CAPÍTULO 4 PI‐P‐TOOL.
6. Respuesta del sistema y de la realimentación (system response and feedback signals) : Esta ventana muestra las respuestas de las señales e de
4.3. ALGUNOS EJEMPLOS ILUSTRATIVOS
Debris will be cleared from the seabed after the installations are removed from their various fields (see Royal Decree of 26 October 1979, Provisional Regulations on Littering and Pollution from Petroleum Operations on the Norwegian Continental Shelf).
Potential litter is therefore associated with Alternatives involving final disposal in the sea.
No floating material will be disposed of in the sea. The potential for littering is thus considerably reduced, and is linked to steel and concrete, and the purely aesthetic concerns of leaving material in the sea.
Alternative IIA – reefs in-place Steel Jackets
This Alternative involves the leaving of large quantities of steel in the sea. Gradually, as the protective anodes are sacrificed, the steel will start to rust and the structure will weaken. Parts of it will gradually fall apart, and may be subject to powerful forces (like fishing trawls) which would tend to spread them out of the area. Constraints on trawling and similar activities can reduce the risk of this type of trash dispersal. It also is assessed as being very improbable that spreading in this manner could ever attain significant
Removal of marine growth by high pressure hoses
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proportions. It is also possible to remove remains of reef structures after their function as a reef ceases. The lifetime of an artificial reef is estimated at 150–200 years. Since the time factor here is not particularly critical, there is a good chance of taking mitigation measures if the situation ultimately proves negative to other users of the sea, for example.
The consequences of this type of impediment are more aesthetic than environmental. The fact that this is an effect that may arise in a very extended time period, and last for a similarly extended period, means however that the impacts are deemed «large negative». This is then due to the effect of leaving in-place something that was not there before petroluem activities commenced (cf. methodology Section 2.3).
Ekofisk Tank
The Ekofisk Tank when left in-place will contain no buoyant materials. The only chance of litter is fragments of the structure getting caught in fishing gear and being spread about. There is very little chance that this can attain significant proportions.
Debris will be cleared from the seabed around the Ekofisk Center after the various installations are removed. Therefore, no litter effect is expected and it has been determined that using the Ekofisk Tank as an artificial reef has a con- sequence of «none/insignificant».
Overall Littering Effect – Alternative IIA
The overall littering effect for Alternative IIA is «large negative». Alternative IIB – cluster reef around Tank
Relative to Alternative IIA, the steel reef components here will be assembled closer together and the potential for spreading and litter formation is thus somewhat smaller. The consequences are therefore deemed «moderate negative».
The assessments for the Ekofisk Tank will be as described for Alternative IIA, i.e. no litter effect of any significance.
The overall littering effect for Alternative IIB is evaluated as «moderate negative».
Alternative IIC – jackets to shore, Tank left in-place
No litter effect is expected in the sea due to removal of the steel jackets to shore. This assumes that waste generated from demolishing and recycling the steel is collected and processed according to current requirements and procedures. Similarly, it is assumed that any disposal is in accordance with current requirements for waste deposits. Therefore no littering effects from removal, demolition or recycling are expected.
The assessment for the Ekofisk Tank will be as described for Alternative IIA and IIB, i.e. no litter effect of any significance.
Alternative IID – jackets to shore, Tank deposited in deep sea The situation for the steel jackets will be as for Alternative IIC.
Debris will be cleared off the seabed after the various installations are removed. Therefore no litter impact is expected as the result of removal of the Ekofisk Tank.
Implosion when the Tank is sunk in deep water will cause concrete rubble and steel reinforcement to spread over an underwater area of several hundred square metres. The choice of a deep water site will avoid places popular with fishing skippers. Therefore there is very small probability that further spreading of the material will occur. Nor will the installation contain floating materials when deposited on the sea bed. The scale of the littering effect from sinking the Ekofisk Tank in deep water – inshore or offshore – is therefore expected to be insignificant to slightly negative.
The overall effect for Alternative IID is evaluated as «small negative». Alternative IIE – jackets and Tank to shore for demolition and recycling
The situation for the steel jackets will be as for Alternative IIC, i.e. no littering effects are expected.
As in Alternative IID, no littering impact is expected at the Tank’s original location after it is removed.
Waste from demolition of the Tank should be collected and processed in accordance with the demolition contractor’s procedures and licensing terms. Disposal is expected to comply with the current regulations and legislation in this field (SFT 1994). Even so, demolition may nonetheless cause concrete chunks in some cases to fall to the bottom at the site of the demolition operation, despite precautions being taken. The chunks will sink and have no tendency to spread. Marine growth should also be collected to avoid spreading. The litter effect of all this is considered insignificant.
The overall litter effect of removing and demolishing the Ekofisk Tank is considered small. The overall impact of the operation of Alternative IIE is deemed «none/insignificant».