A Chesterfield man has pleaded guilty to involuntary manslaughter and second degree assault for the head-on crash in August that lead to the death of a Whitfield school teacher.Prosecutors say 53-year-old Patrick McCormick was drunk when his vehicle crossed the center line and collided with a vehicle driven by 50-year-old Janet Esrock, who died weeks later from her injuries. Her 16-year-old son was seriously injured in the crash.