The Environmental Protection Agency (EPA) is approving revisions to the Washington State Implementation Plan (SIP) that were submitted by the Department of Ecology (Ecology). In 1991, Ecology established source-category regulations for kraft pulp mills, sulfite pulping mills, and primary aluminum plants. These source-category regulations contain requirements specific to these types of facilities. However, the source-category regulations also rely upon cross- references to the general air quality regulations to implement program elements such as new source review permitting. Since 1991, many of the cross-references to the general regulations for air pollution sources have changed. The EPA is approving a revision to the SIP updating the cross-references and other miscellaneous changes.