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Fig. 4. Design, results, and interpretation of a pump test for collection of CCl2F2 (CFC12) in a piezometer with slow recovery (HC1 at 12.5 m) (see Fig. 3 for location): (A) the piezometer was purged and then allowed to recover for 48 h by inflow of ground water through the screen at the bottom of the tube; (B) water was pumped out through a Cu tube from the bottom of the piezometer and samples were taken in the sequence 1 to 4 until the piezometer was empty; (C) analyses indicate that the first three samples were uniformly undersaturated with respect to atmospheric CFC12, whereas the last sample was somewhat nearer to saturation. Gas exchange between ground water and air in the piezometer during the recovery stage may have been limited to the top of the water column (Sample #4, the first to enter the piezometer during recovery).
