This story was updated at 4:55 p.m., Sept. 19, 2013.
Students and staff evacuated Col. Zadok Magruder High School Thursday afternoon after a gas odor was reported, but it turned out there was no gas leak, a gas company spokesman said.
The odor was reported at about 2 p.m. on the second floor of the school on Muncaster Mill Road in Rockville, according to Montgomery County Fire and Rescue spokeswoman Beth Anne Nesselt.
Seven students and two teachers were taken to a local hospital after feeling ill, Nesselt said.
Dana Tofig, a spokesman for the county school system, said an initial determination sourced the odor to a sewer pipe in one of the classrooms and perhaps sewer gas.
“That pipe was capped and the building was cleared for re-entry around 3:30 p.m.,” Tofig said in an email.
Four classrooms will be closed Friday, Tofig said.
School maintenance and facilities staff are continuing to investigate and identify possible repairs needed, he said.
Tofig said a total of 11 students and two staff members reported not feeling well and were evaluated at the scene.
The school building was evacuated shortly after the smell was detected. As of about 3 p.m., most students had left the school, he said.
An after-school class was canceled. A field hockey game was played at the school as scheduled.
Hazmat officials were taking atmospheric readings inside the building, but did not find any evidence of toxic gas, according to Nesselt.
And a short time later, Washington Gas and county fire officials determined that the smell was not from gas but from a blocked sewer trap, said company spokesman Ruben Rodriguez.