Abstract: A system for rapid collection of large volumes of dissolved gases from groundwater pumps the water from a large-diameter passage through a small-diameter restrictor passage, and then into a flow-through collection chamber. The small-diameter passage causes a drop in the hydrostatic pressure of the groundwater traveling therein, causing spontaneous ebullition of gas bubbles, which are then collected in the collection chamber. A treatment station within the passages selectively alters the concentration of dissolved gases within the groundwater. Testing reveals that the gases are collected in proportion to their presence in the groundwater, and thus the system allows accurate quantification of concentrations of dissolved gas in groundwater. The system may beneficially be made easily portable, thereby allowing its use in the field, as well as in laboratory settings.