The Hawaii Department of Health is investigating the cause of a dust storm that blanketed Central Maui last week, turning the air the color of red dirt and spurring a slew of complaints from residents.

Gusty winds of up to 45 miles per hour on Wednesday sent clouds of red dust swirling around Central Maui, drastically limiting visibility to the point where residents in Kihei couldn’t see the top of Haleakala. Upcountry residents, meanwhile, weren’t able to make out the shape of Mauna Kahalawai, the air was so thick with dirt.

In the days that followed, the health department received 20 complaints from residents, prompting the agency’s Clean Air Branch to investigate. State employees are now looking into the origins of the dust and whether more should have been done to prevent it from blowing through Maui’s central valley.

“It’s not like dust can’t happen at all,” said Lisa Young, an environmental health specialist for the state. “Dust happens. You’ve got to try to minimize it.”

Young said the health department is looking into Mahi Pono, which is one of the largest landowners in the area, and also working to figure out if there are other property owners who might have engaged in dusty activities last week.

Mahi Pono in 2018 purchased 41,000 acres of Alexander & Baldwin’s former sugarcane fields and is currently in the process of trying to farm sections of that land.

Late Monday, Mahi Pono issued a statement saying that it warned its crews of the windy weather forecast on the morning of Aug. 10. As the winds picked up as the day went on, the company told its roughly 300 field workers to shut down tractors and cease operations for the rest of the day. By early afternoon, everything was shut down, and crews used water trucks to weigh down the dirt.

“Dust mitigation protocols are essential to Mahi Pono’s operation, and we prioritize the ongoing refinement of these protocols as our operations continue to expand,” the statement read.

Across the U.S., governments ban and regulate what’s known as “fugitive dust,” which are particles lifted into the air from activities like tilling soil, driving over unpaved roads or heavy construction. The dust pollutes the air, waterways and oceans and has also been linked to a number of respiratory diseases, including aggravated asthma, chronic bronchitis and emphysema, according to the U.S. Environmental Protection Agency.

In Hawaii, it’s against the law for property owners to cause “visible fugitive dust” that blows beyond their property lines without taking “reasonable precautions.” Property owners who fail to comply with those rules can face fines of up to $25,000 per day.

But figuring out whether property owners were doing enough to prevent dust can make enforcement difficult, Young said.

Under state rules, “reasonable precautions” to prevent dust can range from watering down dry areas to installing windbreaks to planting cover crops so soil doesn’t blow away.

“The other issue that we don’t regulate is how much land gets opened up at a time,” said Young.

As of March 2022, Mahi Pono planted about 5,500 acres and prepared another 7,400 acres as pastureland, according to its website. Right now, there’s a large swath of land along Haleakala Highway that’s been prepared into rows of soil for planting.

But when it’s windy and dry, and especially when crews are working there, plumes of dust blow into the air and sometimes onto the highway. 

“It seems like the Mahi Pono guys don’t have a plan B if the wind threshold hits 25 or 30 or 40 (miles per hour),” said Gerry Ross, who runs an organic farm in Kula that overlooks the former sugar cane fields. “They just keep doing what they’re doing, so it generates amazing amounts of dust.”

In the past, when Maui’s central valley was covered in sugar cane, there would occasionally be dust problems when the plantation prepared and planted fields, when there weren’t crops growing to keep the dust down. But in recent years, Mahi Pono has tilled and opened up even larger sections of land, leaving soil exposed, Ross said.

Ross started reporting what he calls “catastrophic dust events” to the health department in 2019. He said they now happen almost once a month. Over the last couple years, he’s taken numerous photographs and videos of dirt drifting across the island, out into the ocean.

Maui’s central valley is a notoriously windy place. And as a farmer, Ross knows that growers are legally protected to work their land — something protected by the “Right to Farm,” which acknowledges that agricultural operations often create a certain level of dust and noise.

But leaving fields of tilled soil unplanted “for weeks on end” during the dry summer months makes it vulnerable to being to be blown away, he said.

There are lots of ways to stop that from happening, ranging from planting a dense barrier of trees of different heights to block the wind, using mulch or wood chips to weigh down the soil or planting fields instead of letting them sit empty.

Covering as little as 30% of an area with plants or mulch can cut the amount of dust that rises into the air in half — while at the same time hold the important nutrients found in the soil on farmland, Ross said.

“More dust moves in a morning or afternoon of poor planning than we would see in a year,” Ross said. “I have pictures of the streams of dust heading all the way out offshore from Maalaea to Kahoolawe.”

Civil Beat’s coverage of Maui County is supported in part by grants from the Nuestro Futuro Foundation and the Fred Baldwin Memorial Foundation.