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Report:Groundwater-quality Monitoring—September 11,2001: 7500 West Eleventh Street, Tracy, CA. Page 5 <br /> �:_`:! -1 It has been SJC's experience, after characterizing a large number of sites in a wide range <br /> of hydrostratigraphic settings where groundwater has been affected by a variety of <br /> contaminants, that, in purging shallow wells in which groundwater has been affected by <br /> hydrocarbons, it is necessary to remove a true well volume of water(i.e.,the total volume <br /> of water in the submerged well boring over the depth where the well construction <br /> includes a screen and annular filter pack) to ensure that a groundwater sample <br /> representative of the formation water is recovered. This protocol is of particular <br /> importance where groundwater levels vary seasonally and where soils around the water <br /> table affected by fuel hydrocarbons are successively submerged and then stranded in the <br /> vadose zone where they can be a source of seepage into filter pack material. <br /> Thus, regardless of the quantity of purge water removed when the temperature, <br /> conductivity and pH stabilized to within 10%, the purging of each well continued until a <br /> minimum of 15 gallons had been extracted. <br /> 2.3 Recovery of Groundwater Samples from Monitoring Wells <br /> After purging, samples were recovered from each monitoring well using a dedicated <br /> bailer that was left suspended in the well casing for future use. Water brought to the <br /> surface in the bailer was decanted so as to completely fill clean glassware supplied by the <br /> laboratory. The sample vials and jars were then tightly closed, labeled for identification, <br /> entered into- chain-of-custody control, packed on chemical ice and held in refrigerated <br /> storage until they were transported, -within three hours, to Chromalab, Inc.'s <br /> J (Chromalab) laboratory in Pleasanton, California for analysis. <br /> 2.4 Analyses of Groundwater Samples <br /> i <br /> Each groundwater sample was analyzed at the laboratory for the following suite of <br /> analytes. <br /> � t <br /> Anal e Method of Analysis <br /> i <br /> Total Petroleum Hydrocarbons EPA Method 5030/8015M <br /> (quantified as Diesel) <br /> Total Petroleum Hydrocarbons EPA Method 8020A/8015M <br /> (quantified as Gasoline) <br /> Benzene EPA Method 8020 <br /> Toluene EPA Method 8020 <br /> Ethyl benzene EPA Method 8020 <br /> i Total Xylene Isomers EPA Method 8020 <br /> 1 <br /> sic <br /> i ' <br />