On March 27, 2008, the Environmental Protection Agency (EPA) amended the National Ambient Air Quality Standards (NAAQS) for ozone. The federal agency did so after reviewing scientific evidence linking exposures to ambient ozone to adverse health and welfare. The EPA set the primary 8-hour standard at a level of 75 ppb. (This was based on the 3-year average of the annual fourth-highest daily maximum 8-hour average ozone concentrations measured at each monitor within an area.)
The secondary standard was also set at 75 ppb, a level identical to the primary standard. The primary standard is intended to protect public health. The secondary standard is meant to protect "public welfare," which includes a wide variety of activities, from forestry and agriculture to the visual enjoyment of scenic areas such as South Carolina's Cape Romain National Wildlife Refuge.
On April 30, 2012, the EPA issued final area designations for the 2008 ozone NAAQS. (77 FR 30144) At that time, all of South Carolina was classified as unclassifiable/attainment with the exception of a portion of York County. Although the monitor in York County was meeting and continues to meet the standard, EPA included the eastern, urbanized area of York County in the Charlotte-Rock Hill, NC-SC nonattainment area (York NAA) because of its belief that emissions in that area contributed to violations at monitors in the Charlotte area. This is the same portion of York County that was designated in 2004 as nonattainment for the 1997 ozone standard, with the exception of the Catawba Indian Nation Reservation. (69 FR 23932) The York NAA was designated marginal for the 2008 ozone NAAQS and as such South Carolina has already implemented NAA requirements in the area due to its 1997 moderate designation.
On May 30, 2014, DHEC submitted a Pre-Hearing SIP package to EPA addressing the requirements for a 2008 ozone marginal nonattainment area, including an emissions inventory. A final submittal is due July 20, 2014.
On April 30, 2004, the EPA designated and classified a portion of York County, South Carolina within the Rock Hill-Fort Mill area as a moderate nonattainment area for the 8-hour ozone NAAQS of 0.08 ppm set in 1997. This area is part of the larger Charlotte-Gastonia-Rock Hill (Metrolina) nonattainment area.On August 31, 2007, DHEC submitted its state implementation plan (SIP) (later adjusted April 29, 2010) for the nonattainment area. The SIP addressed how the area would attain the NAAQS (i.e., the attainment demonstration), reasonably available control measures, reasonable progress, emissions statement, and contingency measures.
Air quality monitoring data from 2008 to 2010 indicated that the York County portion of the Charlotte-Gastonia-Rock Hill NC-SC nonattainment area met the 1997 8-hour ozone NAAQS of 0.08 ppm. So in 2011, DHEC formally asked the EPA to redesignate the York County portion of the Metrolina Nonattainment Area to attainment for the 1997 8-hour ozone NAAQS. The revised State Implementation Plan prepared by South Carolina as part of this request included a maintenance plan that fulfills the requirements of Section 175A of the Clean Air Act as amended to ensure the area remains in attainment of the 1997 8-hour ozone NAAQS through 2022.
In November 2011, the EPA determined (76 FR 70656, November 15, 2011) that this area was meeting the 1997 8-hour ozone NAAQS. This determination suspends the requirements for South Carolina to submit an attainment demonstration, associated reasonably available control measures (RACM), reasonable further progress (RFP) plans, contingency measures, and other planning measures related to attainment of the 1997 8-hour ozone NAAQS. This suspension of requirements will remain in effect for as long as the area continues to meet the 1997 8-hour ozone NAAQS.
On December 26, 2012, EPA published a final approval (77 FR 75862) of the redesignation plan for the South Carolina portion of the Metrolina nonattainment area. This redesignated the area from nonattainment to attainment. EPA also approved South Carolina's 1997 8-hour ozone NAAQS maintenance plan.