Modo de sintonía

Locations for demolition and processing the waste from the steel jackets, if taken to shore, have not been finalised. This assessment of the waste issue thus looks only at types and volumes, not directly at the local consequences at each potential locality, treatment plant, or waste dump.

Disposal of the steel jackets as an artificial reef either in-place or collectively around the Tank will not generate waste. Removal of the jackets (but not the Tank) will generate a total volume of waste of almost 79,000 tonnes. This is made up of steel, concrete, anodes, and marine growth.

In the case of the Ekofisk Tank, waste problems largely arises in the case of Alternative IIE (removal and demolition).

Alternatives IIC, IID, and IIE Steel

Steel in the jackets amounts to about 63,000 tonnes. The jackets could, theoretically, be used again as jackets for new platforms. However, it has not been possible to identify specific re-use options for the various parts of the

installations, and re-use of the steel structures is not therefore considered further in this Impact Assessment.

Essentially all the steel from the jackets is expected to go to the scrap furnace. Recycling of steel is discussed further in Section 6.2.6, to which we refer for a further assessment of waste arising in connection with the solution for the steel.

Concrete

There are 7,000 tonnes of concrete associated with the steel jackets, including that in the legs and foundation piles of the jackets. The concrete will remain inside the jackets when the jackets are removed to the demolition yard.

Concrete from the jackets could mainly be used for recycling as filler mate- rial, or otherwise will be disposed of in a landfill.

Anodes

The jackets of the various installations are protected from corrosion (rust) by aluminium or zinc based sacrificial anodes. These also contain small quantities of silicon and other metals, including copper, iron, and mercury. The weight of these anodes totals about 1,440 tonnes.

The anodes are engineered for a predicted lifetime of at least 20 years. It is assumed that they corrode by 2.5–3 per cent per year, which will have resulted in the consumption of between 50 and 80 per cent of the Ekofisk I anodes already, depending on date of installation in each case (DNV 1999-b).

Reuse of the Ekofisk I anodes is not feasible. All materials from these anodes are melted down again (O. Lyngstad, Norsk Metallretur, personal communication).

The material of the anodes is well suited to recycling, and the metals can either form the raw material for new anodes or similar products, or go into entirely different products. Recycling anode material is a well-established industry. Almost all anode metal recovered on the Norwegian side is sent to Germany for melting down. The various components of the anodes are separated by their melting points. The products, mainly aluminium and zinc, are standard commodities that are traded on the international market (O. Lyngstad, Norsk Metallretur, personal communication).

When Odin was broken up, all anode materials were sent for melting down (plus a small fraction which was re-commissioned) (F. Rogne, Aker Stord, personal communication).

Disposal of anode materials can result in leaching of metals into the run-off water and then to the surrounding environment. Any disposal would therefore demand special and extensive measures to preclude leaching. Anode materials must be treated as special waste under the Special Waste Regulations (Ministry of the Environment, 1994). Disposal of anode materials in special waste facilities is subject to a disposal fee, and therefore this alternative is less economic than recycling.

We assume that anodes on the steel jackets will be recycled. Therefore no waste is anticipated from anode materials on the jackets.

Marine growth

The total weight of fouling on the steel jackets is estimated at over 7,000 tonnes. The estimate is based on assumed colonisation space, an average fouling thickness of 50 mm, and a specific density of fouling which is put at 1 tonne per cubic metre.

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Mussels and anemones are generally the bulk of the growth, plus acorn barnacles and algae (weed). Thus the growth consists both of soft, organic material and a harder, calciferous portion made up of shells and skeletons. The greatest volume of growth will be in the upper 10–30 metres as it is here that light penetrates, nutrient salts concentrate, and the water is warmer.

Marine fouling can be removed mechanically from steel panels using a jet hose or similar. Calciferous deposits (barnacles etc) could also be scraped off. Practices regarding removal of the resulting organic material varies. Usually it is hosed into the sea without any treatment. Composting or other forms of disposal are not commonplace. Smaller volumes of organic growth from offshore structures can be washed into the sea without problem, if the location, existing organic impact, tidal flows etc are taken into account. The material is quickly degraded with the sole result that natural components of the marine ecosystem are repatriated.

If the steel jackets are taken to shore this will occur over many years. In that sense the marine growth that needs to be processed at each demolition yard will be far less (some 200–1000 tonnes per installation) than the field total. Compostation onshore might provide an alternative to disposal in the sea. It is more controllable, and causes less nuisance to the local community. Alternative IIE – Removal and demolition of Ekofisk Tank Steel

There are about 46,000 tonnes of steel (pre-stress cables and reinforcement bars) in the Tank structure and Protective Barrier Wall. This steel can be expected in all essentials to be melted down. The recycling options for steel in general are discussed above.

The steel reinforcement would accompany the concrete if disposed of without being broken into rubble first. More likely, however, the concrete would be separated from the reinforcement so that almost all the steel could be recycled.

If removed and demolished, a total of 99 per cent of the steel is expected recycled as scrap.

Concrete

Concrete in and around the Ekofisk Tank with its Protective Barrier Wall provides the major contribution to the total estimated volume of Ekofisk I concrete, constituting about 470,000 tonnes of the total of 520,000 tonnes of Ekofisk I concrete.

Much of the concrete can theoretically be recycled. Concrete used offshore is generally of high quality, with great strength and low permeability. Generally therefore it is suitable for material recycling (S.W. Danielsen, Franzefoss Bruk, personal communication). The concrete can be crushed and used as aggregate in fresh concrete, asphalt for roads, rubble for roads, filler, etc. It is expected that there is a potential market for broken concrete as a filler on the Continent. The effort to make the concrete recyclable (i.e. refloating the Tank, crushing the structures, processing the concrete and transporting it) must however not be underestimated.

The immense volumes of concrete in the Tank and PBW make demolition operations for these structures a real challenge. During cutting, lifting and crushing, concrete chunks can loosen and get spread about on land and in the

sea at the demolition yard. Concrete waste from crushing should be gathered up and processed according to the demolition contractor’s procedures and licensing terms. It is assumed that all disposal would take place in accordance with current rules and regulations for waste (SFT 1994).

The concrete in the Ekofisk Tank and PBW occupies huge volumes, and is therefore expensive to dispose of. Also, the concrete would occupy huge areas, and disposal in a landfill is therefore considered a poor solution.

A separate report (DNV 1999-c) provides a thorough assessment of alternative disposal methods for concrete.

Marine growth

See the discussion on marine growth under steel jackets, above. Here we mention other factors of particular importance for the demolition of the Ekofisk Tank.

The marine fouling on the Tank structure is estimated to weigh about 3,700 tonnes. If the Tank and Barrier Wall are broken up, this quantity would be processed over a longish period of time (some 18 months). Marine organic material very quickly rots and decomposes. The marine growth on the Tank structure represents a significant volume of organic material. Therefore it must be treated and removed quickly to avoid foul odors at the demolition yard and adja- cent areas.

The disposal of large volumes of marine growth by hosing into the sea at the demolition yard would lead to a concentration of organic waste in the water and seabed close by. Therefore this potential method is deemed a poor solution when demolishing the Ekofisk Tank. Marine growth, alternatively, can be processed as wet organic material and fed into a composter at a waste disposal site. The marine growth will be tested for metals before disposal.