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Drajt.• April S, 1999 Page C-3 <br />' C.3 F1ELD SAMPLING PROCEDURE <br />This section gives the step-by-step procedures for collecting samples in the field. <br />' Observations made during sample collection will be recorded in the field notebook and/or field data <br />sheet as specified in Section C.5 of this SOP. <br />C.3.1 Equipment Decontamination <br />Before any evacuation or sampling begins, all well probes, bailers, and other sampling <br />' devices shall be decontaminated, as specified in the accompanying document Standard Operating <br />Procedures for Decontamination of Equipment, Groundwater, and Surface Water Sampling. <br />t C.3.2 Instrument Calibration <br />' Electronic equipment used during sampling will generally include a pH meter with <br />temperature scale, a conductivity meter, and a water level measurement probe, although additional <br />equipment may be used for special studies. Before going into the field, sampling personnel shall <br />verify that all of the equipment is operating properly. The pH and conductivity meters require <br />' calibration prior to use every day. Calibration times and readings will be recorded in a notebook to <br />be kept by the field sampling personnel. Specific instructions for calibrating the instruments aze <br />' described in Section 6 and in the instruction manuals for each instrutnent. <br />C.3.3 Well Purging <br />' The purpose of well purging is to remove standing water from the well, in order to collect <br />a representative water sample from the geologic formation being sampled while minimizing <br />' disturbance to the collected samples. Before a sample is taken, the well may be purged until three <br />well casing volumes have been removed, or one or more of the field pazameters (temperature, pH, <br />' and conductivity) have stabilized, or until the well is purged dry. Alternatively, micropurging <br />' techniques may be employed. Micropurging involves using a pump with the suction point within <br />the screened interval of the monitoring well. Small diameter tubing is typically used to transfer <br />' formation water to this pump and to the surface. Purging this system involves removing a volume <br />of water equivalent to one volume of water retained in the tubing. During micropurging, [he water <br />' level will be monitored. The pumping rate will be adjusted such that drawdown in the well does <br />not exceed 0.1 meter. Samples should be collected within 2 hours of purging. Evacuated well water <br />' can be disposed down-gradient of well head. <br />1 <br />' Agapito Associates, Inc. <br />