Hundreds of residents near Tampa Bay are being allowed home after they were evacuated over fears of a toxic flash flood from a nearby wastewater reservoir.
Emergency work has been completed on the containment wall surrounding the Florida facility.
Investigations by the US Army Corps of Engineers found a “diminished risk of a catastrophic collapse” at the site of the former Piney Point phosphate plant.
The Army Corps and local public safety crews have worked around the clock for days pumping hundreds of millions of gallons of water out of the reservoir to ease pressure on its weakened containment wall.
The crisis began last Thursday when officials discovered leaks in the structure, lined with tall stacks of phosphogypsum waste – an industrial by-product from fertilizer manufacturing.
The substance is known to emit radon, a cancer-causing radioactive gas.
State environmental officials have said tests of water seeping from the reservoir showed it was not radioactive.
But local authorities said they feared that an uncontrolled breach of the wall could unleash a 20ft torrent of untreated wastewater into the surrounding area.
More than 300 homes were ordered to evacuate over the weekend as a precaution.
While the pumping operation has eased the threat to homes and businesses next to the reservoir, the wastewater drainage is being routed into a nearby Gulf Coast seaport, posing environmental concerns there.
Ed Sherwood, executive director of the Tampa Bay Estuary Program, said pumping the nutrient-dense discharge into Port Manatee at the mouth of Tampa Bay could spawn algal blooms toxic to marine life in the estuary.
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