Abstract: A system for adding a gas to a liquid including a gas over liquid accumulator having an interior volume with a headspace, a liquid level, an accumulator liquid inlet, an accumulator gas inlet, and an accumulator gas outlet connected to the headspace. A contactor having a contactor gas inlet and a contactor gas outlet and a first supply of gas connected to the accumulator gas inlet. A second supply of gas connected to the contactor gas inlet and a supply of liquid connected to the accumulator liquid inlet. A first valve disposed between the first supply of gas and the accumulator gas inlet, a second valve connected to the accumulator gas outlet, a third valve disposed between the supply of liquid and the accumulator liquid inlet, a fourth valve disposed between the contactor gas inlet and the second supply of gas; and a fifth valve connected to the contactor gas outlet.