The victors (Israel) dictate terms, not the losers (Palestinians).I think sewage can kill too. In any case, its not Israeli land and Gazans have every right to dig as deep as they like there.
Israel can, without killing, close off tunnels which are in Israel. Or they could make a just peace to take away the fear and conflict.
the Pals have not lost yet, they are still there.
How much longer before nature takes a hand in it and visits them with a plague, showing the world that every God is against them.