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Lo which provides a temporary, closed-system, hydraulic connection. Groundwater samples are obtained directly from the Enviro Probe into the pre-evacuated sample vials. The pressure transducer is used to monitor filling of the sample vial and to measure hydrostatic pressure of the formation after the sample vial has filled. If needed, the pore pressure unit or the GMS groundwater sampling unit can be used independently. The time allowed to fill the vial depends on the physical properties of the target formation and.the groundwater pressure at the depth of the probe. Lr After the sample vial has filled, the sample housing is withdrawn from the drive rods and the LM sample vial removed. The Enviro Probe is generally purged by removing one probe volume (approximately 15.ml) of groundwater prior to collecting a sample for preservation and transport to the laboratory. The probe can be sampled repeatedly at the same depth by repeating the sample collection procedures. 3.2 HYDROPUNCH° SAMPLING PROCEDURES �- HydroPunch° I groundwater samples are usually collected under hydrostatic conditions, whereby groundwater flows from the formation through the screen section and into the sample. reservoir. Accordingly, HydroPunchm I cannot be used at depths less than approximately 5 feet below the water table. The sample reservoir is allowed to fill until groundwater enters the L. drive rod. The water level inside the drive rod can be detected using a well sounder. The ' actual sample collection time at each depth depends upon the physical properties of the target La zone and the fluid pressure outside the probe. Once the sample reservoir is filled, the HydroPuncb' is returned to the surface. Although the sample reservoir is sealed at both ends by internal one-way check valves, care must be taken to avoid sample cross-communication with transmissive units or borehole fluids at a higher potentiometric head than the target zone. Before retrieving the tool, deionized water should be added to the drive rod to a level that exceeds the highest potentiometric surface in the borehole. �. HydroPunch° H can be used below the water table, in a manner similar to HydroPuncb® 1, or it can be used at the water table in the "hydrocarbon mode." If HydroPuncY 11 is used in the Lr DISCRETE-DEPTH SAMPLING Page 4 of 6 MSCIPROTO-DS.= REVISION DATE:MARCH 1996 DS-4 I.r