As for energy, no quantification of atmospheric emissions has been attempted. However, emissions will follow the same pattern as energy (above), with Alternative IVC having the best performance.
9.3.3 Discharges to sea, water or ground
The most relevant environmental issues are identified as:
• Swirling/re-suspension of fine particulate matter and contaminants • Leaching of pollutants (by natural means)
• Discharges/environmental detriments during treatment/disposal on shore.
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Alternative IVA – Injection of cuttings in disposal well
As mentioned above, there are no methods available for retrieving/removing drill cuttings from beneath an offshore platform that adequately addresses environmental concerns. The biggest concern is re-suspension or dispersion of contaminated material during retrieval operations. A significant portion of the contaminants may not be recovered by the dredging mechanism and could be rapidly spread into the surrounding environment. This is considered when evaluating the overall environmental impact of this Alternative. In addition and as described below, re-injection raises issues concerning capacities, methods, and regulations.
Some of the cuttings piles have a fairly soft surface and consistency (Bell et al. 1998), and the sediments therefore may easily be re-suspended by physical disturbance. Re-suspension of these anaerobic sediments may release gases – among them methane, which is not water-soluble and whose bubbles will rise to the surface. The bubbles may contain variable volumes of other gases (like CO2 and H2S). These gases will dissolve in water and
their concentration will decrease as the bubbles rise to the surface. Similarly, fractions of readily-soluble hydrocarbons would spread through the water masses. This would also be the case for some metallic components. Particulate matter would gradually re-settle on the bottom and would have the potential to contaminate adjacent areas. The augmented particle content of the water and the pollutants present could trigger acute effects in marine organisms in the vicinity for a limited time period. It is likely that the effects would mainly impact the immobile or slightly mobile organisms close to the cuttings piles. This is because the occurrence of any marine organisms in or on the piles themselves is very limited (Cripps et al.1998). It is further expected that a greater level of leaching of pollutants to the water body would occur as the contaminated sediments were uncovered during the collection process. The scope of effects caused by recovery of the sediments would be related to the history of the pile and the level of disturbance. It would therefore be advantageous to assess each pile’s surface and contamination level before chososing a recovery method.
Water will accompany the cuttings recovered for slurrification. The cuttings-and-water mix to be injected into the well (slurry) would consist of 70–80 per cent water. This means that water accompanying the cuttings could be used to form the pumpable slurry. Any extra water could be pumped into the injection well. It is expected that the surface installation or equipment would be designed so that any soilage from slurrification and injection would be kept to a minimum. Therefore, no discharge of any environmental significance is anticipated into the sea in this connection.
The evaluations by Rogaland Research (RF 1999) determined that different methods of removal could cause anything from large to small environmental impacts. Removal by mechanical means was considered to have large negative consequences, as it potentially could cause extensive re-suspension and dispersion of the sediments. Suction-dredging methods were assessed to result in somewhat less negative environmental impacts.
According to Rogaland Research (RF 1999), re-injection is generally a solution with small environmental impact, although the recovery process itself is fraught with technological uncertainty and is assessed to have the potential for releases in large quantities by re-suspension and dispersion of
particles and pollutants. The Alternative is thus assessed as having «moderate negative» impacts.
Alternative IVB – Remove for onshore disposal
The environmental issues associated with removal of the drill cuttings from the seabed are the same as those for Alternative IVA (see above).
The water volume accompanying the cuttings may be a larger problem for onshore treatment and disposal than is the case with re-injection. The cut- tings that are pumped to the surface would be collected in containers for transportation to shore. The cuttings would sink to the bottom of the tank in which they are stored, while an oily layer may form at the top of the water. The oily layer could be removed by employing skimmers, while some of the water could be released to the sea. The water discharged to the sea would typically have a hydrocarbon content of less than 40 mg/l, and the discharge will be subject to permit from the Norwegian Pollution Control Authority (SFT). Such a discharge is not expected to have measurable impacts on the environment. Another solution might be to collect the liquids before transport to shore and send them through the offshore installation’s processing facility for produced water. Due to the large quantities of drill cuttings that would be retrieved, it is uncertain whether this would be feasible in practice.
Overall, Alternative IVB – removal for onshore disposal – was assessed to have «moderate negative» impacts.
Alternative IVC – Leave the cuttings in-place
Re-suspension and release of suspended substances could occur in connection with removal or toppling of the jackets. Use of explosive charges, or removal of sediments around the legs/pilings before they are cut, could also cause re- suspension of the deposited material. Effects from re-suspension will be as described for Alternative IVA. The scope of this re-suspension if the cuttings are left in-place, however, is assessed to be small.
A gradual leakage of hydrocarbons and metals from the cuttings piles into the water body and the underlying and near-by sediments could also occur. Studies done at the Heather A platform (ERT 1993) suggest that hydrocarbons in the cuttings piles migrate toward the pile surface, as is also supported by Rogaland Research’s study of Ekofisk (RF 1999). A laboratory test done by Delvigne (1995) concludes that the leach rate is largely predicated by the molecular weight of the hydrocarbon. According to this study, the leach rate declines with increasing molecular weight. The leach rate was below measurable limits after 21 days. However, there is limited knowledge about the factors that determine the leach rate from cuttings piles. One study (RF 1999) evaluated the environmental impacts of the various proposed Disposal Alternatives for Ekofisk I cuttings. The study estimated that the leaching of organic components and metals from the cuttings piles will be small and will decrease over time, but believed the effects will vary depending on the history of the cuttings pile in question.
Some of the cuttings piles are almost fluid or soft on the surface. This means that if a fishing implement or anchor is pulled across them it could cause re-suspension of contaminated sediments. This would affect primarily
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finer particles, would result in a local reduction of water quality for a limited period, and cause release of hydrocarbons and metals or their compounds. A study done by Petersen et al. (1994)17 shows that metal-contaminated,
oxygen-starved sediments which are re-suspended due to anchor operations were quickly reoxidised in the water column. As much as 5 per cent of the particulate-bound Cd, Cu, Pb and Zn was re-mobilised from the sediments.
The results of the Rogaland Research study (RF 1999) also indicate that considerable natural erosion occurs on these piles where they lie. It is not known whether metals are slowly dispersed in the water mass or are buried further down in the sediment as the pile flattens with time. If dispersed to the sea, it is likely to occur as a very gradual release of contaminants to the water body and perhaps a spreading of the particulate matter. Organic components will thus quickly be subject to decomposition, while metals will be spread or re-deposited.
Metals bound within the barite matrices, with the low possibility of leaching and low bio-availability, combined with a limited total quantity and concentrations under SFT’s Class V, result in Alternative IVC (leave in-place) being evaluated as having «insignificant» to «small negative» consequences from potential discharges and erosion. Studies show that since barite has a low solubility in water, only small quantities of metal will leach out, if any at all (Sintef, 1996). It is also known that metals are in general less detrimental to the environmental in seawater than in fresh water.
The evaluation of leaving the cuttings piles in-place is thus a question of how large an environmental risk it involves. The risk depends on the content of the pile and the distribution of the pollutants within it, but also in particular the activities relating to disposal of the steel jackets. A program for monitoring has been suggested to increase the industry’s general know- ledge on drill cuttings (see Section 11.4).
The steel jackets protect the cuttings piles from external disturbances, at the same time that the piles naturally erode. Thus the timing of removal of the steel jackets has an impact on the drill cuttings and their environmental impacts.
If jackets are removed soon, then leaving of the cuttings in-place is believed to cause negative consequences of «moderate» scope.
If the steel installations over the cuttings piles can be left for an extended period («cold phase»), then the Rogaland Research results suggest that the piles will erode naturally, and thus, ultimately, will represent a smaller environmental problem than is the case today. This simultaneously reduces the environmental risk of Alternatives that involve digging and/or mixing the cuttings (for example for removal or covering, see above).
An effect of the cold phase for the steel jackets is thus that the cuttings piles can lie undisturbed for a number of years. This means at the same time that there is no need to dispose of the cuttings as waste somewhere else. The direct environmental risk connected with the solution is deemed limited, since the steel structures will serve to stop foreign objects (e.g. trawls) from encounte- ring the piles, and thus prevent any sudden release occurring from the pile. The steady release of leachants following from natural erosion is assessed as relatively less harmful to the environment.
The impact of leaving the drill cuttings with removal of the steel jackets in the period 2015–2018 is assessed as resulting in «insignificant» to «small negative» impacts. An earlier removal of the jackets, before the piles are significantly eroded, would give a more negative impact.
Alternative IVD – Cover cuttings with gravel or rock
It is expected that dumping stone or gravel on the cuttings could cause some re-suspension of contaminated sediments from the piles. Effects from re- suspension would be as for Alternative IVA. The scope of the biological effects in this context would largely depend on the level of contamination of the cuttings pile and the scope of the re-suspension. The material dumped, as well as the dumping technique employed, would also affect the degree of re- suspension. An assessment by Cripps et al. (1998), concludes that gravel would cause less re-suspension of sediments as it hits the cuttings pile than rock. Positioning chutes (fall pipe), which are fitted on most dredging and dumping vessels, should be used. According to Cripps et al. (1998), the chutes would clearly reduce the chance of re-suspension of the sediments compared with use of a method involving dumping from the surface.
Once covered, the cuttings only represent an «insignificant» environmental risk. There remains uncertainty, however, regarding how large a release one can expect from the actual operation of dumping the gravel onto the cuttings pile. The overall impact is considered «small negative».
9.3.4 Physical impacts and impacts on habitat
Alternative IVA – Inject the cuttings in disposal wells
Removal of the cuttings will obviously change the local habitat at the site. As described for Discharges (above) re-suspension may occur, resulting in fine particles settling on the seabed, covering immobile marine organisms and changing the local seabed condition.
This is considered a local effect but of some magnitude. The overall impact is thus evaluated as «small negative».
Alternative IVB – Remove the cuttings for onshore disposal The physical impacts will be as for Alternative IVA.
Alternative IVC – Leave the cuttings in-place
No physical impacts are identified associated with this Alternative. Alternative IVD – Cover the cuttings with gravel or rock
Despite the fact that the cover materials would cause changes in the local fauna, the cover itself will constitute a new, clean substrate. This can be argued to represent a «small positive» effect. The scale is very small, and the consequences «insignificant».
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9.3.5 Aesthetic effects
Alternative IVA – Inject the cuttings in disposal wells
Cuttings retrieved from the seabed may contain some gases (e.g. H2S) which could give some bad odours. This would only take place offshore, and the impact is considered «insignificant».
Alternative IVB – Remove the cuttings for onshore disposal
The impacts of retrieval of the cuttings would be the same as for Alternative IVA.
Cuttings would be brought onshore in in bulk or in containers on ships, and would be temporarily stored at the quayside or at a similar location. Such storage has a certain potential visual impact, though its impact is assessed as having little importance.
Processing the cuttings and further handling the various waste streams could also result in some negative aesthetic impacts to the local environment. The overall aesthetic impact is assessed as as «small negative».
Alternative IVC – Leave the cuttings in-place This Alternative would result in no aesthetic impacts.
Alternative IVD – Cover the cuttings with gravel or rock This Alternative would result in no aesthetic impacts.
9.3.6 Waste/Resource utilization
Alternative IVA – Inject the cuttings in disposal wells
Removing the drill cuttings would create waste that would have to be disposed. Reinjection is therefore considered as having a «small negative» impact.
Alternative IVB – Remove the cuttings for onshore disposal
The total volume of cuttings in all Ekofisk piles is probably over 17,000 cubic metres (some 30,000 tonnes). By comparison, in 1997 a total of 25,000 tonnes of cuttings were delivered for treatment at the existing treatment facilities in Norway (SFT 1999). The annual capacity at the two largest treatment plants is some 40,000 tonnes combined. Thus the plants seem to be capable of handling the capacity that Ekofisk cuttings would require. In any case, this Alternative would have an effect on the capacity for treating fresh cuttings.
Ash, which remains after incineration of cuttings, would be disposed in a landfill. The cuttings, whether treated or untreated, could also possibly be deposited in a landfill. Once deposited, these have the potential to release substances into the run-off water. Current requirements governing operation of landfills should counteract this potential .
Overall, the waste issue for this Alternative is considered has having a «small negative» impact.
Alternative IVC – Leave the cuttings in-place No waste would be generated by this Alternative.
Alternative IVD – Cover the cuttings with gravel or rock
No waste material would be generated by this Alternative. However, the Alternative would utilize some resources (i.e. gravel). The volume of gravel required would be modest, and the overall impact is considered «small negative».
9.3.7 Littering
Alternative IVA – Inject the cuttings in disposal wells Removal of the cuttings would not result in any littering impacts. Alternative IVB – Remove the cuttings for onshore disposal Removal of the cuttings would not result in any littering impacts. Alternative IVC – Leave the cuttings in-place
Cuttings are not «litter» in a normal context. Nevertheless, cuttings are a waste product resulting from the offshore operations, which are discharged in accordance with Authority permits. According to this Alternative these cuttings would be left when the rest of the field operations have terminated. In this context the impact is considered «small negative».
Alternative IVD – Cover the cuttings with gravel or rock The littering impacts would be similar as for Alternative IVC.