All 55 State Implementation Plans (SIPs) are in the process of being amended. The number of fully approved SIPs has dropped from 3 to 0, partly because EPA, in response to court orders, proposed or promulgated regulations for non-significant deterioration, variances and enforcement orders, and public availability of data. Issues that affect the SIP process and the complexities inherent in the SIP framework are discussed. The number of major emitters identified has increased to 19,200; 70 percent of these are now in compliance with an emission standard or an acceptable compliance schedule. The goal of attaining ambient air quality standards will probably not be achieved in all AQCRs by the statutory deadlines, but the SIP process is accomplishing reductions in ambient levels of the criteria pollutants on a nationwide basis.

"April 1975." "EPA-450/2-75-003." PB-241 494.

This is the fourth in a continuing series of reports assessing the progress made by States in implementing the Clean Air Act, specifically Section 110. Although the report is intended to cover the last six months of calendar year 1974, more recent information is provided where aplicable. This document discusses the status of the various components of State Implementation Plans, the progress that enforcement activities have made in bringing major emitters into compliance, and several of the pending issues that affect the SIP process. A description of the SIP process is also included to facilitate an understanding of increments of progress. The ultimate effectiveness of SIPs will be judged in terms of States meeting the national ambient air quality standards. An official determination will be made for a calendar year of data, in most cases beginning with the first quarter of calendar year 1976.