OLD WESTBURY, N.Y. -- An electrical contractor working on a Long Island college campus stumbled upon an elaborate underground marijuana farm Monday morning, police said.

The contractor working at the State University of New York at Old Westbury discovered PVC piping containing electrical wiring that led to three water tanks three feet underground.

The hydroponic operation was used in the past for growing marijuana plants, police said.

The 10-foot by 60-foot tanks were used in succession for seedlings, transplants, and -- finally -- adult plants, police said.

The tanks, which police believe hadn't been used in several years, were dismantled. The plants were in a state of decay and were removed for disposal, police said.

Authorities think the farm, whose growing area covered 1,800 square feet, may have been active for as many as five years.