Point source sampling can be used to profile an open borehole or screened well, to collect samples from distinct levels or points of inflow. There is negligible disturbance as can be caused by pumping and purging. Mixing of the sample with water from different levels in the well is minimized. Purging and disposal of purged water can be avoided, because sampling directly from a specific depth collects the water that has just flowed into the well at that depth. Solinst also manufactures the Model 425 Discrete Interval Sampler which is pressurized before lowering into the well to prevent water from entering the sampler until the sampling zone has been reached. The Model 425T Transportable DIS is similar, but uses special shut-off valves to retain the volatiles in a zero headspace sample, in down-hole condition, during transport to the laboratory.