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SOP NUMBER 0.0 Monitor Well Groundwater Sampling <br />6. Label and place samples on ice in a cooler. <br />7. Record time of sampling and record sample identification in field logbook. <br />8. Replace and lock well cap. <br />9. Complete field documentation <br />Note that preservation techniques are discussed in detail in SOP No. * . <br />Page 7 of 14 <br />4.0 LOW STRESS (LOW FLOW) PURGING AND SAMPLING PROCEDURES <br />The purpose of the low stress purging and sampling procedure is to collect ground water samples <br />from monitoring wells that are representative of ground water conditions in the geological <br />formation with minimal disturbance to the sample. This is accomplished by setting the intake <br />velocity of the sampling pump to a flow rate that limits drawdown inside the well casing. <br />Sampling at the prescribed (low) flow rate has three primary benefits. First, it minimizes <br />disturbance of sediment in the bottom of the well, thereby producing a sample with low turbidity <br />(i.e., low concentration of suspended particles). Typically, this saves time and analytical costs by <br />eliminating the need for collecting and analyzing an additional filtered sample from the same <br />Well. Second, this procedure minimizes aeration of the groundwater during sample collection, <br />which improves the sample quality for VOC analysis. Third, in most cases the procedure <br />significantly reduces the volume of ground water purged from a well and the costs associated <br />with its proper treatment and disposal. <br />Specify the depth to which the pump intake should be lowered in each well. Generally, the target. <br />depth will correspond to the mid -point of the most permeable zone in the screened interval. <br />Borehole geologic and geophysical logs can be used to help select the most permeable zone. <br />However, in some cases, other criteria may be used to select the target depth for the pump intake. <br />Otherwise, the pump should be set at the middle of the screened interval <br />Sample bottles with preservatives added will be obtained from the analytical laboratory. Several <br />extra sample bottles will be obtained in case of breakage and for QA/QC samples. <br />4.0.1 Equipment List <br />Equipment that may be used during well Low Stress (Low Flow) purging sample collection: <br />• Well Construction Data <br />•. Location map <br />© Field data from last sampling event <br />c Polyethylene sheeting <br />• Adjustable rate, positive displacement ground water sampling pump (constructed of stainless <br />steel or Teflon) <br />• Teflon or Teflon — lined polyethylene, PVC, Tygon or polyethylene tubing to collect samples <br />for inorganic analysis. <br />0 -7 <br />