Houston's mayor insists that America's fourth-largest city is "open for business," but with areas under water, people not yet in their homes, and billions in damage to repair, major disasters that Harvey created are by no means resolved.

Mayor Sylvester Turner said much of the city was hoping to get back on track after Labor Day.

"Anyone who was planning on a conference or a convention or a sporting event or a concert coming to this city, you can still come," he told CBS. "We can do multiple things at the same time."

One worry, of further explosions at a damaged chemical plant, eased after officials carried out a controlled burn Sunday evening of highly unstable compounds at the Arkema plant in Crosby. Three trailers had previously caught fire after Harvey's floodwaters knocked out generators.

Authorities said they would keep monitoring the air, and people living within a mile and a half (2.4 kilometers) of the site outside Houston are still evacuated, but floodwaters also have inundated at least five toxic waste Superfund sites near Houston and some may be damaged, though Environmental Protection Agency officials have yet to assess the full extent of what occurred.

Texas Gov. Greg Abbott told CNN that the EPA is "working on some of them already," but "they have restraints on their ability to check out some of them just simply because of the water."

Turner said Houston's drinking water hadn't been affected by the storm, but told CBS, "We would hope that the EPA would be on the ground now to take a look at those Superfund sites, to make sure that contamination is contained and limited."

Other issues across the region: too much floodwater still in houses, but no water to drink.

Utility crews went door-to-door Sunday shutting off power and warning those still in some waterlogged homes in western parts of the city that more flooding was possible — not from rain, but from releases of water from overtaxed reservoirs. Thousands of Houston dwellings were under mandatory evacuation orders, though about 300 people were thought to be refusing to leave.

Harvey slammed into Texas on Aug. 25 as a Category 4 hurricane, but brought the worst flooding to Houston and other areas as a tropical storm. The rain totaled nearly 52 inches (1.3 meters) in some spots, and the storm is blamed for at least 44 deaths.

President Donald Trump has asked Congress for an initial $7.9 billion down payment toward Harvey relief and recovery efforts. Abbott suggested the cost of recovery could be as much as $180 billion.