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SOP #: GW 0001 <br />Region I Low Stress <br />(Low Flow) SOP <br />Revision Number: 2 <br />Date: July 30, 1996 <br />Page 7 of 13 <br />measured within the cell and may also cause an underestimation of <br />turbidity values measured after the cell. If the cell needs to be <br />cleaned during purging operations, continue pumping and disconnect <br />cell for cleaning, then reconnect after cleaning and continue <br />monitoring activities. <br />The flow- through -cell must be designed in a way that prevents air <br />bubble entrapment in the cell. When the pump is turned off or <br />cycling on /off (when using a bladder pump), water in the cell must <br />not drain out. Monitoring probes must be submerged in water at all <br />times. If two flow- through -cells are used in series, the one <br />containing the dissolved oxygen probe should come first (this <br />parameter is most susceptible to error if air leaks into the system). <br />5. Collect Water Samples <br />Water samples for laboratory analyses must be collected before water <br />has passed through the flow- through -cell (use a by -pass assembly or <br />disconnect cell to obtain sample). <br />VOC samples should be collected first and directly into pre - preserved <br />sample containers. Fill all sample containers by allowing the pump <br />discharge to flow gently down the inside of the container with <br />minimal turbulence. <br />During purging and sampling, the tubing should remain filled with <br />water so as to minimize possible changes in water chemistry upon <br />contact with the atmosphere. It is recommended that 1/4 inch or 3/8 <br />inch (inside diameter) tubing be used to help insure that the sample <br />tubing remains water filled. If the pump tubing is not completely <br />filled to the sampling point, use one of the following procedures to <br />collect samples: (1) add clamp, connector (Teflon or stainless <br />steel) or valve to constrict sampling end of tubing; (2) insert small <br />diameter Teflon tubing into water filled portion of pump tubing <br />allowing the end to protrude beyond the end of the pump tubing, <br />collect sample from small diameter tubing; (3) collect non -VOC <br />samples first, then increase flow rate slightly until the water <br />completely fills the tubing, collect sample and record new drawdown, <br />flow rate and new indicator field parameter values. <br />Add preservative, as required by analytical methods, to samples <br />immediately after they are collected if the sample containers are not <br />pre - preserved. Check analytical methods (e.g. EPA SW -846, water <br />supply, etc.) for additional information on preservation. Check pH <br />for all samples requiring pH adjustment to assure proper pH value. <br />For VOC samples, this will require that a test sample be collected <br />during purging to determine the amount of preservative that needs to <br />be added to the sample containers prior to sampling. <br />If determination of filtered metal concentrations is a sampling <br />objective, collect filtered water samples using the same low flow <br />procedures. The use of an in -line filter is required, and the filter <br />