My wife alerted me today - it is a recent thing. My septic tank is covered with gravel and the border starts right at the walkway, extending inside the front lawn. It seems like some sort of a pipe just got exposed from under the gravel. I am sure there should be something that covers it else gravel will keep falling in. What is it and what am I to do about it? Here are the photos. The whole thing and the blow-up.