Cal. Rev. & Tax. Code § 40023

An electric utility is relieved from liability to collect the surcharge insofar as the base upon which the surcharge is imposed is represented by accounts which have been found to be worthless and charged off in accordance with generally accepted accounting principles. If the electric utility has previously paid the amount of the surcharge it may, under regulations prescribed by the board, take as a deduction on its return the amount found to be worthless and charged off. If any such accounts are thereafter collected in whole or in part the surcharge so collected shall be paid with the first return filed after such collection.

The board may by regulation promulgate such other rules with respect to uncollected or worthless accounts as it shall deem necessary to the fair and efficient administration of this part.