Addressing Dredge Residuals in the Diagonal / Duwamish ......Duwamish/Diagonal Boundary Area...
Transcript of Addressing Dredge Residuals in the Diagonal / Duwamish ......Duwamish/Diagonal Boundary Area...
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