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Report:Groundwater-quality Monitoring—July 27,2004: 7500 West Eleventh Street, Tracy,CA. Page 10 are lighter than water, regardless of the temperature, conductivity and pH data obtained, to purge a minimum quantity of groundwater equal to the casing volume plus the void space in the annular filter pack between the casing and the borehole wall. That volume(in this case, 15 gallons) is much greater than the three to five casing volumes that is often erroneously considered to be sufficient to purge adequately a well of that type and it is almost always greater than the volume that would be permissible based on the physical properties of the purge water alone. 1 2.2.1 Disposal of Purge Water Purge water is held in an 1,100-gallon storage tank located on the 7500 West Eleventh Street property. On July 27, 2004, the contents of that tank were discharged into a vacuum truck and transported to the DeMenno/Kerdoon recycling facility in Compton, California where the petroleum hydrocarbons were recycled led into beneficial tial use before the cleaned water was discharged to the municipal sewer under the waste discharge requirements of the Sanitation Districts of Los Angeles County. Copies of the waste manifest and the Certificate of Recycling are included in Appendix B. 2.3 Recovery of Groundwater Samples from Monitoring Wells After purging, samples were recovered from the 22 Monitoring Wells MW-1 through MW-19 using a .disposable bailer. Water brought to the surface in the bailers was j = 3 decanted via a discharge spigot valve placed in the bottom of the bailer so as to completely fill clean glassware supplied by the laboratory containing, where applicable, pre-dispensed preservatives. The sample vials were then tightly closed, labeled for identification, entered into chain-of-custody control and packed on chemical ice for F:- transport,within ten hours, to Severn Trent Laboratories' (STL) laboratory in Pleasanton, California for analysis. 2.4 Analyses of Groundwater Samples Each groundwater sample recovered was analyzed at the laboratory for the following suite of analytes. j Analyte Method of Analysis J Total Petroleum Hydrocarbons EPA Method 8015M 71 (quantified as Diesel) with silica gel cleanup _ Total Petroleum Hydrocarbons EPA Method 8260B j (quantified as Gasoline) Benzene EPA Method 8260B Toluene EPA Method 8260B sic ! j LI