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Report:Groundwater-quality Monitoring—July 29,2002: 7500 West Eleventh Street, Tracy, CA. Page 8 open-topped, 55-gallon drum for temporary storage at the well head. During the purging procedure, the temperature, electrical conductivity and pH of the stream of purge water were monitored by periodically checking those parameters using a :J multi-function electronic meter. Purging continued until all three parameters stabilized, (i.e., 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 was recorded in field notes. (See Field Notes, Appendix A) Inspection of the temperature, conductivity and pH data in the field notes shows that all three 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 -1 SJCEHD (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 k that are lighter than water, regardless of the temperature, conductivity and pH data -j 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 the 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. 2.2.1 Disposal of Purge Water Purge water temporarily held in the 55-gallon drum used to manage it at the well locations was pumped into a 1,000-gal. storage tank located on the 7500 West Eleventh Street property. That water will be shipped to a permitted recycling facility for disposal when sufficient quantity has accumulated for that to be done economically following future rounds of groundwater sampling and analysis. 2.3 Recovery of Groundwater Samples from Monitoring Wells After purging, samples were recovered from each monitoring well (with the exception of Monitoring Well MW-7) using a disposable bailer. Water brought to the surface in the bailer was decanted so as to fill completely clean glassware supplied by the laboratory. The sample vials and jars were then tightly closed, labeled for identification, entered into r`=y chain-of-custody control, packed on chemical ice and held in refrigerated storage until they were transported, within ten hours, to Severn Trent Laboratories' (STL) laboratory in Pleasanton, California for analysis, 2.4 Analyses of Groundwater Samples ' 'I� •; Each groundwater sample was analyzed at the laboratory for the following suite of ` 1 sic