Introduction
Colorado’s Air Quality Control Commission (AQCC) has issued proposed revisions to the state’s Ozone State Implementation Plan (SIP) for the Denver Metro/North Front Range (DM/NFR) nonattainment area, including northern Weld County. The public hearing on these SIP revisions will begin on November 19, 2025. These proposals, detailed in the NOTICE: Ozone SIP & Associated Regulations —Reg 7, Reg 3, and AQS documents —are aimed at satisfying Clean Air Act (CAA) requirements for areas in “Serious” nonattainment under the 2015 Ozone National Ambient Air Quality Standard (NAAQS).
Under the CAA, failure to meet attainment deadlines can lead to classification “bump-ups” to “Severe” or “Extreme” nonattainment, each carrying stricter control requirements, higher offset ratios, and more stringent permitting thresholds. The proposed SIP revisions are aimed at meeting the August 3, 2032 attainment deadline established by the recent redesignation of the DM/NFR area based on the ozone pollution data from 2029 through 2031. This deadline sets the schedule for demonstrating attainment under the 2015 ozone NAAQS. The revisions, which include expanded Reasonably Available Control Technology (RACT) requirements, additional Reasonable Further Progress (RFP) measures, and updated attainment modeling, outline Colorado’s plan to achieve that goal. Successful implementation would demonstrate to EPA that enforceable, region-wide emission reductions are in place- reductions that also complement the requirements in place under the area’s 2008 “Severe” nonattainment classification. The nonattainment area
Expansion of RACT to Transmission and Storage Segments (Reg 7)
One of the most impactful proposals is the expansion of SIP-level RACT requirements to include transmission and storage facilities in northern Weld County emitting 50 tons per year (tpy) or more of volatile organic compounds (VOC) as of July 24, 2024, with compliance required by January 14, 2026. The redlined Reg 7 document makes clear that this change is intended to close a regulatory gap in the “Serious” classification RACT program, as required under CAA §172(c)(1) and §182(c).
This change directly supports the state’s ability to demonstrate that all “major” sources of VOC, one of the primary ozone precursors, are subject to RACT controls. Without such coverage, EPA could potentially find the SIP deficient, triggering sanctions and a possible reclassification to “Severe”. Including onshore natural gas transmission pipelines, transmission and compression facilities, underground natural gas storage, and liquified natural gas (LNG) storage under RACT ensures emissions are reduced and accounted for in the attainment inventory, tightening modeled ozone precursor totals and improving the likelihood of meeting the “Serious” classification deadlines.
For operators, this means a possible reassessment of Potential to Emit (PTE) calculations, early engineering for LDAR programs, closed vent systems, VRUs, and careful attention to the July 2024 emissions threshold that determines applicability.
Ozone-Season Separator Venting Restrictions (Reg 7)
In addition to expanded RACT, the proposed prohibition on uncontrolled planned separator maintenance event venting during ozone season (May 1–September 30) is another key measure Colorado is looking to implement. Separator maintenance activities include inspections for leaks, damage, or liquid and pressure levels, replacement or repairs of parts or components, cleaning of debris, cleaning of filters, lubrications, and efficiency testing. Peak ozone concentrations in the DM/NFR area tend to occur during summer months, and short-duration, high-volume VOC releases from maintenance activities can directly influence the region’s three-year design value, the metric used by EPA to determine attainment.
The prohibition applies to planned maintenance events, requiring that VOC emissions be routed to an approved control device or avoided entirely by scheduling work outside the ozone season. This rule does not apply to unplanned emergency maintenance or situations where venting is necessary to address immediate safety concerns, provided those events are documented in accordance with the SIP’s reporting requirements. By focusing on planned activities, the state is targeting emissions that can be reasonably anticipated and mitigated without compromising operational safety.
Beginning June 30, 2027, operators will also be required to submit monthly reports documenting separator venting events, control methods used, and relevant operational data. This reporting is intended to strengthen the SIP’s ozone season emissions inventory and provide a verifiable basis for Colorado’s attainment demonstration under the “Serious” classification, as well as contingency measures required by CAA §172(c)(9).
For operators, compliance will require both operational and administrative adjustments: shifting planned maintenance to outside the ozone season where feasible, deploying portable VRUs, enclosed combustors, or flares for in-season work, and upgrading data systems to track and report events in SIP-compliant formats. Incorporating safety exception documentation into these systems will be critical to ensure that any emergency venting events are clearly distinguished from prohibited planned activities.
Tightening of Emission Reduction Credit (ERC) Provisions (Reg 3)
The Reg 3 revisions overhaul Emission Reduction Credit (ERC) provisions used for nonattainment new source review (NANSR) offsets, limiting credits to VOC and nitrogen oxides (NOX) reductions achieved within the ozone nonattainment area and requiring rigorous baseline determinations. All credits must meet surplus, permanent, quantifiable, and enforceable criteria consistent with 40 C.F.R. §51.165, and their use is restricted solely to meeting NANSR offset requirements. Notably, the revisions remove provisions that previously allowed credits to be generated from emission reductions outside the nonattainment area or from pollutants other than VOC and NOX. The updated rule also eliminates broader trading flexibility that once permitted credits to be applied in contexts beyond NANSR offsets, narrowing their applicability to ensure that only reductions with a direct and local ozone benefit are counted toward offset obligations.
This tightening of ERCs addresses a key EPA concern: offset integrity. Weak or geographically disconnected offsets undermine the SIP’s ability to show real reductions in the nonattainment area. By narrowing eligibility, Colorado strengthens the credibility of its permitting program, reducing the risk of SIP disapproval under CAA §110(k) and avoiding potential sanctions.
For oil and gas operators, the ERC market will become more competitive, with fewer qualifying credits available and higher acquisition costs likely. Projects triggering NANSR will require earlier offset planning. Strategically, companies should identify potential reduction projects now to generate bankable credits before supply tightens, both as a compliance measure and as a hedge against offset scarcity.
Removal of Pneumatic Controller Requirements from the SIP (Reg 7)
In Reg 7, the pneumatic controller requirements are removed from the federally enforceable SIP but retained as state-only rules. While the operational obligation to use low- or no-bleed controllers remains, the change removes EPA’s direct enforcement authority under the SIP.
CAA §110(l) prohibits SIP revisions that would “interfere with any applicable requirement concerning attainment,” meaning that if EPA views this as a relaxation without adequate replacement, the state could be required to adopt compensatory measures, potentially new controls on other oil and gas equipment categories. The SIP revision notice acknowledges this risk and implies that other proposed controls, such as expanded RACT, are intended to offset any perceived weakening.
Operators should continue to meet pneumatic controller standards as if they were federally enforceable, while closely monitoring EPA’s anti-backsliding analysis. If compensatory measures are proposed, they could result in additional operational requirements or new control obligations in other parts of operations.
Environmental Justice Changes
The updated Disproportionately Impacted (DI) mapping in Reg 3 and Reg 7 expands the reach of environmental justice (EJ)-based permitting reviews, potentially affecting oil and gas facilities that were previously outside of these zones. While EJ considerations already exist in Colorado’s permitting framework, the proposed updates modify the geographic boundaries and underlying mapping criteria in a way that increases the likelihood that a facility will fall within a DI area. This means that sources that have historically avoided EJ review due to their location could now be subject to it under the revised maps.
The expansion represents a significant shift in how location-based equity concerns are factored into air quality compliance. There is no grandfathering provision; any new or modified source within a DI area, regardless of its prior status, will need to go through the EJ review process. Operators should expect more rigorous public engagement, greater scrutiny of cumulative impacts, and the potential for additional permit conditions in these areas. As EPA and CDPHE continue to integrate EJ considerations into attainment planning, these expanded boundaries will play a larger role in determining which facilities face elevated compliance and stakeholder engagement requirements.
Strategic Takeaways for Operators
Every change in these SIP revisions ties back to the core goal of moving Colorado out of ozone nonattainment status by achieving attainment under the 2015 ozone NAAQS. The expansion of RACT coverage ensures that more oil and gas sources are contributing to emission reductions. The ozone-season venting restrictions directly address the short-term emissions peaks from vented maintenance activities. Even the removal of pneumatic controllers from the SIP is being managed in a way that seeks to maintain equivalent stringency under CAA §110(l).
For operators, the practical steps are clear:
- Audit facilities for RACT applicability now, especially in northern Weld County, to ensure compliance with new thresholds.
- Adjust maintenance schedules and prepare control options for separator venting.
- Validate ERC holdings and develop strategies for generating new credits under the tightened eligibility rules.
- Maintain compliance with pneumatic controller requirements and prepare for possible new compensatory controls.
- Map facilities against updated DI boundaries and plan for EJ-driven permit conditions, including enhanced community engagement and documentation.
The deadlines are aggressive, the control requirements are specific, and the regulatory stakes for both the State and the regulated community are high. Oil and gas operators who prepare early will not only meet compliance obligations, but they will also position themselves as active contributors to the state’s attainment strategy, reducing regulatory risk in an environment where every ton of VOC and NOx counts toward moving Colorado out of ozone nonattainment.
Questions and Support
Operators facing the evolving implications from the ozone SIP requirements can reach out to Trinity’s Denver office for expert guidance. From interpreting regulatory changes to supporting compliance strategies and long-term planning, Trinity can help ensure operators effectively manage risks and meet evolving air quality standards.
