The state Public Service Commission has rejected a plan by Melville-based Northville Industries to repurpose an aging oil pipeline that runs along the Long Island Expressway to use for natural gas delivery.

The 22-mile, 16-inch steel pipeline runs from Holtsville, where Northville operates a large storage-tank facility, to Plainview. The plan was to deliver natural gas to 19 large commercial customers along the pipeline’s route, including the Caithness II power plant in Yaphank, which remains on hold.

In a decision April 20, the PSC ruled the Northville plan “does not comply with relevant regulations,” and didn’t provide adequate high-pressure tension testing to meet specifications. Northville had argued that the extensive testing it had completed was adequate for the purpose.

The PSC also cited the “length of time the pipeline has been out of service,” a lack of “original documentation” about the pipeline and the “densely populated area” through which the line traverses.

But the agency left open the prospect that Northville could address those issues in the future, or operate the pipeline at a lower pressure, along with other conditions. A company official suggested neither was feasible.

“We’ve done a lot of things to make sure the line is good and offered to do more but they (the PSC) are sticking to the guidelines,” said Gene Bernstein, chairman of Northville, adding the company was “very disappointed” by the ruling after having spent four years and untold funds seeking approval.

The project remains on hold and “we’re not sure what we’re going to do,” Bernstein said, noting that other large pipelines across the state have been similarly rejected.

The 22-mile pipeline experienced a blowout under the LIE in 2013 when Northville was running a water-pressure test to demonstrate that it could handle higher-pressure natural gas. The blowout scattered debris, flooded the highway with water and damaged six vehicles between Exits 55 and 57, which was closed westbound for more than two hours. No one was hurt.

Last year, Bernstein explained Northville had been testing the pipeline at a pressure “more than twice as high as the target maximum operating pressure,” he said. “Analysis showed that the pipeline had been previously damaged by a third party at the point of failure. The pipeline was repaired and successfully retested.”

In Northville’s application to convert the pipeline, which is not in use, officials said they planned to run “laterals,” or connecting distribution pipelines, from the main line to supply customers, including the gas-starved East End.

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Bernstein last year said the project would have recycled “a very valuable asset” because “there’s a shortage of natural gas on Long Island.”