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<br />(3) All measurements should be made within as brief a period <br />' of time as possible, so that temperature or chemical <br />changes will be minimized. <br />' (4) In some cases, the instruments take a certain amount of <br />time to stabilize. This stabilization time should be <br />noted for each measurement. <br />(5) Instrument probes should be cleaned with de-ionized water <br />between each sampling station to prevent cross- <br />' contamination. <br />Prior to sampling, while water is being evacuated from each well, <br />water will be poured into a separate clean vessel to Measure the <br />field parameters of pH, specific conductance and temperature. The <br />first sample for field parameter measurement shall be collected <br />after approximately three casing volumes have been removed, and <br />during the bailing of the first casing volume for low-yield wells. <br />All instrument probes that come in contact with the sample water <br />' and the measurement vessel will be cleaned between uses by rinsing <br />with laboratory-provided de-ionized water. A minimum of two sets <br />of measurements will be made at each sample location to evaluate <br />whether the parameters have stabilized. <br />' Under normal conditions, samples will not be taken untkl each of <br />the parameters stabilize. If, for whatever reason, field water <br />' quality parameters have not stabilized at a sampling site after <br />purging 3 to 5 casing volumes, this information will be noted on <br />' the chain-of-custody form and the sample taken according to the <br />sampling QA/QC protocols. The criteria for stabilization are ± 0.1 <br />pH units, ± lo$ in specific conductance value, and ± 1 °C for <br />temperature. <br /> <br />-17 <br />1 <br />