County Approves Local “Big Dig” Settlement

The Los Angeles County Board of Supervisors approved a settlement between L.A. County, the Arroyo Seco Foundation and the Audubon Society in the Devil’s Gate sediment removal project.

“This settlement agreement is the result of many years of hard work on the part of the Arroyo Seco Foundation, Pasadena Audubon Society and the community,” said Attorney Mitchell Tsing. “As part of this settlement, the county is committing to preserve as well as restore and establish additional riparian habitat and reduce the Project’s air quality emissions by incentivizing the use of electric and compressed natural gas trucks. I am hopeful that this settlement will preserve and protect one of Pasadena’s greatest biological and recreational resource.”

The county was seeking to remove Los Angeles County Public Works plans to remove up to 1.7 million cubic yards of sediment from the reservoir that’s immediately behind the nearly 100-year-old dam. The controversial project could last four years and has led to hundreds of truck trips in and out of the Arroyo Seco daily. Known as the Big Dig, the project has come under fire by residents of Pasadena and nearby La Cañada Flintridge.

The settlement reduces the scope of the project and pollution by trucks performing the removal.

“We were able to reduce the footprint of the project by 20 acres,” said Tim Brick, managing director of the Arroyo Seco Foundation. “We were able to improve the conditions of the habitat in 20 acres of where they had previous had set. They started with 70 acres and we were able to reduce it. So we were also able to get some substantial improvements in the habitat restoration program and to protect some of the key areas in Hahamongna.”

• As part of the settlement: The County will not clear, excavate or otherwise conduct project activities in a 14-acre area at the upstream northeast area originally designated for clearing and excavation as part of the project.

• Two border areas totaling 4.46 acres at the bottom of the basin and a 1.22-acre area near Flint Wash will be maintained episodically, rather than annually.

• The County will carry out the habitat restoration plan approved by the California Department of Fish and Wildlife in November 2018 and implement measures to address the inflow of trash from the West Altadena Storm Drain.

• During its annual maintenance activities after the initial 1.7 million CY of sediment are removed, the County will excavate no more than 220,000 cubic yards of sediment per year and will conduct no more than 300 round trips of sediment removal per day.

• During the annual maintenance period and unless otherwise required for safe dam operation, the County will reduce the release of water from the dam after the storm season so that, to the extent feasible, a pool of water remains behind the dam until July first of that year.

• The County will maintain rumble strips at the project site and continue to use the tire wash systems adjacent to the truck exit at Oak Grove Drive to ensure there is no track-out of mud or dirt on the local streets, and will remove these items at the conclusion of the initial sediment removal project so that area can be restored.

• Conduct checks of the hauling trucks diagnostics system to verify the emissions control equipment is working appropriately and conduct a Truck Emissions Measurement Program.

• Provide an incentive to encourage the contractor to use alternative-fuel dirt hauling trucks such as trucks equipped with compressed natural gas or electric engines.

• A portion of the native plants and seeds for the project’s ongoing 70 acres of habitat restoration will be obtained from the Hahamongna Watershed Park by the Hahamongna Native Plant Nursery, operated by the Arroyo Seco Foundation.

A large amount of sediment has not been removed from Devil’s Gate since 1994, when workers hauled out 160,000 cubic yards of soil and debris. An additional 1 million cubic yards of soil and debris were dumped into the basin by the Station fire in 2009, which burned more than 160,000 acres in Altadena, Pasadena, La Cañada Flintridge and Acton.

Devil’s Gate is the oldest dam constructed by the LA County Flood Control District, providing flood protection for the cities of Pasadena, South Pasadena and Los Angeles..

“One of our biggest goals was to make sure that this didn’t ever happen again,” Brick said. We knew they needed to do a sediment removal program, but we’ve regretted that they had taken so long to come to that conclusion. The last big removal, which was only a small fraction of what this one was, was in 1994. So they really haven’t moved anything for 26 years until they started a year ago. So we hope that we can prevent future, accumulations of sediment, with the program that will set a target and allow them to remove the sediment that comes in each year rather than having these massive kind of removal programs in the future.”