An improvement in a chemical delivery system for a plunger lift for enhancing oil and gas recovery in a well having a well head and which employs a plunger includes a chamber communicably connected to a top of the well head and operably disposed thereon and including a ball check valve device which controls communication between a first section which receives chemicals therein for delivery into the well and a second section which communicates chemicals from the first section to a plunger in the well, and means for retaining the ball valve in one of an open position and a closed position as a function of the well being shut in.