OSO — Workers on Monday began to construct a temporary wall of rock and dirt across the Oso mudslide debris field.

The berm will connect two areas of high ground and allow crews to drain floodwater from areas that have not yet been searched for bodies.

A 400-foot section of berm was built Monday out of an estimated 1,800 feet that’s needed, said Mike Peele with the U.S. Army Corps of Engineers. Construction could take a week.

Searchers and their dogs have gone over the area in boats, on the east side of the slide near C-Post Road. They have reasons to focus recovery efforts there, slide spokeswoman Meg Matthews said Monday.

Geologists continue to monitor the ground. No unexpected movement has been detected in recent days.

The death toll from the March 22 slide reached 33 on Monday, with 30 of the victims identified. Twelve people remain missing.

Funerals are expected to continue for weeks.

Highway 530 between Darrington and Arlington remains closed indefinitely. The earliest estimate for re-opening so far is still measured in weeks.

Nearly 900 searchers remain on scene, looking for people and recovering property lost when the mudslide devoured homes.

The berm is expected to help crews access the area east of C-Post Road, on the Darrington side of the slide.

Water has been a problem on the site from the beginning, including flooding from the North Fork Stillaguamish River, and rainfall that has turned stable ground into a slurry. A half-inch of rain is expected Tuesday, with drier days to follow.

Crews are making progress on clearing Highway 530, Deputy Snohomish County Executive Mark Ericks told the County Council on Monday.

About 3,000 feet of the highway has been cleared of debris — nearly half of the area that was covered, he said.

“It’s uncertain what the roadway will be like once we do get it all cleared, whether it’ll be passable or will need to be rebuilt; most people believe that it will have to be rebuilt in one form or fashion,” he said.

The Army Corps of Engineers is assisting county crews with the temporary berm.

A piece of equipment that resembles a track hoe on pontoons was helping to dig out the river channel and prevent the river from eroding the bottom of the hillside, Ericks said.

The rock berm will be about 10 feet tall. Up to 10 feet of water remains on the ground nearby, covering an area the size of more than 30 football fields, crews said.

Each area of the debris field must be searched four separate times, according to FEMA.

Meanwhile, solar-powered machines called “spiders” are positioned in the slide area. The machines carry GPS units and deliver real-time information for vibrations and ground movements as small as a centimeter, said Rick LaHusen with the U.S. Geological Survey.

The spiders were developed originally for studying volcanos, he said.

Scientists also are using lasers and other tools to scan the ground. They are taking daily and hourly measurements.

Snohomish County on Monday had documented nearly $4.3 million in expenses during the first two weeks of the slide response, Ericks said.

The county expects to receive reimbursement for 75 percent of eligible costs from the federal government. Washington state is likely to cover half of the remaining 25 percent. There’s some doubt, however, that all disaster-related costs will qualify.

As of Monday evening, 229 people had signed up for housing assistance in connection with the slide, according to FEMA.

“I will tell you right now that not all costs are reimbursable,” Ericks said. “Sometimes, during the emergency phase of an operation, you do what you have to do to save lives without regard to cost or source of revenues.”

Rikki King: 425-339-3449; rking@heraldnet.com.

Tax deadline extended

Families and businesses who were impacted by the March 22 mudslide near Oso have until Oct. 15 to complete their taxes and tax paperwork, according to an Internal Revenue Service announcement on Monday. That includes tribal members.

People who worked in the slide response but don’t live in the disaster area can get help at 866-562-5227.

More info: disasterassistance.gov.