sampling patterns for spills of water miscible and nonmiscible substances at 

 two different types of marine locations are presented below. 



Offshore spills . For analytical documentation of a spill it is desirable 

 to establish both horizontal and vertical concentration gradients, if they 

 do in fact exist. The horizontal gradient should be established from the 

 source of the spill to control or background concentration levels at a dis- 

 tance away from the source. When a water miscible discharge is leaked into 

 offshore waters under steady environmental conditions, horizontal gradients 

 can most easily be defined by sampling a transect directly through the 

 gradient. If the direction of the gradient from the source is not obvious 

 a series of transects emanating from the source of the leak in all directions 

 will usually detect it. This type of sampling pattern is illustrated in 

 Figure 3. Vertical gradients can be detected by sampling at various levels 

 in the water column along a transect that defines the horizontal gradient. 

 In shallow coastal areas, such as bays and estuaries, vertical gradients may 

 not be formed. This is especially true if the spill is large or occurs 

 during a period of intense wave action. In stratified estuaries, concentra- 

 tion breakpoints may be established when sampling vertically. 



In a situation where the spilled substance is not miscible with water it 

 is usually necessary to deal with a water-soluble fraction of the substance, 

 dispersed droplets of the substance, and a slick on the surface of the water. 

 Petroleum will be used hereafter as an illustrative example of this kind of 

 spill . 



Under steady environmental conditions, a slick formed from a point source 

 of leaking oil will form a plume-like slick that eventually breaks up into 

 patches. This process is best documented by aerial color or infrared photog- 

 raphy (Worsley 1970). Samples taken from the intact slick at progressively 

 greater distances from the source can be used to document the weathering proc- 

 ess. Oil taken further from the source would naturally be weathered to a 

 greater extent than oil taken nearer the source. Although the concentrations 

 of dissolved and dispersed oil are generally higher beneath an oil slick, 

 attempts to establish a gradient of petroleum in the water column by sampling 

 from the source outward under the slick are not generally fruitful. This is 

 because the movement of the slick is determined to a large extent by wind 

 direction (Lissauer et al . 1977); movement of the dissolved and dispersed oil 

 in the water column is determined primarily by subsurface water currents. 

 This can result in situations where oil slicks are located at one position 

 in relation to the spill source and the highest concentrations of dissolved 

 and dispersed oil in the water column are located elsewhere (Kuhnhold 1978). 



Analytical delineation of the solublized and dispersed oil in the water 

 column is obviously an extremely difficult problem to solve with any degree 

 of accuracy. The situation is further complicated by observations that oil 

 slicks act as mobile secondary sources of petroleum hydrocarbon contamination. 

 Under extreme conditions, spilled oil can also be driven into the sediment 



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