The 25-HP Trick That Unlocked Years of Dirty Air

Federal clean air rules draw a hard line at 25 horsepower. Stationary engines rated at or below 25 HP that were manufactured before certain compliance dates face lighter regulatory scrutiny under EPA’s NSPS Subpart JJJJ standards. Berry Petroleum knew this. Their solution was elegant in its cynicism: buy the Arrow C-101 engine, which is mechanically identical to the more powerful Arrow C-106, except that the C-101 has a restricted inlet valve on the carburetor — a single component that suppresses the power rating to 24.5 HP on paper.

The Arrow C-106 maxes out at 32 HP. The C-101 maxes out at 24.5 HP — just barely under the threshold. According to the EPA consent agreement, the only difference between the two engines is that restricted valve. Berry bought C-101s by the hundreds, deployed them across oil and gas production sites in the Uinta Basin, and categorized them under the lower-scrutiny regulatory tier. The rating existed to clear a legal threshold, not because the engines needed it to operate.

Even within that lighter regulatory tier, Berry failed to comply. Owners and operators of these engines are still required to purchase certified engines, operate them according to the manufacturer’s maintenance schedule, and keep records proving they did so. Berry did none of these things consistently. By the EPA’s own finding, Berry ran the engines past their 1,000-hour or 5-year useful life limit and provided maintenance records so thin and incomplete that the engines legally became “non-certified” — meaning they were now subject to stricter rules Berry was also violating.

435 Engines. All of Them Suspect.

Appendix A of the consent agreement lists 435 individual engines subject to this agreement. They span well sites across Utah and EPA-jurisdiction territories, manufactured across more than 15 years, from as early as 2007 through 2024. Every single one is an Arrow C-101 rated at 24.5 HP, 376 cubic inches of displacement. The sheer volume makes clear this was a systemic operational choice, applied across the entire fleet, for the full duration of Berry’s ownership of these facilities — many of which Berry acquired from LINN Operating, Inc. in 2017.

The EPA’s inspections only stack-tested 26 engines across two rounds of inspections. Of the 13 engines whose results are detailed in the agreement, every single one exceeded the legal HC + NOx emission limit of 5.97 grams per horsepower-hour. The legal limit existed to protect public health. Berry’s engines treated it as optional.

What Money Can’t Measure: The Real Cost Borne by Real People

The Uinta Basin in northeastern Utah is not an abstraction on a map. It is a place where people live, where children play outside, where elders tend land their families have occupied for generations. It is also, according to the EPA’s own regulatory framework, a region where ground-level ozone already poses a documented threat to public health. Berry Petroleum chose to operate 435 smog-pumping engines in this place, year after year, without proper maintenance, without monitoring equipment, without even the basic logbooks the law required.

The Ute Indian Tribe Air Quality Department was a co-participant in the EPA’s 2021 inspections. That detail is not administrative background noise. It means these engines sat on or near tribal lands — lands with their own histories of industrial extraction and environmental sacrifice. The people whose air was being fouled included Indigenous communities who had no say in Berry’s compliance decisions, who had no access to the internal maintenance spreadsheets Berry finally produced after the inspections, and who had no way of knowing that the engines their neighbors could see and hear were operating at emission levels up to 17 times the federal legal limit.

Ground-level ozone — the pollutant these engines help create — is not a mild inconvenience. The EPA’s own regulatory language, embedded in this very consent agreement, states that short-term exposure causes “acute health effects observed even at low concentrations, including temporary pulmonary inflammation.” Long-term exposure “may cause permanent damage to lung tissue.” Children and active adults outdoors are specifically identified as the most vulnerable. The Uinta Basin is not an industrial park sealed off from human habitation. Families live there. Kids go to school there. People work outside there. Every day Berry’s non-compliant engines ran was another day those people breathed air with more ozone-forming chemicals in it than federal law allows.

Deception Built Into the Hardware

There is something particularly galling about the engine rating trick at the center of this case. The Arrow C-101 is not a different, cleaner engine than the Arrow C-106. It is the same engine with a restricted carburetor valve. The restriction exists to produce a number — 24.5 HP — that sits just below the federal regulatory threshold. Berry did not choose the C-101 because it was better for the environment. Berry chose it because the rating gave them a legal cover they did not operationally earn.

And they did not even honor the terms of that cover. Owning a C-101 still required certified operation, documented maintenance, and adherence to Arrow’s written instructions. Berry’s own response to regulators admitted the engines run “at varying schedules from continuous operations to 25% operation” — yet Berry maintained no hour meters and no continuous parameter monitoring systems. There was no way to know, from Berry’s own records, when any given engine was running, for how long, or in what condition. The regulators had to physically show up with a contractor and stick test probes in the exhaust stacks to find out.

The maintenance spreadsheet Berry produced after the 2021 inspections covered only 16 engines and did not demonstrate that required maintenance had actually been performed according to Arrow’s schedule. Meanwhile, the consent agreement notes that the inspected engines had exceeded the Arrow C-101’s stated useful life of 1,000 hours or 5 years. Some of these engines date back to 2007, 2008, and 2009. They were still running, still pumping pollution, still unmonitored, when the EPA showed up in the fall of 2021.

The Communities Left Holding the Bag

The EPA’s penalty framework is designed to remove the economic incentive to pollute. The logic is: if compliance costs less than noncompliance, companies comply. But Berry’s $373,500 penalty (enough to cover roughly 10 months of average American household expenses for a single family — a rounding error for a publicly traded corporation with operations across multiple states) was structured after EPA “compromised the civil penalty” — meaning it was voluntarily reduced. The agreement itself acknowledges the EPA considered Berry’s “economic impact” and “size of business” in setting the number.

What the agreement does not contain is any acknowledgment of the years those 435 engines ran before the EPA showed up. It does not calculate how much NOx and HC entered Uinta Basin air during that time. It does not name a single resident who breathed that air. The settlement resolves Berry’s “civil penalty liability” — a legal term that covers the company’s financial exposure. The respiratory damage absorbed by Uinta Basin residents over years of excess emissions is not resolved by anything in this document.

Straight From the Document: The Most Damning Passages

“The inspected engines have exceeded the useful life period for the Arrow C-101 engine, which is 1,000 hours or 5 years.”

— EPA Consent Agreement, Paragraph 58

“Respondents have not operated and maintained the engines according to Arrow Engine Company’s written instructions, so the engines are considered non-certified.”

— EPA Consent Agreement, Paragraph 59

“Respondents do not maintain records to support engine operating status, such as hour meters or continuous parameter monitoring systems.”

— EPA Consent Agreement, Paragraph 49

“The stack test results from the inspections conducted on September 8, 2021, September 27, 2021, July 19, 2022, and July 20, 2022, demonstrate that the 13 SI ICE identified in Table 1 below exceeded the HC + NOx emission standard of 8.0 g/kW-hr [5.97 g/hp-hr].”

— EPA Consent Agreement, Paragraph 77

“Respondents have operated and continue to operate Engines, including the SI ICE identified in Table 1, in violation of 40 C.F.R § 60.4233(a) and the emission standards as set forth in 40 C.F.R. § 1054.105(a) Table 1.”

— EPA Consent Agreement, Paragraph 78

“Respondents have not kept a maintenance plan and records of conducted maintenance for non-certified Engines… Nor have Respondents maintained and operated these Engines in a manner consistent with good air pollution control practices for minimizing emissions.”

— EPA Consent Agreement, Paragraph 79