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II SOP #: GW 0001 Region I Low Stress (Low Flow) SOP ' Revision Number: 2 Date: July 30, 1996 Page 6 of 13 parameters. Adjustments are best made in the first fifteen minutes ' of pumping in order to help minimize purging time. During pump start-up, drawdown may exceed the 0.3 feet target and then "recover" as pump flow adjustments are made. Purge volume calculations should utilize stabilized drawdown value, not the initial drawdown. Do not ' allow the water level to fall to the intake level (if the static water level is above the well screen, avoid lowering the water level into the screen). .The final purge volume must be greater than the stabilized drawdown volume plus the extraction tubing volume. ' Wells with low recharge rates may require the use of special pumps capable of attaining very low pumping rates (bladder, peristaltic), and/or the use of dedicated equipment. If the recharge rate of the well is lower than extraction rate capabilities of currently ' manufactured pumps and the well is essentially dewatered during purging, then the well should be sampled as soon as the water level has recovered sufficiently to collect the appropriate volume needed for all anticipated samples (ideally the intake should not be moved ' during this recovery period). Samples may then be collected even though the indicator field parameters have not stabilized. 3b. Subsequent Low Stress Sampling Events ' After synoptic water level measurement round, check intake depth and drawdown information from previous sampling event(s) for each well. Duplicate, to the extent practicable, the intake depth and extraction rate (use final pump dial setting information) from previous event(s). Perform purging operations as above. ' 4. Monitor Indicator Field Parameters During well purging, monitor indicator field parameters (turbidity, temperature, specific conductance, pH, Eh, DO) every three to five minutes (or less frequently, if appropriate). Note: during the early phase of purging emphasis should e put on minimizing and stabilizing pumping stress, and recording those adjustments. Purging is considered complete and sampling may begin when all the above indicator field parameters have stabilized. Stabilization is considered to be achieved when three consecutive readings, taken at three (3) to five (5) minute intervals, are within the following limits: turbidity (10% for values greater than 1 NTU), DO (10s) , specific conductance (3%), temperature (3%), pH (± 0.1 unit), ORP/Eh (± 10 millivolts). All measurements, except turbidity, must be obtained using a flow- through-cell. Transparent flow-through-cells are preferred, because they allow field personnel to watch for particulate build-up within the cell. This build-up may affect indicator field parameter values