Difficult choice
David faced a difficult choice. He couldn’t turn in the material anywhere without casting suspicion on himself. What Boy Scout walks around with a huge amount of radioactive material? They would probably think he had terrorist plans. No, he had to get rid of it in secret.
Burying the material was not an option either. This would poison the soil to such an extent that the area around his house would become uninhabitable. He was very fond of his neighborhood, so this wasn’t a good choice either. There was nothing he could do but to move the material to a place where he would not be bothered by it.