Ground-water studies are often associated with the use of actions or materials which can lead to introduction of errors or contamination. For instance, transfer of liquids from a bailer to a laboratory vial can permit volatile chemicals sampled from water in an open well to escape, or can give rise to external contamination or human contact with the fluids.

A set of devices, the BAT® Groundwater Monitoring System, has been developed which specifically eliminates these and other difficulties. All individual elements of the system are hermetically sealed, permitting in situ conditions (for example pressures and dissolved gases) to be maintained. Hydraulic interconnections and fluid transfers are achieved through use of hypodermic needles, flexible septa, and internally generated pressure gradients. The system permits pressurized sampling of both liquids and gases from virtually any depth in groundwaters, open or sectioned-off wells, and piping systems, as well as directly from surface waters. Groundwater may be extracted in situ from either the saturated or vadose zones of soil or rock formations.

Samples are taken in the field with the same presterilized and pre-evacuated vials that will be sent to the laboratory; no further transfers, pumps, or piping mechanisms are required. Since the samples are sealed and pressurized, the total gas content will remain the same as that at the sampling site, and the samples can truly be said to be representative of the in situ conditions.

The in situ system also contains additional above-ground components for use in ground-water investigations. These measure ground-water pressures or soil suctions, perform tests of hydraulic conductivity, and allow tracer tests to be run. All of these devices use needles and septa to access the only below-ground piece of equipment. This—a permanently installed and sealed filter tip—contains no electronics, and only a single moving part: a flexible septum.