The potentially dangerous situation was created when the contents of a local’s garden shed were dropped off as part of a spring cleanup.
In a statement, Wastebusters general manager Gina Dempster praised the quick thinking of front yard team member Simon McKenzie and the wider crew.
"The team did a great job keeping staff and customers safe by securing the grenade in a safe place and involving the police straight away. Fortunately, it turned out that there was no explosive in the grenade, but no-one could ascertain that until the trained army experts arrived the following day to deal with it safely."
New Zealand Army personnel arrived at Wastebusters on Sunday and confirmed the grenade as being a Mills 23 grenade from the early 1900s.
A Wastebusters spokesperson said in the statement it was able to stay open during the army visit, as the grenade was contained in the upstairs area at a safe distance from staff and customers.
After viewing Wastebusters’ CCTV footage, police were able to track down and speak to the resident.
Senior Constable Bruce McLean said it was important people contacted emergency services when they wanted to get rid of hazardous material.
"If there’s any risk to a person — be it from a biohazard, an explosive, anything — give us a call. Don’t just turn up with it," he said.
Ms Dempster said Wastebusters had procedure and facilities to deal with the unexpected, and had had items such as rabbit poison and ammunition dropped off before, but having a grenade on site was a first for the team.
"We are very grateful to the professionalism of both the Wānaka police and army personnel, who responded and ensured the grenade was safely removed from our site."
She urged anyone using Wastebusters’ facilities to think about the safety of its staff and other customers.
