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City of Stockton A68101.02F July 24, 1997 Page 8 ' of the former excavation and monitoring well MW-1. The purpose of soil probe location SB-2 was to collect data on the west side of the former excavation. The purpose of soil probe location SB-3 was to delimit the westward extent of PPC migration and to investigate the possibility that PPCs may have migrated beneath the maintenance shop building from the former fuel dispenser location. Soil probe SB-3 was installed at an angle of 60 degrees ' from the horizontal due to access limitations. Soil probe location SB-4 was to delimit the extent of PPC migration on the southwest side of the former fuel dispenser location. The purpose of soil probe S13-5 was to delimit the northward extent of PPC migration. The ' purpose of soil probe location SB-5 was to investigate the possibility of gasoline constituents in the vicinity of the former gasoline UST. Field screening during the installation of SB-5 indicated the presence of PPCs in subsurface soil and groundwater. Based on this finding, it was decided to perform a "contingency" soil probe. The contingency soil probe location SB-7 was stepped out approximately 20 feet ' north northwest of soil probe location SB-5. 4.2.2 Groundwater Investigation: Wellhead monuments were located for monitoring wells ' MW-1 and MW-2. We were not able to open the well cover for monitoring well MW-1, the fasteners were locked (by corrosion?). Depth to groundwater was measured in MW-2 at j approximately 10.2 feet BSG. The monument (box and cover) for monitoring well MW-3 was missing, however, the casing for MW-3 was located. Soil was cleared from around the top 2-inches of casing for monitoring well MW-3 and a portland cement concrete lid was placed over the casing top. The integrity of this well has been compromised and it should be repaired and/or properly abandoned. Due to the problems with monitoring wells MW-3 and MW-1, groundwater r samples were not collected from the monitoring wells during this investigation. Groundwater samples were collected from each probe hole prior to backfilling. A temporary, 1-inch diameter, polyvinyl-chloride (PVC) casing was inserted into probe hole. The bottom ten-foot section of the PVC casing was machine cut with 0.01-inch slots. The casing was allowed to stand in the probe hole for a period of time deemed adequate for the groundwater to fill the casing below the water table. A groundwater sample was then collected through a 3/8-inch Teflon® tube with a positive displacement pump. Groundwater samples were decanted into appropriate sample containers, sealed, labeled, and placed in a cooler for transport to Twining's laboratory under chain-of-custody documentation. 4.3 Laboratory Testing Program: Soil and groundwater samples collected from soil probe ' locations were chemically analyzed in the laboratory for the following selected PPCs: benzene, toluene, ethylbenzene, and xylenes (BTEX), methyl tertiary-butyl ether (MTBE), total petroleum hydrocarbons - gasoline range constituents (TPH-G), and total petroleum hydrocarbons-diesel range constituents (TPH-D). Preparation and analytical methods for the laboratory analyses and corresponding detection limits for reporting purposes are summarized in Table 5. i 1