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Chevron Products Company 4 Is weor rFanrr Way. Stockton. CA March 5, 2002 FINDINGS AND WORK PLAN FOR FURTHER ASSESSMENT Geologic cross sections are provided as Figures 3 through 6. These figures may be interpreted as meandering stream deposits comprised by interbedded sand mixtures and fine-grained sediments. The horizontally and vertically discontinuous nature of the sediments appears to control the vertical water quality profile. Concentrations of petroleum hydrocarbons are present in groundwater in the area encompassing SB -5 through SB -8. Review of Table 1 suggests the concentrations of TPHg, benzene, toluene, ethyl benzene, and xylenes were highest in the location around at approximately SB -5, which is positioned near existing monitoring well MW -3. MW - 3 is a well completed within the interval that can monitor water quality the 40 feet bgs zone. SECOR proposes decommissioning MW -1, because MW -1 is screened from approximately 30 to 50 feet bgs. Based on the results of this investigation, CPT data suggests that MW -1 may be screened across two water -bearing zones and as a result the water quality data may not necessarily be representative. Also, SECOR recommends installation of one shallow, one intermediate, and three deep ground water monitoring wells at depths of 30-40 feet bgs, 50-60 feet bgs and 80-85 feet bgs, respectively, at the general locations shown on Figure 2. The specific scope of work is discussed below: Groundwater Monitoring Wells. Five soil borings will be advanced at the locations depicted on Figure 2, using 8 -inch diameter hollow -stem augers to varying depths of approximately 40, 60 and 85 feet bgs. Based on SECOR's January 2001 Site Assessment Report, historically groundwater has been encountered in three separate soil horizons located at depths of approximately 35, 55 and 80 feet bgs.. Upon completion of drilling, a 2 -inch diameter groundwater monitoring well will be installed in each boring. \d MW -4, a shallow monitoring well, will be screened from approximately 35 to 40 feet bgs. (� MW -5, an intermediate well, will be screened from approximately 55 to 60 feet bgs. ■ MW 6, MW -7, and MW -8, the deep monitoring wells, will be screened from approximately 80 to 85 feet bgs. • Well Decommissioning. Monitoring well MW -1 will be decommissioned by pressure grouting from the bottom up, and then drilling out the top five feet of the well. The well box will also be removed and finished to surface grade with cement. • Permitting. The applicable permits for groundwater monitoring wells will be obtained from the City of Stockton and San Joaquin County prior to drilling. Soil Selection and Analysis. Soil samples will be collected at 5 -foot intervals and will be submitted under chain -of -custody procedures to a California state- 1:\Chevron\92033\REP0RTS\9-2033 SA CPT WPFA.doc