AMERICAN FORK — For newcomers who have smelled the air near exit 275 on I-15, don't worry, it's not the people in your carpool.

It's the natural result of 160,000 people flushing their toilets.

All of that waste flows to the Timpanogos Special Services District located just off the freeway, and plant engineers are looking for ways to cut back on the odor while a multimillion-dollar expansion project gets off the ground.

"There's been a couple of times when we have heard complaints, but we're doing everything we can," said district manager Garland Mayne. "This is a regional facility, there's going to be odors periodically. So until we get a new system online and the engineer changes the solids handling process, there's going to be some odor issues."

Odor is is a frequent topic at district board meetings, where members recently decided to incur a $55 million debt to overhaul the plant and significantly diminish the pervasive smell. The overhaul will expand the plant's capacity by 10 million gallons per day and eliminate the need to dry processed sludge in the open air.

The drying process, as well as a composting system, are thought to be the two major sources of stink at the plant.

According to plant engineer Larry Bowen, the new system should be on-line and practically smell-free in about three years.

In the mean time, Mayne has adjusted some of the plant's operations to be sensitive to nearby businesses.

"We're trying to do more of the aeration (of the sludge) during off hours," Mayne said. "We're looking at local businesses around here and trying to go by whatever their schedule is."

Mayne said the plant processes sludge early in the morning and later in the afternoon.

That helps Sophia Jackson, an employee of a newly-opened BMW dealership located near the plant, but she still occasionally gets an unpleasant whiff. She said she avoids talking about the odor when customers come into the showroom.

"I figure if we just don't talk about it, no one will notice," Jackson said.

Luckily for the dealership, Jackson says the smell doesn't usually come inside their building, and as long as it's not sunny— or windy— the odor isn't so overwhelming.

"It's still been kind of bad, but not as bad as I think it could be when it heats up," Jackson said. "In the early morning it's not bad, but when the sun comes up it smells pretty awful."

Bowen said the board may choose to implement other mitigating measures to help ease odors before three years has passed. One option is to add a belt press to the plant that would squeeze excess water from the sludge, instead of evaporating the liquid in the sun.