Monitoring surface spills

It is well known that oil spills on the water surface can be detected and monitored by means of various types of airborne remote sensing instruments. Oils spills are often rather viscous and form relatively thick (> 1 mm) layers that change the physical properties of the water surface and make them possible to be monitored by remote sensing techniques. But, on some occasions, even very thin oil films (< 0.1 mm) can be registered by certain instruments and thus also floating chemical spills which most often form thin films on the surface. Such thin films damp the sea surface’s capillary waves, thus reducing the intensity of the backscatter caused by e.g. a Side-Looking Airborne Radar (SLAR). The smooth area of the surface slick will therefore appear as a relatively dark area in the SLAR image. The slick may also change the UV reflectivity of the surface and could be seen by an UV scanner. It can also change the surface’s radiation temperature an be registered by IR instruments like an IR scanner and a Forward-Looking  Infrared Imager or FLIR (an example of the latter is given in the Styrene Barge Accident  under the respective Accident Report) .

Sampling chemical spills on the water surface  

Thick waterborne layers, small globules and balls

If possible, focus the sampling on thick parts of the spill. If the spill is large it is important to take samples in several positions of the spill to get a representative sample selection.

Globules, balls and thick parts can often be sampled directly by a sample bottle. Fill the bottle with as many balls as possible or skim substance from the surface by repeated sweeps with the bottle. Remove the water which has entered the bottle (see Section for Filling and labelling of sample bottles found INFORMATION COMPONENT). Then continue to skim substance and try to get as much as possible of dewatered chemical (a few millilitres are better than nothing).
 

Floating films (thickness greater than appr. 1 mm) or balls on the water surface can with advantage be sampled by a polyethylene cornet (cf. Figure 4 - 2). The cornet should have a wide hem into which a metal ring could be threaded. First cut off the tip of the cornet as shown in the picture.

A holder is fitted onto the ring and by means of this holder the device can be fastened to a boathook or the like.

Polyethylene cornet

Metal ring

Holder
 

Figure 4 - 2
 

The assembled device is swept through the spill so as to skim as much substance as possible.

Figure 4 - 3

Figure 4 - 4

Figure 4 - 5

The water in the cornet is slowly let out and the drainage is stopped when the last drop of water has escaped. Then the substance in the cornet is filled into a 100 ml wide-neck sample bottle. The same procedure is then repeated once or several times until the bottle is approximately three-quarters full of dewatered substance.

N.B. Do not fill the bottle to a higher level than up to 2 cm below the lower edge of the lid.

Figure 4 - 6

Thin waterborne films (sheens)
A special teflon pad may be used if the substance film on the water surface is very thin (thickness less than appr. 1 mm). The pad material should be teflon because other materials may interfere with the succeeding analytical process in the chemical laboratory.

rod and line

clothes peg

teflon pad

Figure 4 - 7

After a sufficient number of sweeps the teflon pad is carefully put into a sample bottle. The peg can be used to push the pad into the bottle. Another clean wooden peg of any kind can, if necessary, be used to assist in the procedure. It is important to avoid contact with any item that could possibly contain traces of strange substances.

Figure 4 - 8

Take samples in every continuous slick. In a spill which is scattered over a long coastline as many samples should be taken to enable a mapping of the substance distribution on the shores.

The substance should be scraped off smeared items and transferred into sample bottles. Avoid, if possible, contamination in the bottles by sand, grass and other debris. In exceptional cases when it is difficult to obtain clean substance samples, it is acceptable to place small contaminated items (pebbles, small pieces of wood, etc.) in the bottles.

Never take whole animal samples, body tissues, etc. which may become rotten during shipment. Try to cut off small parts of smeared feathers, fur, etc. Put the material directly into a sample bottle.