Construction workers building a new sewer line under a former brewery in Sint-Gillis-Dendermonde, Belgium, uncovered $10.4 million in gold coins and bars this week. Local police said the crew called them in as soon as they realized what they had found.

An 18-year-old worker named Kobe told Belgian broadcaster VRT that he mistook the first pieces for ordinary 1 euro coins. “Our first reaction was actually disbelief, surprise,” he said. “Of course, we didn’t expect to find gold.” The team had removed a piece of the building’s foundation to lay pipe for the new sewage system.

Project leader Mario described the moment as a “crazy feeling.” “They shouted, ‘We found gold!'” he said. “I went to look and took the gold in my hands. We also continued to dig up new coins and bars. Only then did what we had found really dawn.” He called his boss, then the police.

Officers in Sint-Gillis-Dendermonde, a Flemish community outside Brussels, catalogued the find and moved it to a high-security federal government vault. Under Belgian law, the rightful owner has up to five years to come forward and claim the gold.

Mario said keeping the haul was never really an option. “It’s about so many coins and bars, that almost wouldn’t be possible,” he told VRT. “Besides, it would also be theft.” Kobe said he still hopes for a finder’s fee. “That would be nice,” he said.

The building above the dig site belongs to an organization that provides welfare support to the local Flemish community. Its director said he hopes the gold, once its status is resolved, could go toward the “enormous need we experience daily,” according to the BBC.

For now, the coins and bars remain locked away while Belgian authorities work to trace their origin and rightful owner, a process that could take years to resolve. Police have not said how long the gold might have been hidden behind the wall, or who might have put it there.