The ground-water sampler collects a time-averaged or composite sample of the ground water. The sampling system was designed to be self-contained and all sources of power being contained within the well casing. The sampler collects the sample on a sorptive media and the media analyzed by a laboratory. The sampling system prevents the exchange of gases between the ground water and the atmosphere. The exchange is prevented by a well packer which is designed to be placed in well casings of 2 inches or greater. The well packer can be easily and economically placed into the well casing with the use of a packer tool. The sampler is inserted into the well packer and once inserted a one-way check valve opens to the aquifer allowing the water to be sampled. After the sampling episode, the sampler is removed from the well packer and the one-way check valve closes. The media is then analyzed in a laboratory. In the alternative, the sorptive media unit can be replaced with chemical or physical analysis units making possible real-time analysis of the aquifer.