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“Significant quantities” of children’s remains have been found in what was probably a septic tank at a former Catholic orphanage in Ireland, government investigators reported Friday.

The Irish government created a commission to investigate sites around the former Bon Secours Mother and Baby Home in Tuam, County Galway, after a local historian found death certificates for 796 children but a burial record for only one child.

Suspicions of unrecorded and unmarked burials at the site in the west of the country have lingered for decades. The institution run by nuns was one of many "mother and baby" homes across the country where unmarried pregnant women were sent to give birth in an attempt to preserve the country's devout Catholic image.

The entrance to the former Bons Secours home for unmarried mothers in 2104. Reuters, file

The Mother and Baby Homes Commission of Investigation reported that the remains were discovered in an underground structure that appears to have been “related to the treatment/containment of sewage.”

Excavations have been carried out at the site in recent months but people who lived near the home said they have know about the unmarked mass grave for decades.

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Two local boys reportedly unearthed the concrete-covered tank used by the home while playing in 1975 and found hundreds of children's bones inside. The tank has now been surrounded by a housing project.

"Up to now we had rumors. Now we have confirmation that the remains are there."

A DNA analysis of selected remains found they belonged to individuals with age-at-death ranges from approximately 35 fetal weeks to three years, the commission said.

It added that radiocarbon dating of the samples recovered suggest that the remains date from the time the Mother and Baby Home which operated between 1925 and 1961.

The commission did not say how many children's remains were recovered or how many might still be buried.

Ireland’s Minister for Children and Youth Affairs, Katherine Zappone, said that the find was “very sad and disturbing news.”

“It was not unexpected as there were claims about human remains on the site over the last number of years," she said in a statement posted on her ministry's website Friday.

“Up to now we had rumors. Now we have confirmation that the remains are there,” Zappone added.

The former Bons Secours home for unmarried mothers pictured in 2014. Reuters, file

The Mother and Baby Homes Commission of Investigation said it was “shocked by this discovery and is continuing its investigation into who was responsible for the disposal of human remains in this way.”

The commission is also investigating 17 other church-run institutions.

Catholic institutions ran many of Ireland's social services in the 20th century, including mother-and-baby homes where tens of thousands of unmarried pregnant women, including rape victims, were sent to give birth. The revelations have sparked a round of soul-searching in the country, and triggered calls for accountability from government and Catholic Church officials.