dredging 2012 the successful use of aquatic deposition for 450 000 m 3 contaminated sediments from...
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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
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