2001-073

EIA disposal of marine growth from Maureen at Aker Stord

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Title:EIA disposal of marine growth from Maureen at Aker Stord
ISBN no.:82-490-0117-6

Category:

Reports (Rapporter)
Authors:Tvedten, Ø.F.
Research group:Biomiljø (Biomiljø)
Distribution restriction:Open
Order no.:2001/073
Price.:60
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Abstract:
The oil platform Maureen Alpha (MA) and the Articulated Loading Column (ALC) ;are to be decommissioned at Aker Stord, at the island Stord on the, western ;coast of Norway. After mooring the structures at Digernessundet, Aker is ;planning to discharge marine growth above sea level to the recipient. The ;growth consists of mussels, seaweed, corals, anemones, worms, sea-squirts etc. ;The purpose of removing the biota inshore is mainly to avoid odour problems ;from decaying marine life. It will also make the construction clean and safer ;to work on (e.g. cut into parts) later. The recipient is deep (270-310 m) and ;has good capacity for degradation of organic material, due to large water ;masses and favourable water currents and water renewal. ;Rogaland Research (RF) was contacted by Aker to perform an environmental impact ;assessment (EIA) of the disposal of marine growth to the recipient. This is a ;part of the EIA of the whole decommissioning process of the MA and ALC.;Two main subjects are of most important environmental concern:;v The organic load to the recipient;v Possible content of harmful substances;A total of approximately 570 tonnes of wet growth is expected to be exposed to ;air after refloat. The dry organic matter in this growth is estimated to be ;10-20%, that is 57-114 tonnes. Approximate 60 tonnes are to be discharged in a ;new operation in 2002. ;Depending on how dry the growth will be at removal time some part of it might ;float on the surface. A contingency boom should be used to prevent spreading of ;this material, and make it possible to collect. ;A reasonable course of events will be that most of the mussels and other heavy ;parts will sink to the bottom close to the platform, and the rest of the ;material will be spread over a larger area. We believe that this will lead to ;spots on the seabed close to, and under, the platform that will be overloaded ;with organic material, causing temporary oxygen deficiency in the sediment. In ;the rest of the influenced area the growth will be a source of food supply and ;make less effect, but may cause some temporary changes in the benthic ;community. We do not suspect oxygen deficiency in the water column. Since the ;material has marine origin there is natural scavengers (e.g. bacteria, ;crustaceans, worms, fishes) which will digest and decompose the growth. We ;assume that most of the organic material will be decomposed within a year after ;disposal. The benthic community may need a year extra to resemble the original ;situation.;At this date there is not sufficient knowledge about the content of potential ;harmful substances in the growth on MA to make a good description of effect ;from this on the seabed environment. Nevertheless it can be assumed that the ;levels are not in a magnitude that would lead to detectable elevated levels in ;the sediment. The growth will also be spread over a large area. ;Without knowledge about the benthic fauna in the area before, during or after ;the decommissioning it is not possible to be certain of the disposal effects of ;the marine growth.;

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Final-report28.03.01.pdf;;;;;;;;;;;

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International Research Institute of Stavanger
Mailing address:
Visiting address:
P.O. Box 8046, N-4068 Stavanger, Norway
Prof. Olav Hanssensvei 15, 4021 Stavanger


Phone:
Fax:

+47 51 87 50 00
+47 51 87 52 00

General email address: firmapost@iris.no