The hole in the Ellerslie track is almost certainly an inspection chamber for a waste water drain that could date back to the war years.
That was the conclusion yesterday when engineers from Harrison Grierson inspected the cavity which was exposed during Saturday's meeting at Ellerslie.
"It's wonderful that we've got at least some answers to the mystery that nearly caused a catastrophic accident," said Auckland Racing Club boss Cameron George last night.
"The hole has been identified as an inspection chamber for the main Watercare sewer line that runs 6m below the surface of the track. The advice of Harrison Grierson suggests the isolated problem has been caused by the cap of this access chamber perishing over time."