(1) Customer bills must:

(a) Be issued at intervals not to exceed two one-month billing cycles, unless the utility can show good cause for delaying the issuance of the bill. The utility must be able to show good cause if requested by the commission;

(b) Show the total amount due and payable;

(c) Show the date the bill becomes delinquent if not paid;

(d) Show the utility's business address, business hours, and toll-free telephone number and emergency telephone number by which a customer may contact the utility;

(e) Show the beginning and ending meter readings for the current billing period, the current monthly or bimonthly read date, as applicable, and the total amount of therms used for the billing cycle, provided that the customer bill must provide the meter readings and read date for the final reading for the applicable monthly or bimonthly billing cycle; the bill need not include interval readings, although customers must be provided access to their usage data in accordance with WAC 480-90-153;

(f) Show the amount of therms used for each billing rate, the applicable billing rates per therm, the basic charge or minimum bill;

(g) Show the amount of any municipal tax surcharges or their respective percentage rates, if applicable;

(h) Clearly identify when a bill has been prorated. A prorated bill must be issued when service is provided for a fraction of the billing period. Unless otherwise specified in the utility's tariff, the charge must be prorated in the following manner:

(i) Flat-rate service must be prorated on the basis of the proportionate part of the period that service was rendered;

(ii) Metered service must be billed for the amount metered. The basic or minimum charge must be billed in full;

(i) Clearly identify when a bill is based on an estimation.

(i) A utility must detail its method(s) for estimating customer bills in its tariff;

(ii) The utility may not estimate for more than four consecutive months unless the cause of the estimation is inclement weather, terrain, or a previous arrangement with the customer; and

(j) Clearly identify determination of maximum demand. A utility providing service to any customer on a demand basis must detail in its filed tariff the method of applying charges and of ascertaining the demand.

(2) The minimum time allowed for payment after the bill's mailing date must be fifteen days, if mailed from within the states of Washington, Oregon, or Idaho, or eighteen days if mailed from outside the states of Washington, Oregon, and Idaho.

(3) The utility must allow a customer to change a designated payment-due date when the customer has a satisfactory reason for the change. A satisfactory reason may include, but is not limited to, adjustment of a designated payment-due date to parallel receipt of income. The preferred payment date must be prior to the next billing date.

(4) With the consent of the customer, a utility may provide billings in electronic form if the bill meets all the requirements for the use of electronic information in this chapter. The utility must maintain a record of the consent as a part of the customer's account record, and the customer may change from electronic to printed billing upon request, as provided in this chapter. The utility must complete the change within two billing cycles of the request.

(5) Corrected bills:

(a) A utility must issue a corrected bill upon finding that an underbilling or overbilling occurred as a result of a meter failure, meter malfunction, meter with unassigned energy usage, or any other situation where energy usage was not billed or was inaccurately billed. The utility must use the rates and rate schedule in effect during the billing period(s) covered by the corrected bill. The utility must issue the corrected bill within sixty days from the date the utility discovered that an account had been underbilled or overbilled. Except as provided in subsection (7) of this section, when a utility's investigation finds that it has underbilled energy usage, it may not collect underbilled amounts for any period greater than six months from the date the error occurred. The maximum period for which utilities are required to adjust bills for overbilling is six years.

(b) For the purposes of this rule:

(i) A meter failure or malfunction is defined as: A mechanical malfunction or failure that prevents the meter or any ancillary data collection or transmission device from registering or transmitting the actual amount of energy used. A meter failure or malfunction includes, but is not limited to, a stopped meter, a meter that is faster or slower than the metering tolerance specified in WAC 480-90-338, or an erratic meter.

(ii) An unassigned energy usage meter is defined as a meter that is installed at a valid service address and accurately records energy usage during a period of time where there was no active gas service account at that premises.

(c) A utility must develop and maintain procedures that establish practices for the prompt identification, repair and replacement of meters that are not functioning correctly and for identification of unassigned usage meters. The objective of such procedures shall be to mitigate the number of underbilling occurrences that exceed six months in duration. These procedures must address, at a minimum:

(i) Practices to prevent the issuance of corrected bills due to incorrect prorated bills, improperly assigned meters, incorrectly installed meters, incorrect billing rate schedules, incorrect billing multipliers, or any other event that may affect billing accuracy.

(ii) Processes for the investigation of meter issues include, but are not limited to, stopped, slowed, and erratic usage meters.

(iii) Processes for the investigation of meter usage from unidentified usage meters.

(6) For the purpose of this rule, a corrected bill may take the form of a newly issued bill or may be reflected as a line item adjustment on a subsequent monthly or bimonthly bill. When a corrected bill is issued, the utility must provide the following information on the corrected bill, in a bill insert, letter, or any combination of methods that clearly explains all the information required to be sent to the customer:

(a) The reason for the bill correction;

(b) A breakdown of the bill correction for each month included in the corrected bill;

(c) The total amount of the bill correction that is due and payable;

(d) The time period covered by the bill correction; and

(e) When issuing a corrected bill for underbilling, an explanation of the availability of payment arrangements in accordance with WAC 480-90-138(1) payment arrangements.

(7) Exceptions to billing correction rules:

(a) Corrected bills related to an underbilling due to tampering or interference with the utility's property, use of the utility's service through an illegal connection, or the fraudulent use of a utility's service, are exempt from the six-month restriction set forth in subsection (5)(a) of this section.

(b) Adjustments for underbilling of nonresidential customers will be limited to six months. However, the utility may extend this period for good cause if a longer period is appropriate due to circumstances such as the complexity of specific accounts, changing metering configurations, load changes of large industrial customers, special meter configuration involving current transformers, or wiring reconfigurations by the customer. Utilities must report to the commission within sixty days the reasons for any adjustments longer than six months.

(c) The utility may choose not to issue a corrected bill to recover underbilled amounts less than fifty dollars.

(8) An estimated meter read made in accordance with subsection (1)(i) of this section is not considered a meter failure or malfunction or a billing error. A bill true-up based on an actual meter reading after one or more estimated bills is not considered a corrected bill for purposes of subsection (5)(a) of this section.