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<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, a representative sample from the surface water <br />stream monitoring point will be poured into a separate clean vessel <br />' to measure the field parameters of pH, specific conductance, <br />temperature and dissolved oxygen. All instrument probes that come <br />into contact with the sample water and the measurement vessel will <br />be cleaned between uses using laboratory-provided de-ionized water. <br />' A minimum of two sets of measurements will be made at each sample <br />location to evaluate if the measured parameters are repr@sentative. <br />Replicate measurements will be made a minimum of on@ time per <br />sample period in the following manner: <br />' (1) collect a sample of water into the measurement vessel; <br />1 (2) measure field parameters; <br />' (3) rinse instrument probes in de-ionized water; and <br />t (4) re-measure field parameters in the same sample. <br />' 3.2.6 Sample Filtration: Surface water samples requiring on-site <br />filtration will be filtered using a filter apparatus, which filters <br />' through a 0.45-micron membrane. <br />' Samples will be preserved directly following filtration. <br />' Filter apparatus, unless disposable, will be cleaned by having the <br />solutions "pulled" through the apparatus prior to and after each <br />use in the following manner: <br />' -24 <br /> <br />