(a)
(1) Once an extension project that has been granted a certificate is placed into service and is used and useful, the gas utility may collect the excess expenditures through a rate or surcharge approved by the Arkansas Public Service Commission. The tariff and rate filing made at the time of the certificate application shall include estimated excess expenditures upon which the commission may grant the certificate.
(2) The commission may subsequently modify the previously approved rates in any reasonable manner if the actual total costs and excess expenditures differ significantly from the estimated total costs and excess expenditures.
(3) If the actual total costs and excess expenditures significantly exceed the estimated costs and excess expenditures and the difference is caused by imprudence or other unsatisfactory causes, the commission may disallow recovery of a portion of the actual excess expenditures in the approved rates.
(b) The rate or surcharge implemented under this section remains effective until the implementation of new rate schedules in connection with the next general rate filing of the gas utility wherein such extension project investments can be included in the gas utility's base rate schedules.
(c) The rate or surcharge for each class of customer shall be determined consistent with the most recent determination by the commission in its order addressing the gas utility's most recent application for a general change or modification in its rates and charges.