According to many reports this week, a mass grave was found in Kamloops, BC, containing the remains of at least 215 indigenous children. For example: "Indigenous groups call for Canada to identify graves after remains of 215 children found" (Reuters article).
The original source appears to be this statement from the Tk'emlúps te Secwépemc First Nation, which says:
This past weekend, with the help of a ground penetrating radar specialist, the stark truth of the preliminary findings came to light – the confirmation of the remains of 215 children who were students of the Kamloops Indian Residential School...
“We had a knowing in our community that we were able to verify. To our knowledge, these missing children are undocumented deaths,” stated Kukpi7 Rosanne Casimir. “Some were as young as three years old."
It appears that no one actually dug up any bodies and counted them; instead, the remains were identified using ground-penetrating radar (GPR). Of course, there's nothing wrong with using modern imaging technology for archaeology, but all technology has limits. Is GPR truly reliable enough to justify the strong claims in the statement?
An article in The Star describes the process in more detail:
Ground-penetrating radar was originally designed for geology and geophysics; it’s not like an X-ray for the ground that shows you a simple picture of what’s beneath the surface, [Dr. Kisha] Supernant says. Rather, it is able to detect disruptions in the soil that her team must then interpret.
“What it’s looking for is actually the pit that was dug when the grave was placed,” she says. “And if it was a coffin burial, sometimes it will reflect off of the coffin. It does not actually see the body.”
Based on this quote, I don't understand how GPR can be sufficiently precise to identify 215 human bodies and their exact ages. Indeed, if the technology can only detect disruptions in the soil, do we know that the radar images even represent a human grave site? Incorrect detections appear to be fairly common in GPR; one paper points out that "the presence of subsurface features such as tree roots, buried debris, cobbles, or buried pipes may result in false positives."
It's clear that many horrible abuses were perpetrated in the Canadian residential school system. I don't mean to suggest otherwise, and I'm all in favor of investigating the school sites more carefully. Rather, my question is: for the specific claims regarding the Kamloops grave site, how strong is the available evidence at this point in time? How confident can we be that the site actually contains the remains of 215 children and that some of them were as young as three years old when they died?