I've seen this a few times. It's always a head that is at the front of the yard near the road at the bottom of a slope. I've always assumed this was water draining out of the system. Today a guy stopped me and said that when he turns the main irrigation valve off the water stops leaking out and if he doesn't it will not stop leaking. So I'm guessing the control valve is not closing all the way. Can this be fixed or does the control valve need to be replaced? Or is it something else? I don't know if this makes a difference but the head is about 10 ft directly below the main irrigation valve. None of the other heads leak in that zone but the one near the road.