The purpose of an EPA Record of Decision is to evaluate a Superfund Site with the goal of protecting human health and the environment while ensuring consistency of evaluations in contamination and clean-up of all Superfund sites. The ROD is a public document signed by the appropriate Regional Administrator which details cleanup, cost estimates, and EPA's responsiveness to the public comment summary. The ROD may be litigated, thus it is important to have all current updates to the signed EPA decision. The ROD may be amended with an Amendment or supplemented by an Explanation of Significant Difference (ESD). A Superfund Site may have multiple RODs, as each Superfund Site may be further redefined as Operable Units and Events. This allows EPA's decisions to evolve as new technology presents itself. Average clean-up time for a Superfund Site can range from 12 to 100 years.