Dredging 2012

THE SUCCESSFUL USE OF AQUATIC DEPOSITION FOR 450 000 M3 CONTAMINATED SEDIMENTS FROM OSLO HARBOR, Norway. Arne PettersenGijs D. BreedveldAmy M. P. OenEspen EekAnita Whitlock NybakkAudun Hauge

Remedial solutions in Oslo, a combination of several methods

• Dredging• Deposition of dredged material in deep water

disposal facility • Capping of deep water disposal facility by

sand• Capping of seabed with clay and sand

– The 4 R’s

Dredging

photo by Viktor Jæger courtesy www.stopp-giftdumping.org

Deep water disposal facility near Malmøykalven

Placement of dredged material in deep water disposal facility at ~70 m water depth

Capping material: 0-8 mm sand

Capping of the deep water facility

Placing the cap by reversing a Hopper

Does the isolation cap work?

• Success criteria• Is the hole CAD area covered by

the required 0,4 m cap?• Is the cap mixed with the

underlying contaminated dredged material?

• The key is hands on control during construction

• Success criteria• Is the isolation cap clean?• Does the cap prevent

contaminant migration to the overlaying watercolumn?

• Is it tick enough to prevent animals from bioturbate into the dredged material? What is status on the recolonisation?

SPI after first layer of cap

Map based on SPI

Map based on multibeamecho sounder

Geotechnical control after first layer of cap• Further capping in

layers to 0,4 m thickness is OK (safety factor of 2)

Control by sediment corer

Control by sediment corer

Control by measuring rods

• On the basis of the conducted measurements of cap thickness it is concluded that the requirement of 0,4 m cap is met in the entire CAD.

0

4

8

12

16

20

Deponi Nord for deponi Bekkelagsbasseng Utenfor tersklene

20052009

PAH (mg/kg)

Sediment quality in the CAD area (0-5 cm)Hg Cd Pb PAH-16 PCB-7 TBT

mg/kg mg/kg mg/kg mg/kg µg/kg µg/kgConsentration

Before establishing the CAD 0,80±0,49 1,39±0,97 94±50 3,58±1,38 28±20 112±92

After capping of CAD 0,03±0,03 0,06±0,06 5,2±2,7 0,30±0,58 < 18 2,4±2,5Change in sediment quality

Persent -96 % -95 % -94 % -92 % > -47 % -98 %Statistical signifikan Yes Yes Yes Yes No Yes

Cap quality

Controlling the sediment to water flux of contaminants

• NGI flux chamber– Sits on seabed for ~2

months– SPMD membrane– Allow calculation of flux of

organic hydrophobic compounds

• Recommended reading: Espen Eek et. al “Field measurement of diffusional mass transfer of HOCs at the sediment-water interface”. Environ. Sci. Technol. (2010)

Reduction in contaminant flux after the isolation capping of the CAD by 0,4 m sand

0

500

1000

1500

2000

2500

3000

PAH-16

Flux

(ng/

m2/

day)

0

20

40

60

80

100

PCB-7

Flux

s (n

g/m

2/da

y)

Summary

• Deep water disposal facility is environmental efficient, especially when a contaminated area is used.

• Control during construction was important to achieve the required cap.

• For monitoring of effect, sufficient pre remedial data are important.

• Time series in monitoring after complete work to ensure the longtime effect.

Thank you for your attention