A Somerville man who found himself stuck in one of the tunnels under Boston is now facing trespassing charges.

Daniel J. Kelly, 27, called police Monday night around 9:20 p.m. to report he was trapped in a storm drain and could not find a way out of his location.

Troopers searched the Ted Williams Tunnel based on Kelly describing what he could see — white walls with a light blue bottom. State troopers drove around with their sirens activated in the hopes Kelly would hear them, according to authorities.

The search was eventually narrowed to the D ramp of the tunnel, with Kelly reporting he could hear a siren. The ramp was closed down for about 20 minutes while police checked vent slots, doors and ceiling openings. One trooper eventually spotted a hand waving from an upper vent located about 15 feet up on the tunnel wall.

Kelly was stuck in the vent shaft; he was sitting atop a pipe when police found him. It was not immediately clear Tuesday why he was in the tunnels.

He was consequently charged with trespassing and was taken to the State Police Tunnel Barracks. He could be arraigned in Boston Municipal Court as early as today.