a)
b)
magnetitegrains
Iron content in TCAAP sediments
567 ± 1129,16411,190 ± 125015-20
649 ± 10910, 25112,450 ± 182010
556 ± 156,5157,820 ± 1100-5
BioavailableTotal(Nitric Acid)
Total(XRF)
Depth BelowWater Table(Approx ft)
D e e p S e d i m e n t s
y = 9.3e-0.0016x
y = 4.0e-0.0014x
1.00
10.00
100.00
0 200 400 600 800
Time (days)
[1,1
-DC
E],
ug/
L
Live
Autoclaved
y = 1667.8e-0.0015x
y = 432.02e-0.0002x
100
1000
10000
0 200 400 600 800
Time of Incubation (days)
[cis
-DC
E]
(ug/
liter
)
Live Microcosms
Autoclaved Controls
Container Controls
Monitoring well near contaminant sourceat TCAAP
0.1
1
10
100
1000
10000
0 1000 2000 3000 4000 5000 6000
Time of Monitoring (days)
Co
nce
ntr
atio
n (u
g/L)
cis-DCE
1,1-DCE
Y=6.9e-0.0015x
Cis-DCE rates of removal (per year)
0.310.43Deep,
Oxidized
2.282.30Intermediate,
Reduced
0.570.55Shallow,reduced
AutoclavedControl
LivingLocation
• TCAAP sediments are 0.3 wt% magnetite.
• Magnetite accounts for 25% of total iron inthe sediments.
• There is ample magnetite in the sedimentsto reduce all of the DCE added to themicrocosms.
TCAAPSite 102
Site 102 ground water chemistry
NDNDNDNDNDND4.601U582
ND0.06NDND> 0.7ND0.701U581
NDNDNDND.024.2.601U580
ND0.01NDND0.74.1.601U579
EtheneCH4SH2Fe+2Mn+2NO3-DO
(Concentrations in ppm)
Site A and Site 102 Microcosms
• Ground water sediment was air dried.
• Microcosms were prepared underaerobic conditions.
• Microcosms were heat-killed.
• The microcosms were sealed andincubated for 300 days on the lab benchand sampled quarterly.
cis-DCE
y = 41.449e-0.0019x
R2 = 0.8053
y = 28.453e-0.0033x
R2 = 0.9312
y = 59.013e-0.0005x
R2 = 0.8537
1
10
100
0 50 100 150 200 250 300 350
Time of Incubation
cis-
DC
E (
ug
/L)
Container Conrol
Site A
Site 102
Expon. (Site 102)
Expon. (Site A)
Site 102Lab and Field Attenuation rates
• TCE– Microcosms: 1.1 yr-1
– Field data: 8.7 yr-1
• DCE– Microcosms: 0.7 yr-1
– Field data: 9.8 yr-1
• Non-biological mechanisms may bemore important than biological reductivedehalogenation for chlorinated solvents.
• Natural attenuation studies shouldconsider the possibility of abioticdegradation processes for chlorinatedsolvents.
• Abiotic degradation products ofchlorinated ethenes are not present.
• Screening for abiotic degradation ofchlorinated ethenes is not yet possible.
• Demonstrating abiotic degradation inground water:– Contaminant fate and transport modeling– Microcosms
Future work• What is the mechanism of non-biological degradation
of chlorinated aliphatic compounds (What ishappening)?
• Are there inexpensive field indicators of abioticdegradation processes in ground water (Is ithappening)?
• How prevalent is abiotic degradation of chlorinatedaliphatic compounds in ground water (How much is ithappening)?
• Other chlorinated contaminants?
Site 102 Hydrogen vs Time
0.000.020.040.060.080.100.120.140.160.180.20
0.00 50.00 100.00 150.00
Time (Days)
H2
(ug
/L)
TCE
DCE