Morris Cove as a Confined Aquatic i l (CA ) C llDisposal (CAD) Cell

Bridgeport Maintenance Dredging ProjectBridgeport Maintenance Dredging Project Public Meeting

25 October 201025 October 2010

Thomas J Fredette PhDThomas J. Fredette, PhDUSACE Army Engineer Research Lab

Vicksburg, MSg,

• Sediment d f I 95used for I-95

construction• About 650 x

2450 ft• About 30 ft

deepp• 610,000 cubic

yard capacityyard capacity

3-D view of Morris CoveMorris Cove with vertical exaggerationexaggeration

C fi d A i Di l C ll

New England CAD Alternative ExperienceConfined Aquatic Disposal Cells

1981 – Norwalk Harbor, ~ 2,500 cu m

1989 – New Bedford Harbor Pilot

1997-2000 – Boston Harbor, 1,200,000 cu m

1998 – Hyannis Harbor, 57,000 cu m

2003-? - Providence Harbor, 900,000 cu m2003 ? Providence Harbor, 900,000 cu m

2006 - Norwalk Harbor, 27,000 cu m

2005 ? New Bedford Harbor TBD2005-? – New Bedford Harbor - TBD

2006 - New London Harbor, 117,000 cu m

2008-2010 – Boston Harbor

2010 – New London Harbor

Boston Harbor CADsMystic River

Providence 71°21'16"W71°21'46"W71°22'16"W71°22'46"W71°23'16"W71°23'46"W71°24'16"W71°24'46"W

N N

Massachusetts

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CADs41°4

9'11

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41°4

9'11

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N N

Rhode Island

SeRive

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Providence

41°4

8'41

"

41°4

8'41

"

N N

41°4

8'11

"

41°4

8'11

"

N N

Providence River

41°4

7'41

"N

41°4

7'41

"

N NFields

41°4

7'11

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41°4

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71°21'16"W71°21'46"W71°22'16"W71°22'46"W71°23'16"W71°23'46"W71°24'16"W71°24'46"W

Z0 1,000 2,000500 Meters Approximate CAD cell boundaries

Morris Cove Borrow Pit FillingMorris Cove Borrow Pit FillingPotential Benefits Public Concerns

Increase Oyster Habitat Potential Health Impacts from Contaminated Sediments

Decrease Potential Anoxic Zone Potential for Contaminated Water Infiltrating Residential Basements

Improve Benthic Habitat Loss of Sediments During Filling of Pit

Provide Cost Effective Sediment  Placement Alternative

Morris Cove Borrow Pit FillingMorris Cove Borrow Pit Filling

Loss of sediments during filling of pit concernLoss of sediments during filling of pit concern– Sediment & water plume denser than surrounding

waterwater– Friction with water & bottom slow spread– Steep side slopes limit spread– Steep side slopes limit spread

CAD Surge

Morris Cove Borrow Pit Profile & 70’ x 200’ barge – no vertical exaggeration - All scales in feet

‐50

0

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Series3

Series4

F t ViFront View

‐50

0

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Series3

Series4

dSide View

Morris Cove Borrow Pit FillingMorris Cove Borrow Pit Filling

Potential Health Impacts from ContaminatedPotential Health Impacts from Contaminated Sediments Concern

Potential pathway Sediment loss to water column– Potential pathway – Sediment loss to water column Transport in water Swimmers

– Prime risk assessment factors: Exposure durationPrime risk assessment factors: Exposure duration and exposure concentration

Morris Cove Borrow Pit FillingExposure duration and exposure

E li i d i i– Exposures limited to time spent in water– Concentrations limited by loss from sediment and

dil tidilution• Contaminants largely remain on sediment• Extremely large dilution volumes relative to expected• Extremely large dilution volumes relative to expected

volume of release• Transport direction? Season?• Low release, dilution, & transport very short-term

Comparison of tPCBs in Select Harbors

1400000

1000000

1200000

ppb)

400000

600000

800000

Total PCB

s (p

0

200000

Bridgeport New Haven USCG‐NH New London

CLIS‐Ref Norwalk Providence Harbor

New Bedford Harbor

Comparison of tPCBs in Select Harbors

5000

3000350040004500

(ppb

)

1500200025003000

Total PCB

s 

05001000

T

Comparison of tPCBs in Select Harbors

600

500

600

300

400

l PCB

s (ppb

)

100

200Total

0

Bridgeport New Haven USCG‐NH New London CLIS‐Ref

PCB SolubilityPCB Solubility

• “all PCBs are lipophilic and poorly soluble inall PCBs are lipophilic and poorly soluble in water” -http://www.chem.unep.ch/pops/pops inc/procep p p p p p _ pedings/bangkok/FIEDLER1.html

• “Owing to their low solubility's in water, PCBs g yare often associated with the solid fraction (e.g., particulate matter, sediments)” -h // b / / /BC id lihttp://www.env.gov.bc.ca/wat/wq/BCguidelines/pcbs/pcbs-02.htm

New Bedford Harbor CAD StudyNew Bedford Harbor CAD Study

• “…contaminant breakthrough of the cap at a…contaminant breakthrough of the cap at a concentration of 0.01% of the pore water contaminant concentration (e.g., 0.01% of 7 ppb PCB or 0.0007 ppb PCB) will take more than 1800 years as predicted by the USACE RECOVERY d l Wi h b i l d bRECOVERY model. With burial promoted by the dredged material settlement, the transport of contaminants through the captransport of contaminants through the cap and burial material will take tens of thousands of years ” PR Schroeder C E Ruiz T J Fredette and E Hayter 2010of years. P.R. Schroeder, C.E. Ruiz, T.J. Fredette, and E. Hayter. 2010. 

Assessment of Contaminant Loss and Sizing for Proposed Lower Harbor Confined Aquatic Disposal (CAD) Cell New Bedford Harbor Superfund Site Massachusetts

Morris Cove Borrow Pit FillingMorris Cove Borrow Pit Filling

• Decrease Potential Anoxic ZoneDecrease Potential Anoxic Zone– Existing data show some periods of low oxygen in

the borrow pit but other data clearly showthe borrow pit, but other data clearly show considerable periods of good water quality

– The depth, stratification, and subsequentThe depth, stratification, and subsequent stagnation do have strong potential to lead to anoxic conditions

Dissolved OxygenNMFS August 2002

• Green – outside• Red – inside• Blue - tide

Morris Cove Borrow Pit FillingMorris Cove Borrow Pit Filling

• Increase Oyster HabitatIncrease Oyster Habitat– Once appropriate depths are achieved the

likelihood of increasing oyster habitat is highlikelihood of increasing oyster habitat is high– Potential increase is 22 acres

Morris Cove Borrow Pit FillingMorris Cove Borrow Pit Filling

• Improve Benthic HabitatImprove Benthic Habitat– Data show that benthic communities are less

populated in the pit than reference locationspopulated in the pit than reference locations outside the pit

– Returning the area to depths similar to theReturning the area to depths similar to the surrounding bottom has very strong potential to improve habitat quality

Morris Cove Borrow Pit FillingMorris Cove Borrow Pit Filling

Contaminated water infiltrating residentialContaminated water infiltrating residential basements concern

Bottom of pit much lower than basements– Bottom of pit much lower than basements– Hydraulic gradient will push water from land to

covecove– Pit water would need to flow up hill

Morris Ground WaterCove Pit Ground Water

Max depth 30 ft

Basic Principle

Groundwater

MC Pit

Valve

Morris Cove Borrow Pit FillingMorris Cove Borrow Pit FillingPotential Benefits Public Concerns

Increase Oyster Habitat Potential Health Impacts from Contaminated Sediments

Decrease Potential Anoxic Zone Potential for Contaminated Water Infiltrating Residential Basements

Improve Benthic Habitat Loss of Sediments During Filling of Pit

Provide Cost Effective Sediment  Placement Alternative