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+•+ Work Plan for Extended Site Ch` Kcterization: 7500 West Eleventh Street, Tracy,CA. %MV Page 12 ,,. 6.9 Determination of Groundwater Elevations After a delay of at least one week following well development, the depth from the top of the +.. casing to the water table will be measured using a conductivity meter in each pre-existing and newly-installed well as part of the planned extended site characterization program. That data will be used to compute the groundwater table elevations relative to MSL. The computed groundwater table elevations will be used to produce a contour map of the groundwater table and determine the direction and magnitude of the groundwater flow gradient. 6.10 Well Purging After the depths to groundwater are measured, a small-diameter, submersible pump will be used to purge each groundwater-quality monitoring well of stagnant water. The pumped water will be discharged into 5-gal. pails, each of which will, in turn, be discharged into an `" open-topped, 50-gallon drum equipped with a securable lid. The 50-gallon drums will be staged on the 7500 West Eleventh Street property. During the purging procedure, the temperature, electrical conductivity and pH of the stream of purge water will monitored by periodically checking those parameters using a multi- function electronic meter. Purging will continue until all three parameters stabilize, i.e., +" variations between measurements are less than 10%. The array of parametric results for each well will be recorded in field notes. 6.11 Groundwater Sampling Procedure After purging, samples will be recovered from each monitoring well to be sampled using a `! dedicated bailer that will be left suspended in the well casing when not in use. Water brought to the surface in the bailers will be decanted via a discharge spigot valve placed in the bottom of the bailer so as to completely fill clean glassware supplied by the laboratory. The sample vials will then be tightly closed, labeled for identification, entered into chain-of-custody control and packed on chemical ice for transport, within 24 hours, to Chromalab's laboratory in Pleasanton, California. The grab sample of groundwater recovered from the push probe hole to be drilled on the west side of Chrisman Road will be obtained and managed in a manner similar to that described above, except that the boring will be purged by hand, no conductivity or other water-quality parameters will be measured and a 0.5-in. (nominal size) bailer will be used to recover the sample from the boring. S]C �I