A day after a CSX train derailed in Northeast Washington, leaking hazardous substances along a busy rail corridor, local officials and activists turned their attention to the transportation company responsible, while emergency personnel continued to work clearing the wreckage.

By early Monday afternoon, CSX Transportation was in the process of removing the damaged cars from the site, and all the tank cars had been offloaded, D.C. fire emergency officials said. Officials said all of the leaks had been contained but provided no clues into the cause of the wreck.

The Federal Railroad Administration is investigating the early-Sunday derailment of the 175-car train, which kept some residents away from their homes for hours, forced the closure of a Metro station and snarled traffic for much of the day. The wreck also disrupted MARC and Amtrak service, which use the tracks.

Officials had said Sunday that 14 cars derailed but upped the number to 16 Monday. Three of the tank cars were found to be leaking, including 750 gallons of the liquid content of a tanker containing sodium hydroxide. CSX described sodium hydroxide — also known as lye — as a chemical “used to produce various household products, including paper, soap and detergents.”

Officials said there was no threat to the air or water supply.

One scrap-metal hopper car is too damaged and will be cut up on site and removed using industrial equipment, officials said. After the train cars are removed from the site, CSX will begin soil remediation in the area affected by the sodium hydroxide spill, the company said. Following that process, track will be laid to begin the process of restoring service.

“This will be done at walking speed, under the direction of FRA and with air monitoring in place,” D.C. Fire Department officials said in a statement.

Rob Doolittle, chief spokesman for CSX, declined to provide a time estimate for restoring rail service.

“We know many people are relying on Amtrak and MARC, and we want to let them know what’s going on, but we don’t have enough information to give a hard deadline for when service will be restored,” Doolittle said.

Maryland transportation officials said MARC riders on the Brunswick Line can expect the service disruptions to continue Tuesday.

In addition to the inconvenience to those who depend on the rail corridor for travel, the derailment also revived long-standing concerns about freight trains carrying hazardous materials through the nation’s capital.

In a press conference, Mayor Muriel Bowser updates the public on the details surrounding a CSX train derailment in NE Washington, D.C. (WUSA)

Del. Eleanor Holmes Norton (D-D.C.), who visited the site Monday, said she was worried about a possible chemical spill in the Rhode Island Avenue NE neighborhood where the wreck occurred. She also sought answers about whether hazardous materials will be prohibited from being transported through the Virginia Avenue Tunnel, which CSX is rebuilding and enlarging.

D.C. Council member Mary M. Cheh (D-Ward 3), who chairs the panel’s committee on transportation and the environment, said the derailment is a wake-up call that the city needs to boost its oversight of freight rail.

Cheh said she’s resuming efforts to create a rail-safety office that tracks what materials are moved through the city, conduct inspections, and coordinate vulnerability assessments and safety response plans. Maryland and Virginia have similar rail-safety oversight, but District EMS personnel acknowledged two years ago that the city doesn’t inspect freight rail shipments or the city’s rail infrastructure.

“We need to do something about it,” said Cheh, who introduced legislation to create the office a year ago, but it has remained stuck in committee. She plans to include the proposal as part of budget negotiations.

“I don’t want to wait for another accident,” she said. “Maybe you can’t stop the accidents from happening, but we need to create the expertise and the training and have the standards and security and safety plans in place. . . . The whole point is to minimize risks and to maximize effective responses.”

Concerns about potentially toxic materials being transported through the Washington region were raised in the aftermath of the Sept. 11, 2001, terrorist attacks. Since 2004, CSX says, it has not transported certain categories of hazardous materials, including chlorine, ammonia and certain kinds of explosives through the District. Potentially explosive crude oil or gases that could be toxic if inhaled are not routed through the area, CSX officials said.

The material that leaked Sunday, sodium hydroxide, is not flammable and doesn’t vaporize, officials said.

Under FRA rules, railroads are required to use routing software that transports crude oil and other hazardous materials along the safest routes. The software takes into account 27 factors, among them the population along the route, the length of the trip, the number of river crossings and the speed at which the train would move.

Hours after Sunday’s derailment, Maureen Cohen Harrington, a Navy Yard resident and member of DCSafeRail, an organization fighting against CSX transporting hazardous materials through the neighborhood, snapped photos of another CSX train passing through the District with tankers labeled “chlorine,” a chemical the company says it does not transport through the city.

A CSX statement Monday said any such cars were empty and pointed to federal safeguards in place to ensure the safe transportation of hazardous materials.

“CSX does not move certain categories of hazardous materials or crude oil through the District, including the Virginia Avenue Tunnel,” spokeswoman Kristin Seay said.

“CSX does move empty rail cars that previously contained high-hazard materials through the District,” Seay said. [The U.S. Department of Transportation] assesses CSX’s hazardous materials routes and conducts reviews and audits. Those audits have confirmed that CSX is in compliance with its shipments of hazardous materials.”

Empty or not, the residue created by such materials raises the potential for dangerous chemical interactions in the event of a derailment, Harrington said.

“The burden should be on CSX to prove that these chlorine cars were empty. It’s not enough to offer merely its word and a reference to complicated, secret, minimal and poorly enforced federal regulation,” Harrington said. “Just imagine if those chlorine cars had collided with the molten sulfur and other hazardous materials that surrounded them. What a witches’ brew of chemicals that would have been. Even if the chlorine cars were ‘empty.’ ”

Since the beginning of the year, nine CSX trains carrying hazardous materials have derailed in the United States, according to data published by FRA. The most common primary cause was a misaligned railroad switch, which was the case in three separate derailments.

Sunday’s derailment occurred near a rail switch in the vicinity of Rhode Island Avenue and Ninth Street NE, but officials have not said whether it was a factor in the incident.

It also appeared to be most the serious derailment involving a CSX train with hazardous materials this year. In January, 16 rail cars of a CSX train derailed in western Tennessee, but no hazardous material was spilled, according to the FRA. The cause in that incident was wide gauge, a track defect that causes the wheels to lose contact with the rails.

Sunday’s derailment also was not the first involving CSX to occur near the Rhode Island Avenue Metro station. In October 2004, a derailment tossed at least eight boxcars from the tracks, spilling loads of gravel and snarling traffic on the rail line owned by CSX. That incident occurred near Rhode Island Avenue and Eighth Place NE.

The culprit in that case was apparently a faulty wheel. Officials at the time called on then-Homeland Security Secretary Tom Ridge to reroute rail shipments of hazardous materials away from Washington, citing the threat of terrorists.

If the derailed cars had been carrying chlorine instead, said the lawmakers, D.C. emergency workers “would have been dealing with an evacuation and mass casualties.”

Ashley Halsey III contributed to this report.