The representativeness of pore water samples collected from the unsaturated zone using pressure-vacuum lysimeters

Pressure-vacuum lysimeters are an inexpensive means of collecting numerous water samples from the same location in the unsaturated zone over a period of time. However, prior studies have indicated that the chemistry of water samples may be altered by the collection technique, creating concern about the representativeness of the pore water samples obtained. A study conducted using soil water pressure-vacuum lysimeters in outwash sand and glacial till deposits demonstrates that for non-dilute-solution samples the effect on pH of sampling with lysimeters is minimal, and that measured major cation and anion concentrations are representative of the natural pore water; trace-metal concentrations can be significantly altered by collection procedures at low concentrations.