HOUSTON (KHOU)- Firefighters have extinguished the tank farm fire that sent a plume of smoke over Houston for three days. The investigation and cleanup continue, however.

At a 10 a.m. press conference, Environmental Protection Agency spokesman Adam Adams said they are continuing to monitor air and water samples, which so far have shown no hazardous levels. The EPA says they have monitored air quality from La Porte to Katy.

“We’ve measured no hazardous levels of concentrations,” said Adams.

What sparked the fire is still unknown, and the investigation is on-going.

“We are sorry for what happened,” ITC spokeswoman Alice Richardson said, apologizing again on Wednesday. “Sorry for our neighbors, the community, the employees. Our goal is to be a good neighbor.”

Richardson said the company will conduct a “root cause investigation” and will then implement changes moving forward based on what the investigation shows.

ITC says at least 11 of the 15 tanks in the burned area were damaged or destroyed. The remaining four will require further examination. The tanks can hold more than three million gallons but none were at capacity at the time of the fire, according to the company.

The newest video from early Wednesday morning outside the tank farm showed there are no flames visible from the ground.

“Crews continue to spray foam and water on the tanks to facilitate cooling and prevent reigniting of the remaining material,” stated an ITC in the early morning.

At this time many schools are still closed Wednesday, including Deer Park, KIPP Northeast, KIPP East End, KIPP Southeast, La Porte, Channelview, Galena Park and Sheldon ISDs. San Jacinto College and Rhodes School for Performing Arts, Channelview campus are also closed.