(1) Deposit criteria for nonresidential customers. A utility may require an applicant for nonresidential service to demonstrate that the applicant is a satisfactory credit risk by reasonable means appropriate under the circumstances.

(2) Deposit amount. Deposits required for a customer or location must not exceed:

(a) Two-twelfths of the estimated annual billings for utilities billing monthly; or

(b) Three-twelfths of estimated annual billings for utilities billing bimonthly.

(3) Transfer of deposit. When a customer moves to a new address within the utility's service territory, the deposit plus accrued interest, less any outstanding balance owing from the old address, must be transferred to the new address or refunded.

(4) Additional deposit. If a deposit or additional deposit amount is required after the service is established, the reasons must be specified to the customer in writing. Any request for a deposit or additional deposit amount must comply with the standards outlined in subsection (1) of this section. If the original deposit was secured by a guarantor and the guarantor does not agree to be responsible for the additional deposit amount, the customer will be held responsible for paying the additional deposit.

(5) Deposit payment date. Any deposit or additional deposit amount required after service is established is due and payable not earlier than 5:00 p.m. of the sixth business day after notice if the deposit requirement notice is mailed from within the states of Washington, Oregon, or Idaho, or the ninth business day if mailed from outside the states of Washington, Oregon, and Idaho. If the utility delivers the notice to the customer in person, the deposit or additional deposit amount is due and payable not earlier than 5:00 p.m. of the sixth business day from the date of delivery.

(6) Interest on deposits. Utilities that collect customer deposits must pay interest on those deposits calculated:

(a) For each calendar year, at the rate for the one-year Treasury Constant Maturity calculated by the U.S. Treasury, as published in the Federal Reserve's Statistical Release H.15 on January 15 of that year. If January 15 falls on a nonbusiness day, the utility will use the rate posted on the next following business day; and

(b) From the date of deposit to the date of refund or when applied directly to the customer's account.

(7) When refund of deposits is required. A utility must apply deposits plus accrued interest to the customer's account, or refund deposits plus accrued interest when there has been satisfactory payment, as defined in (a) of this subsection, or when service is terminated.

(a) "Satisfactory payment" means a customer has paid for service for twelve consecutive months in a prompt and satisfactory manner as evidenced by the following:

(i) The utility has not started a disconnection process against the customer; and

(ii) The utility has sent no more than two delinquency notices to the customer.

(b) Termination of service. When service is terminated, the utility must return to the customer the deposit amount plus accrued interest, less any amounts due the utility by the customer.