In the search for unmarked graves at residential school sites, what do radar 'anomalies' mean?

CTV National News: Residential school discovery Around 2,000 anomalies were found during a radar search of a former Sask. residential school site, officials says. Jill Macyshon reports.

More than 2,000 "anomalies" were found using ground-penetrating radar at the site of a former residential school in Saskatchewan, but do these all represent unmarked graves?

The search by Star Blanket Cree Nation is part of a nationwide effort to find unmarked graves on grounds of former residential schools, where at least 4,100 Indigenous children died between the late 1800s and 1990s, when the last school closed. Approximately 150,000 First Nations, Métis and Inuit children were separated from their families and placed in the boarding schools, which sought to replace Indigenous language and culture with English and Christian beliefs. To date, at least 1,800 confirmed or suspected unmarked graves have been identified.

With the aid of historical records and testimonies from residential school survivors, much of the search for potential graves has been conducted with ground-penetrating radar; a technology that has long been used by geologists, archeologists, militaries and more.

WHAT IS GROUND-PENETRATING RADAR?

Ground-penetrating radar (GPR) technology creates images of what lies underground by sending out radio waves and then measuring how they are reflected back, providing insights into different densities, as well as potentially hidden objects.

Like conventional radar, GPR does not provide clear photo-like pictures, but images that are more like rough outlines. GPR devices usually look a lot like high-tech lawnmowers, and have been used for a variety of purposes, like detecting groundwater, utility lines, archeological features and buried explosives in warzones.

"In the case of looking for unmarked graves and burial locations, what this piece of equipment is able to show are areas that have been disturbed," Kisha Supernant, director of the Institute of Prairie and Indigenous Archaeology at the University of Alberta, previously told The Canadian Press. "When you dig a grave, the soil changes – the composition changes, the density can change – and the ground-penetrating radar can actually pick up that change."

WHAT ARE GPR 'ANOMALIES'?

When searching for potential unmarked graves, investigators using GPR are essentially looking for subterranean anomalies, or areas that look different from their surroundings.

"When looking for unmarked graves we may be looking for breaks in soil structure (i.e., something missing) that are similar in size to a dug grave," Carl-Georg Bank, an associate professor at the University of Toronto's Department of Earth Sciences, told CTVNews.ca in an email. "Grave anomalies will look different depending on soil conditions, geology of the site, environment, and climate."

Such anomalies, however, are not necessarily indicators of human burial.

"GPR can’t definitively say that’s something," Sheldon Poitras, the ground search project lead for Star Blanket Cree Nation, explained last week. "It could be a stone under the ground, it could be a clump of clay, it could be a piece of wood or it could be something. We don’t know yet."

HOW ANOMALIES ARE INVESTIGATED

At Star Blanket Cree Nation, local knowledge keepers and elders have advised investigators to avoid disturbing human remains. They are now considering following up on the GPR anomalies with miniature core drilling. Soil samples taken from areas of interest could then be tested for the presence of human DNA.

"In order for us to confirm what it is under the ground, this is the best option that we came up with so that we don't disturb what might be there," Poitras said. "But at least we can determine whether it's nothing or something."

The discovery of a jaw bone fragment at the site, thought to be a young child's and over a century old, has bolstered the investigation

"This is physical proof of an unmarked grave," Poitras said.

Archeologist Whitney Spearing has been leading the investigation into potential unmarked graves at Williams Lake First Nation in B.C.'s Central Interior. In January of 2022, Williams Lake First Nation announced that GPR had aided in the discovery of 93 possible burial sites at a former residential school.

"All of them display varying characteristics indicative of potential human burials," Spearing said at the time. "It must be emphasized that no geophysical investigation can provide certainty into the presence of human remains. Excavation is the only technique that will provide answers as to whether human remains are present."

Many communities, however, have been reluctant to dig up potential burial sites – and that ought to be respected, says Brenda Wastasecoot, an assistant professor at the University of Toronto's Centre for Indigenous Studies.

"It's just very triggering," Wastasecoot told CTVNews.ca. "I think it's important that that the community leads those searches: the community leaders, in consultation with our community members and elders."

Bank agrees, and believes answers could be found with limited disruption.

"Sometimes confirming buried remains for one anomaly can be sufficient to claim that other anomalies are actually graves," Bank said. "What I see is that the surveys are now confirming what indigenous groups have known for decades."

With files from CTV News Regina and The Canadian Press

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If you are a former residential school student in distress, or have been affected by the residential school system and need help, you can contact the 24-hour Indian Residential School Crisis Line: 1-866-925-4419. Additional mental-health support and resources for Indigenous Peoples are available here.