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