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Report:Groundwater-quality Monitoring—October 25, 2002: 7500 West Eleventh Street, Tracy, CA. Page 8 in the details of the groundwater elevation contours, the direction of groundwater flow remained substantially unchanged from the north-northeasterly direction that has prevailed since depths to groundwater were first measured in May 2000. 2.2 Purging of Monitoring Wells rAfter the depths to groundwater were measured, a small-diameter, submersible pump was used to purge each groundwater-quality monitoring well of stagnant water. The pumped s_ water was discharged into 5-gal. pails, each of which was, in turn, discharged into an l open-topped, 55-gallon drum for temporary storage at the well-head. During the purging procedure, the temperature, electrical conductivity and pH of the purge of stream water were monitored b p g y periodically checking those parameters using a multi-function electronic meter. Purging continued until all three parameters stabilized, j (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 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 ( 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 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 =3 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 i sic ii