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4.2.2 Mechanical Recovery and Containment

When oil is spilled on the surface of the water or rises from a deep water discharge and then accumulates on the surface it is possible to concentrate the oil by placement of booms in the pathway of the oil transport.  As the oil accumulates next to the booms it can be recovered by pumping the captured oil into collection containers.  Oil can also be collected e.g. using boats and surface water booms that accumulate the oil as the vessels travel through oil slicks.  The success of these processes depends on the encounter rate and efficacy of the mechanical collection techniques and the success of containment or accumulation.  Ice can act as a natural boom that allows oil to collect along its edges, within leads, under the ice in pockets, and within polynyas.  Ice can also hold the oil for extended periods of time, allowing mechanical recovery to occur over more extended periods of time from its formation to when it begins to melt.  Many of the tools used for mechanical recovery are not unique to application in the Arctic but for some adaptations have been made to collect oil mixed with ice (Broje and Keller 2007).   The tools used to mechanically recover oil after it is concentrated are described in more detail in the Artic response technology report by SL Ross (2012). Environmental impacts from Mechanical Recovery and Containment

Moving ice, either as ice floes or frazzle ice can interfere with containment and recovery equipment deployment and operations (Potter et al. 2012, EPPR 1998).  On the other hand, ice can also slow the spreading of oil on water, keeping a slick thicker during recovery, which increases the efficiency of this type of response activity.  Environmental impacts of mechanical recovery are usually considered in terms of emissions of response equipment, noise, and the impacts of the presence of large numbers of personnel.  However, it is important to consider that mechanical containment and recovery is a slow, tedious, and challenging response method. Mobilizing and supporting such activities in remote areas adds further inefficiencies and time constraints.  Impacts from a containment and recovery response effort are:  the impact from oil that is left behind (oil that escapes containment), and impacts from the activities necessary to reclaim or dispose of the recovered oil and associated oily debris.

The impacts considered with natural attenuation are also associated with the residual oil left behind from mechanical recovery.  Historically, mechanical recovery in open water spills is often reported as less than 15% of the spill volume and in most cases less than 5%, although specific performance can vary widely from incident to incident (EPPR 1998). Thus, for this report, impacts considered under MNR will also be a large part of any mechanical containment response scenario.  Our consideration of the ISB, dispersants and OMA and herder technologies will therefore compare tradeoffs using either mechanical response or naturally attenuation as their baselines. Conclusions

Mechanical recovery in an Arctic spill situation may have marginal improvements in effectiveness due to the presences of some types of ice conditions, or may have additional inefficiencies brought on by different types of ice.  Impacts of residual oil left in the environment due to the low effectiveness of mechanical recovery can also serve as the baseline assessments for evaluating tradeoffs for ISB (with or without herders), chemical and physical dispersants. The areas of proposed work are the same as those included in the natural attenuation section of this report.