Indirect Sources Rules in Colorado: Denver Regional Authority Moves Forward to Regulate Four Key Sectors

Key Takeaways

• Denver’s Regional Air Quality Council (RAQC) is developing Indirect Source Rules (ISRs) to curb emissions from trucks and passenger vehicles by regulating facilities such as warehouses, entertainment venues, universities, and airports.
• Initial comments are due June 1, 2026, with further stakeholder workshops in July and August.
• RAQC plans to present more detailed recommendations for updates to its Control Strategy Blueprint in Fall 2026 and to present a proposal to the Colorado Air Quality Control Commission in November 2026.
• Other jurisdictions are also moving forward with similar rules; California’s South Coast Air Quality Management District, New York, and Illinois have recently taken key steps.

RAQC, which oversees air quality planning for the Denver Metro/North Front Range Ozone Non-Attainment Area, is moving forward with developing ISRs targeting warehouses, entertainment venues, universities, and airports, which will regulate the mobile sources “attracted” to these facilities, in particular trucks and passenger vehicles. On May 18, 2026, RAQC convened a meeting of its Indirect Sources Technical Working Group (ISTWG), where - following the Control Strategy Blueprint endorsed by the RAQC Board last November - it laid out a three-step process for developing and implementing ISRs, starting with data reporting, moving to voluntary plans, and then ultimately requiring mandatory facility emissions reduction plans.

Following the meeting, RAQC has requested feedback on its Considerations for an Indirect Source Data Reporting program presentation by June 1, 2026. Stakeholders can provide feedback using this Google Form. Potentially affected stakeholders, including fleet owners and operators, should provide input on the data reporting program, as it will serve as the foundation for RAQC’s voluntary and mandatory programs.

In addition, RAQC’s work could establish important ISR precedents, including first-of-their-kind ISRs for airports, entertainment venues, and universities, while building on the Warehouse ISR (Rule 2305) already adopted by California’s South Coast Air Quality Management District (SCAQMD). The regulatory initiative in Colorado thus provides an important opportunity for stakeholders to shape regulations that other states and cities may look to as they consider promulgating similar ISRs in their jurisdictions. 

Background on ISRs and the Colorado Program

As highlighted in our previous Client Alert, ISRs regulate facilities (such as warehouses, airports, ports, and railyards) to control emissions from mobile sources that are “attracted” to these facilities (including trucks, planes, ships, and locomotives). ISRs are recognized under Section 110(a)(5) of the Clean Air Act, which allows states to include them in State Implementation Plans (SIPs) for attaining the National Ambient Air Quality Standards (NAAQS).  State and local governments can also perceive ISRs as a potentially effective means of circumventing federal laws that preempt them from regulating mobile sources by establishing strict requirements for facilities that those vehicles serve. 

Since early 2025, RAQC has been developing its Control Strategy Blueprint, a strategic plan that considers options to improve air quality in the Denver Metro Region and attain the NAAQS for ozone. In addition to ISRs, the Blueprint sets out strategies for addressing other sources, including oil and gas production, stationary sources, non-road engines, and non-point sources (e.g., consumer products). 

Regarding ISRs, RAQC is initially focusing on data reporting. This is a critical stage, as the type and scope of data collected will likely determine the scope of sources affected and the requirements imposed under the voluntary and mandatory programs to be developed. The data collected will vary by facility.

Data collected through the reporting program will help establish a baseline of on-road emissions and provide a better understanding of the portion of the emissions inventory attributableto indirect sources, thereby shaping RAQC’s voluntary and mandatory emissions-reduction programs.

Next Steps

Most immediately, RAQC is seeking stakeholder input on its Considerations for an Indirect Source Data Reporting presentation by June 1, 2026.  RAQC will also host stakeholder workshops that will incorporate discussions of indirect sources and mobile source strategies. As of now, these workshops are scheduled for July 15, July 28, and an additional date in August (to be determined).

Whether online or through these workshops, RAQC is looking for feedback on its suggested data collection: whether certain data are more difficult to collect or report, whether other data could be substituted, whether any data is already being collected or could be replaced by facilities’ sustainability plans, and the anticipated effort and time necessary to collect the requested data.

Ultimately, RAQC plans to present more detailed recommendations to the Board for approval. RAQC intends to present the Board-approved updates to the Control Strategy Blueprint to the Colorado Air Quality Control Commission in November 2026.

Stakeholders should engage with RAQC now to provide feedback that inform and ultimately shape the Region’s voluntary and mandatory facility emissions reduction plans.

Other ISR Developments

Other jurisdictions are also actively considering implementation of ISR programs (see previous B&D Client Alert). As part of the ongoing implementation of its Warehouse ISR, the South Coast Air Quality Management District (SCAQMD) is developing a WAIRE mitigation program that will provide incentive funding for emission-reduction projects at warehouses and in surrounding communities.  The SCAQMD Board also approved a Cooperative Agreement with the Ports of Long Beach and Los Angeles instead of adopting a Port ISR (proposed Rule 2304), which requires the Ports to develop zero-emission infrastructure for sources (cargo handling equipment, harbor craft, trucks, trains, and ocean-going vessels) that serve the facilities.  The San Diego County Air Pollution Control District, however, recently declined to adopt a proposed Warehouse ISR.

In January 2026, New York City proposed Int 0053-2026, a local law to amend the administrative code of the city of New York and enable the Department of Environmental Protection to promulgate an ISR for facilities, including warehouses. The state of New York has also proposed S.1180B, a bill for warehouse ISRs. The bill has passed the Senate and is currently with the Assembly Committee.

Illinois has also proposed SB3732, the Warehouse Pollution Reduction Act, which would require the Pollution Control Board to adopt rules establishing a warehouse review program.

B&D's ESG and Climate Change practice groups help clients navigate complex and interrelated legal and reputational issues in the fast-moving area of sustainability. Our experience and capabilities extend to: required or voluntary disclosures, interactions with sustainability rating agencies, supply chain and product stewardship, interactions with suppliers and customers, responsible sourcing, climate change law and policy, GHG emissions credit trading, facility issues, and more. Coupled with B&D’s robust Clean Air Act regulatory, enforcement, and litigation practice, we offer companies significant and well-rounded capability to understand and incorporate emerging GHG legal and regulatory requirements across their enterprises.