Spills of Nonfloating Oils Risk and Response (1999) / Chapter Skim
Currently Skimming:
3 Technologies and Techniques
3 Technologies and Techniques
Pages 33-51
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From page 33... ...
MODELING AND INFORMATION SYSTEMS The following discussion begins with a brief overview of the state of the art in spill modeling and information systems (Box 3-1~. This is followed by the extension of spill models to include the subsurface transport and deposition of dispersed oil and a history of the use of these models to "hindcast" (analyze a past event)
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From page 34... ...
With the incorporation of the GIS and other data management tools, users can input, organize, manipulate, archive, and display georeferenced information relevant to spill modeling. With the extension of spill models to include supporting data management tools, spill information systems have been developed that can provide valuable data to support spill responses and planning.
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From page 35... ...
Both models correctly predicted the general subsurface transport of the highly dispersible, Gulfaks crude oil that was spilled. The predicted location of the subsurface oil was consistent with the pattern of sedimented oil found on the seabed.
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From page 36... ...
The subsurface current structure is of limited importance when the flows are principally tidal and water depths are shallow, but they become particularly important when stratification and multilayer flows are present. Finally, Michel and Gait (1995)
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From page 37... ...
. In situ detectors FIGURE 3-1 Decision tree based on oil density and water depth.
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From page 38... ...
Airborne photography and visual-based systems, which are widely available and can rapidly survey large areas, are widely used to locate submerged oil. The performance of these systems is limited by water clarity and depth, the quantity of oil, and the characteristics of bottom sediment.
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From page 39... ...
The effectiveness of sampling methods is strongly dependent on the composition of the oil and oiled sediment and environmental factors, such as current speed, water depth, and substrate type. In Situ Detectors In situ and towed fluorometric detection are widely available and routinely used to detect and map petroleum leaks and spills (Turner Designs, 1999~.
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From page 40... ...
In general, visual and photobathymetric techniques are restricted to water depths of 20 meters or less and are suitable for both suspended and deposited oil. Diver-based visual observations can only be used in low-current and small wave areas.
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From page 41... ...
The effectiveness of trawls and nets declines rapidly as current speeds increase or as nets become clogged. During the Presidente Rivera spill in the Delaware River, fish nets were able to recover eight tons of oil before they became fouled (NOAA, 1992~.
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From page 42... ...
Low probability; field personnel would have to know how to operate all equipment. Realistic only for water depths <30 ft; sea conditions may restrict vessel operations.
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From page 43... ...
Low; sorbents are designed to pick up oil, so they would be less likely to be stained by other materials Difficult to deploy and retrieve in strong currents; sea conditions may restrict vessel operations Uses material available anywhere Very slow; very limited sampling area High; system images all submerged features, have to learn to identify patterns for different features, thus requires extensive ground trothing Weather may restrict flights; minimum detectable size of oil particle is not known, but other individual features detected are usually feet in size or schools of small fish Can cover large areas quickly using standard resources available at spills; permanent record of image that is georeferenced Not proven for detecting suspended oil droplets; very limited availability
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From page 44... ...
bathymetry. Operational Requires good water clarity Sea conditions may restrict Water depths of 20 m (for Limitations and light conditions; vessel operations.
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From page 45... ...
High probability; photography can be used to identify potential sites, which require ground trothing. Specifications call for low sun angles and calm sea state; water penetration is limited by water clarity; maximum penetration is 10m for very clear water,lm for turbid water; best if baseline "before" photography is available for comparison.
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From page 46... ...
TV SPILLS OF NONFLOATING OILS Water Depth ~ Containment Methods 0-2 m i = >| · Physical barrier l 0~ m ~ I| · Silt curtain l Maximum working depth not established ~ · Pneumatic curtain ~ · Onshore containment Water Depthl > 0-2m+ = No depth restriction I\ · Allow oil to collect in natural or artificial depression · Onshore containment FIGURE 3-2 Decision tree for containment options for sunken oil. Source: Castle et al., 1995.
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From page 47... ...
I/ 47 Water Depth 0-2mi ~>: Working depth ~ a. Midwater trawls l varies ~ · Pump/decant systems ~ · Onshore recovery Recovery methods · Permeable barrier · Manual recovery Oil characteristics Pumpable Not pumpable Water Depth 0-5 me Mud cat Dustpan/cutterhead dredge Hopper dredge Handheld dredge Dozer dredge Vacuum systems Progressive cavity pump Airlift pumps Combination systems 0-1 5 me 0-20 me 0-30 me 0~0 me Working depths vary Water Depth 0-5 me 0-1 5 me 0-30 me Working depths vary Mud cat Cutterhead dredge Divers Bottom trawls Clamshells dredge Robotic systems FIGURE 3-3 Decision tree for recovery options for sunken oil.
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From page 48... ...
Accurate vertical control of the dredge depths is critical to minimizing the amount of dredged material and the amount of clean sediment contaminated with oil as the result of the dredging operation. Operational costs and logistics requirements are lower for land-based than for bargebased methods of handling and storing dredged materials.
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From page 49... ...
Only effective under very limited conditions; takes time to fabricate and deploy, thus only effective where predeployed; little data available to assess performance. There are commercially available net booms have been developed and tested for containing spills of Orimulsion; little availability in the United States.
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From page 50... ...
The selection of containment and recovery methods is highly dependent on the specific location and environmental conditions during the spill, the
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From page 51... ...
On-water systems will be very complicated and subject to weather, vessel traffic, and other safety issues. Water depths up to 60-80 ft for routine dive operations; water visibility of 1-2 ft so divers can see the oil; bad weather can shut down operations; solid oil which is not pumpable Sites adjacent to shore, requiring minimal on-water systems; liquid or semi-solid oil; thick oil deposits, good visibility; low currents Most experience is with this type of recovery; diver can be selective in recovering only oil and effective with scattered deposits; Very large manpower and logistics requirements, including large volumes of water-oil-solids handling, separation, storage, and disposal; problems with contaminated water diving and equipment decon; slow recovery rates; weather dependent operations Special purpose dredges, usually small and mobile, with ability for accurate vertical control.
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