The National Stone, Sand & Gravel Association (NSSGA) offers the following comments on EPA’s proposed disapproval of the Texas State Implementation Plan (SIP) provisions for maintenance, startup and shutdown (MSS) provisions for visible emissions and particulate matter.1 NSSGA urges EPA to abandon its proposal as inconsistent with the fundamental principles underlying the Clean Air Act (CAA) and relevant judicial decisions, and to approve the Texas SIP provisions at issue. The CAA grants states primary authority to choose the emission control measures necessary to comply with the Act in that state. Where EPA proposes to disapprove a state provision that previously was approved, the agency bears a heavy burden to show that the provision is substantially inadequate to meet the Act’s applicable requirements. The agency has failed to meet that burden here. These issues are discussed in detail below.