Lisichansk, Ukraine - What Konstantine Zarubin and his childhood friend Edek didn't realise that summer evening two years ago, was that the quarry in their hometown they were about to climb through had just been littered with landmines.
It was a July evening in 2014, just months into an ongoing conflict between Moscow-backed rebels in country's east and the fledgling post-Maidan government in Kyiv. The boys could hear fighting from their Soviet-era apartment building and were curious to get a closer look.
"We were over halfway over the quarry," 14-year-old Konstantine remembers, describing how his friend was a metre, maybe two ahead of him, "when we heard a 'pop'." He didn't hear the explosion, he said, but he felt its impact and watched as a wave of gravel and earth descended upon him.
Although the fighting in Lisichansk is over, the scars of war are still visible on the bullet-pocked buildings on the city's outskirts.
Beyond the lace curtains of Konstantine's sitting room, it's a grey autumnal day. The quarry where Edek died is visible through a light fog. Konstantine's grandmother, sitting in an armchair on the other side of the living room, tears up as he recounts what happened that evening.
When, seconds after the explosion, the boy picked himself up and shook the earth from his clothes, he was in a state of shock. Then he noticed the blood splattered on his legs and shoulders.
Konstantine is not the only young man to lose a friend to explosive remnants of war (ERW) in a conflict that has claimed 10,000 lives.
No one knows exactly how many civilians or fighters have been injured or killed by landmines, booby traps, or unexploded ordnance.
This is partly because there isn't yet any central authority responsible for keeping track. Plans are under way, however, to establish a national mine-action authority.
Among the estimates based on publicly available reports, Marcus Brand, the democratic governance adviser for the United Nations Development Programme in Ukraine, told Al Jazeera, his agency estimates that 1,400 people have been killed by landmines, booby traps or unexploded ordinance since the conflict began in 2014. Forty percent of those, he said, are assumed to be civilians, like Edek.
But it isn't just the number of deaths that is unknown. Exactly how many mines, including the OZM-72 anti-personnel mine that is propelled into the air at waist height before it explodes, and booby traps have been deployed and where are questions de-mining groups may not know the answer to for years.
The UK-based Halo Trust said that 97 mine-hazardous areas, totalling more than 1,000 hectares, have been identified in the Ukraine, mostly outside the 15km buffer zone in the government-controlled areas since early 2016. But this initial estimate of the area affected by mines is likely to be the tip of the iceberg.
"Until we have completed a comprehensive, non-technical survey of eastern Ukraine, we won't know the full extent of ERW contamination or the resources required to tackle it," Halo Trust's Ukraine director Yuri Shahramanyan said.
When those surveys will happen is anyone's guess. Because the conflict is ongoing and knowledge of where mines are is of strategic military advantage, de-mining is not an immediate priority for either side.
"Due to the ongoing conflict, survey and clearance cannot happen everywhere," Shahramanyan added.
Moreover, initial clearance and surveying efforts have so far been limited to areas controlled by the Ukrainian government in Kyiv. De-mining groups have yet to be granted access to survey or de-mine in rebel-held Luhansk or Donbass.