Encyclopedia of Environmental Science and Engineering, Volume I and II

PCBs AND ASSOCIATED AROMATICS 913

again (by EPA definition) even if it had been initially reclassi-

fied as ‘ non-PCB ’.

From the experimental curve of Figure 41, at t  90

days,

X

X

90 560

785

0 713

∞

==.

hence, b 1/2  0.0617

D^  7.6  10 −10 cm^2 /sec(by experiment)

hence, d  1.25 cm.

If the transformer is left in operation long enough to allow

the viscosity of the residual impregnating fluid to increase

due to the preferential migration of chlorobenzenes then,

eventually, the diffusion coefficient will shift from

D  7.6  10 ^10 cm^2 /sec

→ D 


 10 −10 cm^2 /sec.

The transformer will need to be drained and the oil

decontaminated to less than 2 ppm PCB (EPA requirement)

when these new conditions are met. An alternative would

be to dispose of the contaminated oil as PCB fluid and use

new oil to refill the transformer. There is considerable doubt

that the diffusion coefficient will become low enough to

merit this technique. A further drawback in the method lies

in the fact that, during the long waiting period which would

12

10

8

6

4

2

0

0 500 1000

Time (days)

Depth of

Cleaned Layer

(cm)

Recontamination of Bulk Oil to 500 ppm PCB

D = 10-8

D = 10-9

D = 7.6 x 10-10

D = 10-10

FIGURE 42 The time for the bulk retrofill oil to reach 500 ppm PCB depends on the extent of cleaning

and the type of paper used.

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