(CNN) After Hurricane Harvey spawned epic flooding along the Gulf Coast, insured flooding victims will be able to get financial relief a little bit faster.

The Federal Emergency Management Agency announced a temporary change Monday that would "rush recovery money" into the hands of National Flood Insurance Program policyholders.

"When a policyholder contacts his/her insurer and verifies his/her identity, he/she can receive an advance payment for up to $5,000 on a flood claim, without an adjuster visit or additional documentation," FEMA said.

"Up to $20,000 may be advanced to a policyholder who provides photos and/or videos depicting damage and receipts validating out-of-pocket expenses related to flood loss, or a contractor's itemized estimate."

In addition, policyholders affected by Hurricane Harvey who have not been able to renew their policies will get a grace period of 120 days to do so, FEMA said.

It's part of the slow, arduous road to recovery as tens of thousands of people were uprooted from the historic hurricane and floods.

Also on Monday, residents were able to return to the 1.5-mile evacuation zone near the Arkema chemical plant in Crosby, Texas. Organic peroxide overheated and ignited, causing multiple fires at the flooded chemical plant near Houston

Officials let chemical containers catch fire and burn out rather than endanger firefighters, the EPA and the Texas Commission on Environmental Quality said in a joint statement.

People living within 1.5 miles of the Arkema site were evacuated days before the explosions. The evacuation order was lifted after local officials determined it was safe to let residents return home.

"I want to once again apologize to the people of Crosby and Harris County," said Richard Rowe, CEO of Arkema North America. "The implications of the evacuation, the implications of Hurricane Harvey on our Crosby site layered upon the impact it's had on their personal lives -- I can only begin to imagine."

The Arkema plant represents just a snapshot of Hurricane Harvey's cascading effects. At least 53 people have died from the catastrophic storm, and tens of thousands of people are still living in shelters.

Toxic waste sites flooded

At least 13 toxic waste sites in Texas were flooded or damaged by Hurricane Harvey, the Environmental Protection Agency said. The 13 affected sites have industrial waste from petrochemical companies, acid compounds, solvents and pesticides.

Photos: Hurricane Harvey slams Texas Photos: Hurricane Harvey slams Texas Downtown Houston is seen behind the flooded Buffalo Bayou a few days after Hurricane Harvey came ashore in August 2017. The Category 4 storm caused historic flooding. It set a record for the most rainfall from a tropical cyclone in the continental United States, with 51 inches of rain recorded in areas of Texas. An estimated 27 trillion gallons of water fell over Texas and Louisiana during a six-day period. Hide Caption 1 of 22 Photos: Hurricane Harvey slams Texas NASA astronaut Jack Fischer photographed Hurricane Harvey from the International Space Station. Hide Caption 2 of 22 Photos: Hurricane Harvey slams Texas Steve Culver comforts his dog Otis in the hurricane aftermath. Harvey destroyed most of his home in Rockport while he and his wife were there. Hide Caption 3 of 22 Photos: Hurricane Harvey slams Texas Houston police officer Daryl Hudeck carries Catherine Pham and her 13-month-old son, Aiden, after rescuing them from floodwaters. Hide Caption 4 of 22 Photos: Hurricane Harvey slams Texas A damaged home is seen in the Key Allegro neighborhood of Rockport. Hide Caption 5 of 22 Photos: Hurricane Harvey slams Texas A car is submerged by floodwaters on a freeway near downtown Houston. Hide Caption 6 of 22 Photos: Hurricane Harvey slams Texas Melani Zurawski cries while inspecting her home in Port Aransas, Texas. Hide Caption 7 of 22 Photos: Hurricane Harvey slams Texas A graveyard is flooded in Pearland, Texas. Hide Caption 8 of 22 Photos: Hurricane Harvey slams Texas Soldiers with the National Guard patrol Rockport, looking for residents trapped in their homes. Hide Caption 9 of 22 Photos: Hurricane Harvey slams Texas Evacuees are loaded onto a truck in Houston. Hide Caption 10 of 22 Photos: Hurricane Harvey slams Texas People push a stalled pickup through a flooded street in Houston. Hide Caption 11 of 22 Photos: Hurricane Harvey slams Texas Rockport residents return to their destroyed home. Hide Caption 12 of 22 Photos: Hurricane Harvey slams Texas Rescue boats fill Tidwell Road in Houston as they help flood victims evacuate the area. Hide Caption 13 of 22 Photos: Hurricane Harvey slams Texas People wait to be rescued from their flooded home in Houston. Hide Caption 14 of 22 Photos: Hurricane Harvey slams Texas Volunteers in Dallas organize items donated for hurricane victims. Hide Caption 15 of 22 Photos: Hurricane Harvey slams Texas When Harvey slammed the Texas coast and flooded much of Houston, volunteers sprang into action. Some came from as far away as the Florida Everglades, boats in tow, ready to rescue people trapped in their homes. Hide Caption 16 of 22 Photos: Hurricane Harvey slams Texas Larry Koser Jr. and his son Matthew look for important papers and heirlooms inside a flooded home in Houston. Hide Caption 17 of 22 Photos: Hurricane Harvey slams Texas Members of the National Guard rest at a furniture store in Richmond, Texas. Hide Caption 18 of 22 Photos: Hurricane Harvey slams Texas Volunteer rescue workers help a woman from her flooded home in Port Arthur, Texas. Hide Caption 19 of 22 Photos: Hurricane Harvey slams Texas This aerial photo shows flooded residential neighborhoods in Houston. Hide Caption 20 of 22 Photos: Hurricane Harvey slams Texas Tammy Dominguez and her husband, Christopher, sleep on cots at the George R. Brown Convention Center, where thousands of people were taking shelter in Houston. Hide Caption 21 of 22 Photos: Hurricane Harvey slams Texas An elderly patient waits to be rescued from the Gulf Health Care Center in Port Arthur. The facility was evacuated with the help of first responders and volunteers. Hide Caption 22 of 22

The EPA announced over the weekend that it had assessed 41 Superfund sites using aerial images.

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 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.

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

Mayor: Houston open for business

Most of Houston is operational and more than 95% of the city is dry, Mayor Sylvester Turner told CBS' "Face the Nation" on Sunday. He said most businesses will reopen Tuesday.

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"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 continue going door-to-door to check on the elderly, housing conditions and disabled people.

Mexico set to send help

Relief supplies and up to 50 Mexican medical professionals will soon cross the border to help thousands of flood evacuees in Texas, Mexican officials said.

Mexico offered the United States aid last week, and Texas officials gave Mexico the green light Saturday to start sending help, said Carlos Manuel Sada, Mexico's undersecretary for North-American relations.

More than a dozen trailers loaded with beds, portable generators, mobile community kitchens and other supplies will cross the border into Laredo, Texas, "in the coming days" and be taken to the Houston area.

"On top of everything, there is a deep relationship between Mexico and Texas," Sada said.

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In 2005, Mexico sent drinking water and a convoy of soldiers among other supplies to help Hurricane Katrina victims.