Contractors are trying to learn whether a large sinkhole is spreading, south of the future light-rail station in Seattle’s Roosevelt neighborhood.

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Sound Transit contractors drilled test holes Tuesday to learn whether there are more underground voids in Seattle’s Roosevelt neighborhood, where a wide sinkhole appeared Sunday.

That investigation followed an operation Sunday night that required six truckloads of concrete to fill the hole, along 12th Avenue Northeast near Northeast 62nd Street. The site is three blocks south of the future Roosevelt light-rail station, scheduled to open in 2021. Twin subway tunnels were carved out last fall, about 50 feet below, so transit officials initially suspect the sinkhole resulted from tunnel excavation.

Laser and visual inspections found that though the hole was only 6 feet by 2 feet at the surface, it spread to 39 to 42 feet beneath the front yards and sidewalk, and went 6 to 9 feet deep, said transit spokeswoman Kimberly Reason.

Marcella Dean said the sinkhole collapsed at 4 p.m. Sunday, while she was taking a stroll through the neighborhood. She watched big rocks tumble from the residents’ landscaping, and said she rushed to tell neighbors.

“Rocks, not small, were falling into the ground right beside the sidewalk, just as I passed,” she said.

Dean said she told a neighbor to call 911, then returned “with some trepidation” to learn the hole extended wide and deep, below the ground where she had walked.