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HOUSTON — At least 13 toxic waste sites in Texas were flooded or damaged by Hurricane Harvey, adding to the challenges as the state and the region begin cleanup efforts after the deadly storm.

The Environmental Protection Agency announced Saturday that it had assessed 41 Superfund sites using aerial images, and determined the ones badly affected by the storm.

The impact of flooding on the sites is unknown. The EPA said its workers have not been able to “safely access the sites” but are ready to do so as soon as the floodwaters recede.

A Superfund site is land that is contaminated by hazardous waste and identified by the EPA as a candidate for cleanup because it poses a risk to human health and/or the environment.

The 13 affected sites have industrial waste from petrochemical companies, acid compounds, solvents and pesticides.

In the Houston area, authorities had said it would take 10-15 days for floodwaters to recede.

The toxic waste sites are not the first environmental threat Texas has faced since Harvey swept through the region.

Fires broke out over two days at a flooded chemical plant near Houston.

People living within 1.5 miles from the Arkema site in Crosby were evacuated days before the explosions and now officials are letting chemical containers catch fire and burn out rather than endanger firefighters, the EPA and the Texas Commission on Environmental Quality said in a statement.

The Superfund sites and the Arkema plant represent just a snapshot of the cascading effects of the catastrophic storm.

Houston Mayor Sylvester Turner and Texas Gov. Greg Abbott appeared Sunday on morning talk shows.

The city is 95 percent operational and most businesses will reopen Tuesday, Turner said on CBS’ “Face the Nation.”

“And so if you have a conference, a convention, a concert, any of those things that were planned, that you were planning to come to this city, we are still ready to welcome you,” he said.

“On Tuesday, we are getting back on our feet, and I’m expecting employees — employers to open, employees to go to work. And all city employees, you are due back at work on Tuesday.”

But Turner said residents are still struggling and first responders will go door-to-door to check on the elderly, housing conditions and disabled people.

Abbott said his state was going to need a massive commitment from the federal government as it begins to recover from the storm.

The recovery from Harvey would require even more money than the package Congress appropriated for Hurricane Katrina relief, he said.

The total population and geographic range affected by Harvey could surpass Hurricane Katrina and Hurricane Sandy combined, he said.

“It’s going to take years for us to be able to overcome this challenge,” Abbott said.

More than a week after Hurricane Harvey swept through Texas, thousands of people are still unable to return home.

At least 53 people died from the storm and tens of thousands of people are still living in shelters seeking aid.

“Please don’t come home,” Brazoria County Judge Matt Sebesta said at a news conference Saturday.

Residents were evacuated last week when floodwaters breached a levee in the county south of Houston.

Water is going through septic systems in rural areas, creating a health hazard for residents.

“It’s like a huge lake sliding across the county,” he said.

In Houston, nearly 300 people who chose to stay in flooded homes after Hurricane Harvey are expected to evacuate before the CenterPoint Energy utility turns off power to those residences.

Turner ordered the evacuation after emergency workers scouted the area Friday and learned that many people had not left their flooded homes.

Areas of western Houston have seen sustained flooding in part because the Army Corps of Engineers has intentionally released water from two swollen reservoirs — and the flooding there won’t recede soon, Turner said.