The basement levels of the World Trade Center are flooded with between 15 feet and 30 feet of water, government officials and Port Authority of New York and New Jersey sources say, the result of the surging sea levels during Superstorm Sandy.

The flooding equals millions of gallons of water that could potentially cause costly damage to equipment and electrical systems at the multi-billion dollar construction project, though preliminary evaluations appear to show the site was not severely damaged.

Adding to the difficulties is an ongoing power outage in lower Manhattan that has interfered with efforts to pump out the damaging saltwater, which sources say is significantly more corrosive to electrical wiring and systems than freshwater.

Of special concern is equipment underground at the site that will generate ventilation for large portions of the World Trade Center, including the retail space, subterranean pedestrian and transit corridors, National September 11 Memorial and Museum and the PATH hub. Another source said on Wednesday morning that preliminary inspections of the site showed the costly plant had not been significantly damaged.

Another source said that the basement of Four World Trade Center, a nearly 2 million-square-foot office tower being built at the site by Silverstein Properties, was also not damaged. Those estimates provide an early indication that the WTC site may have been spared the worst of the storm, though several sources said that estimates of the damage were still being made.

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Those sources said it would be impossible to fully assess the severity of the storm's impact until the seawater has been pumped from the site, which could take more than a week. Water had collected in deep pools some 70 feet below street level, where the World Trade Center's subterranean labyrinth of roads, corridors and infrastructure rests on bedrock.

A retaining wall surrounds the site underground. Referred to as the bathtub, the wall is in place to seal off the WTC from the Hudson River, but in the case of the flooding, has ironically acted as a basin for the floodwaters.

"The bathtub usually holds water out; now it's actually holding the water in," a government source said.

Officials described massive flooding at the site, when surging seas, which rose over 13 feet above normal levels, rushed down West Street. Most of the World Trade Center has been covered over with nearly complete components of its street-level infrastructure, including the Memorial Plaza space and a new section of Greenwich Street that will run through the site. When the waters flowed south, however, they breached one of the few remaining openings underneath the site, the Vehicle Security Center, which is still under construction and will serve as the WTC's main entrance point for automobile traffic when complete. That structure's ramps and open shaftways acted as a chute for the massive flooding.

During a press conference Tuesday morning, Gov. Andrew Cuomo described a catastrophic scene at the WTC site.

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"What I saw last night in downtown Manhattan were some of the worst conditions I had ever seen," Gov. Cuomo said at the press conference. "The Hudson River was literally pouring into the Ground Zero site with such a force we were worried about the structure of the pit itself."

Patrick Foye, the executive director of the Port Authority and the bi-state agency's top New York official, also spoke during Tuesday's press conference and said he doubted the storm surge had caused any structural damage at the WTC site, but that equipment and electrical systems being installed may have been damaged by the flood waters.

"There was a substantial incursion of water," Mr. Foye said. "I think it's fair to say that salt water and modern electrical equipment don't mix well. We don't expect structural damage but damage to equipment. That assessment is underway and is a high priority."

There has been no clear estimate yet of what equipment and systems have been damaged at the site and what the cost will be to either fix of replace them.

Daniel Geiger is a reporter at Crain's New York Business, a sister publication of Business Insurance.