By Mike DeNardo

PHILADELPHIA (CBS) — The School District says a North Philadelphia elementary school will start classes on time next week, as crews work to eradicate a mold outbreak in the building.

Two weeks ago, when Jerry Roseman walked through Munoz-Marin Elementary School in the Fairhill section of North Philadelphia, he says he saw mold everywhere — on the tables, on the chairs, even in the mail slots in the main office.

“We saw thousands of square feet of mold on surfaces throughout the entire school,” said Roseman.

Roseman is an environmental scientist for the Philadelphia Federation of Teachers. He blames a faulty air conditioning system in the building.

The district is paying a contractor $305,000 to clean the mold, and district spokesman Lee Whack says the school will be ready to open September 5 on time, and students and staff will be safe.

Roseman says the nearby Clemente School had a summer mold issue as well.

“Both buildings are only 20 to 23 years old and shouldn’t be having these kids of problems with the ventilation system,” said Roseman.