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SOP #: GW 0001 Region I Low Stress (Low Flow) SOP Revision Number: 2 Date: July 30, 1996 Page 5 of 13 total well depth (to 0.1 ft.) be measured the day before, in order to allow for re-settlement of any particulates in the water column. If measurement of total well depth is not made the day before, it should not be measured until after sampling of the well is complete. All measurements must be taken from the established referenced point. Care should be taken to minimize water column disturbance. Check newly constructed wells for the presence of LNAPLs or DNAPLs before the initial sampling round. If none are encountered, subsequent check measurements with an interface probe are usually not needed unless analytical data or field head space information signal a worsening situation. Note: procedures for collection of LNAPL and DNAPL samples are not addressed in this SOP. IV.PURGING AND SAMPLING PROCEDURE Sampling wells in order of increasing chemical concentrations (known or anticipated) is preferred. Install Pump Lower pum safety cable, tubing and electrical lines slowly (to minimize disturbance) into the well to the midpoint of the zone to be sampled. The Sampling and Analysis Plan should specify the sampling depth, or provide criteria for selection of intake depth for each well (see Section I). If possible keep the pump intake at least two feet above the bottom of the well, to minimize mobilization of particulates present in the bottom of the well. Collection of turbid free water samples may be especially difficult if there is two feet or less of standing water in the well. Measure Water Level Before starting pump, measure water level. If recording pressure transducer is used-initialize starting condition. Purge Well 3a. Initial Low Stress Sampling Ebent Start the umQ at its lowest speed setting and slowly increase the speed until discharge occurs. Check water level. Adjust pump speed until there is little or no water level drawdown (less than 0.3 feet). If the minimal drawdown that can be achieved exceeds 0.3 feet but remains stable, continue purging until indicator field parameters stabilize. Monitor and record water level and pumping rate every three to five minutes (or as appropriate) during purging. Record any pumping rate adjustments (both time and flow rate). Pumping rates should as needed, be reduced to the minimum capabilities of the pump (for example, 0.1 - 0.4 1/min) to ensure stabilization of indicator