DARRINGTON, Wash. — The rains that have bedeviled crews searching for victims in the debris field from the deadly Washington state mudslide are expected to ease this week, but searchers faced other challenges at the site like household chemicals and sewage.

The number of confirmed dead has increased from 18 to 21, Jason Biermann, program manager at the Snohomish County Department of Emergency Management, said Sunday evening.

Fifteen of the victims have been identified by the Snohomish County medical examiner, and six have yet to be identified, Biermann said. Another four bodies were found Sunday, but they won’t be added to the official count until the medical examiner receives them. Biermann said 30 people remain missing.

The March 22 landslide, one of the deadliest in U.S. history, struck a rural community about 55 miles northeast of Seattle.

Crews have completed a makeshift road that will link one side of the debris field to the other, significantly aiding the recovery operation. They have also been working to clear mud and debris from the highway, leaving piles of gooey muck, splintered wood and housing insulation on the sides of the road.

Searchers have had to contend with treacherous conditions, including septic tanks, gasoline and propane containers. When rescuers and dogs leave the site, they are hosed off by hazardous materials crews.