The green lichen seemed to melt off the headstone as Sarah Insalaco sprayed it with water. She used a plastic scraper to scrub clean the gray granite.

“There they are,” Insalaco said as the carved names became visible. “This is Martha and Torsten Lee.”

The Lees were buried together near the end of the 19th century in Pioneers and Soldiers Memorial Cemetery, off Lake Street in south Minneapolis. Their headstone was just one of dozens being cleaned and reset this week by an AmeriCorps group working under the oversight of Northern Bedrock Historic Preservation Corps, a nonprofit headquartered in Duluth.

From May to October, the crew will don their bright blue hard hats, rain or shine, to work on a number of eight-day preservation projects across Minnesota. Part of the program’s goal is to teach participants, who range in age from 18 to 25, the trade skills needed to maintain and repair historic places and structures.

“The pool of tradespeople that does that work, it’s dwindling. They’re moving out of the workforce and retiring,” said Rhea Harvey, operations director at Northern Bedrock. “We’re trying to collect this knowledge and pass it on.”

At Pioneers and Soldiers cemetery, that means resetting, edging and cleaning headstones. Armed with a water pump, her scraper, a bristle brush and D2 — a commercial biological solution that removes stains from mold, lichen and other natural substances — Insalaco cleared away decades of dirt from the Lees’ monument.

“It’s really pretty easy if you know what to do,” she said.

A few yards away, crew leader Haven Epstein and AmeriCorps participants Addison Galagan, Daquan Johnson and Mahoo Ya repositioned the shiny black stone marking Ole Dahl’s final resting place. Galagan used a crowbar to prop up the granite while the others shoveled pea gravel beneath it to raise the half-sunken memorial. Before moving to the next gravestone, they checked to see that Dahl’s was level, plumb and in line with the rest of the row.

Sometimes the crew had to use a hoist chain to reposition heavy markers. “These stones can be hundreds of pounds,” Epstein said.

By midday Monday, their sixth day on the job, the team had worked on 78 tombstones at Pioneers and Soldiers. In all, about 21,000 people are buried at the cemetery, which sold its last plot in 1919.

“It’s a big place,” Harvey said. “The rich history of the cemetery really attracted us. It allows us to connect with the stories of each of these monuments.”

The cemetery was established in 1853, before the city of Minneapolis was incorporated, making it one of the oldest in the state. About half the graves belong to children, many of whom died after drinking tainted Mississippi River water. There are a few local notables, including early city street layout designer Charles Christmas and black abolitionist William Goodridge.

“Addison and I spent an entire afternoon cleaning the grave of Goodridge and his son, Toussaint, over there,” Insalaco said. “We don’t know what happened, but there was some black tar-like substance on them.”

The duty of maintaining gravestones is supposed to fall to one’s family members, Harvey said. Cemetery caretakers usually focus on upkeep of the grounds.

But she cautioned those wanting to spruce up great-great grandma’s burial site to make sure they’re using the proper materials.

“Some substances, like bleach, can be very harmful to the stones,” Harvey said. “The last thing you want to do is ruin or damage them.”