How loud is too loud at Denver International Airport?

For years, the airport has paid millions of dollars in fines to nearby cities for noise violations. It's money from the airport budget that comes from landing fees, concessions and other operations.

But 7NEWS Investigator John Ferrugia said that some of the noise standards are so low, it's virtually impossible to meet them.

The standards were set in 1989, long before the airport was built, and were based on noise projections by the Federal Aviation Administration.

But in some high-flight paths, the noise threshold was set lower than at any other airport in the world, and DIA is paying millions because it simply can't reduce noise any further.

It may be hard to believe, but in the specialized world of evaluating noise, the chirp of a prairie dog is louder than noise allowed from an airplane.

That's because in the area near Buckley air base, the annual average noise level from an airplane cannot exceed 34.5 decibels, and that is next to impossible.

"We're seeing the 40, 45 decibel levels here in a pretty much open field without anything very close," said Mike McKee with DIA's noise abatement.

That background noise not only includes prairie dogs, but the sound of a single truck passing by, which is far above the average allowable noise level of an aircraft.

"The fact is that the prairie dogs we heard also would have violated the average over the year, " 7NEWS Investigator John Ferrugia asked McKee.

"If there were a prairie dog agreement, you're right, they would have," said McKee.

To get the airport open, DIA negotiated noise agreement in 1989 which set limits for areas around the airport that are on airline flight paths. There are more than 100 points where various noise limits are set. When the annual average noise level exceeds the level set by the agreement, DIA pays $500,000 per violation.

It has paid for noise violations in the Buckley area for every year the airport has been open.

"It's definitely far below what any other airport tends to try to monitor ... in the country and possibly in the world," McKee said.

But according to the agreement, Adams County and other signatories would have to agree to change it. And that isn't going to happen.

"I think that it would remove any motivation to minimize noise impacts over our citizens. It would mean a lessening of people's quality of lives in Adams county and our cities," said Robert Coney, the Adams County director of planning and development.

He said if the agreement with DIA is reopened, it can now be voided because agreements are no longer allowed by the FAA, and that would be disastrous for Adams County.

"It establishes that balance between airspace efficiency and the reduction of noise exposure to our citizens," Coney said. "Without the agreement there is no reason to operate the airport in a way that minimizes noise exposure."

So the noise meters scattered all over the metro area will continue to monitor specific noise levels at given locations, like the one near Northglenn, where anything above 38.5 decibels is a violation.

"Has there ever been a year when you've been able to keep it under 38.5 decibels in this area?" Ferrugia asked.

"Not generally. It has shifted from one point to another at times, but they were all in the same general area. So we've had violations in this area every year at one point or another," McKee said.

"So it's cost $500,000?" Ferrugia asked.

"At least," McKee said.

Even though he agrees noise thresholds in some areas may be exceptionally low, Coney said that's not Adams County's problem.

"It does point out that when local governments enter into these types of agreements, they need to consider the long-term ramifications. This was not a temporary agreement," Coney said.

"So essentially, they got into it, it's their problem?" Ferrugia asked.

"It's a contract that we will continue to enforce," Coney said.

DIA has met or exceeded the noise requirements in 98 percent of the metro area. But it has been paying at least $1 million a year for the two trouble spots -- near the Buckley area and near Northglenn. But how has this growing sum of tens of millions of dollars been spent?

It is, in part, supposed to help residents soundproof their homes. But wait until you see what 7NEWS Investigator Tony Kovaleski found as we continue to follow the money. Whatch that part of the story on 7NEWS Friday night at 10.

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