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Report: Groundwater-quality Monitoring—May 30,2001: 7500 West Eleventh Street, Tracy, CA. Page 5 The submerged casing volume of each well is approximately 2.45 gallons and, if a filter pack porosity of 33% is assumed, the actual volume of stagnant water in the 8-in. diameter well borings in which the wells were constructed is 14.56 gallons. It has been SJC's experience, after characterizing a large number of sites in a wide range of hydrostratigraphic settings where groundwater has been affected by a variety of contaminants, that, in purging shallow wells in where groundwater has been affected by hydrocarbons it is necessary to remove a true well volume of water(i.e., the total volume of water in the submerged well boring over the depth where the well construction includes a screen and annular filter pack) to ensure that a groundwater sample representative of the formation water is recovered. This protocol is of particular importance where groundwater levels vary seasonally and where soils around the water table affected by fuel hydrocarbons are successively submerged and then stranded in the vadose zone where they can be a source of seepage into filter pack material. Thus, regardless of the quantity of purge water removed when the temperature, conductivity and pH stabilized to within 10%, the purging of the wells continued until a minimum of 15 gallons had been extracted from them. € 2.3 Recovery of Groundwater Samples from Monitoring Wells After purging, samples were recovered from each monitoring well using a dedicated bailer that was left suspended in the well casing for future use. Water brought to the surface in the bailer was decanted so as to completely fill clean glassware supplied by the laboratory..The sample vials and jars were then tightly closed, labeled for identification, entered into chain-of-custody control, packed on chemical ice and held in refrigerated " storage until they were transported to Chromalab, Inc.'s (Chromalab) laboratory in Pleasanton, California for analysis. 2.4 Analyses of Groundwater Samples Each groundwater water sample was analyzed at the laboratory for the following suite of analytes. Anal e Method of Analysis Total Petroleum Hydrocarbons EPA Method 5030/8015M %; (quantified as Diesel) Total Petroleum Hydrocarbons EPA Method 8020A/8015M (quantified as Gasoline) Benzene EPA Method 8020 Toluene EPA Method 8020 ' sic