Excavation workers found the source of an oil sheen Tuesday that was spotted in Fall Creek on April 11, according to The Ithaca Journal.
The source was an oil tank buried underneath a parking lot at 726 University Ave., Cornell’s Arts and Sciences Alumni Building, The Journal reported. 
Before the tank was discovered Tuesday, officials had suspected that the oil came from a tank that was removed from the site in 1995.
The tank found under the parking lot contained about 100 gallons of oil. It will be removed this week, the Journal reported.
On March 12, emergency response contractors vacuumed oil from the site, where the tank was removed in 1995.
University-hired contractors, overseen by officials from the New York State Department of Environmental Conservation, are spending the next few days removing the contaminated soil around the building, according to the University.
Meanwhile, employees with offices at 726 University Avenue are currently working elsewhere on campus, according to Steven Beyers, an environmental engineer in Cornell’s office of facilities engineering.
Work began Monday after contractors removed some soil to access the contaminated area around the building.
The NYS DEC approved the University’s plan to hire a contractor, and it remains on-site to monitor the situation, Beyers said.
Beyers said the unusually high water table resulting from recent rainfall may have caused the oil to resurface, according to The Ithaca Journal.
Beyers told The Sun  on April 19 that the effects of the oil contamination are likely to be minimal and that the situation is “under control.”
However, Walter Hang, president of Toxics Targeting, a local environmental advocacy firm, told The Sun on April 19 that the contamination is a “catastrophe.”
“Cornell has been in a 13-year fight about its role in polluting southern Cayuga Lake, so they knew full well that the water quality is impaired, they understand what the law requires and it’s just shocking that this fiasco occurred," Hang said.