State Implementation Plans

What is a SIP attainment plan? What is a Maintenance Plan?

A State Implementation Plan (SIP) as defined by the U.S Environmental Protection Agency (EPA) is a living comprehensive collection of regulations and documents used by a state or region to implement, maintain, and enforce the federal National Ambient Air Quality Standards (NAAQS), and to comply with other Clean Air Act requirements. EPA has established NAAQS for pollution from carbon monoxide, lead, nitrogen oxide, ozone, particulate matter (PM), and sulfur dioxide. When a state or region is not meeting, or “attaining”, NAAQS, EPA designates it as a nonattainment area that must develop an attainment plan as part of the overall SIP. Those SIP attainment plans  have different required elements based on the EPA nonattainment classification scale. If the state or area does not attain the relevant NAAQS by a set statutory deadline, EPA will reclassify the level of nonattainment and the state or region must develop another SIP. Once an area has attained the relevant standard, EPA redesignates it as a maintenance area and requires it to develop a Maintenance Plan to ensure that it continues to meet the standard.

The RAQC leads the development of attainment SIPs in the Denver Metro/North Front Range (DM/NFR) region in partnership with the Colorado Department of Public Health and Environment’s Air Pollution Control Division and in collaboration with other partners and stakeholders. For a detailed overview of Colorado attainment plans developed by the RAQC as well as roles and responsibilities in developing SIPs, please see Colorado’s SIPs for all pollutants.

Current Colorado SIP Efforts

The DM/NFR region is currently in Severe nonattainment for the 2008 ground-level ozone standard of 75 parts per billion (ppb) and Serious nonattainment for the 2015 ozone standard of 70 ppb, according to EPA classification levels. Based on EPA policy, the region must meet both standards successfully and therefore must develop and implement SIPs for both. Documents and background information about the SIP development process are available on the 2015 ozone standard and 2008 ozone standard pages. To attain these two standards, the RAQC explores potential air pollution control strategies that might be included in SIPs, incorporated into state or local government policies, or promoted through voluntary programs. For a high-level overview of 2022 SIP development efforts, please see the Public’s Guide to the SIP.

The Denver Metro region is still designated as a maintenance area for PM10 and CO, although it has not violated those standards since 1987 and 1995, respectively. The RAQC supports data collection on a long-running Street Sanding Program as part of the PM10 Maintenance Plan.

Historical Colorado SIP Efforts

The RAQC has previously supported development of SIPs for the 1997 (84 ppb) 8-Hour Ozone Standard and 1979 (125 ppb) 1-Hour Ozone Standard, Carbon Monoxide (CO), and Particulate Matter (PM) for the region. The Denver Metro/North Front Range region has since attained these standards. More information on these previous air quality planning efforts are available at the links above.