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L.0 11.0 %MI La City of Stockton A68107.07A May 29, 1996 Page S L advanced to the greatest depth at which PPCs were detected with field screening in soil probe SP-1 or to within three feet of the groundwater depth, whichever occurs first. Soil probe SP-4 will be advanced at an angle of approximately 30 degrees from vertical in a LA southerly direction to collect soil samples beneath the fire house building. A cross section showing the orientation of soil probe SP-1 and SP-4 to the former UST location is shown on Drawing 3. If field screening indicates the presence of PPCs in soil probes SP-2, SP-3, and/or SP-4, additional data will be needed to complete the assessment of the lateral extent of PPC migration. Contingency soil probe location(s) will be used to further assess PPC lateral migration in the soil. These contingency soil probe locations would be "stepped out" away from the presumed source to collect additional data for PPC concentration attenuation and regarding the extent of PPC migration in soil. In the event evidence in the field indicates the need for these contingency soil probes, their proposed locations are shown on Drawing 2, k. After completion of sampling, the soil probe holes will be backfilled with a cement slurry (grout). The grout is pumped into the open probe hole as the probe sampler is withdrawn. �' The grout will be placed in one continuous operation from the bottom to the top of the probe hole. Decontamination rinsate of sampling tools will be used in mixing the backfill grout. 4.1.2 Groundwater Investigation: A groundwater sample will be collected after collecting the final soil sample from soil probe SP-1's location. The soil sampler is removed from the end of the probe and a groundwater sampler attached. The groundwater sampler contains a 41-inch screen with 0.004-inch slots. The groundwater sampler will then be advanced �. approximately 36 inches into the groundwater. Then the probe tool string is retracted approximately 40 inches exposing the screen. The groundwater sample will be collected from within the screen by lowering a stainless-steel bailer into the groundwater. The bailer will then be retrieved and the groundwater sample decanted into appropriate sample containers (i.e., 40 milliliter vials and/or 1 liter brown-glass jars). The groundwater sample will represent the top 3 feet of the groundwater. Groundwater samples will be handled L, consistent with our SOPS. Groundwater samples will be submitted for laboratory testing consistent with the analytical La methods outlined in Section " 4.2 Laboratory Testing Program". The analytical results of groundwater samples collected are expected to provide data on the presence or absence of PPCs in groundwater beneath the former UST location. L..