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Report:Groundwater-quality Monitoring—October 20-21,2005, 7500 West Eleventh Street, Tracy, Cl. Page 12 of purge water were monitored by checking those parameters periodically using a multi- function electronic meter. Purging continued until both parameters stabilized (i.e., 1 variations between measurements were less than 10%) or, in the case of wells screened above the water table, until a minimum of 15 gallons of groundwater had been removed, whichever was greater. The array of parametric results for each well is recorded in SJC's field notes see Field Notes, Appendix A Inspection of the temperature and conductivity data in the field notes shows that both parameters stabilized to within plus or minus 10% after the first few measurements were made on the purge water discharged from each well. This parametric stability is sufficient to demonstrate adequate well purging according to criteria suggested by the SJCEHD r- (San Joaquin County Public Health Services 2000). However, it is SJC's standard practice when purging shallow monitoring wells that have casings slotted in the zone above the water table at sites where groundwater is affected by analytes of concern that 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 i almost always greater than the volume that would be permissible based on the physical properties of the purge water alone. 2.2.1 Disposal of Purge Water As noted above, purge water extracted from the monitoring wells was discharged periodically into in a 1,100-gallon storage tank located on the Navarra Site. For economy and efficiency, water will be held in that tank until it is full. It will then be pumped into a vacuum truck and transported to a recycling facility, where the petroleum hydrocarbons will be recycled into beneficial use before the cleaned water is discharged. 2.3 Recovery of Groundwater Samples from Monitoring Wells After purging, samples were recovered using disposable bailers. Water brought to the surface in the bailers was decanted via discharge spigot valves laced in the bottom of gP :+ each 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 fortransport, within ten hours, to Severn Trent Laboratories' (STL) laboratory in Pleasanton, California for analysis. i - I'=r 2.4 Analyses of Groundwater Samples Each groundwater sample recovered was analyzed at the laboratory for the following suite of analytes. sic