At a rate of one per minute, double-bottomed dump trucks loaded with 25 years’ worth of sediment washed down from the San Gabriel Mountains powered out of the sinking mud behind Devil’s Gate Dam in Pasadena on Tuesday, marking the start of an off-and-on, four-year mechanized march.

After almost a decade of planning, 100-plus community meetings, thousands of pages of environmental documents and two lawsuits, the first of tons of debris north of the NASA/Jet Propulsion Laboratory — behind the county’s oldest dam — finally were trucked away.

The sediment that formed a makeshift nature preserve in the south end of Pasadena’s Hahamongna Watershed Park, a favorite of bird watchers and school groups, was on its way to a landfill in Irwindale.

Nico Galindo directs traffic as a truck filled with dirt leaves Devil’s Gate Dam reservoir as Los Angeles County Public Works begins removing 1.7 mil cubic yards of sediment from behind the Pasadena dam on Tuesday, May 21, 2019. The trucks will go from 7 a.m. to 3:30 p.m. on Monday through Friday for four years to remove the sediment, a majority from the Station fire. (Photo by Sarah Reingewirtz, Pasadena Star-News/SCNG)

A truck filled with dirt leaves Devil’s Gate Dam reservoir as Los Angeles County Public Works begins removing 1.7 mil cubic yards of sediment from behind the Pasadena dam on Tuesday, May 21, 2019. The trucks will go from 7 a.m. to 3:30 p.m. on Monday through Friday for four years to remove the sediment, a majority from the Station fire. (Photo by Sarah Reingewirtz, Pasadena Star-News/SCNG)

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A truck filled with dirt leaves Devil’s Gate Dam reservoir as Los Angeles County Public Works begins removing 1.7 mil cubic yards of sediment from behind the Pasadena dam on Tuesday, May 21, 2019. The trucks will go from 7 a.m. to 3:30 p.m. on Monday through Friday for four years to remove the sediment, a majority from the Station fire. (Photo by Sarah Reingewirtz, Pasadena Star-News/SCNG)

Trucks are filled with dirt in Devil’s Gate Dam reservoir as Los Angeles County Public Works begins removing 1.7 mil cubic yards of sediment from behind the Pasadena dam on Tuesday, May 21, 2019. The trucks will go from 7 a.m. to 3:30 p.m. on Monday through Friday for four years to remove the sediment, a majority from the Station fire. (Photo by Sarah Reingewirtz, Pasadena Star-News/SCNG)

Los Angeles County Public Works employees are on hand as the removal of dirt from Devil’s Gate Dam begins on Tuesday, May 21, 2019. They began removing 1.7 mil cubic yards of sediment from the reservoir. Trucks will go from 7 a.m. to 3:30 p.m. on Monday through Friday for four years to remove the sediment, a majority from the Station fire. (Photo by Sarah Reingewirtz, Pasadena Star-News/SCNG)



With JPL in the background, trucks are filled with dirt in Devil’s Gate Dam reservoir as Los Angeles County Public Works begins removing 1.7 mil cubic yards of sediment from behind the Pasadena dam on Tuesday, May 21, 2019. The trucks will go from 7 a.m. to 3:30 p.m. on Monday through Friday for four years to remove the sediment, a majority from the Station fire. (Photo by Sarah Reingewirtz, Pasadena Star-News/SCNG)

Sabott Ali, of Altadena, and Jabari Akil, of Westminster, discover a hiking trail closed as they walk up The Arroyo Seco in Pasadena from Brookside as the removal of dirt from behind Devil’s Gate Dam begins on Tuesday, May 21, 2019. Los Angeles County Public Works began removing 1.7 mil cubic yards of sediment from behind the Pasadena dam. The trucks will go from 7 a.m. to 3:30 p.m. on Monday through Friday for four years to remove the sediment, a majority from the Station fire. (Photo by Sarah Reingewirtz, Pasadena Star-News/SCNG)

Trucks are filled with dirt in Devil’s Gate Dam reservoir as Los Angeles County Public Works begins removing 1.7 mil cubic yards of sediment from behind the Pasadena dam on Tuesday, May 21, 2019. The trucks will go from 7 a.m. to 3:30 p.m. on Monday through Friday for four years to remove the sediment, a majority from the Station fire. (Photo by Sarah Reingewirtz, Pasadena Star-News/SCNG)

Trucks are filled with dirt in Devil’s Gate Dam reservoir as Los Angeles County Public Works begins removing 1.7 mil cubic yards of sediment from behind the Pasadena dam on Tuesday, May 21, 2019. The trucks will go from 7 a.m. to 3:30 p.m. on Monday through Friday for four years to remove the sediment, a majority from the Station fire. (Photo by Sarah Reingewirtz, Pasadena Star-News/SCNG)

A truck filled with dirt leaves Devil’s Gate Dam reservoir as Los Angeles County Public Works begins removing 1.7 mil cubic yards of sediment from behind the Pasadena dam on Tuesday, May 21, 2019. The trucks will go from 7 a.m. to 3:30 p.m. on Monday through Friday for four years to remove the sediment, a majority from the Station fire. (Photo by Sarah Reingewirtz, Pasadena Star-News/SCNG)



The idea is simple, the task gargantuan: Remove 1.7 million cubic yards of sediment to return the circa 1920 dam to full functionality, protecting Pasadena, South Pasadena, Highland Park and other northeast Los Angeles communities downstream — including the Rose Bowl, Brookside Park and the Arroyo Seco Parkway — from the potential flooding of a 100-year storm.

Because no major dredging has been done since 1994, the accumulation has grown, making the project more daunting and the dam more suspect. The 2009 Station Fire burned 160,000 acres of the watershed, much of which washed up against the dam during the 2010 winter storms, forming the bulk of the sediment, county engineers said.

Removal will take four years of trucks making 425 round trips a day. The amount of dirt and debris would fill the Rose Bowl four times.

Hauling will continue from 7 a.m. to 3:30 p.m. weekdays until mid-November, then cease until April to allow winter rains to pass. Then the parade of trucks will begin anew. The break also keeps bulldozers away from birds during nesting season, even though several were spotted on Tuesday while trucks roared past them.

A team of engineers from the Los Angeles County Department of Public Works, accompanied by biologists and air quality specialists monitoring emissions from nearly 100 diesel-powered dump trucks, combed the massive construction site on the first hauling day of the $66 million dredging project.

Steve Burger, engineer and assistant deputy director of the Department of Public Works, surveyed the work from a perch on Oak Grove Drive.

“So far, this has been a very successful first day,” Burger proclaimed.

The county installed six air quality monitoring stations run by the South Coast Air Quality Management District after parents from nearby La Cañada High School complained the truck emissions would make their children sick. Burger said the SCAQMD onsite advisers told him so far, the monitors did not show signs of airborne PM-10, fine particulates emitted from diesel vehicles which can lodge in the lungs, causing asthma and other respiratory diseases.

“They told us they are satisfied with our operation so far, that everything looked appropriate,” he said.

The county insisted that trucks meet 2010 EPA standards for diesel emissions. Opacity tests from tailpipes showed diesel soot at 0.6%, far below the maximum acceptable level of 5%, said Edel Vizcarra, a department spokesman.

Only the newest trucks were accepted onto the site, Burger said. “They are an order of magnitude cleaner than those on the freeways,” he said. If onsite monitors show above acceptable levels, the hauling could be slowed, roads watered more thoroughly to prevent airborne dust, or hauling temporarily shut down, he said.

But Tim Brick, managing director of the Arroyo Seco Foundation, wrote in an emailed response the county’s efforts at preventing air pollution fall short.

“Los Angeles County has the worst air pollution in the nation. The county government should be leading the way to the future by using trucks that are truly clean air trucks, such as those with electric and natural gas engines that are now available,” Brick wrote.

The county cleared a 50-acre swath behind the dam of trees and all vegetation in late November. That area remains as a permanent maintenance zone that will be scraped every year, county officials said. However, the county is planting native trees and plants to help restore 70 acres around the dam.

Brick wants to see the project reduced to 1.1 million cubic yards, a level the city of Pasadena’s Sediment Working Group requested. “Scraping the Hahamongna basin will have a very detrimental impact on habitat, wildlife and recreational opportunities for local residents,” he wrote.

Staff biologist Lauren Simpson of Ecorp Consulting Inc. in La Verne said her team found great-horned owls nesting in the site and they set up a buffer zone to protect the birds and their young. Also, a yellow warbler, designated as a species of special concern by the state Department of Fish and Wildlife, was spotted. No trucks or workers can enter the buffer zones, she said.

Neither sightings have stopped the project, she said.

Not all birds will get a buffer zone. The county has a permit to destroy the endangered least Bell’s vireo, a rare songbird listed on both federal and state endangered species lists, spotted in the reservoir area and in the park on several occasions from 2012 to 2015. “We have not seen it yet, but we have definitely been monitoring it,” Simpson said.