PCBs, Lake Hartwell Superfund site (SC), 1994 ROD. â« Active remediation technically impracticable or too costly. â« EPA and public agreed that fishing advisories ...
Natural Recovery of Contaminated Sediments
Victor Magar Battelle, Columbus, Ohio
MNR Definition Monitored 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 billion Active remediation would disturb existing habitat Sediments likely to be buried, or diluted by flushing and mixing
Lead, Interstate Lead Company Superfund site (AL),1995 ROD Historical 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 ecosystem Natural recovery would result in minimal environmental disturbance
PCBs, Lake Hartwell Superfund site (SC), 1994 ROD Active remediation technically impracticable or too costly EPA and public agreed that fishing advisories and education could adequately reduce risk Simple 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 efficacy Advances 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
RTDF SMWG EPA & DoD
MNR Principles 1. Containment through natural capping (deposition of increasingly clean sediment)
Requires net depositional areas
Provides natural barrier to aquatic environment
Largest contributor to natural recovery
2. Contaminant weathering
Biodegradation/Dechlorination
Other physical/chemical processes
Contaminant sorption/sequestration
3. Assess sediment stability to determine the potential for resuspension of buried contaminants 4. Modeling to predict long-term sediment recovery 5. Demonstrate ecological recovery, or potential recovery
Lake Hartwell Site
Fresh 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 Profiling
100-cm sediment, 7.6-cm diameter cores Vertically subdivided into 5-cm segments 210Pb & 137Cs (Battelle Marine Science Labs) PCBs analyzed for 107 congeners (Battelle Ocean Science Labs)
Core Segment Depth (cm)
Containment: Vertical contaminant profiling and age dating (210Pb & 137Cs) 2.5
y = 9.58Ln(x) - 0.563 R2=0.9685
12.5 22.5 32.5 42.5 52.5
1999 1995 1992 1989 1986 1983 1979 1975 1971 1967 1963 1959
62.5 72.5 82.5 0
10,000
20,000
30,000
40,000
Concentration (µg/kg) dry weight
50,000
Silt
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 para Dechlorination Rates Average No. of Chlorines
2.5
Average Rates (n = 11)
2.0
meta = 0.053 ± 0.04 para = 0.037 ± 0.03
ortho meta para
1.5 1.0
18 yr per meta Cl 27 yr per para Cl
0.5 0.0 0
20
40
60
80
100
Depth (cm)
Average No. of Chlorines
2.5
meta ortho ortho
2.0
meta rate = 0.048 mol Cl yr-1 para rate = 0.034 mol Cl yr-1
1.5
meta
para
para
1.0
ortho meta para
0.5
meta ortho
0.0 1995
1985
1975
1965
Depth (cm)
1955
1945
1935
ortho meta
Percent t-PCB (%) 12 9
6 3 0 12 9 6 3 0 -3 -6
PCB Congener
PCB1 PCB3 PCB4/10 PCB6 PCB7/9 PCB8/5 PCB12/13 PCB16/32 PCB17 PCB18 PCB19 PCB22 PCB24/27 PCB25 PCB26 PCB28 PCB31 PCB33/20 PCB40 PCB41/64/7 PCB42 PCB43 PCB44 PCB45 PCB46 PCB47/75 PCB48 PCB49 PCB51 PCB52 PCB53 PCB56/60 PCB59 PCB63 PCB66 PCB70/76 PCB74 PCB82 PCB83 PCB84 PCB85 PCB87/115 PCB91 PCB92 PCB95 PCB97 PCB99 PCB100 PCB101/90 PCB105 PCB107 PCB110 PCB114 PCB118 PCB119 PCB124 PCB128 PCB129 PCB130 PCB131 PCB132 PCB134 PCB135/144 PCB136 PCB137 PCB138/160 PCB141 PCB146 PCB149 PCB151 PCB153 PCB156 PCB158
PCB Dechlorination
12
9
6
Core L, Section 1, 0-5 cm depth interval Total PCB = 1.58 mg/kg
3
0
32.2%
28.7%
Less ClLower dioxin equivalents Core L, Section 10, 35-40 cm depth interval Total PCB = 48.7 mg/kg
Core L: Relative Change Section 8 (35-40 cm) minus Section 1 (0-5 cm)
More ClHigher dioxin equivalents
Ecological Recovery Hybrid Bass Average t-PCB (mg/kg)
10 SV-107
8
SV-106
6 4 2 0 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002
Time (years)
Largemouth Bass Average t-PCB (mg/kg)
20 SV-106 16
SV-107
12 8 4 0 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002
Time (years)
Core Segment Depth (cm)
Do fish PCB concentrations over time reflect reduced surface sediment concentrations? 2.5
1999 1995 1992 1989 1986 1983 1979 1975 1971 1967 1963 1959
12.5 22.5 32.5 42.5 52.5 62.5 72.5 82.5 0
10,000
20,000
30,000
40,000
Concentration (µg/kg) dry weight
50,000
Sediment Stability
Lake Hartwell Site
Historical storms
Drought conditions
Hunters Point Shipyard
Sedflume
Hydrodynamic studies
