Under the Oil Pollution Act of 1990, onshore oil pipeline operators are required to maintain Facility Response Plans in which each operator ensures that it has the resources necessary to remove, to the maximum extent practicable, a worst case oil discharge and to prevent a substantial threat of a worst case discharge. Operators must obtain regulatory approval for their Response Plans from the Department of Transportation. On January 28, 2014, DOT issued a bulletin providing guidance to operators on how to prepare proper Response Plans prompted by a 2010 spill in Michigan in which cleanup and remediation costs exceeded $1 billion and where there were substantial Response Plan deficiencies. The bulletin advises operators on how to conform their Response Plans to the relevant regulatory requirements and it highlights frequent Response Plan deficiencies, such as missing, incorrect or incomplete methodology and calculations used to determine a worst case discharge; failure to identify response resources; and failure to identify specific environmentally and economically sensitive areas. Operators may also refer to DOT's website for redacted versions of approved Response Plans.