pcb risk reduction

Use of Food Chain Models and Ecological

Risk Reduction Curves to Develop and

Apply Wetland Sediment Cleanup Goals

Phillip M. Rury and David J. Turton

Arthur D. Little, Inc., Cambridge, MA

Susan C. Svirsky, USEPA, Boston, MA

Kenneth Munney, USFWS, Concord, NH

Presentations to SETAC, November 1998

Site Historical Background and Ecological Overview

Superfund Site: New Hampshire Drum

Reconditioning Facility

Polychlorinated biphenyl (PCB), pesticide,

chromium, and lead contamination in adjacent, 60

acre Red Maple swamp with hummock terrain and

dense shrub layer

Wetland Soil PCB Cleanup Goal of 1 mg/kg set in

ROD without full spatial extent mapping or ERA

Total PCBs mapped and ERA done to justify and

guide remediation with minimal wetland destruction

Preliminary Wetland Contamination Assessment

Methods of Ecological Risk-based Remedial Design

Grid Sampling and GIS to Map PCB Contamination

Probabilistic Methods (Monte Carlo) to Validate

and Calibrate Deterministic Food Chain Exposure

Models for Mink and American Woodcock

Calibrate Woodcock and Shrew Models with Site-

specific Earthworm Contaminant Uptake Factors

Deterministic Models to Calculate Cleanup Goals

for Mink, Woodcock, and Short-tailed Shrew

Set Total PCB Action Levels and Cleanup Goals

with Deterministic Models and Risk Reduction

Curves for Spatially-weighted PCB Concentrations

Evaluate Spatial Co-location of PCBs et al. COCs

to Affirm Prediction of Total Risk Reduction Based

on Attainment of Total PCB Cleanup Goals

Distribution of PCBs in Red Maple

Swamp

Calculation of Baseline Weighted Average PCB Concentrations (ppm)

Contour Sector Area (Sq.Ft.) Area (acres) % of Total Unweighted Mean Weighted Mean

ND - 1 ppm 201,782 4.6 24% 0.41 0.0979

1-10 ppm 430,220 9.9 51% 3.62 1.8472

10-20 ppm 127,400 2.9 15% 13.99 2.1164

20-50 ppm 76,146 1.7 9% 29.58 2.6750

50-300 ppm 6,419 0.1 1% 85.58 0.6525

Total Area (ft2) 841,967 19.3 100%

26.63 1.48 PCB Concentrations

Realistic Wetland Exposure: Spatially-weighted Total

PCB Concentration is 6% of the Unweighted Mean

Sector-specific Weighted Total PCB Concentrations

Used to Predict Risk Reduction for PCB Action Levels

Influence of Sample Size and Averaging Method on PCB

Deterministic Risk: 100% Wetland Foraging Scenario

Analyte/Species

Total PCBs (mg/kg)

Mink HQ

Amer. Woodcock HQ

Short-tailed Shrew HQ

5 Samples

81.0

179.0

162.0

223.2

142 Samples

14.7

32.5

29

40.5

142 Samples

1.4

3.1

3

3.9

Spatially Unweighted

Averaging Method and Hazard Quotients

Spatially-weighted

Exposure Assessment

Hazard Indices for Ecological Receptors and Exposure Scenarios

Mink

Deterministic Exposure Models

NA

3

664

Total PCB HIs

Unweighted O&G Site Average

Spatially Weighted O&G Site Average

Maximum Detected at O&G Site (SD-07)

100% Wetland

Probabilistic Exposure Models (Monte Carlo)

11

NA

NA

90% Probability

70

NA

NA

10% Probability

0.7

10.0

Total Pesticide HIs


Maximum Detected at O&G Site (SD-E1)

1.7

NA

6

NA

28

94

Inorganic HIs


Maximum Detected at O&G Site

16

NA

55

NA

NA

32

768

TOTAL RISK (HIs):

O&G SITE WETLAND:


Partially Weighted O&G Site Average

Maximum Detected at O&G

NA

34

NA

NA

120

NA

Chemicals of Concern, Concentration Terms & Hazard

Indices (HIs)

Summary: Deterministic and Probabilistic Risks for Mink

Monte Carlo Analysis: TRVs Held Constant

0.0

0.2

0.4

0.6

0.8

1.0

14 28 43 57 71 86 100

114

128

143

157

171

186

200

214

229

243

257

271

286

300

Pro

bab

ilit

y o

f V

alu

e >

= t

o

Haza

rd I

nd

ex

Hazard Index (HI)

Average Deterministic HI = 32 for

100% Wetland Foraging

Maximum

Deterministic

HI = 768

for 100%

Wetland

(off chart)

Probability Distribution of Total Hazard Index for Mink

Hazard Indices for Ecological Receptors and Exposure Scenarios

American Woodcock

Deterministic Exposure Models

NA

3

600

Total PCB HIs


Spatially Weighted O&G Site Average

Maximum Detected at O&G Site (SD-07)

100% Wetland

Probabilistic Exposure Models (Monte Carlo)

90% Probability 10% Probability

2

26

Total Pesticide HIs


Maximum Detected at O&G Site (SD-E1)

1,260

4,010

Inorganic HIs


Maximum Detected at O&G Site

NA

1,265

4,636

TOTAL RISK (HIs):

O&G SITE WETLAND:


Partially Weighted O&G Site Average

Maximum Detected at O&G

Chemicals of Concern, Concentration Terms & Hazard

Indices (HIs)

3

NA

NA

0.4

NA

252

NA

NA

259

NA

41

NA

NA

3

NA

1234

NA

NA

1,268

NA

Summary of Deterministic and Probabilistic Risks: Woodcock

Monte Carlo Analysis: TRVs Held Constant

0.0

0.2

0.4

0.6

0.8

1.0

36 134

232

331

429

527

625

723

822

920

1,01

8

1,11

6

1,21

4

1,31

3

1,41

1

1,50

9

1,60

7

1,70

5

1,80

4

1,90

2

2,00

0

Pro

bab

ilit

y o

f V

alu

e >

= t

o H

aza

rd I

nd

ex

Hazard Index (HI)

Average Deterministic

HI = 1,265 for for 100%

Foraging in Wetland

Maximum

Deterministic

HI = 4,636 for for

100% Foraging in

Wetland

(off chart)

Average Deterministic

HI = 433 for 35%

Foraging in Wetland

Probability Distribution of Total Hazard Index for Woodcock

Risks to Invertebrates & Wildlife Warranted Remediation

Average and maximum risks are highest for sediment

invertebrates, but also are significant for the American

woodcock, mink, and short-tailed shrew

Site risks for all COCs/receptors significantly exceed

those of the reference wetland

PCBs Co-located with Pesticides, Lead & Chromium

Based on a linear regression, it is highly likely that all

COCs are co-located:

Pesticides versus Total PCBs: r2 = 0.92

Chromium versus Total PCBs: r2 = 0.97

Lead versus Total PCBs: r2 = 0.92

Corresponding

Hazard Quotients

for Chemicals of

Concern

Short-tailed

Shrew Mink

American

Woodcock

Reference

Wetland

Based on HQ = 10 Soil Conc. Soil Conc. Soil Conc. Soil Conc.

Total PCBs 3.63 4.51 5 0.07

Total Pesticides 0.11 7.3 2.77 0.018

Chromium 104 115.9 5 10.1

Lead 228 790.1 8 54.8

Based on HQ = 1 Soil Conc. Soil Conc. Soil Conc. Soil Conc.

Total PCBs 0.36 0.45 0.5 0.07

Total Pesticides 0.011 0.73 0.277 0.018

Chromium 10.4 11.59 0.5 10.1

Lead 22.8 79.01 0.8 54.8

Species-specific Cleanup Goals

Short-tailed Shrew, Mink, & American Woodcock Soil

Cleanup Goals (mg/Kg) : 100% Wetland Foraging

Cleanup Goals: Higher of Lowest Species-specific or Mean Background

Wildlife Risk Reduction Curves: Evaluated 3 Total

PCB Cleanup Scenarios for Mink, Shrew & Woodcock

Given the difficulties of forested wetland

remediation, realistic exposure parameters were used

to calculate residual PCB risks that might remain after

focused remediation

Since PCBs and other COCs are Co-Located, Used

Spatially-weighted Mean PCB Concentrations

3 Action/Attainment Levels Used to Target

Removals and Calculate Post-removal Total PCB

Residual Risk: 1 mg/kg, 3.63 mg/kg, and 10 mg/kg

Figure 2. Ottati & Goss Risk Reduction Curves: Mink, Woodcock and Short-tailed Shrew

Deterministic Scenario of 100 Percent Foraging in the Site-Affected Wetland:

Total PCB HQ vs. Acres of Wetland Soils Remediated to Total PCBs of 1 mg/kg

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 2 4 6 8 10 12 14 16

Acres of Wetland Soils/Sediments Remediated to Total PCBs of 1 mg/kg

Ha

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for

a S

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CB

Co

nce

ntr

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Mink Hazard Quotient

Woodcock Hazard Quotient

Shrew Hazard Quotient

Acreage with a

Total PCB

concentration >

10 mg/kg

Additonal 10

Acres with a

Total PCB

concentration >

1 mg/kg

4.7

Acres 14.6

Acres

PCB Risk vs. Acres Remediated to 1 ppm Total PCBs

Figure 3. Ottati & Goss Risk Reduction Curves: Mink, Woodcock, and Short-tailed Shrew

Deterministic Scenario of 100 Percent Foraging in the Site-Affected Wetland:

Percentage Reduction of Total PCB Risk vs. Acres Remediated to Total PCBs of 1 mg/kg

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 2 4 6 8 10 12 14 16


Pe

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of

Ris

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d f

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CB

Co

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Woodcock Risk Reduction

Shrew Risk Reduction

Mink Risk Reduction

Acreage with a Total

PCB concentration >

10 mg/kg

Additonal 10 Acres

with a Total PCB

concentration > than 1

mg/kg

4.82

Acres 14.7

Acres

Percentage PCB Risk Reduction: Remediated to 1 ppm


Total PCB HQ vs. Acres of Wetland Soils Remediated to Total PCBs of 3.63 mg/kg

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 1 2 3 4 5 6

Acres of Wetland Soils/Sediments Remediated to Total PCBs of 3.63 mg/kg

Ha

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CB

Co

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PCB Risk vs. Acres Remediated to 3.63 ppm Total PCBs


Percentage Reduction of Total PCB Risk vs. Acres Remediated to Total PCBs of 3.63 mg/kg

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 1 2 3 4 5 6

Acres of Wetland Soils/Sediments Remediated to Total PCBs of 3.63 mg/kg

Pe

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To

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PC

B C

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Mink Risk Reduction



Percentage PCB Risk Reduction: Remediated to 3.63 ppm


Total PCB HQ vs. Acres of Wetland Soils Remediated to Total PCBs of 10 mg/kg

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 1 2 3 4 5 6


Ha

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Co

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PCB Risk vs. Acres Remediated to 10 ppm Total PCBs


Percentage Reduction of Total PCB Risk vs. Acres Remediated to Total PCBs of 10 mg/kg

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0 1 2 3 4 5 6


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Mink Risk Reduction



Percentage PCB Risk Reduction: Remediated to 10 ppm

Conclusions - Baseline Ecological Risks

• Incremental risks to benthic and wildlife species

relative to background, warrant remedial action

• Spatially weighted averaging provides a more realistic

concentration term for mink and woodcock

• Unweighted average COC concentrations are more

appropriate for sediment biota and the shrew

• There was good agreement of risks estimated by

deterministic vs. probabilistic approaches

Baseline Ecological Risk Conclusions (cont.)

• In terms of probability the deterministic food chain

model underestimated the average risk and

overestimated the maximum risk to the mink

• A 70% probability was found that risk to the

woodcocks would equal/exceed average deterministic

risk (HI = 433) from foraging 35% in the Wetland

• 90% probability that average mink risk will exceed the

deterministic risk from mink foraging 100% in

Wetland

Baseline Ecological Risk Conclusions (cont.)

• Deterministic models were defensible for calculating

cleanup goals for all 3 species, because:

– Cleanup goals for Total PCBs ranged from 3.6 to 5

mg/kg among the species

– The 5 mg/kg Total PCB cleanup goals for the

American woodcock was 90% protective

– They were based on 100% foraging in the Wetland

(conservative)

• There is only a 10% probability that the Total Site HI

for the woodcock would exceed the deterministic HI

for 100% foraging in the Wetland (HI = 1,265)

Results and Conclusions - Remedial Design

Remediating Areas with a Total PCB Concentration

> 10 mg/kg and Cleanup to a Post-removal, Residual

Level of 1 mg/kg Adequately Protects All 3 Indicator

Species

70% of the Total PCB Risk to All 3 Indicator

Species can be Eliminated by Remediating 25% of the

Wetland (i.e., the most contaminated 4.7 acres)

EPA Raised tPCB Action Level for Sediments

EPA issued an Explanation of Significant Differences

(ESD) in 1999, increasing the area of wetland to be

remediated but raising the sediment cleanup goal

Probablistic (Monte Carlo) risk analyses assured 90%

confidence in deterministic models and risk reduction

ESD Raised the Action Level to 10 ppm Total PCBs

The most contaminated 5 acres will be remediated

Army Corps of Engineers will Remediate to 1 ppm

Risks to all 3 species will be reduced 70% or more

Wetland to be replanted using quantitative baseline

floristic analysis performed in 1998

UPF

UPFUMF

RMS

RMS

SS

UMF

EM

CP

RMS

RMS

UFUMF

RMS

60 acre Wetland

between source area

and Country Pond:

• red maple swamp

• broad-leafed deciduous

scrub/shrub-buttonbush

and speckled alder

• a persistent emergent

wetland.

Emergent Marsh = EM

Country Pond = CP

Re-Colonizing Species = RCS/UF Intermixed in Upland Field (Gravel Pit)

Red Maple Swamp = RMS

Shrub Swamp = SS

Upland Field = UF

Upland Mixed Forest = UMF

Upland Pine Forest = UPF

Key: Vegetative Cover Types

Wetland Characteristics

Total PCBs range from ND to 300 ppm in the 20 acres sampled

Uncertainties and Limitations of Risk Analysis 100% Wetland Foraging and Spatially-weighted Mean

Total PCB Concentration of 1.47 mg/kg is Most Realistic

for Mink and Woodcock

Smaller (0.5 acre) Foraging Range May Put Some

Individual Shrews at Post-Cleanup Risk in Hot Spots with

Residual Total PCBs > 3.63 mg/kg

Risk Reduction Curves Predict Only the Residual Total

PCB Risks; Some Additional Risk may Remain from

Pesticides, Lead, and Chromium

Risk Reduction Estimates Cautiously Assume Residual

Total PCB Levels No Lower than 1 mg/kg, but Even Lower

Residual Levels are Conceivable

Presumed Co-location of PCBs with Other COCs is

Based on 5 Samples from a Limited Area, for which

Complete COC Data were Available

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