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Mr.Ron Rowe November 24, 1997 Page 3 The dual completion groundwater monitoring wells MW-7-S and MW-7-D were developed and sampled on October 31, 1997. The wells were developed by alternately bailing and surging. Well development continued until the groundwater was reasonably free of sediment. Approximately ten casing volumes of water were removed from each well during development. During well development,measurements and observations of pH, electrical conductivity,temperature,color,and turbidity were recorded and are included on a Groundwater Sample Field Data Sheet(Attachment Q. Following well development, SECOR collected groundwater sample from each monitoring well for chemical analysis. Prior to sampling the well was allowed to recover to 80%of the initial water level prior to development. The groundwater sample was collected using a disposable PVC bailer and decanted directly into laboratory- supplied sample containers. Each of the sample containers was labeled,sealed in plastic bags,and placed in an ice-filled cooler. The samples were submitted to Superior along with a completed chain-of-custody record and were analyzed for TPHg and BTEX by EPA Methods 8015,modified and 8020,respectively. The samples were also analyzed by North State for methanol,ethanol,TBA,MTBE,DIPE,ETBE, and TAME by EPA Method 8260. The laboratory analytical results are included in Table 1 and the laboratory analytical reports and chain-of- custody records are included in Attachment B. Monitoring wells MW-7-S and MW-7-D will be surveyed for top of casing elevation to relative mean sea.level (msl) by a professional land surveyor and tied into the City of Stockton Benchmark No. 186 upon completion of additional groundwater monitoring wells. FINDING Stratigraphy and Hydrogeology Undisturbed native soil was encountered below the pea gravel of the former UST pit excavation at an approximate depth of 12.5 feet bgs. Native soils consisted of interbedded gravel,sand, silt,and clay. The upper 44.5 feet of sediments were preddoinantly silt and clay with variable amounts of fine sand. Poorly-graded sand layers up to 7 feet thick interbedded with intervening silt and clay layers were encountered between 44.5 to 63 feet bgs. A fine sand with abundant fines(silt)extended between 63 and 78.5 feet bgs, Underlying the fine silty sand and extending to the total depth explored (86.5 feet bgs)were a well sorted sand layer grading into a sandy gravel During drilling,groundwater was first encountered in a sandy silt layer at approximately 32,5 feet bgs.The static water level measured in the dual completion wells(19,5 feet bgs in well MW-7-S and 26.4 feet bgs in well MW- 7-D) indicate that first encountered groundwater occurs under semi-confined or confined conditions. The sequence of sand layers between 44.5 feet to 63 feet and the sand and gravel layers between 78.5 and 86.5 feet appear to be the primary water-bearing and permeable sediments encountered within the depths explored. Soil and Groundwater Analytical Results Chemical analytical results for soil samples are presented on Table 1. Results of the soil field screening for VOCs using the PID are displayed on the boring logs included with Attachment B. In general,the field screening results corresponded with the reported laboratory analytical data. Soil laboratory analytical data reports and chain-of-custody records are provided with Attachment A. A maximum soil TPHg concentration of 390 parts per million(ppm)was observed at 34.5 feet bgs at 390 parts ( per million (ppm). TPHg concentrations decreased from 19 to 1.0 ppm at 46 feet bgs and 79 feet bgs, respectively. Benzene concentrations of 2,300 parts per billion(ppb) were observed at 34.5 feet bgs and 2,900 ppb at 46 feet bgs. Benzene concentrations decreased from 520 to 66 ppb at 53.5 to 79 feet bgs. Toluene,ethyl H:\SPFHXST0CKT0N\WKP2.RPT