The manifold consists of a series of sampling chambers connected to a common vacuum line and operated by manipulating three-way stopcocks. The reliability of the system was tested in a 51-day tracer experiment using Iodine-131 and Strontium-85 (Williams et al. , 1985a, b). The multilevel samplers were installed in glacial sand interbedded between two clay horizons, at depth of up to 8 m below ground level, with a rest water level about 2. 5-3. 0 m below ground level. An Edwards EB3A pump provided the vacuum, and proved sufficient for the 25 sampling points. Compared with applying vacuum to each tube in turn, the manifold allowed a single operator to complete sampling in about a fifth of the time, with the added advantage that two or three operators could work at once.
