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' GEOMATRIX If a bailer is being used to collect the sample, it will be gently lowered into the well below the point where the purge device was located. Samples will collected in the following order: (1) volatile organic compounds; (2) semi- volatile organic compounds; (3) metals; (4) other analytes. ' If a bladder pump or electric submersible pump is being used to sample the well for volatile compounds, the flow rate will be adjusted to either ' 1) approximately 100 milliliters per minute; 2) a rate specifically selected for the well based on groundwater flow rates and well hydraulic conditions; or 3) as low as possible. This rate will be maintained until the ' discharge line has been purged and the sample collected. A.3 Purging and Sampling Wells With Slow Recharge Wells that recharge very slowly may be purged dry once, allowed to recharge, and then sampled as soon as sufficient water is available. In this case, at least two sets of parameter readings of field water quality should ' be taken, one initially and one after recharge. A.4 Purging and Sa=ling Wells Using "Micropurge" Sampling Method Based on current research, a low-flow-rate, reduced purge method may be used to purge and sample a well with a dedicated pump (Barcelona et al., 1994; Kearl et al., 1994). This method may be used if acceptable to applicable agencies. This method assumes the water within the screened interval is not stagnant, and a small ' change to the natural flow rate in the screened interval will result in samples with particulates and colloidal material representative of groundwater. The pump should be preset in the screen interval at least 24 hours before the sampling event. A minimum of two pump plus riser pipe volumes should be purged at a flow rate of approximately 100 milliliters per minute or as low as possible ' based on groundwater flow and well hydraulic conditions. Purging should progress until water quality parameters (pH, SEC, ' temperature) have reached relatively constant values. Dissolved oxygen readings are recommended, if practical. ' B. Water Supply Wells Water supply wells will be sampled by purging the wells for a period of time ' adequate to purge the pump riser pipe. Alternatively, if the volume of the riser pipe is unknown, the pressure tank will be drained until the pump cycles on, or the ' well may be purged until three successive field measurements performed 5 to 10 ' SAMPLING OF GROUNDWATER MONITORING WELLS AND WATER SUPPLY WELLS Page 3 of 10 ' DISCPROTO.MW.T\T REVISION DATE: MARCH I1)06 VI`V-=