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December 23, 1999 • Page C-3 ~_ C.3 FIELD SAMPLING PROCEDURE ' This section gives the step-by-step procedures for collecting samples in the field. Observations made during sample collection will be recorded in the field notebook and/or field data ' sheet as specified in Section C.5 of this SOP. C.3.1 Equipment Decontamination ' Before any evacuation or sampling begins, all non-dedicated well probes, bailers, and other sampling devices shall be decontaminated, as specified in the accompanying document Standard Operating Procedures for Decontamination of Equipment, Groundwater, and Surface Water Sampling. C.3.2 Instrument Calibration Electronic equipment used during sampling will generally include a pH meter with ' temperature scale, a conductivity meter, and a water level measurement probe, although additional ' equipment may be used for special studies. Before going into the field, sampling personnel shall verify that all of the equipment is operating properly. The pH and conductivity meters require ' calibration prior to use every day. Calibration times and readings will be recorded in a notebook to be kept by the field sampling personnel. Specific instructions for calibrating the instruments are ' described in Section 6 and in the instruction manuals for each instrument. C.3.3 Well Purging ' The purpose of well purging is to remove standing water from the well, in order to collect a representative water sample from the geologic formation being sampled while minimizing ' disturbance to the collected samples. Before a sample is taken, the dedicated sampling equipment will be purged until two sampling equipment volumes have been removed, or until the well is purged ' dry. Alternatively, this method is referred to as "micropurging." Micropurging involves using a ' pump with the suction point within the screened interval of the monitoring well. Small diameter tubing is typically used to transfer formation water to this pump and to the surface. Purging this ' system involves removing a volume of water equivalent to approximately two volumes of water retained in the tubing and pump. During micropurging, the water level will be monitored. The ' pumping rate will be adjusted such that drawdown in the well does not exceed 0.1 meter. Samples ' should be collected immediately after purging. Evacuated well water will be collected and disposed i of properly. ~' Agapito Associates, Inc.