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• 70 PROCEDURE 5 Screen headspace of well with an appropriate <br />' monitoring instrument to determine the <br /> 7.1 Preparation presence of volatile organic compounds and <br /> record in site logbook <br />' 1 Determine the extent of the sampling effort, <br /> the sampling methods to be employed, and 6 Lower water level measuring device or <br /> the types and amounts of equipment and equivalent (i e , permanently installed <br /> supplies needed (i e, diameter and depth of transducers or airline) into well until water <br />' wells to be sampled) surface is encountered <br /> 2 Obtain necessary sampling and monitoring 7 Measure distance from water surface to <br /> equipment, appropriate to type of reference measuring point on well casing or <br />' contaminant being investigated For protective barrier post and record in site <br /> collection of volatile organic samples,refer logbook Alternatively,if no reference point, <br /> to the work plan to ensure that 40 mL glass note that water level measurement is from <br />' sample vials with Teflon lined septa are top of steel casing, top of PVC riser pipe, <br /> ordered and in sufficient numbers Check from ground surface, or some other position <br /> sampling supplies, field kit for chlorine, on the well head <br /> preservatives, Parafilm, foam sleeves and <br />' coolers Due to extreme trace levels at If floating organics are of concern, this can <br /> which volatile organics are detectable, cross be determined by measuring the water level <br /> contamination and introduction of with an oil/water interface probe which <br /> contaminants must be avoided Trip blanks measures floating organics <br />' are incorporated into the shipment package to <br /> provide a check against cross contamination confirm <br /> Measure total depth of well (at least twice to <br /> confirm measurement) and record in site <br />'. 3 Decontaminate or preclean equipment, and logbook or on field data sheet <br /> ensure that it is in working order <br /> 9 Calculate the volume of water in the well and <br /> 4 Prepare scheduling and coordinate with staff, the volume to be purged using the <br />' clients,and regulatory agency, if appropriate calculations in Section 8 0 <br /> 5 Perform a general site survey prior to site to Select the appropriate purging and sampling <br />' entry in accordance with the site specific equipment <br /> Health and Safety Plan <br /> 11 If residual chlorine is suspected, use the <br /> 6 Identify and mark all sampling locations Hach Field Test Kit for chlorine to determine <br /> if there is residual chlorine in the water to be <br /> 7.2 Field Preparation sampled if there is, treat the sample vial <br /> with a crystal of sodium thiosulfate prior to <br /> 1 Start at the least contaminated well, if sample collection <br /> known <br /> 7.3 Purging <br /> 2 Lay plastic sheeting around the well to <br />' minimize likelihood of contamination of The amount of flushing a well receives prior to sample <br /> equipment from soil adjacent to the well collection depends on the intent of the monitoring <br /> program as well as the hydrogeologic conditions <br />' 3 Remove locking well cap,note location,time Programs where overall quality determination of water <br /> of day, and date in field notebook or resources are involved may require long pumping <br /> appropriate log form periods to obtain a sample that is representative of a <br /> large volume of that aquifer The pumped volume can <br />' 4 Remove well casing cap be determined prior to sampling so that the sample is <br /> 6 <br />