The Environmental Protection Agency (EPA) is proposing to approve and disapprove portions of a state implementation plan (SIP) revision submitted by the State of Colorado to meet Clean Air Act (CAA) requirements for the 2008 8-hour ozone national ambient air quality standards (NAAQS) in the Denver Metro/North Front Range nonattainment area (DMNFR Area). Specifically, the EPA is proposing approval of the submitted enhanced monitoring SIP element as meeting applicable Serious area requirements for the 2008 8-hour ozone NAAQS, and is proposing disapproval of the contingency measure element and certain reasonably available control technology (RACT) SIP submittals. The EPA is taking this action pursuant to the CAA.