Not realising what she had come across, she picked it up and was about to throw it out with the other garage rubbish when it dawned on her what she was holding.
"I was pretty worried when I saw that the pin was still in it and I saw the wire around it and I could read the instructions on the little tin tag that said how to detonate it.
"I just wanted to get as far away outside as I could ... then I called the police."
Officers arrived shortly after and closed off Abbot St between Heads Road and Bignell Street.
Ms Mackie and nearby neighbours were evacuated from the area and the bomb squad in Wellington was called to the scene. It took the nearly four hours for the bomb squad to arrive.
Senior constable Tanya Ross said the bomb - an eight-pound aircraft practice bomb - was live.
SAFETY FIRST: Bomb disposal staff get to work at the army base. Photo / Stuart Munro
The bomb disposable unit contacted the army to get authority to let it explode.
"The army base out at Landguard Bluff was the only safe area in Whanganui to detonate the bomb in the sand," Ms Ross said.
She said it had to be destroyed by 4.30pm before the flight training started at the Whanganui Airport.
"It is likely the bomb had been there for more than 37 years because that's how long Colleen had been living there and she had not come across anything like it before."
The bomb was detonated at 4.20pm at army base, and Ms Mackie was able to return home with Abbot St re-opened.
Bomb destroyed at Langaurd Bluff in Whanganui. Photo/ Stuart Munro
