An excavation worker was briefly buried in collapsing earth Monday at the Marshfield High School construction site, but he was not seriously injured. At about 11:50 a.m., the worker, an employee of J. Derenzo Co., was standing next to a hole dug for utilities, said Scott Borstel, Marshfield’s superintendent of schools. An apparatus called a “trench box” had been placed in the hole to prevent it from collapsing, but the earth next to the hole gave way and buried the worker completely except for one hand, he said. Co-workers began trying to free him, and the Marshfield fire and police departments responded. The worker was conscious when he left in the ambulance, said Borstel, who added that he was released from the hospital and was recovering from bumps and bruises.