A 15-year effort to build a school in the city’s Dunning neighborhood is underway with an unusual complication: Construction workers are taking careful steps to avoid disturbing human remains that may lie beneath the soil.

The $70 million school is to be built on the grounds of a former Cook County Poor House where an estimated 38,000 people were buried in unmarked graves. Among the dead are residents who were too poor to afford funeral costs, unclaimed bodies and patients from the county’s insane asylum.