The area, known as the Wickaninnish Sand Dunes, was used as a target range for Second World War soldiers learning to toss grenades, fire artillery and drop bombs.
Part of the dunes, an area roughly the size of three football fields, was closed 16 months ago, after an unexploded mortar shell was discovered.
Canada's Department of National Defence has since conducted two electromagnetic sweeps of the area, but says one more sweep is necessary to find any other dangerous devices.
Renee Wissink, resource conservation manager for Pacific Rim National Park Reserve, said the final sweep won't take place until this fall. He said the unpredictability of the dunes is partly responsible for the delay.
"The terrain is difficult, it's up and down, it's shifting," he said.
The dunes are also home to several endangered species, including plants and moths that can't be disturbed at certain times of the year.
Wissink said that, so far, no more live ammunition has been found.
"There's been lots of the sorts of fragments that we've always seen in there over the years: shells from high-calibre rifles, fragments of smoke flares," he said. "They also find other cultural artifacts, including such popular items as beer cans."
He expects the area will be reopened to the public early in the new year.