The answer to the monthlong mystery about the source of an oily sheen that reached Fall Creek through a storm drain on March 11 may start to be uncovered April 25, when a contractor will begin work at 726 University Ave.

"We won't be sure until we start digging out a larger area whether the contamination at the Fall Creek site is related to the site of an oil tank that was removed in 1995 or some other source," said Steve Beyers, environmental engineer in Cornell's Office of Facilities Engineering. "From the reports filed at the time and from our recent investigations, we think that the contaminated soil has remained in the same area for years -- until the March spring thaw."

Beyers said that it is hard to surmise why the residual oil in the ground should have surfaced years later, but he thinks that the extremely wet weather in March -- the same time that flooding was reported across the area -- may be accountable.

The first indication of a problem surfaced March 11, when people in the 726 building smelled petroleum. Cornell Environmental Health and Safety staff discovered oil in water on the basement floor, seeming to come from a spot on the wall. The New York State Department of Environmental Conservation (DEC) responded that day and Cornell contacted an emergency response contractor. On March 12, the contractor excavated soil in the nearby outside area, finding evidence of contamination, and pumped oily water from the ground. Later that weekend a sheen appeared in Fall Creek from oil that apparently had passed through the building's drainage system on March 11 but was invisible at 726. The Ithaca Fire Department put a boom on the creek and notified Cornell, which placed sorbent pads in the catch basins near the building as a further precautionary measure until the ground could dry out and they could do further excavation at 726.

The university and DEC made subsequent site visits, and the oil contamination looked stabilized until last week. On April 11, a man fishing near Ithaca Falls noted a new sheen, and the DEC was called in again. After checking out other suspect sites, the DEC notified Cornell on April 13 of the spill and discussed the possibility that 726 might again be the culprit.

Although the source was still unclear, Cornell called the emergency contractor back that day and again pumped out water from the ground around the building. The timetable for comprehensive remediation, already planned and just approved by the DEC, was accelerated to ensure there would not be a repeat incident.

"We need to work between a retaining wall, the building foundation and a number of service utilities," said Beyers, "so we need to be both timely but also very careful to address this situation."

Beyers expects the remediation effort, which will be overseen by the DEC, to take several days.