PASADENA, Texas — The U.S. government received reports of three spills at one of Houston’s dirtiest Superfund toxic waste sites in the days after the drenching rains from Hurricane Harvey finally stopped.

Aerial photos show dark-colored water surrounding the site as the floods receded, flowing through Vince Bayou and into the city’s ship channel.

The reported spills, which have not been publicly detailed, occurred at U.S. Oil Recovery, a former petroleum industry waste processing plant contaminated with a dangerous brew of cancer-causing chemicals.

On Aug. 29, the day Harvey’s rains stopped, a county pollution control team sent photos to the Environmental Protection Agency of three large concrete tanks flooded with water. That led PRP Group, the company overseeing the ongoing cleanup, to call a federal emergency hotline to report a spill affecting nearby Vince Bayou.

Over the next several days, the company reported two more spills of potentially contaminated storm water from U.S. Oil Recovery, according to reports and call logs from the Coast Guard, which operates the National Response Center hotline. The EPA requires that spills of oil or hazardous substances in quantities that may be harmful to public health or the environment be immediately reported to the 24-hour hotline when public waterways are threatened.

The EPA has not publicly acknowledged the three spills that PRP Group reported to the Coast Guard. The agency said an on-scene coordinator was at the site last Wednesday and found no evidence that material had washed off the site. The EPA says it is still assessing the scene.

In the days after Harvey, at least seven Superfund sites in and around Houston were underwater during the record-shattering storm. Journalists surveyed the sites by boat, vehicle and on foot. EPA said at the time that its personnel had been unable to reach the sites, though they surveyed the locations using aerial photos.

EPA Administrator Scott Pruitt reiterated that safeguarding the intensely-polluted sites is among his top priorities during a visit Friday to the San Jacinto River Waste Pits.

Pruitt then boarded a Coast Guard aircraft for an aerial tour of other nearby Superfund sites flooded by Harvey, including U.S. Oil Recovery.

Photos taken Aug. 31 by the National Oceanic and Atmospheric Administration show dark-colored water surrounding the site two days after the first spill was reported to the government hotline. While the photos do not prove contaminated materials leaked from U.S. Oil Recovery, they do show that as the murky floodwaters receded, they flowed through Vince Bayou and emptied into a ship channel that leads to the San Jacinto River. The hotline caller identified Vince Bayou as the waterway affected by a spill of unknown material in unknown amounts.

Thomas Voltaggio, a retired EPA official who oversaw Superfund cleanups and emergency responses for more than two decades, reviewed the aerial photos, hotline reports and other documents.

“It is intuitively obvious that the rains and floods of the magnitude that occurred during Hurricane Harvey would have resulted in some level of contamination having been released to the environment,” Voltaggio said. “Any contamination in those tanks would likely have entered Vince Bayou and potentially the Houston Ship Channel.”