The Suncor oil refinery upwind of Denver that recently belched pumpkin-colored gas and dust into the sky, worrying residents and prompting highway closures, released far more sulfur dioxide than previously known — 75,600 pounds, 150 times beyond a 24-hour limit that triggers an investigation, according to a company letter obtained Friday.

Suncor spokeswoman Lisha Burnett told reporters shortly after the Oct. 14 event that no sulfur dioxide had been detected near the refinery, but company officials later acknowledged the sulfur dioxide release had exceeded the daily limit of 500 pounds. The company and state officials say the release did not pose any health risks.

In a letter to Colorado and Adams County emergency management officials this week, the company said the release totaled 37.8 tons of excess sulfur dioxide from the Plant 1 main flare, the tail gas incinerator, Plant 2 main flare and Plant 3 main flare.

“There are no known or anticipated acute or chronic health risks associated with the release, and there is no need for persons to take any precautions or seek medical attention related to this release,” the company said in the letter.

The refinery has been under scrutiny by state regulators for years over air pollution problems and remains under investigation.

Colorado Department of Public Health and Environment officials say that because an Xcel Energy power outage triggered the refinery release, Suncor probably won’t be penalized.

But the CDPHE is moving toward possible penalties for multiple previously identified deficiencies, including excessive sulfur dioxide and other gas emissions. The CDPHE in June notified Suncor it could face penalties of up to $15,000 a day for violations.

In addition, state regulators in 2015 ordered Suncor to fix other pollution problems detected in 2013 and 2014. And Suncor negotiated a deal to avoid admitting law violations in return for paying a $214,050 administrative penalty. Company officials said they have paid $46,785 to CDPHE, $3,975 to the U.S.Environmental Protection Agency and $171,240 to Groundwork Denver to conduct projects to improve the environment. State regulators have opened five cases against Suncor since 2013 for possible air-quality violations, according to CDPHE records.

And, in 2012, state regulators hit Suncor with a $2.2 million penalty for air quality violations related to benzene air pollution from the refinery.

Suncor officials this month declined to discuss refinery problems and their plans. A corporate spokesman asked for written queries, and on Thursday e-mailed prepared responses to The Denver Post.

“The refining industry in general is one of the most regulated industries in the country. As Colorado’s only refinery, we understand the importance of our business to the Colorado economy and take that responsibility very seriously. This means running our facilities in a reliable manner that supports Colorado’s energy needs, meets our regulatory requirements, continuously improves environmental performance, and minimizes impacts to the community. As we supply the energy needs of Colorado, we are committed to doing so in an environmentally responsible manner and to make changes to ensure our continuous improvement goal is achieved. Our Commerce City refinery has made a number of investments since 2003 to improve our environmental performance and comply with regulations, and we will continue to work with regulators and stakeholders to improve further in the future.”

An environmental watchdog group on Thursday called for a shutdown of the refinery.

“The Suncor refinery is old and in many respects outdated, which makes it more vulnerable to events like power outages,” said WildEarth Guardians climate and energy program director Jeremy Nichols. “It needs to be completely rebuilt or shut down.

“What appears to be happening is a pay-to-pollute scheme where Suncor violates, pays a nominal fine, but continues business as usual,” Nichols said.

“It is clear this plant is aging and unable to operate in compliance on a continual basis, which is what the law and public health requires. If it can’t be fixed, it needs to be scrapped. … And we need to lean into a conversation about transitioning away from fossil fuels.”

The refinery sits just north of Denver in Commerce City at an 80-year-old industrial site.

“Suncor has generally been proactive in identifying issues and self-reporting any potential compliance issues that it identifies,” Colorado Air Pollution Control Division director Will Allison said in response to Denver Post queries.

“The division also anticipates it will enter into a compliance order with Suncor to address compliance issues identified in the division’s 2015 inspection. Finally, we’re still reviewing the reports Suncor recently submitted, but based on what we know so far, the October 14, 2016 events appear to be related to a power outage. We have no information to suggest these events were related to the age of the plant.”

Two weeks ago on Oct. 14, a refinery emissions stack spewed hydrocarbon-coated dust and gas — prompting road closures, a school lockdown and a warning to residents to remain indoors.

Suncor officials initially said no sulfur dioxide was detected in surrounding communities, perhaps implying none was released.

CDPHE air pollution control compliance and enforcement manager Shannon McMillan put it differently. “Suncor’s sulfur-dioxide release that resulted from the malfunction — caused by a power outage — exceeded the limit of 500 pounds in 24 hours,” McMillan said.

State health officials later issued a statement saying Suncor’s emissions didn’t cause “a public health concern.” Allison said air quality monitors in the Denver area did not detect sulfur dioxide levels beyond a limit of 75 parts per billion.

Sulfur dioxide can hurt people and the environment. Short-term exposure can impair breathing, especially for children and people with asthma. Higher concentrations in air can worsen particulate air pollution, which penetrates lungs causing problems. And sulfur dioxide damages leaves, stunting growth of plants and trees.

“Once the investigation is completed, any violations that occurred are identified and next steps are determined. If any exceedences were due to the power outage and Suncor is determined to not be at fault, no formal enforcement is likely to occur,” McMillan said. “Suncor has provided estimates of sulfur dioxide emission rates during the event, but hasn’t yet submitted an estimate of the total sulfur dioxide emissions for the duration of the event.”

Xcel spokesman Mark Stutz confirmed a power outage — lasting for seconds. This apparently triggered a refinery shutdown.

Canada-based Suncor in 2003 bought the refinery from Conoco Phillps in a $150 million deal. Suncor over the past 13 years has invested $1.6 billion in the plant.

Suncor officials said it would provide a key link between Suncor’s huge oil sands resources in Canada and a growing U.S. energy market. Suncor produces up to 98,000 barrels a day of gasoline and diesel fuel, as well as jet fuel for Denver International Airport, and asphalt. About 20 percent of oil processed at the refinery is heavy Canadian crude from the Athabasca oil sands.