Natural Recovery of Contaminated Sediments

Victor MagarVictor MagarBattelle, Columbus, OhioBattelle, Columbus, Ohio

MNR DefinitionMonitored Natural Recovery (MNR) involves leaving contaminated sediments in place and allowing ongoing aquatic, sedimentary, and biological processes to reduce the bioavailability of the contaminants in order to protect receptors

It must be the result of a deliberate, thoughtful decision-making process following careful site assessment and characterization NRC, 1997. Contaminated Sediments in Ports and Waterways

Past Sites that Identified and Selected Natural Recovery their RODs

Kepone, James River (VA)Active remediation estimated at $3 to $10 billionActive remediation would disturb existing habitat Sediments likely to be buried, or diluted by flushing and mixing

Lead, Interstate Lead Company Superfund site (AL),1995 RODHistorical trends indicated a general decline in sediment lead concentrations, attributed to dispersal, dilution, and burial No evidence of damage to existing ecosystem In situ capping and sediment removal would damage existing ecosystemNatural recovery would result in minimal environmental disturbance

PCBs, Lake Hartwell Superfund site (SC), 1994 RODActive remediation technically impracticable or too costly EPA and public agreed that fishing advisories and education could adequately reduce riskSimple 1-D model predicted recovery to 1 mg/kg within a reasonable time, once terrestrial PCB source was removed

Current Direction of MNR:Develop a more rigorous approach to

evaluate and demonstrate MNR efficacyAdvances in environmental science & engineering

Computers and modeling capability Analytical chemistry Understanding of sediment transport and contaminant mass transport processes

Time: Decades since original releases EPA acceptance of MNR Efforts to establish principles to evaluate MNR

RTDFSMWGEPA & DoD

MNR Principles 1. Containment through natural capping

(deposition of increasingly clean sediment)Requires net depositional areasProvides natural barrier to aquatic environment Largest contributor to natural recovery

2. Contaminant weathering Biodegradation/Dechlorination Other physical/chemical processesContaminant sorption/sequestration

3. Assess sediment stability to determine the potential for resuspension of buried contaminants

4. Modeling to predict long-term sediment recovery5. Demonstrate ecological recovery, or potential recovery

Lake Hartwell SiteFresh water lake

Sangamo-Weston Capacitor Manufacturing (1955 – 1978)

Aroclors 1016, 1242, 1254

Terrestrial PCB sources removed in mid-90s

MNR selected by Region 4 (EPA/ROD/R04-94/178)

Sediment Coring and Profiling100-cm sediment, 7.6-cm diameter cores Vertically subdivided into 5-cm segments210Pb & 137Cs (Battelle Marine Science Labs)PCBs analyzed for 107 congeners (Battelle Ocean Science Labs)

Containment: Vertical contaminant profiling and age dating (210Pb & 137Cs)

Silt

199919951992198919861983197919751971196719631959

0 10,000 20,000 30,000 40,000 50,000

82.5

72.5

62.5

52.5

42.5

32.5

22.5

12.5

2.5

Cor

e Se

gmen

t Dep

th (c

m)

Concentration (µg/kg) dry weight

y = 9.58Ln(x) - 0.563R2=0.9685

Brenner et al., ES&T 2004

Time to Achieve ROD (U.S. EPA 1994) Cleanup Goals

ROD surface sediment cleanup goal (1 mg/kg)Mean site-specific sediment quality criteria (0.4 mg/kg)NOAA effects range-low (0.05 mg/kg)

Time to Achieve Cleanup Goals 1 mg/kg t-PCB

0.4 mg/kg t-PCB

0.05 mg/kg t-PCB

1 – 5 yrs 2 – 10 yrs 10 – 30 yrs

95% confidence levels increased the time frame up to 95 yrs

Relative meta and paraDechlorination Rates

0.0

0.5

1.0

1.5

2.0

2.5

1935194519551965197519851995Depth (cm)

Ave

rage

No.

of C

hlor

ines

orthometapara

meta rate = 0.048 mol Cl yr-1

para rate = 0.034 mol Cl yr-1

0.0

0.5

1.0

1.5

2.0

2.5

0 20 40 60 80 100Depth (cm)

Ave

rage

No.

of C

hlor

ines

orthometapara

Average Rates (n = 11)

meta = 0.053 ± 0.04para = 0.037 ± 0.03

18 yr per meta Cl27 yr per para Cl

para

ortho meta

para

ortho

metaorthoorthometa

meta

para

ortho meta

para

ortho

metaorthoorthometa

meta

PCB Dechlorination

More Cl-Higher dioxin equivalents

Less Cl-Lower dioxin equivalents

0369

12Core L, Section 10, 35-40 cm depth interval

Total PCB = 48.7 mg/kg32.2%

0369

12Core L, Section 1, 0-5 cm depth interval

Total PCB = 1.58 mg/kg

-6-30369

12

PCB1

PCB3

PCB4

/10

PCB6

PCB7

/9PC

B8/5

PCB1

2/13

PCB1

6/32

PCB1

7PC

B18

PCB1

9PC

B22

PCB2

4/27

PCB2

5PC

B26

PCB2

8PC

B31

PCB3

3/20

PCB4

0PC

B41/

64/7

PCB4

2PC

B43

PCB4

4PC

B45

PCB4

6PC

B47/

75PC

B48

PCB4

9PC

B51

PCB5

2PC

B53

PCB5

6/60

PCB5

9PC

B63

PCB6

6PC

B70/

76PC

B74

PCB8

2PC

B83

PCB8

4PC

B85

PCB8

7/11

5PC

B91

PCB9

2PC

B95

PCB9

7PC

B99

PCB1

00PC

B101

/90

PCB1

05PC

B107

PCB1

10PC

B114

PCB1

18PC

B119

PCB1

24PC

B128

PCB1

29PC

B130

PCB1

31PC

B132

PCB1

34PC

B135

/144

PCB1

36PC

B137

PCB1

38/1

60PC

B141

PCB1

46PC

B149

PCB1

51PC

B153

PCB1

56PC

B158

Core L: Relative Change Section 8 (35-40 cm) minus Section 1 (0-5 cm)

28.7%

PCB Congener

Per

cent

t-P

CB

(%)

Ecological RecoveryHybrid Bass

0

2

4

6

8

10

20022001200019991998199719961995199419931992Time (years)

Ave

rage

t-PC

B (m

g/kg

) SV-107SV-106

Largemouth Bass

0

4

8

12

16

20

20022001200019991998199719961995199419931992

Time (years)

Ave

rage

t-PC

B (m

g/kg

) SV-106SV-107

Do fish PCB concentrations over time reflect reduced surface sediment concentrations?

199919951992198919861983197919751971196719631959

0 10,000 20,000 30,000 40,000 50,000

82.5

72.5

62.5

52.5

42.5

32.5

22.5

12.5

2.5

Cor

e Se

gmen

t Dep

th (c

m)

Concentration (µg/kg) dry weight

Sediment StabilityLake Hartwell Site

Historical storms Drought conditions

Hunters Point Shipyard

Sedflume Hydrodynamic studies