The skeletons could provide anthropologists with more information about such things as the health of people in the 1800s, said Ryan Weller, an archaeologist who is excavating the remains.
"This is an era we know very little about,'' Weller said. "There are very few skeletal remains out of the ground to be examined.
"It's very rare to get an intact pelvis, but we have half of one right there,'' he said yesterday, pointing to a light area of bone beneath dark layers of gravel, brick and asphalt in a section of the wall of a trench.
Work on the sewer line was halted yesterday after Weller and his colleague Adam McCauley found a third grave site in two days.
"This part of the project will be shut down for a couple of weeks,'' said Mary Carran Webster, the city's assistant director of public service. She said the site will be fenced off and additional archaeologists brought in to excavate the rest of the sewer-project area, which is 110 feet long and 3 to 4 feet wide.
Based on the spacing of the three graves found so far, as many as 20 sets of remains could be on the site, she said.
The 11-acre North Cemetery dates from July 1813 and was in use until the growing city needed more room for development around 1870, Webster said. The graves were to have been moved at that time to Green Lawn Cemetery.
"The question is whether they just removed the headstones,'' she said.
In 1873, the Columbus City Council established a fund to remove graves from the site. The original market house, now the site of the North Market, was built in 1876.
Weller owns Applied Archaeological Services, a Grandview Heights company whose 10 employees often do archaeological screening at construction sites. The company was hired for the sewer project even before evidence of the cemetery was found.
Franco Ruffini of the Ohio Historic Preservation Office said an archaeological review is a standard requirement for sewer projects that include federal funds administered through the U.S. Environmental Protection Agency.
Crews knew they might find remains, Webster said. "They knew there had been a cemetery there.'' The remains will be carefully removed "and kept intact for historical value but also because that is the decent thing to do,'' she said.
Weller said the remains will be studied by a physical anthropologist and eventually reinterred.
Webster said the city doesn't know yet how much that will add to the cost of the project.
Mark Law, a supervisor in the city Construction Inspection Division, said sewer-project work is being done to separate what is now a combined sanitary and storm sewer.