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down 90 feet to groundwater. Therefore, samples were collected by Hydropunch after the borings had been drilled with a hollow stem auger. i Exploratory groundwater samples were collected by Hydropunch from six soil borings drilled with a hollow stem auger(SB-1', SB-2, SB-3, SB-6, SB-7, and SB-8). Sample Iocations were selected to determine the lateral extent of the gasoline plume. Figure 5=1 shows the position of groundwater samples collected. SB-1, -2, and -3 were placed offsite in the City of Stockton right-of-way along North Filbert Street; SB-6 was placed on private property north of an alley that tees into the 100 block of N. Filbert Street; and SB-7 and SB-8 were placed onsite, southeast of the former USTs. All six soil borings were drilled to 80 feet bgs. The auger cuttings were visually inspected and used to geologically log each boring to a depth of 70 feet. At 70, 75, and 80 feet, soil was sampled with a split spoon sampling device to more accurately describe the hydrogeology of the boring in the zone just above the groundwater level. Soil samples were not submitted for laboratory analysis. When a soil depth of 80 feet was reached, a Hydropunch was driven 4 feet into an undisturbed portion of the formation. Groundwater entered the Hydropunch and was subsequently sampled with a stainless steel bailer. The sample was poured from the stainless steel bailer into 40 milliliter glass containers and shipped to CHROMALAB in Pleasanton, California, for analysis for TPH(g) and BTEX. Typically, the analyses were performed within 12 hours of the laboratory's receipt of the sample. Laboratory reports with analytical results are presented in Appendix A. Drill cuttings were placed in onsite debris boxes and steel drums. Clean soil was used as onsite fill material in the depression left after pump island piping removal. Drummed :�i �A material contaminated with gasoline was sent offsite for remediation by therm incineration ....• at Port Costa Materials in Crockett, California. ; f" Lateral Limit of the Gasoline Plume Figure 3-1 shows the lateral limits of benzene in the A Zone groundwater. The bulk of the plume has migrated predominantly west from the site; however, the plume has also migrated } eastward from MW-DIS-1 toward MW-DIS-9. Monitoring Well Installation Using the data collected during the exploratory sampling, monitoring well locations were selected to lie just beyond the known extent of the gasoline plume. + The Hydropunch sample collected from SB-1 contained TPH(g) and BTEX concentrations near the detection limits. Therefore, SB-1 was considered to be near the northwestern edge of the gasoline plume. Two 4-inch-diameter monitoring wells were constructed near SB-1 and labeled MW-DIS-8D and MW-DIS-8S. MW-DIS-8D was placed in the same location as SB- I and screened from 132 to 142 feet bgs. MW-DIS-8S was completed in the sidewalk 5 feet to the west of MW-DIS-8D, with the screened interval extending from 65 to 85 feet bgs. The sand filter pack for both wells extends 2 feet above the screened section of casing; the filter SF0I0030982.DOC 3-2