Sec. 13. (a) If a public utility makes a substantial change in a cost and schedule estimate for developing and implementing an environmental compliance plan or a modified environmental compliance plan after the estimate has been approved by the commission under this chapter, the public utility shall file with the commission for the commission's review and approval the revised cost and schedule estimate.
(b) To the extent the commission approves a revised cost and schedule estimate, the estimate shall be the approved cost and schedule estimate for the plan.