220 ILCS 5/9-213
The cost of new electric utility generating plants and significant additions to electric utility generating plants shall not be included in the rate base of any utility unless such cost is reasonable. Prior to including the cost of plants or additions to utility plants in the rate base, the Commission shall conduct an audit of such costs in order to ascertain whether the cost associated with the new generating plant or the addition to electric utility generating plant is reasonable. However, the Commission may, for good cause shown in individual cases, waive the auditing requirement for any generating facility which meets all of the following requirements:
If the Commission is unable to conduct such an audit, the Commission shall arrange for it to be conducted by persons independent of the utility and selected by the Commission. The cost of such an independent audit shall be borne initially by the utility, but shall be recovered as an expense through normal ratemaking procedures. Any such audits shall be conducted in accordance with generally accepted auditing standards and shall include but not be limited to costs associated with materials, labor, equipment, professional services and other direct and indirect costs.
"Significant additions to the electric utility generating plant", as used in this Section, shall not include a public utility's investment in pollution control devices for the control of sulfur dioxide emissions. Nothing in this Section is intended to affect the provisions of Section 9-214 of this Act.
"Reasonable", as used in this Section, means that a utility's decisions, construction, and supervision of construction, underlying the costs of new electric utility generating plants and significant additions to electric utility generating plants resulted in efficient, economical and timely construction. In determining the reasonableness of plant costs, the Commission shall consider the knowledge and circumstances prevailing at the time of each relevant utility decision or action.
Nothing in this Section shall prevent or limit the Commission from either entering into and conducting joint audits concerning such electric generating plants with the regulatory authority of another state, or from relying on audits conducted by the regulatory authority of another state in lieu of an audit as required by this Section.
220 ILCS 5/9-213