914 PCBs AND ASSOCIATED AROMATICS

be necessary to observe a reduction in the rate of diffusion,

the transformer would have to be considered PCB filled as

though no retrofill operation had taken place.

The continued leaching of PCBs with a lowered diffu-

sion coefficient of 
 10 ^10 cm^2 /sec will cause the PCB con-

centration of the bulk oil to increase above 500 ppm PCB in

a period of time which can be calculated as follows:

X

X

t

∞

==

500

785

0 637.

hence, b 1/2  0.036 as found earlier

(^) hence, t  234 days.
Thus, even if the transformer is reclassified at the end of the
EPA mandated 90 day period by a process which involves
simple vapor cleaning, leaching and re-retrofill, the tech-
nique cannot provide continued, reclassified use of the trans-
former for its remaining useful life. Indeed, it is not likely
to be able to maintain the unit’s reclassified status as a PCB
contaminated transformer for as long as one year.
If it is hoped that the transformer can be reclassified as a
non-PCB unit then,
X
X
t
∞

50
785
0 0637.
then, b 1/2  0.0215
and, t  84 days.
6 5 4 3 2 1 0
0 1000 2000
Time (days)
Depth of Cleaned
Layer (cm)
Recontamination of Bulk Oil to 50 ppm PCB
D = 10-10
D = 7.6 x 10-10
D = 10-11
FIGURE 43 Correlations between the depth of the cleaned layer and the time to reach 50 ppm PCB in the
bulk retrofill fluid.
C016_003_r03.indd 914C016_003_r03.indd 914 11/18/2005 1:12:40 PM11/18/2005 1:12:40 PM