(a) In order to guarantee performance, a utility may require from an applicant before construction is commenced a deposit equal to the estimated cost of construction. This deposit is in addition to the applicant's payment of its share of costs for installation and such deposit shall be returned to the applicant with interest on a pro rata basis as each new customer is connected with service from the utility at the rate specified by the commission for interest on deposits.

(b) Any portion of the deposit remaining unrefunded five years after the date the utility is first ready to render service from the underground telephone distribution facility shall be retained by the utility and credited to the appropriate plant account.

(c) Upon the mutual agreement of both a utility and an applicant, a bond may be posted in lieu of any deposit.