An adjustable contaminated mixing apparatus includes a reactor head and a down tube extending from the reactor head. A plurality of ports are formed in the reactor head and configured to impart a spinning motion to the contaminated liquid as it passes from the reactor head into the down tube. Each port is adapted to receive a flow restrictor to permit selectively control of velocity and flow volume of the liquid through the down tube. Typically, the flow restrictors are removable flow restriction plugs inserted into in a removable cartridge of the reactor head.