Addressing Dredge Residuals in the Addressing Dredge Residuals in the Diagonal / Duwamish Sediment Diagonal / Duwamish Sediment

Cleanup Cleanup

Jeff SternJeff Stern

Dept. Natural Resources and ParksDept. Natural Resources and Parks

Pat Romberg and Scott Mickelson, DNRPPat Romberg and Scott Mickelson, DNRP

Anchor Environmental, LTD; Anchor Environmental, LTD; EcochemEcochem, Inc., Inc.

Elliott Bay / Duwamish River Elliott Bay / Duwamish River Restoration ProgramRestoration Program

Elliott Bay Elliott Bay Duwamish Duwamish Restoration Restoration ProgramProgram(EBDRP)(EBDRP)Project SitesProject Sites•• Members:Members:

–– NOAANOAA–– USF&WUSF&W–– State of WAState of WA–– SuquamishSuquamish TribeTribe–– MuckleshootMuckleshoot TribeTribe–– City of SeattleCity of Seattle–– King CountyKing County

Contaminated sediments that either:Contaminated sediments that either:1)1) Remain within the dredge prism after Remain within the dredge prism after

dredging; ordredging; or2)2) Have been spread to nonHave been spread to non--cleanup areas as cleanup areas as

a result of dredginga result of dredging

Sediment Residuals DefinedSediment Residuals Defined

Neat Line

Residual Sediment

Residual Sediment CharacteristicsResidual Sediment CharacteristicsTypical physical propertiesTypical physical properties

•• Fine GrainedFine Grained•• UnconsolidatedUnconsolidated•• High moisture contentHigh moisture content•• May exist as a May exist as a ““fluid mudfluid mud””

layerlayerTypical chemical propertiesTypical chemical properties

•• Constituent concentrations Constituent concentrations typically equal the average typically equal the average dredge prism concentrationdredge prism concentration

Residuals ≈ 1.5 cm

Nepheloid ≈ 3.5 cm

Turbid Water

Z-layer

PrePre-- and Postand Post--Dredge Sampling Data Dredge Sampling Data HylebosHylebos Waterway Middle Waterway Middle –– PCB DepositPCB Deposit

Contaminated Sediment

Clean Sand

First Pass Dredge Cut

MassMass--Balance Approach Balance Approach 10 cm (C) = t (B) + (10 10 cm (C) = t (B) + (10 –– t)(At)(A))

calculated rcalculated residual thickness esidual thickness ≈≈ t cmt cm

CCPostPost--Dredge Dredge

Grab Grab SampleSample

BBZZ--layerlayer

AADredge Dredge Prism Prism

AverageAverage

Average PCB Average PCB Concentrations (ppb)Concentrations (ppb)

Primary Sources of Sediment Primary Sources of Sediment ResidualsResiduals

Contaminated Sediment

Clay

SandBedrock

Nepheloid LayerNepholoid layer flows

Some material left behind

Slight turbidity

Slope failure into bite

Residuals vs. Resuspension MeasurementsResiduals vs. Resuspension Measurements

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.0001 0.001 0.01 0.1 1

Fraction of Dredged Sediment Mass Released

Cum

ulat

ive

Freq

uenc

y of

Mea

sure

men

ts

Average Hydraulic and Mechanical Dredge Resuspension = 1%

Average Dredge Residuals = 5%

Diagonal/Duwamish Combined Sewer Diagonal/Duwamish Combined Sewer Overflow (CSO) & Storm Drain Outfall, Overflow (CSO) & Storm Drain Outfall,

Duwamish River Duwamish River -- 20042004

Final Cleanup Area Boundary Final Cleanup Area Boundary Area B AddedArea B Added

PrePre-- and Postand Post--Dredge Sampling Data Dredge Sampling Data Duwamish/DiagonalDuwamish/Diagonal

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

100 1,000 10,000 100,000Sediment PCB Concentration (ug/kg dry wt)

Cum

ulat

ive

Freq

uenc

y

Pre-Dredge Surface

Dredge Prism

Post-Dredge Surface

Cleanup Level

Lateral Spreading of Dredge ResidualsLateral Spreading of Dredge ResidualsSTFATE Model Predictions STFATE Model Predictions –– Duwamish/DiagonalDuwamish/Diagonal

-850

-650

-450

-250 -50

150

350

550

750

950

1,15

0

1,35

0

1,55

0 -700

-150

400950

0

1

2

3

4

5

6R

esid

uals

Thi

ckne

s s [c

m]

Distance (meters)

Approximate dredge prism boundary

Observed vs. Predicted PostObserved vs. Predicted Post--Dredge Dredge Sediment PCB ConcentrationsSediment PCB Concentrations

Duwamish/Diagonal Boundary Area Sampling StationsDuwamish/Diagonal Boundary Area Sampling Stations

0.0

0.4

0.8

1.2

1.6

Surfa

ce S

edim

ent P

CB

Con

c. (p

pm; d

ry w

t.)

Obs

erve

d A

vera

geP

re-D

redg

e C

onc.

(Oct

-03)

Pre

dict

ed Y

ear 0

Pos

t-Dre

dge

Con

c.at

Ave

rage

Sam

ple

Loca

tion

Obs

erve

d A

vera

geY

ear 0

Pos

t-Dre

dge

Con

c. (M

ar-0

4)

Pre

dict

ed A

vera

geY

ear 5

Bas

elin

eC

onc.

Ass

umin

g N

oA

ctio

n

Pre

dict

ed Y

ear 5

Pos

t-Dre

dge

Con

c.at

Ave

rage

Sam

ple

Loca

tion

PostPost--Dredge PCB Sediment Dredge PCB Sediment Concentrations at Monitoring StationsConcentrations at Monitoring Stations

Comparisons to model predictionsComparisons to model predictions

PCBs below predicted levelsPCBs above predicted levels

0.84 PCBs (mg/kg dw)

Proposed ThinProposed Thin--Layer PlacementLayer Placement

RemediateRemediate Area of Highest ResidualsArea of Highest Residuals

Monitoring to Track Both Monitoring to Track Both Enhanced and Natural Recovery AreasEnhanced and Natural Recovery Areas

Duwamish/Diagonal Natural RecoveryDuwamish/Diagonal Natural Recovery

0

200

400

600

800

1,000

1,200

1,400

PCB

s (u

g/kg

wet

wt)

Pre-Dredge Post-Dredge Year 1

Surface Sediment Samples

Duwamish/Diagonal Natural RecoveryDuwamish/Diagonal Natural Recovery

0

20

40

60

80

100

120

PCB

s (m

g/kg

OC

)

Pre-Dredge Post-Dredge Year 1

Surface Sediment Samples

0

10

20

30

40

Apr-02 Apr-03 Apr-04 Apr-05 Apr-06 Apr-07 Apr-08 Apr-09

Time

PCB

s in

Sur

face

Sed

imen

ts (m

g/kg

OC)

0

5

10

15

20

25

Diss

olve

d P

CBs

in W

ater

(ng/

l)

Surface Sediments (SWAC)Water (modeled)

Water and Sediment PCB Concentrations Water and Sediment PCB Concentrations Throughout a Dredging ProjectThroughout a Dredging Project

With Thin Layer Placement Over Dredged Residuals

4% Residuals ~ 11 mg/kg TSS Average in the water column Average measured over dredging period = 15mg/kg TSS

Predicted Tissue Concentration Predicted Tissue Concentration Change Over TimeChange Over Time

0

200

400

600

800

Apr-02 Apr-03 Apr-04 Apr-05 Apr-06 Apr-07 Apr-08 Apr-09Time

PCB

s in

Mod

eled

Fis

h (w

hole

bod

y ug

/kg

ww

)

0

1000

2000

3000

4000

PCB

s in

Sam

pled

Fis

h (w

hole

bod

y ug

/kg

ww

)PiscivorePlanktivoreBenthic ForagerSmall FishS i 5

Tissue Concentration Change Over Tissue Concentration Change Over Time Compared to Effects LevelsTime Compared to Effects Levels

0

200

400

600

800

1000

Apr-02 Apr-03 Apr-04 Apr-05 Apr-06 Apr-07 Apr-08 Apr-09

Time

PCB

s in

Who

le B

ody

Fish

Tis

sue

(ug/

kg w

w)

Piscivore

Planktivore

Benthic Forager

Small Fish

Adult Recreational Angler (1E5)

Osprey (Egg LOAEL)

Otter (LOAEL)

Child Recreational Angler (1E5)

Implications of Residuals Implications of Residuals on Meeting Remediation Goalson Meeting Remediation Goals

•• Dredging can produce spikes in contaminant Dredging can produce spikes in contaminant concentrationsconcentrations–– Water: 10Water: 10--30 times (during construction)30 times (during construction)–– SWAC: 1 to 5 times (after construction)SWAC: 1 to 5 times (after construction)–– Tissue: Greater during; lesser afterTissue: Greater during; lesser after

•• Risk to receptors can increase significantly over short Risk to receptors can increase significantly over short termterm

•• Active management of residuals can reduce longActive management of residuals can reduce long--term term exposureexposure–– Protect receptors of concern with longer life spans or Protect receptors of concern with longer life spans or

needing longerneeding longer--term exposuresterm exposures–– Receptors affected by short exposures can be at risk Receptors affected by short exposures can be at risk

(children; some birds and mammals; most fish)(children; some birds and mammals; most fish)

ConclusionsConclusions

Residuals happenResiduals happen•• PostPost--dredge surface often higher than predredge surface often higher than pre--dredgedredge•• Dredging can raise onDredging can raise on-- & off& off--site levels above site levels above

sediment and risk reduction goalssediment and risk reduction goals

Plan accordinglyPlan accordingly•• Estimate and design for residualsEstimate and design for residuals•• Post dredge data to determine appropriate actionPost dredge data to determine appropriate action•• Simple tissue modeling to determine if receptors at Simple tissue modeling to determine if receptors at

riskrisk

jeff.stern@metrokc.gov