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SOP #: GW 0001 Region I Low Stress (Low Flow) SOP Revision Number: 2 Date: July 30, 1996 Page 8 of 13 size (0.45 um is commonly used) should be based on the sampling objective. Pre-rinse the filter with approximately 25 - 50 ml of ground water prior to sample collection. Preserve filtered water sample immediately. Note: filtered water samples are not an acceptable substitute for unfiltered samples when the monitoring objective is to obtain chemical concentrations of total mobile contaminants in ground water for human health risk calculations. Label each sample as collected. Samples requiring cooling (volatile or anics, cyanide, etc.) will be placed into a cooler with ice or refrigerant for delivery to the laboratory. Metal samples after acidification to a pH less than 2 do not need to be cooled. ' 6. Post Sampling Activities If recording pressure transducer is used, remeasure water level with tape. After collection of the samples, the pump tubing may either be dedicated to the well for resampling (b hanging the tubing inside the well), decontaminated, or properly discarded. Before securing the well, measure and record the well depth (to 0.1 ft.), if not measured the day before purging began. Note: measurement of total well depth is optional after the initial low stress sampling event. However, it is recommended if the well has a ' "silting" problem or if confirmation of well identity is needed. Secure the well. ' V.DECONTAMINATION Decontaminate sampling equipment prior to use in the first well and following sampling of each subsequent well. Pumps will not be removed between purging and samp ing operations. The pump and tubing (including support cable and electrical wires which are in contact with the well) will be decontaminated by one of the procedures listed below. ' Procedure 1 The decontaminating solutions can be pumped from either buckets or ' short PVC casing sections through the pump or the pump can be disassembled and flushed with the decontaminating solutions. It is recommended that detergent and isopropyl alcohol be used sparingly in the decontamination process and water flushing steps be extended to ensure that any sediment trapped in the pump is removed. The pump exterior and electrical wires must be rinsed with the decontaminating solutions, as well. The procedure is as follows: ' Flush the equipment/pump with potable water.