Dredging 2012 THE SUCCESSFUL USE OF AQUATIC DEPOSITION FOR M 3 CONTAMINATED SEDIMENTS FROM OSLO HARBOR, Norway. Arne Pettersen Gijs D. Breedveld Amy M. P. Oen Espen Eek Anita Whitlock Nybakk Audun 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

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 multibeam echo 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 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.

Sediment quality in the CAD area (0-5 cm) HgCdPbPAH-16PCB-7TBT mg/kg µg/kg Consentration Before establishing the CAD 0,80±0,491,39±0,9794±503,58±1,3828±20112±92 After capping of CAD0,03±0,030,06±0,065,2±2,70,30±0,58< 182,4±2,5 Change in sediment quality Persent-96 %-95 %-94 %-92 %> -47 %-98 % Statistical signifikanYes NoYes 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

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.

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