Calculation Procedure:
- Establish a work-measurement equation from a beach model
After the Exxon Valdez ran aground on Bligh Reef in Prince William Sound, a study was
made to develop a model and an equation that would give the relative amount of work
needed to rid a beach of spilled oil. The relative amount of work remaining, expressed in
clydes, is defined as the amount of work required to clean 100 yd (91.4 m) of lightly pol-
luted beach. As the actual cleanup progressed, the actual work required was found to
agree closely with the formula-predicted relative work indicated by the model and equa-
tion that were developed.
The work-measurement equation, developed by on-the-scene Commander Peter C.
Olsen, U.S. Coast Guard Reserve, and Commander Wayne R. Hamilton, U.S. Coast
Guard, is S = (LfIOO)(EWPTCD), where S = standardized equivalent beach work units,
expressed in clydes; L = beach-segment length in yards or meters (considered equivalent
because of the rough precision of the model); E = degree of contamination of the beach
expressed as: light oil = 1; moderate oil = 1.5; heavy oil = 2; random tar balls and very
light oil = 0.1; W= width of beach expressed as: less than 3Om= 1; 30 to 45 m = 1.5;
more than 45 m = 2; P = depth of penetration of the oil expressed as: less than 10 cm = 1;
10 to 20 cm = 2; more than 30 cm = 3; T= terrain of the beach expressed as: boulders,
cobbles, sand, mud, solid rock without vertical faces = 1; gravel/pebbles = 2; solid rock
faces = 0.1; C = percent of oil coverage of the beach expressed as: more than 67 percent
coverage = 1; 50 to 67 percent = 0.8; less than 50 percent = 0.5; D = debris factor ex-
pressed as: heavy debris =1.2; all others = 1. - Determine the relative work required
Using the given conditions, S = (300/100)(2 x 1.5 x 1 x 1 x 0.8 x 1.2) = 8.64 clydes. This
shows that the work required to clean this beach would be some 8.6 times that of cleaning
100 yd of lightly oiled beach. Knowing the required time input to clean the "standard"
beach (100 yd, lightly oiled), the approximate time to clean the beach being considered
can be obtained by simple multiplication. Thus, if the cleaning time for the standard light-
ly oiled beach is 50 h, the cleaning time for the beach considered here would be 50 (8.64)
= 432 h.
Related Calculations: The model presented here outlines—in general—the proce-
dure to follow to set up an equation for estimating the working time to clean any type of
beach of oil pollution. The geographic location of the beach will not in general be a factor
in the model unless the beach is in cold polar regions. In cold climates more time will be
required to clean a beach because the oil will congeal and be difficult to remove.
A beach cleanup in Prince William Sound was defined as eliminating all gross
amounts of oil, all migratory oil, and all oil-contaminated debris. This definition is valid
for any other polluted beach be it in Europe, the Far East, the United States, etc.
Floating oil in the marine environment can be skimmed, boomed, absorbed, or other-
wise removed. But oil on a beach must either be released by (1) scrubbing or (2) steaming
and floated to the nearby water where it can be recovered using surface techniques men-
tioned above.
Where light oil—gasoline, naphtha, kerosene, etc.—is spilled in an accident on the
water, it will usually evaporate with little damage to the environment. But heavy oil—No.
6, Bunker C, unrefined products, etc.—will often congeal and stick to rocks, cobbles,
structures, and sand. Washing such oil products off a beach requires the use of steam and
hot high-pressure water. Once the oil is freed from the surfaces to which it is adhering, it
must be quickly washed away with seawater so that it flows to the nearby water where it
can be recovered. Several washings may be required to thoroughly cleanse a badly pollut-
ed beach.