When Larimer County’s three commissioners voted in May 2025 to approve Platte River Power Authority’s application to build five natural gas turbines at its Rawhide Energy Station, the decision capped seven months of public hearings, technical filings, and negotiated conditions. Opponents had argued the project was unnecessary, financially risky, and inconsistent with the region’s climate commitments. Supporters said the grid couldn’t function without it. The commissioners voted 3-0 to approve, with 38 conditions attached.
The question of air quality was assumed to be managed by Colorado’s regulatory government, but details of measurement have been complicated by recent federal policy that undermines the assumption that the Rawhide coal plant will close. A different process under another agency with different rules is in process — and as of March 2026, any decision remains open.
Larimer County’s 1041 land use process addresses whether a facility is compatible with local land use standards — siting, design, mitigation, and consistency with county land use plans. The Colorado Department of Public Health and Environment’s Air Pollution Control Division is tasked with determining whether a facility will comply with federal and state air regulations. PRPA made this division explicit in its March 2025 supplemental filing to the county, stating that air quality compliance was CDPHE’s responsibility, not that of the Larimer County commissioners. The commissioners accepted that framing.
The work of CDPHE had begun well before the county hearing. PRPA’s air quality consultant, Ramboll, met with CDPHE’s modeling staff in April 2023. By August of that year, CDPHE had directed PRPA to proceed as a minor modification to its existing major source permit — a regulatory classification that carries significantly lower requirements than a major modification. The agency had calculated that the Rawhide coal plant would retire on a schedule previously guaranteed by PRPA in its efforts to decarbonize.
The agency that approved PRPA’s air quality modeling protocol confirmed this directly in an August 2023 email: “we do not anticipate reaching out to EPA in advance for this project as this is a minor source permit application.” CDPHE’s minor modification classification meant in practice: no requirement for the most stringent emission controls under federal non-attainment area rules, no mandatory emissions offsets, and a permitting process that doesn’t require participation of EPA Region 8 — the federal oversight office for Colorado’s air program.
Originally projected by PRPA to cost ratepayers $350M, the project price tag continues to increase. By late 2025, commenters in the CDPHE public meeting cited a current projected cost of $623 million — a 78% increase attributed to supply chain disruptions and federal tariffs. The rate increase to wholesale customers revised from 6.3% per year to 7.5% per year.
For ratepayers in the four owner communities, those percentages connect to a concrete comparison. The turbines are being built to replace the capacity of a coal plant that, once retired, will no longer produce the pollutants that have made Larimer County a perennial F-grade jurisdiction in the American Lung Association’s national air quality rankings. Rawhide Unit 1 is currently the single largest point source of air pollution on the Front Range. Its retirement by December 31, 2029, if it happens, is projected to reduce carbon dioxide equivalent emissions by approximately 1.3 million tons per year. Comparatively, the pollution arithmetic for new turbines – running on natural gas with selective catalytic reduction controls – very much favors the transition.
However, both sources could operate simultaneously. Neither the 1041 permit conditions nor the draft air construction permit contains specific mitigation requirements for the overlap period’s combined emissions. Comments from local activist group NCP4CE raised this gap explicitly during the 1041 proceeding; it was not addressed in PRPA’s formal responses.
The permit that has emerged from this process — draft construction permit 24LR0705, issued for public comment in November 2025 — drew a formal legal and technical challenge that runs to 155 pages.
The challenger is Ethan Augreen, a Longmont resident and PRPA ratepayer who submitted his comment on December 10, 2025, the last day of the public comment window. His comment identifies ten categories of what he calls fatal defects in the draft permit, each carrying the same bottom line: the permit as written does not meet the federal legal standard for enforceable emission limits, and CDPHE cannot lawfully issue it in its current form.
The arguments are specific. Federal law — established in a 1989 EPA rule and confirmed in decades of case law — requires that emission limits used to restrict a source’s potential to emit must be specific, technically accurate, and verifiable through reports and records. Limits that rely on unenforceable operating assumptions, or that leave interpretation to the operator, do not qualify. Augreen argues the draft permit fails this standard in multiple ways.
The permit’s primary operational constraint is a cap on combined turbine operating hours — 21,410 or 21,630 per rolling 12-month period, depending on which page of the permit you read. Augreen said this figure is the sole mechanism the permit uses to limit emissions, and that it fails as a limit because the permit provides no definition of what constitutes an operating hour. He cites a November 2025 Longmont Sustainability Advisory Board meeting at which PRPA staff, responding to a question about the cap, said that operating one turbine for one minute counts as one hour. That interpretation — if operative — would allow the five turbines to run at full capacity for nearly the entire year while consuming only a fraction of the combined hour allotment. The permit is silent on which interpretation governs.
A second argument concerns startup and shutdown emissions. The draft permit’s Preliminary Analysis acknowledges that emissions during startup and shutdown are conservatively assumed to be uncontrolled — meaning no credit is taken for the selective catalytic reduction system that controls NOx during normal operations. This produces higher emission estimates, which, while being conservative, also means the permit contains no specific enforceable limit for NOx in startup and shutdown. Then on January 27, 2025, EPA Region 8 finalized its approval of Colorado’s removal of startup/shutdown affirmative defense provisions. Before that date, sources could invoke those provisions to shield excess startup emissions from federal enforcement. After it, they cannot. The draft permit does not appear to have been updated to reflect this change.
An overarching criticism of the permit is that the classification for minor modification of air quality should not have been given.
PRPA’s permit relies on a calculation that the emissions increase from five new turbines is more than offset by the emissions decrease from retiring the 280-megawatt coal unit — Rawhide Unit 1 — by December 31, 2029. This is what allowed the project to avoid major modification requirements.
The enforceability mechanism CDPHE relied on — Colorado’s Regional Haze State Implementation Plan (SIP), — incorporated the closure date of Unit 1 coal plant — but that closure has been decertified by the EPA. This potentially invalidates the SIP.
CDPHE’s Preliminary Analysis was finalized November 7, 2025, and cited Colorado’s Regional Haze SIP as the regulatory basis for treating Unit 1’s retirement as an emissions decrease. EPA’s proposed disapproval of that SIP provision had been published July 16, 2025 — four months earlier. EPA’s final disapproval of Colorado’s plan to reduce haze became effective February 25, 2026. The Preliminary Analysis relied on a federal commitment that the EPA had already proposed to remove when the document was written, and that EPA had finally removed before the permit revision process completed.
PRPA’s response to this sequence is available in the record: Unit 1’s retirement date is also a condition in its Title V operating permit — permit 96OPLR142, Condition 1.15.2 — which is independently enforceable by CDPHE and by citizens under the Clean Air Act.
PRPA submitted supplements to its CDPHE application on March 10 and 11, 2026. Those supplements collapsed the permit from a two-scenario structure — one covering the period before Unit 1 retires, one covering the period after — into a single scenario based on post-retirement conditions. This revision eliminates the pre-retirement scenario that Augreen’s comment most directly challenged. No formal response to Augreen’s comment is on the record.
On review of both proceedings, as well as the 1041 record and the air permit record, a question about hydrogen remains.
PRPA’s 2024 Integrated Resource Plan states that the new turbines will use a 50% green hydrogen blend by 2035 and transition to 100% green hydrogen by 2040. This framing — hydrogen as the eventual decarbonization pathway — was central to PRPA’s presentation of the project as consistent with its climate commitments.
The language softened across documents. Board resolutions from August 2024 describe the turbines as having the “potential” to use green hydrogen. At the March 10, 2025 county hearing, PRPA’s General Manager said he doesn’t know if the turbines will ever run on hydrogen.
What happens to NOx emissions if the turbines do eventually use hydrogen? PRPA’s own consultant, Black & Veatch, documented the answer in April 2024: cofiring 35% hydrogen with natural gas reduces greenhouse gas emissions by roughly 15% while increasing nitrogen oxide emissions by approximately 20%. That finding appears in a document PRPA submitted to Larimer County. It does not appear in PRPA’s formal commitments to either the county or CDPHE. The draft construction permit’s emission limits are based on natural gas operation. If hydrogen-mode NOx is not addressed in the permit, one may consider that a transition to hydrogen will require a permit modification.
If all of the conditions required by Larimer County are met, the 1041 proceeding will result in a permit. The air quality proceeding has much further to go.
In April 2025 Larimer County commissioners voted on the question of land use. Now CDPHE must work through the question of the air quality around Rawhide Energy Station when these turbines are running — and under what conditions.
The people who testified at the April 21 hearing — opponents and supporters alike — are largely not the same people who filed comments in the CDPHE proceeding. The technical arguments being made at CDPHE require a fluency with federal air permitting law that the county’s public hearing process does not.
The Colorado Air Quality Control Commission’s procedural rules provide a formal pathway for any affected party to request a public comment hearing on the permit application, and to pursue adjudicatory review if permit conditions are disputed. Any party may exercise that option when CDPHE concludes its permitting process, which was incomplete when this report was written.
Construction of the turbines at Rawhide is planned to begin in the first quarter of 2026. The turbines are scheduled to be operational by the first quarter of 2028. Rawhide Unit 1 planned retirement was December 31, 2029. The sequence is set. The permit is not.
The report was updated on 3/26/26 to reflect these points: 1) the county’s 1041 permit is not guaranteed, but contingent on satisfying conditions of approval; 2) updates to the March 2026 draft allow for 180 days of emissions from turbines and coal, modified from 3 yrs.
Sources: PRPA Initial Permit Application (June 2024); CDPHE Modeling Review (Project MA_20250728, August–September 2025); CDPHE Draft Preliminary Analysis for Permit 24LR0705 (November 2025); Ethan Augreen Primary Comment on Draft Permit 24LR0705 (December 2025); PRPA Public Comments on Draft Permit (November–December 2025); PRPA Supplemental Response to 1041 Continuance (March 2025); Larimer County Findings and Resolution Approving 1041 Permit 24-ZONE3715 (May 2025); BOCC Land Use Hearing documents (March 10, March 24, April 21, 2025); Black & Veatch Characterizations of Supply Side Options (April 2024); PRPA 2024 Integrated Resource Plan; PRPA Title V Operating Permit 96OPLR142; CDPHE Modeling Protocol Email Chain (August 2023); EPA Regional Haze SIP Proposed Partial Disapproval (July 2025); EPA Regional Haze SIP Final Disapproval (January 2026); EPA SSM SIP Final Approval (December 2024); Colorado Air Quality Control Commission Procedural Rules (5 CCR 1001-1); Loveland City Council Study Session Minutes (September 2024).